[数据库原理]【英文版】Chapter15
Chapter_15 The Demand for Money(宏观经济学,多恩布什,第十版)
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The more money a person holds, the less likely he or she is to incur the costs of illiquidity
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The more money a person holds, the more interest he/she will give up → similar tradeoff encountered with transactions demand for money
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Standard of deferred payment
Money units are used in long term transactions (ex. loans)
15-5
The Demand for Money: Theory
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The demand for money is the demand for real money balances → people hold money for its purchasing power
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As liquidity of an asset decreases, the interest yield increases
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A typical economic tradeoff: in order to get more liquidity, asset holders have to sacrifice yield
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At the end of 2005, M1 = $4,596 per person Debate whether broader measure, M2, might better meet the definition of money in a modern payment system
市场调查方法(英文版)第十五章
15–14
EXHIBIT 15.2 Independent Samples t-Test Results
© 2007 Thomson/South-Western. All rights reserved.
15–15
What Is ANOVA?
• Analysis of Variance (ANOVA)
➢ An analysis involving the investigation of the effects of one treatment variable on an interval-scaled dependent variable
➢ A hypothesis-testing technique to determine whether statistically significant differences in means occur between two or more groups.
❖ Behavior, characteristics, beliefs, opinions, emotions, or attitudes
• Bivariate Tests of Differences
➢ Involve only two variables: a variable that acts like a dependent variable and a variable that acts as a classification variable.
❖ Differences in mean scores between groups or in comparing how two groups’ scores are distributed across possible response categories.
数据库系统原理(英文)-0--course introdu
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PART 2 China Computing Curricula 2005/2008
China Computing Curricula 2005/2008
数据模型
概念模型（如：实体—联系模型）
面向对象模型（语义对象模型）
关系数据模型
IM4 关系数据库（核心） 知识点：
概念模式映射为关系模式
实体完整性与参照完整性
关系代数与关系演算
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Body of Knowledge in Computer Science(cont.) —— Knowledge Topics in CS-IM信息管理
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Body of Knowledge in Computer Engineering (cont.) —— Knowledge units in CE-DBS 数据库系统
CE-DBS
数据库 系统 （10）
DBS0 历史与概述 （1） DBS1 数据库系统 （2） DBS2 数据建模 （2） DBS3 关系数据库 （3） DBS4 数 据 库 查 询 语 言 （2）
IM9 物理数据库设计（选修） 知识点：
存储结构和文件结构 索引结构（顺序文件上的索引、辅助索引） B树 散列表 签名文件 稠密索引文件 变长记录文件 数据库效率和协调
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Body of Knowledge in Computer Engineering
包括如下18个知识领域： CE-ALG 算法与复杂度 CE-CAO 计算机体系结构和组织 CE-CSE 计算机系统工程 CE-CSG 电路和信号 CE-DBS 数据库系统 CE-DIG 数字逻辑 CE-DSP 数字信号处理 CE-ELE 电子学 CE-ESY 嵌入式系统 CE-HCI 人机交互
数据库系统原理英文PPT课件
I/O system : drivers
memory controllers (i.e. disk controller),
on the basis of secondary storage’s physical structures, such as storage structures, access method
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§1.2 Purpose of Database Systems (cont.)
• Data management on the basis of file systems
• Example
— customer_record=<c_name, c_id, street, city> in Customer_File
February 2011
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第1页/共70页
§1.0 DB, DBMS, DBS
• Definitions in the textbook • Database (DB) — a collection of interrelated data, stored in systems as files • Database management system (DBMS) — DB, or a collection of interrelated data — set of programs to access the data in DB
• Databases and DBS touch all aspects of our lives • Banking: all transactions • Airlines: reservations, schedules • Universities: registration, grades • Sales: customers, products, purchases • Manufacturing: production, inventory, orders, supply chain • Human resources: employee records, salaries, tax deductions
审计学：一种整合方法阿伦斯英文版第12版课后答案Chapter15SolutionsManual
审计学：⼀种整合⽅法阿伦斯英⽂版第12版课后答案Chapter15SolutionsManualChapter 15Audit Sampling for Tests of Controls andSubstantive Tests of TransactionsReview Questions15-1 A representative sample is one in which the characteristics of interest for the sample are approximately the same as for the population (that is, the sample accurately represents the total population). If the population contains significant misstatements, but the sample is practically free of misstatements, the sample is nonrepresentative, which is likely to result in an improper audit decision. The auditor can never know for sure whether he or she has a representative sample because the entire population is ordinarily not tested, but certain things, such as the use of random selection, can increase the likelihood of a representative sample.15-2Statistical sampling is the use of mathematical measurement techniques to calculate formal statistical results. The auditor therefore quantifies sampling risk when statistical sampling is used. In nonstatistical sampling, the auditor does not quantify sampling risk. Instead, conclusions are reached about populations on a more judgmental basis.For both statistical and nonstatistical methods, the three main parts are:1. Plan the sample2. Select the sample and perform the tests3. Evaluate the results15-3In replacement sampling, an element in the population can be included in the sample more than once if the random number corresponding to that element is selected more than once. In nonreplacement sampling, an element can be included only once. If the random number corresponding to an element is selected more than once, it is simply treated as a discard the second time. Although both selection approaches are consistent with sound statistical theory, auditors rarely use replacement sampling; it seems more intuitively satisfying to auditors to include an item only once.15-4 A simple random sample is one in which every possible combination of elements in the population has an equal chance of selection. Two methods of simple random selection are use of a random number table, and use of the computer to generate random numbers. Auditors most often use the computer to generate random numbers because it saves time, reduces the likelihood of error, and provides automatic documentation of the sample selected.15-5In systematic sampling, the auditor calculates an interval and then methodically selects the items for the sample based on the size of the interval. The interval is set by dividing the population size by the number of sample items desired.To select 35 numbers from a population of 1,750, the auditor divides 35 into 1,750 and gets an interval of 50. He or she then selects a random number between 0 and 49. Assume the auditor chooses 17. The first item is the number 17. The next is 67, then 117, 167, and so on.The advantage of systematic sampling is its ease of use. In most populations a systematic sample can be drawn quickly, the approach automatically puts the numbers in sequential order and documentation is easy.A major problem with the use of systematic sampling is the possibility of bias. Because of the way systematic samples are selected, once the first item in the sample is selected, other items are chosen automatically. This causes no problems if the characteristics of interest, such as control deviations, are distributed randomly throughout the population; however, in many cases they are not. If all items of a certain type are processed at certain times of the month or with the use of certain document numbers, a systematically drawn sample has a higher likelihood of failing to obtain a representative sample. This shortcoming is sufficiently serious that some CPA firms prohibit the use of systematic sampling. 15-6The purpose of using nonstatistical sampling for tests of controls and substantive tests of transactions is to estimate the proportion of items in a population containing a characteristic or attribute of interest. The auditor is ordinarily interested in determining internal control deviations or monetary misstatements for tests of controls and substantive tests of transactions.15-7 A block sample is the selection of several items in sequence. Once the first item in the block is selected, the remainder of the block is chosen automatically. Thus, to select 5 blocks of 20 sales invoices, one would select one invoice and the block would be that invoice plus the next 19 entries. This procedure would be repeated 4 other times.15-8 The terms below are defined as follows:15-8 (continued)15-9The sampling unit is the population item from which the auditor selects sample items. The major consideration in defining the sampling unit is making it consistent with the objectives of the audit tests. Thus, the definition of the population and the planned audit procedures usually dictate the appropriate sampling unit.The sampling unit for verifying the occurrence of recorded sales would be the entries in the sales journal since this is the document the auditor wishes to validate. The sampling unit for testing the possibility of omitted sales is the shipping document from which sales are recorded because the failure to bill a shipment is the exception condition of interest to the auditor.15-10 The tolerable exception rate (TER) represents the exception rate that the auditor will permit in the population and still be willing to use the assessed control risk and/or the amount of monetary misstatements in the transactions established during planning. TER is determined by choice of the auditor on the basis of his or her professional judgment.The computed upper exception rate (CUER) is the highest estimated exception rate in the population, at a given ARACR. For nonstatistical sampling, CUER is determined by adding an estimate of sampling error to the SER (sample exception rate). For statistical sampling, CUER is determined by using a statistical sampling table after the auditor has completed the audit testing and therefore knows the number of exceptions in the sample.15-11 Sampling error is an inherent part of sampling that results from testing less than the entire population. Sampling error simply means that the sample is not perfectly representative of the entire population.Nonsampling error occurs when audit tests do not uncover errors that exist in the sample. Nonsampling error can result from:1. The auditor's failure to recognize exceptions, or2. Inappropriate or ineffective audit procedures.There are two ways to reduce sampling risk:1. Increase sample size.2. Use an appropriate method of selecting sample items from thepopulation.Careful design of audit procedures and proper supervision and review are ways to reduce nonsampling risk.15-12 An attribute is the definition of the characteristic being tested and the exception conditions whenever audit sampling is used. The attributes of interest are determined directly from the audit program.15-13 An attribute is the characteristic being tested for in a population. An exception occurs when the attribute being tested for is absent. The exception for the audit procedure, the duplicate sales invoice has been initialed indicating the performance of internal verification, is the lack of initials on duplicate sales invoices.15-14 Tolerable exception rate is the result of an auditor's judgment. The suitable TER is a question of materiality and is therefore affected by both the definition and the importance of the attribute in the audit plan.The sample size for a TER of 6% would be smaller than that for a TER of 3%, all other factors being equal.15-15 The appropriate ARACR is a decision the auditor must make using professional judgment. The degree to which the auditor wishes to reduce assessed control risk below the maximum is the major factor determining the auditor's ARACR.The auditor will choose a smaller sample size for an ARACR of 10% than would be used if the risk were 5%, all other factors being equal.15-16 The relationship between sample size and the four factors determining sample size are as follows:a. As the ARACR increases, the required sample size decreases.b. As the population size increases, the required sample size isnormally unchanged, or may increase slightly.c. As the TER increases, the sample size decreases.d. As the EPER increases, the required sample size increases.15-17 In this situation, the SER is 3%, the sample size is 100 and the ARACR is 5%. From the 5% ARACR table (Table 15-9) then, the CUER is 7.6%. This means that the auditor can state with a 5% risk of being wrong that the true population exception rate does not exceed 7.6%.15-18 Analysis of exceptions is the investigation of individual exceptions to determine the cause of the breakdown in internal control. Such analysis is important because by discovering the nature and causes of individual exceptions, the auditor can more effectively evaluate the effectiveness of internal control. The analysis attempts to tell the "why" and "how" of the exceptions after the auditor already knows how many and what types of exceptions have occurred.15-19 When the CUER exceeds the TER, the auditor may do one or more of the following:1. Revise the TER or the ARACR. This alternative should be followed onlywhen the auditor has concluded that the original specifications weretoo conservative, and when he or she is willing to accept the riskassociated with the higher specifications.2. Expand the sample size. This alternative should be followed whenthe auditor expects the additional benefits to exceed the additionalcosts, that is, the auditor believes that the sample tested was notrepresentative of the population.3. Revise assessed control risk upward. This is likely to increasesubstantive procedures. Revising assessed control risk may bedone if 1 or 2 is not practical and additional substantive proceduresare possible.4. Write a letter to management. This action should be done inconjunction with each of the three alternatives above. Managementshould always be informed when its internal controls are notoperating effectively. If a deficiency in internal control is consideredto be a significant deficiency in the design or operation of internalcontrol, professional standards require the auditor to communicatethe significant deficiency to the audit committee or its equivalent inwriting. If the client is a publicly traded company, the auditor mustevaluate the deficiency to determine the impact on the auditor’sreport on internal control over financial reporting. If the deficiency isdeemed to be a material weakness, the auditor’s report on internalcontrol would contain an adverse opinion.15-20 Random (probabilistic) selection is a part of statistical sampling, but it is not, by itself, statistical measurement. To have statistical measurement, it is necessary to mathematically generalize from the sample to the population.Probabilistic selection must be used if the sample is to be evaluated statistically, although it is also acceptable to use probabilistic selection with a nonstatistical evaluation. If nonprobabilistic selection is used, nonstatistical evaluation must be used.15-21 The decisions the auditor must make in using attributes sampling are: What are the objectives of the audit test? Does audit sampling apply?What attributes are to be tested and what exception conditions are identified?What is the population?What is the sampling unit?What should the TER be?What should the ARACR be?What is the EPER?What generalizations can be made from the sample to thepopulation?What are the causes of the individual exceptions?Is the population acceptable?15-21 (continued)In making the above decisions, the following should be considered: The individual situation.Time and budget constraints.The availability of additional substantive procedures.The professional judgment of the auditor.Multiple Choice Questions From CPA Examinations15-22 a. (1) b. (3) c. (2) d. (4)15-23 a. (1) b. (3) c. (4) d. (4)15-24 a. (4) b. (3) c. (1) d. (2)Discussion Questions and Problems15-25a.An example random sampling plan prepared in Excel (P1525.xls) is available on the Companion Website and on the Instructor’s Resource CD-ROM, which is available upon request. The command for selecting the random number can be entered directly onto the spreadsheet, or can be selected from the function menu (math & trig) functions. It may be necessary to add the analysis tool pack to access the RANDBETWEEN function. Once the formula is entered, it can be copied down to select additional random numbers. When a pair of random numbers is required, the formula for the first random number can be entered in the first column, and the formula for the second random number can be entered in the second column.a. First five numbers using systematic selection:Using systematic selection, the definition of the sampling unit for determining the selection interval for population 3 is the total number of lines in the population. The length of the interval is rounded down to ensure that all line numbers selected are within the defined population.15-26a. To test whether shipments have been billed, a sample of warehouse removal slips should be selected and examined to see ifthey have the proper sales invoice attached. The sampling unit willtherefore be the warehouse removal slip.b. Attributes sampling method: Assuming the auditor is willing to accept a TER of 3% at a 10% ARACR, expecting no exceptions in the sample, the appropriate sample size would be 76, determined from Table 15-8.Nonstatistical sampling method: There is no one right answer to this question because the sample size is determined using professional judgment. Due to the relatively small TER (3%), the sample size should not be small. It will most likely be similar in size to the sample chosen by the statistical method.c. Systematic sample selection:22839 = Population size of warehouse removal slips(37521-14682).76 = Sample size using statistical sampling (students’answers will vary if nonstatistical sampling wasused in part b.300 = Interval (22839/76) if statistical sampling is used (students’ answers will vary if nonstatisticalsampling was used in part b).14825 = Random starting point.Select warehouse removal slip 14825 and every 300th warehouse removal slip after (15125, 15425, etc.)Computer generation of random numbers using Excel (P1526.xls): =RANDBETWEEN(14682,37521)The command for selecting the random number can be entered directly onto the spreadsheet, or can be selected from the function menu (math & trig) functions. It may be necessary to add the analysis tool pack to access the RANDBETWEEN function. Once the formula is entered, it can be copied down to select additional random numbers.d. Other audit procedures that could be performed are:1. Test extensions on attached sales invoices for clerical accuracy. (Accuracy)2. Test time delay between warehouse removal slip date and billing date for timeliness of billing. (Timing)3. Trace entries into perpetual inventory records to determinethat inventory is properly relieved for shipments. (Postingand summarization)15-26 (continued)e. The test performed in part c cannot be used to test for occurrenceof sales because the auditor already knows that inventory wasshipped for these sales. To test for occurrence of sales, the salesinvoice entry in the sales journal is the sampling unit. Since thesales invoice numbers are not identical to the warehouse removalslips it would be improper to use the same sample.15-27a. It would be appropriate to use attributes sampling for all audit procedures except audit procedure 1. Procedure 1 is an analyticalprocedure for which the auditor is doing a 100% review of the entirecash receipts journal.b. The appropriate sampling unit for audit procedures 2-5 is a line item,or the date the prelisting of cash receipts is prepared. The primaryemphasis in the test is the completeness objective and auditprocedure 2 indicates there is a prelisting of cash receipts. All otherprocedures can be performed efficiently and effectively by using theprelisting.c. The attributes for testing are as follows:d. The sample sizes for each attribute are as follows:15-28a. Because the sample sizes under nonstatistical sampling are determined using auditor judgment, students’ answers to thisquestion will vary. They will most likely be similar to the samplesizes chosen using attributes sampling in part b. The importantpoint to remember is that the sample sizes chosen should reflectthe changes in the four factors (ARACR, TER, EPER, andpopulation size). The sample sizes should have fairly predictablerelationships, given the changes in the four factors. The followingreflects some of the relationships that should exist in student’ssample size decisions:SAMPLE SIZE EXPLANATION1. 90 Given2. > Column 1 Decrease in ARACR3. > Column 2 Decrease in TER4. > Column 1 Decrease in ARACR (column 4 is thesame as column 2, with a smallerpopulation size)5. < Column 1 Increase in TER-EPER6. < Column 5 Decrease in EPER7. > Columns 3 & 4 Decrease in TER-EPERb. Using the attributes sampling table in Table 15-8, the sample sizesfor columns 1-7 are:1. 882. 1273. 1814. 1275. 256. 187. 149c.d. The difference in the sample size for columns 3 and 6 result from the larger ARACR and larger TER in column 6. The extremely large TER is the major factor causing the difference.e. The greatest effect on the sample size is the difference between TER and EPER. For columns 3 and 7, the differences between the TER and EPER were 3% and 2% respectively. Those two also had the highest sample size. Where the difference between TER and EPER was great, such as columns 5 and 6, the required sample size was extremely small.Population size had a relatively small effect on sample size.The difference in population size in columns 2 and 4 was 99,000 items, but the increase in sample size for the larger population was marginal (actually the sample sizes were the same using the attributes sampling table).f. The sample size is referred to as the initial sample size because it is based on an estimate of the SER. The actual sample must be evaluated before it is possible to know whether the sample is sufficiently large to achieve the objectives of the test.15-29 a.* Students’ answers as to whether the allowance for sampling error risk is sufficient will vary, depending on their judgment. However, they should recognize the effect that lower sample sizes have on the allowance for sampling risk in situations 3, 5 and 8.b. Using the attributes sampling table in Table 15-9, the CUERs forcolumns 1-8 are:1. 4.0%2. 4.6%3. 9.2%4. 4.6%5. 6.2%6. 16.4%7. 3.0%8. 11.3%c.d. The factor that appears to have the greatest effect is the number ofexceptions found in the sample compared to sample size. For example, in columns 5 and 6, the increase from 2% to 10% SER dramatically increased the CUER. Population size appears to have the least effect. For example, in columns 2 and 4, the CUER was the same using the attributes sampling table even though the population in column 4 was 10 times larger.e. The CUER represents the results of the actual sample whereas theTER represents what the auditor will allow. They must be compared to determine whether or not the population is acceptable.15-30a. and b. The sample sizes and CUERs are shown in the following table:a. The auditor selected a sample size smaller than that determinedfrom the tables in populations 1 and 3. The effect of selecting asmaller sample size than the initial sample size required from thetable is the increased likelihood of having the CUER exceed theTER. If a larger sample size is selected, the result may be a samplesize larger than needed to satisfy TER. That results in excess auditcost. Ultimately, however, the comparison of CUER to TERdetermines whether the sample size was too large or too small.b. The SER and CUER are shown in columns 4 and 5 in thepreceding table.c. The population results are unacceptable for populations 1, 4, and 6.In each of those cases, the CUER exceeds TER.The auditor's options are to change TER or ARACR, increase the sample size, or perform other substantive tests to determine whether there are actually material misstatements in thepopulation. An increase in sample size may be worthwhile inpopulation 1 because the CUER exceeds TER by only a smallamount. Increasing sample size would not likely result in improvedresults for either population 4 or 6 because the CUER exceedsTER by a large amount.d. Analysis of exceptions is necessary even when the population isacceptable because the auditor wants to determine the nature andcause of all exceptions. If, for example, the auditor determines thata misstatement was intentional, additional action would be requiredeven if the CUER were less than TER.15-30 (Continued)e.15-31 a. The actual allowance for sampling risk is shown in the following table:b. The CUER is higher for attribute 1 than attribute 2 because the sample sizeis smaller for attribute 1, resulting in a larger allowance for sampling risk.c. The CUER is higher for attribute 3 than attribute 1 because the auditorselected a lower ARACR. This resulted in a larger allowance for sampling risk to achieve the lower ARACR.d. If the auditor increases the sample size for attribute 4 by 50 items and findsno additional exceptions, the CUER is 5.1% (sample size of 150 and three exceptions). If the auditor finds one exception in the additional items, the CUER is 6.0% (sample size of 150, four exceptions). With a TER of 6%, the sample results will be acceptable if one or no exceptions are found in the additional 50 items. This would require a lower SER in the additional sample than the SER in the original sample of 3.0 percent. Whether a lower rate of exception is likely in the additional sample depends on the rate of exception the auditor expected in designing the sample, and whether the auditor believe the original sample to be representative.15-32a. The following shows which are exceptions and why:b. It is inappropriate to set a single acceptable tolerable exception rate and estimated population exception rate for the combined exceptions because each attribute has a different significance tothe auditor and should be considered separately in analyzing the results of the test.c. The CUER assuming a 5% ARACR for each attribute and a sample size of 150 is as follows:15-32 (continued)d.*Students’ answers will most likely vary for this attribute.e. For each exception, the auditor should check with the controller todetermine an explanation for the cause. In addition, the appropriateanalysis for each type of exception is as follows:15-33a. Attributes sampling approach: The test of control attribute had a 6% SER and a CUER of 12.9%. The substantive test of transactionsattribute has SER of 0% and a CUER of 4.6%.Nonstatistical sampling approach: As in the attributes samplingapproach, the SERs for the test of control and the substantive testof transactions are 6% and 0%, respectively. Students’ estimates ofthe CUERs for the two tests will vary, but will probably be similar tothe CUERs calculated under the attributes sampling approach.b. Attributes sampling approach: TER is 5%. CUERs are 12.9% and4.6%. Therefore, only the substantive test of transactions resultsare satisfactory.Nonstatistical sampling approach: Because the SER for the test ofcontrol is greater than the TER of 5%, the results are clearly notacceptable. Students’ estimates for CUER for the test of controlshould be greater than the SER of 6%. For the substantive test oftransactions, the SER is 0%. It is unlikely that students will estimateCUER for this test greater than 5%, so the results are acceptablefor the substantive test of transactions.c. If the CUER exceeds the TER, the auditor may:1. Revise the TER if he or she thinks the original specificationswere too conservative.2. Expand the sample size if cost permits.3. Alter the substantive procedures if possible.4. Write a letter to management in conjunction with each of theabove to inform management of a deficiency in their internalcontrols. If the client is a publicly traded company, theauditor must evaluate the deficiency to determine the impacton the auditor’s report on internal control over financialreporting. If the deficiency is deemed to be a materialweakness, the auditor’s report on internal control wouldcontain an adverse opinion.In this case, the auditor has evidence that the test of control procedures are not effective, but no exceptions in the sample resulted because of the breakdown. An expansion of the attributestest does not seem advisable and therefore, the auditor shouldprobably expand confirmation of accounts receivable tests. Inaddition, he or she should write a letter to management to informthem of the control breakdown.d. Although misstatements are more likely when controls are noteffective, control deviations do not necessarily result in actualmisstatements. These control deviations involved a lack ofindication of internal verification of pricing, extensions and footingsof invoices. The deviations will not result in actual errors if pricing,extensions and footings were initially correctly calculated, or if theindividual responsible for internal verification performed theprocedure but did not document that it was performed.e. In this case, we want to find out why some invoices are notinternally verified. Possible reasons are incompetence,carelessness, regular clerk on vacation, etc. It is desirable to isolatethe exceptions to certain clerks, time periods or types of invoices.Case15-34a. Audit sampling could be conveniently used for procedures 3 and 4 since each is to be performed on a sample of the population.b. The most appropriate sampling unit for conducting most of the auditsampling tests is the shipping document because most of the testsare related to procedure 4. Following the instructions of the auditprogram, however, the auditor would use sales journal entries asthe sampling unit for step 3 and shipping document numbers forstep 4. Using shipping document numbers, rather than thedocuments themselves, allows the auditor to test the numericalcontrol over shipping documents, as well as to test for unrecordedsales. The selection of numbers will lead to a sample of actualshipping documents upon which tests will be performed.。
曼昆经济学原理Chapter15垄断 中英文笔记
Chapter 15 Monopoly 垄断§1. 垄断Monopoly一．对比竞争企业是价格接受者，垄断企业是价格制定者。
a competitive firm is a price taker, a monopoly firm is a price maker二．定义垄断企业：作为一种没有相近替代品的产品的唯一卖者的企业A firm is considered a monopoly if it is the sole seller of its product & its product does not have close substitutes. 如果一个企业是其产品唯一的卖者，而且如果其产品并没有相近的替代品，这个企业就是垄断者。
§2. 为什么会产生垄断Why Monopolies Arise一．（1）垄断的基本原因fundamental cause：进入障碍barriers to entry（2）进入障碍的三个主要来源Barriers to entry have three sources1.垄断资源：生产所需要的关键资源由一家企业拥有Ownership of a key resource.2.政府管制：政府给予一个企业排他性地生产某种产品或服务的权利The government gives a single firm the exclusive right to produce some good.3.生产流程：生产成本使一个生产者比大量生产者更有效率Costs of production make a single producer more efficient than a large number of producers.二．垄断资源Monopoly Resources虽然关键资源的排他性所有权是垄断的一个潜在原因，但垄断很少产生于这种原因Although exclusive ownership of a key resource is a potential source of monopoly, in practice monopolies rarely arise for this reason.三．政府制造的垄断Government-Created Monopolies1.政府给予一个企业排他性地出售某种物品或劳务的权利，限制其他企业进入市场，从而造成垄断。
数据库原理(双语)-Chapter03
3.1 Brief History of the Relational Model
Relational model was first proposed by E. F. Codd in his seminal(开创性的) paper „A relational model of data for large shared data banks‟ (Codd, 1970) (关系模型 由E. F. Codd 在其开创性论文“～”中首次提出). This paper is now accepted as a landmark in DBS(这篇 论文现在已被看成DBS发展过程中的一个地标). Relational model‟s objectives (关系模型的目标) : To allow a high degree of data independence. (允许高 度的数据独立性) To enable the expansion of set-oriented DML. (扩充面 向集合的DML)
3.1 Brief History of the Relational Model
Owing to the popularity of the relational model, many nonrelational systems now provide a relational user interface (鉴 于关系模型日益流行，许多非关系系统都提供了关系型用户 接口，例如早期的层次和网状数据库). Relational model have been extended to(关系模型已在以下两 个方面得到扩充): support object-oriented concepts(支持面向对象的概念， 产生: 对象关系模型); support deductive capabilities(支持演绎推理能力，产生: 演绎数据库)
北邮-数据库系统原理(英文)-11-15
内部传输速率
disk drive
track
on-board cache: set of blocks Fig. 11.11.0 on-board in device controller
Operating System Concepts - Chapter11 File System Implementation 11
Database System Concepts - Chapter 11 Storage and File Structures - 7
11-I-2 Magnetic Disk
(3) (5) (4) (1)
seeking
rotation
磁柱
(2)
Fig.11.2 Moving-head disk mechanism
Database System Concepts - Chapter 11 Storage and File Structures - 17
11-II Storage Access (cont.)
Application programs call on the buffer manager when they need a block to read or write from disk if the block is already in the buffer, the requesting program is given the address of the block in the buffer if the block is not in the buffer, the buffer manager allocates space in the buffer for the block, replacing (throwing out) some other block, if required, to make spare space for the new block the block that is thrown out is written back to disk only if it was modified since the most recent time that it was written to/fetched from the disk
ch1-数据库系统原理课件(英文版)
Difficulty in accessing data
Data isolation — multintegrity problems
Integrity constraints (e.g. account balance > 0) become ―buried‖ in program code rather than being stated explicitly Hard to add new constraints or change existing ones
Purpose of Database Systems
View of Data Database Languages Relational Databases
Database Design
Object-based and semistructured databases Data Storage and Querying Transaction Management Database Architecture Database Users and Administrators Overall Structure History of Database Systems
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files Need to write a new program to carry out each new task
Language for accessing and manipulating the data organized by the
[数据库原理]【英文版】Chapter03
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Chapter 3
The Relational Model
Relational Model Terminology
A relation is a table with columns and rows. – Two-dimensional table
» Rows: individual records » Columns: attributes
Foreign Key
– Attribute, or set of attributes, within one relation that matches candidate key of some (possibly same) relation.
13
14
Integrity Constraints
7 8
Mathematical Definition of Relation
Any subset of Cartesian product is a relation; e.g., a relation R = {(2, 1), (4, 1)} May specify which pairs are in relation using some condition for selection; e.g., – second element is 1: R = {(x, y) | x ∈D1, y ∈D2, and y = 1} – first element is always twice the second: S = {(x, y) | x ∈D1, y ∈D2, and x = 2y}
Dn .
» {A1: D1, A2: D2, …, An: Dn} is a relation schema » A relation R defined by a relation schema S is a set of mappings from the attribute names to their corresponding domains. » {A1: d1, A2: d2, …, An: dn} such that d1 ∈D1, d2 ∈D2, . . . , dn∈Dn
北邮-数据库系统原理(英文)-12-15
(account-number, branch-name, balance)
logical file account
index file
indexed file
Note: the file account is logically a sequential file, A-217 A-215 A-222 physical but its records may be A-101 A-201 A-305 file account stored non-contiguously A-102 A-218 A-110 or non-ordered on the disk Fig. 12.1 DB indexed file account and its index file
Database System Concepts - Chapter 12 Indexing and Hashing -
3
目 标！！！
Hale Waihona Puke 学会准确建立、管理索引，提高数据访问速 度 索引类型 select、insert、update时的索引管理
Database System Concepts - Chapter 12 Indexing and Hashing -
s1 s2 s3 …
hash indices
B, b1 b2 b3 … bi s1 s2 s3 … si S, …. , … … … … … , D) d1 d2 d3 … di
h(s1)
s1 s2 s3 . . si . . sj . sn 搜索键 (search key)
数据库系统概念(database system concepts)英文第六版 PPT 第15章
requesting and releasing locks. Locking protocols restrict the set of possible schedules.
Database System Concepts - 6th Edition
15.5
©Silberschatz, Korth and Sudarshan
The Two-Phase Locking Protocol (Cont.)
There can be conflict serializable schedules that cannot be obtained if
two-phase locking is used.
However, in the absence of extra information (e.g., ordering of access
to data), two-phase locking is needed for conflict serializability in the following sense: Given a transaction Ti that does not follow two-phase locking, we can find a transaction Tj that uses two-phase locking, and a schedule for Ti and Tj that is not conflict serializable.
©Silberschatz, Korth and Sudarshan
Lock-Based Protocols (Cont.)
Lock-compatibility matrix
数据库原理 英文
数据库原理英文Database PrinciplesIntroduction:Database principles are fundamental concepts that govern the design, management, and use of databases. A database is a structured collection of data that is organized and stored in a manner that allows for efficient retrieval, manipulation, and analysis.Data Models:Data models are used to represent how data is organized and structured within a database. These models determine the relationships between data elements and define the rules for how data is stored and manipulated. Common data models include hierarchical, network, relational, and object-oriented.Relational Model:The relational model is the most widely used data model in modern databases. It organizes data into relations, which are tables with rows and columns. Each row represents a record, and each column represents a characteristic or attribute of that record. Relationships between tables are established through primary keys and foreign keys.Normalization:Normalization is the process of designing database tables to reduce redundancy and improve data integrity. It involves breaking down large tables into smaller ones and creating relationships between them. The goal is to eliminate data anomalies and ensure that eachpiece of data is stored in one place only.Query Languages:Query languages allow users to retrieve, manipulate, and update data in a database. The most common query language is Structured Query Language (SQL), which is used to interact with relational databases. SQL provides a set of commands and functions that enable users to perform operations such as data retrieval, insertion, deletion, and modification.Indexing and Query Optimization:Indexes are data structures that improve the speed of data retrieval operations. They provide a way to locate data quickly based on specific criteria. Query optimization involves analyzing and rearranging queries to execute them in the most efficient way possible. Techniques such as storing intermediate results, using parallel processing, and selecting appropriate indexing strategies are commonly employed.Transaction Management:A transaction is a unit of work that consists of one or more operations performed on a database. Transaction management ensures the atomicity, consistency, isolation, and durability of database operations. Transactions are usually managed by a database management system (DBMS) through the use of transaction logs and concurrency control mechanisms. Concurrency Control:Concurrency control prevents conflicts when multiple users try to access or modify the same data simultaneously. Techniques suchas locking, timestamping, and optimistic concurrency control are used to manage concurrent access and ensure data consistency. Backup and Recovery:Backup and recovery involve creating copies of a database to protect against data loss and ensuring that data can be restored in the event of a failure. Backups can be performed at different levels (database, table, or file) and can be either full or incremental. Recovery mechanisms restore the database to a consistent state after a failure, using backup copies and transaction logs. Conclusion:Understanding database principles is essential for designing efficient and robust databases. Data modeling, normalization, query languages, indexing, transaction management, concurrency control, and backup and recovery are key concepts that form the foundation of database systems. By applying these principles, database professionals can optimize data storage, retrieval, and manipulation, leading to better performance and data integrity.。
[数据库原理]【英文版】Chapter14
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Methodology Overview - Physical Database Design for Relational Databases
Step 3 Translate logical data model for target DBMS – Step 3.1 Design base relations – Step 3.2 Design representation of derived data – Step 3.3 Design general constraints Step 4 Design file organizations and indexes – Step 4.1 Analyze transactions – Step 4.2 Choose file organization – Step 4.3 Choose indexes – Step 4.4 Estimate disk space requirements Step 5 Design user views Step 6 Design security mechanisms Step 7 Consider the introduction of controlled redundancy Step 8 Monitor and tune the operational system
Critical Success Factors in Database Design
Work interactively with users as much as possible. Follow a structured methodology throughout the data modeling process. Employ a data-driven approach. Incorporate structural and integrity considerations into the data models. Combine conceptualization, normalization, and transaction validation techniques into the data modeling methodology. Use diagrams to represent as much of the data models as possible. Use a Database Design Language (DBDL) to represent additional data semantics. Build a data dictionary to supplement the data model diagrams. Be willing to repeat steps.
曼昆经济学原理英文版文案加习题答案15章
曼昆经济学原理英⽂版⽂案加习题答案15章stic CompetitionWHAT’S NEW IN THE S EVENTH EDITION:There are no major changes to this chapter.LEARNING OBJECTIVES:By the end of this chapter, students should understand:what market structures lie between monopoly and competition.competition among firms that sell differentiated products.how the outcomes under monopolistic competition and under perfect competition compare.the desirability of outcomes in monopolistically competitive markets.the debate over the effects of advertising.the debate over the role of brand names.CONTEXT AND PURPOSE:Chapter 16 is the fourth chapter in a five-chapter sequence dealing with firm behavior and the organization of industry. The previous two chapters developed the two extreme forms of market structure —competition and monopoly. The market structure that lies betweenMONOPOLISTIC COMPETITION16competition and monopoly is known as imperfect competition. There are two types of imperfect competition—monopolistic competition and oligopoly. This chapter addresses monopolistic competition while the final chapter in the sequence addresses oligopoly. The analysis in this chapter is again based on the cost curves developed in Chapter 13.The purpose of Chapter 16 is to address monopolistic competition—a market structure in which many firms sell products that are similar but not identical. Monopolistic competition differs from perfect competition because each of the many sellers offers a somewhat different product. As a result, monopolistically competitive firms face a downward-sloping demand curve while competitive firms face a horizontal demand curve at the market price. Monopolistic competition is extremely common.KEY POINTS:A monopolistically competitive market is characterized by three attributes: many firms,differentiated products, and free entry.The long-run equilibrium in a monopolistically competitive market differs from that in a perfectly competitive market in two related ways. First, each firm in a monopolistically competitive market has excess capacity. That is, it chooses a quantity that puts it on the downward-sloping portion of the average-total-cost curve. Second, each firm charges a price above marginal cost.Monopolistic competition does not have all of the desirable properties of perfectcompetition. There is the standard deadweight loss of monopoly caused by the markup of price over marginal cost. In addition, the number of firms (and thus the variety ofproducts) can be too large or too small. In practice, the ability of policymakers tocorrect these inefficiencies is limited.The product differentiation inherent in monopolistic competition leads to the use ofadvertising and brand names. Critics of advertising and brand names argue that firms usethem to manipulate consumers’ tast es and to reduce competition. Defenders of advertising and brand names argue that firms use them to inform consumers and to compete morevigorously on price and product quality.CHAPTER OUTLINE:I. Between Monopoly and Perfect CompetitionA. The typical firm has some market power, but its market power is not as great as thatdescribed by monopoly.B. Firms in imperfect competition lie somewhere between the competitive model and themonopoly model.C. Definition of oligopoly: a market structure in which only a few sellers offer similaror identical products.1. Economists measure a market’s domination by a small number of firms with astatistic called a concentration ratio.2. The concentration ratio is the percentage of total output in the market suppliedby the four largest firms.3. In the . economy, most industries have a four-firm concentration ratio under 50%.D. Definition of monopolistic competition: a market structure in which many firms sellproducts that are similar but not identical.1. Characteristics of Monopolistic Competitiona. Many Sellersb. Product Differentiationc. Free EntryE. Figure 1 summarizes the four types of market structure. Note that it is the number offirms and the type of product sold that distinguishes one market structure fromanother.II. Competition with Differentiated ProductsA. The Monopolistically Competitive Firm in the Short Run1. Each firm in monopolistic competition faces a downward-sloping demand curvebecause its product is different from those offered by other firms.2. The monopolistically competitive firm follows a monopolist's rule for maximizingprofit.a. It chooses the output level where marginal revenue is equal to marginal cost.b. It sets the price using the demand curve to ensure that consumers will demand exactly the amount produced.Figure 23. We can determine whether or not the monopolistically competitive firm is earning a profit or loss by comparing price and average total cost.a. If P > ATC, the firm is earning a profit.b. If P < ATC, the firm is earning a loss.c. If P = ATC, the firm is earning zero economic profit.B. The Long-Run Equilibrium1. When firms in monopolistic competition are making profit, new firms have an incentive to enter the market.a. This increases the number of products from which consumers can choose.b. Thus, the demand curve faced by each firm shifts to the left.c. As the demand falls, these firms experience declining profit.2. When firms in monopolistic competition are incurring losses, firms in the market will have an incentive to exit.a. Consumers will have fewer products from which to choose.b. Thus, the demand curve for each firm shifts to the right.c. The losses of the remaining firms will fall.3. The process of exit and entry continues until the firms in the market are earning zero profit.a. This means that the demand curve and the average-total-cost curve are tangentto each other.b. At this point, price is equal to average total cost and the firm is earningzero economic profit.Figure 3Remember that students have a hard time understanding why a firm willcontinue to operate if it is earning “only” zero economic profit. Remind4. There are two characteristics that describe the long-run equilibrium in a monopolistically competitive market.a. Price exceeds marginal cost (due to the fact that each firm faces a downward-sloping demand curve).b. Price equals average total cost (due to the freedom of entry and exit).C. Monopolistic versus Perfect Competition1. Excess Capacitya. The quantity of output produced by a monopolistically competitive firm is smaller than the quantity that minimizes average total cost (the efficient scale).b. This implies that firms in monopolistic competition have excess capacity, because the firm could increase its output and lower its average total cost of production.c. Because firms in perfect competition produce where price is equal to the minimum average total cost, firms in perfect competition produce at theirefficient scale.2. Markup over Marginal Costa. In monopolistic competition, price is greater than marginal cost because the firm has some market power.b. In perfect competition, price is equal to marginal cost.D. Monopolistic Competition and the Welfare of Society1. One source of inefficiency is the markup over marginal cost. This implies a deadweight loss (similar to that caused by monopolies).2. Because there are so many firms in this type of market structure, regulating these firms would be difficult.3. Also, forcing these firms to set price equal to marginal cost would force them out of business (because they are already earning zero economic profit).4. There are also externalities associated with entry.a. The product-variety externality occurs because as new firms enter, consumers get some consumer surplus from the introduction of a new product. Note thatthis is a positive externality.b. The business-stealing externality occurs because as new firms enter, other firms lose customers and profit. Note that this is a negative externality.c. Depending on which externality is larger, a monopolistically competitive market could have too few or too many products.5. In the News: Insufficient Variety as a Market Failurea. Firms may insufficiently service consumers with unusual preferences in marketswith large fixed costsb. This article from Slate describes how some consumers get left out of the market because of the high fixed costs associated with creating additional varietiesof a product.III. AdvertisingA. The Debate over Advertising1. The Critique of Advertisinga. Firms advertise to manipulate people's tastes.b. Advertising impedes competition because it increases the perception of product differentiation and fosters brand loyalty. This means that consumers will beless concerned with price differences among similar goods.2. The Defense of Advertisinga. Firms use advertising to provide information to consumers.b. Advertising fosters competition because it allows consumers to be betterinformed about all of the firms in the market.3. Case Study: Advertising and the Price of Eyeglassesa. In the United States during the 1960s, states differed on whether or not theyallowed advertising for optometrists.b. In the states that prohibited advertising, the average price paid for a pair ofeyeglasses in 1963 was $33; in states that allowed advertising, the averageprice was $26 (a difference of more than 20%).B. Advertising as a Signal of Quality1. The willingness of a firm to spend a large amount of money on advertising may be a signal to consumers about the quality of the product being offered.2. Example: Kellogg and Post have each developed a new cereal that would sell for $3per box. (Assume that the marginal cost of producing the cereal is zero.) Eachcompany knows that if it spends $10 million on advertising, it will get onemillion new consumers to try the product. If consumers like the product, they will buy it again.a. Post has discovered through market research that its new cereal is not verygood. After buying it once, consumers would not likely buy it again. Thus, itwill only earn $3 million in revenue, which would not be enough to pay for the advertising. Therefore, it does not advertise.b. Kellogg knows that its cereal is great. Each person that buys it will likelybuy one box per month for the next year. Therefore, its sales would be $36million, which is more than enough to justify the advertisement.c. By its willingness to spend money on advertising, Kellogg signals to consumersthe quality of its cereal.3. Note that the content of the advertisement is unimportant; what is important isthat consumers know that the advertisements are expensive.C. Brand Names1. In many markets there are two types of firms; some firms sell products with widelyrecognized brand names while others sell generic substitutes.2. Critics of brand names argue that they cause consumers to perceive differencesthat do not really exist.3. Economists have defended brand names as a useful way to ensure that goods are ofhigh quality.a. Brand names provide consumers with information about quality when qualitycannot be judged easily in advance of purchase.b. Brand names give firms an incentive to maintain high quality, because firmshave a financial stake in maintaining the reputation of their brand names.SOLUTIONS TO TEXT PROBLEMS:Quick Quizzes1. Oligopoly is a market structure in which only a few sellers offer similar oridentical products. Examples include the market for breakfast cereals and the world market for crude oil. Monopolistic competition is a market structure in which many firms sell products that are similar but not identical. Examplesinclude the markets for novels, movies, restaurant meals, and computer games.2. The three key attributes of monopolistic competition are: (1) there are manysellers; (2) each firm produces a slightly different product; and (3) firms can enter or exit the market freely.Figure 1 shows the long-run equilibrium in a monopolistically competitive market.This equilibrium differs from that in a perfectly competitive market because price exceeds marginal cost and the firm does not produce at the minimum point ofaverage total cost but instead produces at less than the efficient scale.Figure 13. Advertising may make m arkets less competitive if it manipulates people’s tastesrather than being informative. Advertising may give consumers the perception that there is a greater difference between two products than really exists. That makes the demand curve for a product more inelastic, so the firms can then chargegreater markups over marginal cost. However, some advertising could make markets more competitive because it sometimes provides useful information to consumers,allowing them to take advantage of price differences more easily. Advertising alsofacilitates entry because it can be used to inform consumers about a new product.In addition, expensive advertising can be a signal of quality.Brand names may be beneficial because they provide information to consumers aboutthe quality of goods. They also give firms an incentive to maintain high quality,since their reputations are important. But brand names may be criticized becausethey may simply differentiate products that are not really different, as in thecase of drugs that are identical with the brand-name drug selling at a much higherprice than the generic drug.Questions for Review1. The three attributes of monopolistic competition are: (1) there are many sellers;(2) each seller produces a slightly different product; and (3) firms can enter orexit the market without restriction. Monopolistic competition is like monopolybecause firms face a downward-sloping demand curve, so price exceeds marginal cost.Monopolistic competition is like perfect competition because, in the long run,price equals average total cost, as free entry and exit drive economic profit tozero.2. In Figure 2, a firm has demand curve D1 and marginal-revenue curve MR1. The firm ismaking profits because at quantity Q1, price (P1) is above average total cost (ATC).Those profits induce other firms to enter the industry, causing the demand curveto shift to D2 and the marginal-revenue curve to shift to MR2. The result is adecline in quantity to Q2, at which point the price (P2) equals average total cost(ATC), so profits are now zero.Figure 23. Figure 3 shows the long-run equilibrium in a monopolistically competitive market.Price equals average total cost. Price is above marginal cost.Figure 34. Because, in equilibrium, price is above marginal cost, a monopolistic competitorproduces too little output. But this is a hard problem to solve because: (1) the administrative burden of regulating the large number of monopolisticallycompetitive firms would be high; and (2) the firms are earning zero economicprofits, so forcing them to price at marginal cost means that firms would lose money unless the government subsidized them.5. Advertising might reduce economic well-being because it manipulates people'stastes and impedes competition by making products appear more different than theyreally are. But advertising might increase economic well-being by providing usefulinformation to consumers and fostering competition.6. Advertising with no apparent informational content might convey information to consumers if it provides a signal of quality. A firm will not be willing to spendmuch money advertising a low-quality good, but may be willing to spend significantly more to advertise a high-quality good.7. The two benefits that might arise from the existence of brand names are: (1) brand names provide consumers information about quality when quality cannot be easily judged in advance; and (2) brand names give firms an incentive to maintain high quality to maintain the reputation of their brand names.Quick Check Multiple Choice1. b2. d3. a4. d5. a6. cProblems and Applications1. a. Tap water is a monopoly because there is a single seller of tap water to a household .b. Bottled water is a monopolistically competitive market. There are many sellersof bottled water, but each firm tries to differentiate its own brand from therest.c. The cola market is an oligopoly. There are only a few firms that control alarge portion of the market.d. The beer market is an oligopoly. There are only a few firms that control alarge portion of the market.2. a. The market for wooden #2 pencils is perfectly competitive because pencils by any manufacturer are identical and there are a large number of manufacturers.b. The market for copper is perfectly competitive, because all copper is identical and there are a large number of producers.c. The market for local electricity service is monopolistic because it is anatural monopoly—it is cheaper for one firm to supply all the output.d. The market for peanut butter is monopolistically competitive because different brand names exist with different quality characteristics.e. The market for lipstick is monopolistically competitive because lipstick fromdifferent firms differs slightly, but there are a large number of firms thatcan enter or exit without restriction.3. a. A firm in monopolistic competition sells a differentiated product from itscompetitors.b. A firm in monopolistic competition has marginal revenue less than price.c. Neither a firm in monopolistic competition nor in perfect competition earnseconomic profit in the long run.d. A firm in perfect competition produces at the minimum average total cost in thelong run.e. Both a firm in monopolistic competition and a firm in perfect competitionequate marginal revenue and marginal cost.f. A firm in monopolistic competition charges a price above marginal cost.4. a. Both a firm in monopolistic competition and a monopoly firm face a downward-sloping demand curve.b. Both a firm in monopolistic competition and a monopoly firm have marginalrevenue that is less than price.c. A firm in monopolistic competition faces the entry of new firms selling similarproducts.d. A monopoly firm earns economic profit in the long run.e. Both a firm in monopolistic competition and a monopoly firm equate marginalrevenue and marginal cost.f. Neither a firm in monopolistic competition nor a monopoly firm produces thesocially efficient quantity of output.5. a. The firm is not maximizing profit. For a firm in monopolistic competition,price is greater than marginal revenue. If price is below marginal cost,marginal revenue must be less than marginal cost. Thus, the firm should reduce its output to increase its profit.b. The firm may be maximizing profit if marginal revenue is equal to marginal cost.However, the firm is not in long-run equilibrium because price is less thanaverage total cost. In this case, firms will exit the industry and the demandfacing the remaining firms will rise until economic profit is zero.c. The firm is not maximizing profit. For a firm in monopolistic competition,price is greater than marginal revenue. If price is equal to marginal cost,marginal revenue must be less than marginal cost. Thus, the firm should reduce its output to increase its profit.。
牛津英语译林版七年级下册阅读训练 --7下英语读本 Chapter 15 - 教师版
Chapter 15诵读Help in need帮助有需要帮助的I often go to the park near my home. I always see a little boy there. He wears a white T-shirt and black trousers. In front of him is a basket of flowers. He sells flowers from early morning to late at night.我经常去我家附近的公园。
我总是在那里看到一个小男孩。
他穿着白色的t恤和黑色的裤子。
在他面前的是一篮花。
他从早到晚卖花。
Some other boys also sell flowers in front of the park. But no one is like this boy. He asks everyone to buy his flowers. When he sees me, he always follows me and says, “Please buy a flower. Pl ease.” I don’t like that, and I never buy any flowers from him.其他一些男孩也在公园前面卖花。
但是没有人能像这个男孩。
他让每个人都买他的花。
当他看到我，他总是跟着我说，“请买一朵花。
”请。
“我不喜欢这样，我从来没有从他那里买过花。
Today, I go to the park again. The boy is there. He sits in the same place. I don’t want him to follow me, so I don’t look at him. I walk past him into the park.今天，我又去了公园。
数据库原理h15
restart the transaction – only if no internal logical error kill the transaction
Committed, after successful completion.
Database System Concchatz, Korth and Sudarshan
Database System Concepts
15.8
©Silberschatz, Korth and Sudarshan
Implementation of Atomicity and Durability (Cont.)
曼昆经济学原理英文版文案加习题答案15章
WHAT ’S NEW IN THE SEVENTH EDITION:There are no major changes to this chapter.LEARNING OBJECTIVES:By the end of this chapter, students should understand:➢ what market structures lie between monopoly and competition.➢ competition among firms that sell differentiated products.➢ how the outcomes under monopolistic competition and under perfect competition compare.➢ the desirability of outcomes in monopolistically competitive markets.➢ the debate over the effects of advertising.➢ the debate over the role of brand names.CONTEXT AND PURPOSE:Chapter 16 is the fourth chapter in a five-chapter sequence dealing with firm behavior and the organization of industry. The previous two chapters developed the two extreme forms of market structure —competition and monopoly. The market structure that lies between competition and monopoly is known as imperfect competition. There are two types of imperfect competition —monopolistic competition and oligopoly. This chapter addresses monopolistic competition while the final chapter in the sequence addresses oligopoly. The analysis in this chapter is again based on the cost curves developed in Chapter 13.MONOPOLISTIC COMPETITION16The purpose of Chapter 16 is to address monopolistic competition—a market structure in which many firms sell products that are similar but not identical. Monopolistic competition differs from perfect competition because each of the many sellers offers a somewhat different product. As a result, monopolistically competitive firms face a downward-sloping demand curve while competitive firms face a horizontal demand curve at the market price. Monopolistic competition is extremely common.KEY POINTS:• A monopolistically competitive market is characterized by three attributes: many firms, differentiated products, and free entry.•The long-run equilibrium in a monopolistically competitive market differs from that in a perfectly competitive market in two related ways. First, each firm in a monopolistically competitive market has excess capacity. That is, it chooses a quantity that puts it on the downward-sloping portion of the average-total-cost curve. Second, each firm charges a price above marginal cost.•Monopolistic competition does not have all of the desirable properties of perfect competition.There is the standard deadweight loss of monopoly caused by the markup of price over marginal cost. In addition, the number of firms (and thus the variety of products) can be too large or too small. In practice, the ability of policymakers to correct these inefficiencies is limited.•The product differentiation inherent in monopolistic competition leads to the use of advertising and brand names. Critics of advertising and brand names argue that firms use them to manipulate consumers’ tastes and to reduce competition. Defenders of advertising and brand names argue that firms use them to inform consumers and to compete more vigorously on price and product quality.CHAPTER OUTLINE:I. Between Monopoly and Perfect CompetitionA. The typical firm has some market power, but its market power is not as great as thatdescribed by monopoly.B. Firms in imperfect competition lie somewhere between the competitive model and themonopoly model.C. Definition of oligopoly: a market structure in which only a few sellers offer similar oridentical products.1. Economists measure a market’s domination by a small number of firms with astatistic called a concentration ratio.2. The concentration ratio is the percentage of total output in the market supplied bythe four largest firms.3. In the U.S. economy, most industries have a four-firm concentration ratio under50%.D. Definition of monopolistic competition: a market structure in which many firms sellproducts that are similar but not identical.1. Characteristics of Monopolistic Competitiona. Many Sellersb. Product Differentiationc. Free EntryE. Figure 1 summarizes the four types of market structure. Note that it is the number offirms and the type of product sold that distinguishes one market structure fromanother.II. Competition with Differentiated ProductsA. The Monopolistically Competitive Firm in the Short Run1. Each firm in monopolistic competition faces a downward-sloping demand curvebecause its product is different from those offered by other firms.2. The monopolistically competitive firm follows a monopolist's rule for maximizingprofit.a. It chooses the output level where marginal revenue is equal to marginal cost.b. It sets the price using the demand curve to ensure that consumers will demandexactly the amount produced.Figure 23. We can determine whether or not the monopolistically competitive firm is earning aprofit or loss by comparing price and average total cost.a. If P > ATC, the firm is earning a profit.b. If P < ATC, the firm is earning a loss.c. If P = ATC, the firm is earning zero economic profit.B. The Long-Run Equilibrium1. When firms in monopolistic competition are making profit, new firms have anincentive to enter the market.a. This increases the number of products from which consumers can choose.b. Thus, the demand curve faced by each firm shifts to the left.c. As the demand falls, these firms experience declining profit.2. When firms in monopolistic competition are incurring losses, firms in the marketwill have an incentive to exit.a. Consumers will have fewer products from which to choose.b. Thus, the demand curve for each firm shifts to the right.c. The losses of the remaining firms will fall.3. The process of exit and entry continues until the firms in the market are earningzero profit.a. This means that the demand curve and the average-total-cost curve are tangentto each other.b. At this point, price is equal to average total cost and the firm is earning zeroeconomic profit.4. There are two characteristics that describe the long-run equilibrium in amonopolistically competitive market. Point out to students that, just like firms in perfect competition, firms in monopolisticcompetition also earn zero economic profit in the long run. Show them that this result occurs because firms can freely enter the market when profits occur, drivingthe level of profits to zero. Any market with no barriers to entry will see zeroeconomic profit in the long run.Remember that students have a hard time understanding why a firm will continue to operate if it is earning “only” zero economic profit. Remind them that zero economic profit means that firms are earning an accounting profit equal to their implicit costs.Figure 3a. Price exceeds marginal cost (due to the fact that each firm faces a downward-sloping demand curve).b. Price equals average total cost (due to the freedom of entry and exit).C. Monopolistic versus Perfect Competition1. Excess Capacitya. The quantity of output produced by a monopolistically competitive firm issmaller than the quantity that minimizes average total cost (the efficient scale).b. This implies that firms in monopolistic competition have excess capacity,because the firm could increase its output and lower its average total cost ofproduction.c. Because firms in perfect competition produce where price is equal to theminimum average total cost, firms in perfect competition produce at theirefficient scale.2. Markup over Marginal Costa. In monopolistic competition, price is greater than marginal cost because the firmhas some market power.b. In perfect competition, price is equal to marginal cost.D. Monopolistic Competition and the Welfare of Society1. One source of inefficiency is the markup over marginal cost. This implies adeadweight loss (similar to that caused by monopolies).2. Because there are so many firms in this type of market structure, regulating thesefirms would be difficult.3. Also, forcing these firms to set price equal to marginal cost would force them out ofbusiness (because they are already earning zero economic profit).4. There are also externalities associated with entry.a. The product-variety externality occurs because as new firms enter, consumersget some consumer surplus from the introduction of a new product. Note thatthis is a positive externality.b. The business-stealing externality occurs because as new firms enter, other firmslose customers and profit. Note that this is a negative externality.c. Depending on which externality is larger, a monopolistically competitive marketcould have too few or too many products.5. In the News: Insufficient Variety as a Market Failurea. Firms may insufficiently service consumers with unusual preferences in marketswith large fixed costsb. This article from Slate describes how some consumers get left out of the marketbecause of the high fixed costs associated with creating additional varieties of aproduct.III. AdvertisingA. The Debate over Advertising1. The Critique of Advertisinga. Firms advertise to manipulate people's tastes.b. Advertising impedes competition because it increases the perception of productdifferentiation and fosters brand loyalty. This means that consumers will be lessconcerned with price differences among similar goods.2. The Defense of Advertisinga. Firms use advertising to provide information to consumers.b. Advertising fosters competition because it allows consumers to be betterinformed about all of the firms in the market.3. Case Study: Advertising and the Price of Eyeglassesa. In the United States during the 1960s, states differed on whether or not theyallowed advertising for optometrists.b. In the states that prohibited advertising, the average price paid for a pair ofeyeglasses in 1963 was $33; in states that allowed advertising, the average pricewas $26 (a difference of more than 20%).B. Advertising as a Signal of Quality1. The willingness of a firm to spend a large amount of money on advertising may be asignal to consumers about the quality of the product being offered.2. Example: Kellogg and Post have each developed a new cereal that would sell for $3per box. (Assume that the marginal cost of producing the cereal is zero.) Eachcompany knows that if it spends $10 million on advertising, it will get one millionnew consumers to try the product. If consumers like the product, they will buy itagain.a. Post has discovered through market research that its new cereal is not very good.After buying it once, consumers would not likely buy it again. Thus, it will onlyearn $3 million in revenue, which would not be enough to pay for the advertising.Therefore, it does not advertise.b. Kellogg knows that its cereal is great. Each person that buys it will likely buyone box per month for the next year. Therefore, its sales would be $36 million,which is more than enough to justify the advertisement.c. By its willingness to spend money on advertising, Kellogg signals to consumersthe quality of its cereal.3. Note that the content of the advertisement is unimportant; what is important is thatconsumers know that the advertisements are expensive.C. Brand Names1. In many markets there are two types of firms; some firms sell products with widelyrecognized brand names while others sell generic substitutes.2. Critics of brand names argue that they cause consumers to perceive differences thatdo not really exist.3. Economists have defended brand names as a useful way to ensure that goods are ofhigh quality.a. Brand names provide consumers with information about quality when qualitycannot be judged easily in advance of purchase.b. Brand names give firms an incentive to maintain high quality, because firmshave a financial stake in maintaining the reputation of their brand names.SOLUTIONS TO TEXT PROBLEMS:Quick Quizzes1. Oligopoly is a market structure in which only a few sellers offer similar or identicalproducts. Examples include the market for breakfast cereals and the world marketfor crude oil. Monopolistic competition is a market structure in which many firmssell products that are similar but not identical. Examples include the markets fornovels, movies, restaurant meals, and computer games.2. The three key attributes of monopolistic competition are: (1) there are many sellers;(2) each firm produces a slightly different product; and (3) firms can enter or exit themarket freely.Figure 1 shows the long-run equilibrium in a monopolistically competitive market.This equilibrium differs from that in a perfectly competitive market because priceexceeds marginal cost and the firm does not produce at the minimum point ofaverage total cost but instead produces at less than the efficient scale.Figure 13. Advertising may make markets less competitive if it manipulates people’s tastesrather than being informative. Advertising may give consumers the perception thatthere is a greater difference between two products than really exists. That makes thedemand curve for a product more inelastic, so the firms can then charge greatermarkups over marginal cost. However, some advertising could make markets morecompetitive because it sometimes provides useful information to consumers,allowing them to take advantage of price differences more easily. Advertising alsofacilitates entry because it can be used to inform consumers about a new product.In addition, expensive advertising can be a signal of quality.Brand names may be beneficial because they provide information to consumersabout the quality of goods. They also give firms an incentive to maintain high quality,since their reputations are important. But brand names may be criticized becausethey may simply differentiate products that are not really different, as in the case ofdrugs that are identical with the brand-name drug selling at a much higher pricethan the generic drug.Questions for Review1. The three attributes of monopolistic competition are: (1) there are many sellers; (2)each seller produces a slightly different product; and (3) firms can enter or exit the market without restriction. Monopolistic competition is like monopoly because firms face a downward-sloping demand curve, so price exceeds marginal cost.Monopolistic competition is like perfect competition because, in the long run, price equals average total cost, as free entry and exit drive economic profit to zero.2. In Figure 2, a firm has demand curve D1 and marginal-revenue curve MR1. The firmis making profits because at quantity Q1, price (P1) is above average total cost (ATC).Those profits induce other firms to enter the industry, causing the demand curve to shift to D2 and the marginal-revenue curve to shift to MR2. The result is a decline in quantity to Q2, at which point the price (P2) equals average total cost (ATC), soprofits are now zero.Figure 23. Figure 3 shows the long-run equilibrium in a monopolistically competitive market.Price equals average total cost. Price is above marginal cost.Figure 34. Because, in equilibrium, price is above marginal cost, a monopolistic competitorproduces too little output. But this is a hard problem to solve because: (1) theadministrative burden of regulating the large number of monopolisticallycompetitive firms would be high; and (2) the firms are earning zero economic profits,so forcing them to price at marginal cost means that firms would lose money unlessthe government subsidized them.5. Advertising might reduce economic well-being because it manipulates people'stastes and impedes competition by making products appear more different thanthey really are. But advertising might increase economic well-being by providinguseful information to consumers and fostering competition.6. Advertising with no apparent informational content might convey information toconsumers if it provides a signal of quality. A firm will not be willing to spend muchmoney advertising a low-quality good, but may be willing to spend significantly moreto advertise a high-quality good.7. The two benefits that might arise from the existence of brand names are: (1) brandnames provide consumers information about quality when quality cannot be easilyjudged in advance; and (2) brand names give firms an incentive to maintain highquality to maintain the reputation of their brand names.Quick Check Multiple Choice1. b2. d3. a4. d5. a6. cProblems and Applications1. a. Tap water is a monopoly because there is a single seller of tap water to ahousehold .b. Bottled water is a monopolistically competitive market. There are many sellers ofbottled water, but each firm tries to differentiate its own brand from the rest.c. The cola market is an oligopoly. There are only a few firms that control a largeportion of the market.d. The beer market is an oligopoly. There are only a few firms that control a largeportion of the market.2. a. The market for wooden #2 pencils is perfectly competitive because pencils byany manufacturer are identical and there are a large number of manufacturers.b. The market for copper is perfectly competitive, because all copper is identicaland there are a large number of producers.c. The market for local electricity service is monopolistic because it is a naturalmonopoly—it is cheaper for one firm to supply all the output.d. The market for peanut butter is monopolistically competitive because differentbrand names exist with different quality characteristics.e. The market for lipstick is monopolistically competitive because lipstick fromdifferent firms differs slightly, but there are a large number of firms that canenter or exit without restriction.3. a. A firm in monopolistic competition sells a differentiated product from itscompetitors.b. A firm in monopolistic competition has marginal revenue less than price.c. Neither a firm in monopolistic competition nor in perfect competition earnseconomic profit in the long run.d. A firm in perfect competition produces at the minimum average total cost in thelong run.e. Both a firm in monopolistic competition and a firm in perfect competition equatemarginal revenue and marginal cost.f. A firm in monopolistic competition charges a price above marginal cost.4. a. Both a firm in monopolistic competition and a monopoly firm face a downward-sloping demand curve.b. Both a firm in monopolistic competition and a monopoly firm have marginalrevenue that is less than price.c. A firm in monopolistic competition faces the entry of new firms selling similarproducts.d. A monopoly firm earns economic profit in the long run.e. Both a firm in monopolistic competition and a monopoly firm equate marginalrevenue and marginal cost.f. Neither a firm in monopolistic competition nor a monopoly firm produces thesocially efficient quantity of output.5. a. The firm is not maximizing profit. For a firm in monopolistic competition, price isgreater than marginal revenue. If price is below marginal cost, marginal revenue must be less than marginal cost. Thus, the firm should reduce its output toincrease its profit.b. The firm may be maximizing profit if marginal revenue is equal to marginal cost.However, the firm is not in long-run equilibrium because price is less thanaverage total cost. In this case, firms will exit the industry and the demandfacing the remaining firms will rise until economic profit is zero.c. The firm is not maximizing profit. For a firm in monopolistic competition, price isgreater than marginal revenue. If price is equal to marginal cost, marginalrevenue must be less than marginal cost. Thus, the firm should reduce itsoutput to increase its profit.d. The firm could be maximizing profit if marginal revenue is equal to marginal cost.The firm is in long-run equilibrium because price is equal to average total cost.Therefore, the firm is earning zero economic profit.6. a. Figure 4 illustrates the market for Sparkle toothpaste in long-run equilibrium.The profit-maximizing level of output is Q M and the price is P M.Figure 4b. Sparkle's profit is zero, because at quantity Q M, price equals average total cost.c. The consumer surplus from the purchase of Sparkle toothpaste is areas A + B.The efficient level of output occurs where the demand curve intersects themarginal-cost curve, at Q C. The deadweight loss is area C, the area abovemarginal cost and below demand, from Q M to Q C.d. If the government forced Sparkle to produce the efficient level of output, the firmwould lose money because average total cost would exceed price, so the firmwould shut down. If that happened, Sparkle's customers would earn noconsumer surplus.7. a. As N rises, the demand for each firm’s product falls. As a result, each firm’sdemand curve will shift left.b. The firm will produce where MR = MC:100/N– 2Q = 2QQ = 25/Nc. 25/N = 100/N–PP = 75/Nd. Total revenue = P⨯Q = 75/N⨯ 25/N = 1875/N2Total cost = 50 + Q2 = 50 + (25/N)2 = 50 + 625/N2Profit = 1875/N2– 625/N2– 50 = 1250/N2– 50e. In the long run, profit will be zero. Thus:1250/N2– 50 = 01250/N2 = 50N = 58. Figure 5 shows the cost, marginal revenue and demand curves for the firm underboth conditions.Figure 5a. The price will fall from P MC to the minimum average total cost (P C) when themarket becomes perfectly competitive.b. The quantity produced by a typical firm will rise to Q C, which is at the efficientscale of output.c. Average total cost will fall as the firm increases its output to the efficient scale.d. Marginal cost will rise as output rises. Marginal cost is now equal to price.e. Profit will not change. In either case, the market will move to long-runequilibrium where all firms will earn zero economic profit.9. a. A family-owned restaurant would be more likely to advertise than a family-owned farm because the output of the farm is sold in a perfectly competitivemarket, in which there is no reason to advertise, while the output of therestaurant is sold in a monopolistically competitive market.b. A manufacturer of cars is more likely to advertise than a manufacturer offorklifts because there is little difference between different brands of industrialproducts like forklifts, while there are greater perceived differences betweenconsumer products like cars. The possible return to advertising is greater in the case of cars than in the case of forklifts.c. A company that invented a very comfortable razor is likely to advertise morethan a company that invented a less comfortable razor that costs the sameamount to make because the company with the very comfortable razor will getmany repeat sales over time to cover the cost of the advertising, while thecompany with the less comfortable razor will not.10. a. Figure 6 shows Sleek’s demand, marginal-revenue, marginal-cost, and average-total-cost curves. The firm will maximize profit at an output level of Q * and aprice of P *. The shaded are shows the firm’s profits.Figure 6b. In the long run, firms will enter, shifting the demand for Sleek’s product to theleft. Its price and output will fall. Firms will enter until profits are equal to zero (as shown in Figure 7).Figure 7c. As consumers become more focused on the stylistic differences in brands, theywill be less focused on price. This will make the demand for each firm’sproducts more price inelastic. The demand curves may become relativelysteeper, allowing Sleek to charge a higher price. If these stylistic features cannot be copied, they may serve as a barrier to entry and allow Sleek to earn profit in the long run.d. A firm in monopolistic competition produces where marginal revenue is greaterthan zero. This means that firm must be operating on the elastic portion of its demand curve.。
数据库系统概念原书第5版(英文)第二章ppt
Jones Smith Curry Lindsay
Main North North Park
customer
Harrison Rye Rye
Pittsfield
tuples (or rows)
July 25, 2021
r(R) is a relation on the relation schema R
E.g. customer (Customer_schema)
July 25, 2021
Dept. of Comp. Sci. & Tech., Tongji Uni.
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Relation Instance (关系实例)
available and legal values of the attribute Attribute values are (normally) required to be atomic
E.g. multi-valued attribute values are not atomic E.g. composite attribute values are not atomic The special value null is a member of every domain The null value causes complications in the definition of many operations
July 25, 2021
Dept. of Comp. Sci. & Tech., Tongji Uni.
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Relation Schema (关系模式)
[数据库原理]【英文版】Chapter13
![[数据库原理]【英文版】Chapter13](https://img.taocdn.com/s3/m/029b52e85ef7ba0d4a733b0a.png)
Characteristics of Functional Dependencies
Main characteristics of functional dependencies used in normalization: – There is a one-to-one relationship between the attribute(s) on the left-hand side (determinant) and those on the right-hand side of a functional dependency. – Holds for all time. – The determinant has the minimal number of attributes necessary to maintain the dependency with the attribute(s) on the right hand-side.
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Lossless-join and Dependency Preservation Properties
Two important properties of decomposition: - Lossless-join property enables us to find any instance of original relation from corresponding instances in the smaller relations. - Dependency preservation property enables us to enforce a constraint on original relation by enforcing some constraint on each of the smaller relations.
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How to derive a set of relations from a conceptual data model. How to validate these relations using the technique of normalization.
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Step 2.1 Derive relations for logical data model
(a) Mandatory participation on both sides of 1:1 relationship – Combine entities involved into one relation and choose one of the primary keys of original entities to be primary key of the new relation, while the other (if one exists) is used as an alternate key. (b) Mandatory participation on one side of a 1:1 relationship – Identify parent and child entities using participation constraints. Entity with optional participation in relationship is designated as parent entity, and entity with mandatory participation is designated as child entity. A copy of primary key of the parent entity is placed in the relation representing the child entity. If the relationship has one or more attributes, these attributes should follow the posting of the primary key to the child relation. (c) Optional participation on both sides of a 1:1 relationship – In this case, the designation of the parent and child entities is arbitrary unless we can find out more about the relationship that can help a decision to be made one way or the other.
Conceptual data model for Staff view showing all attributes
Step 2.1 Derive relations for logical data model
– To create relations for the logical data model to represent the entities, relationships, and attributes that have been identified.
Chapter 15
Methodology Logical Database Design for the Relational Model
How to validate a logical data model to ensure it supports the required transactions. How to merge local logical data models based on one or more user views into a global logical data model that represents all user views. How to ensure that the final logical data model is a true and accurate representation of the data requirements of the enterprise.
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Step 2.1 Derive relations for logical data model
(1) Strong entity types – For each strong entity in the data model, create a relation that includes all the simple attributes of that entity. For composite attributes, include only the constituent simple attributes. (2) Weak entity types – For each weak entity in the data model, create a relation that includes all the simple attributes of that entity. The primary key of a weak entity is partially or fully derived from each owner entity and so the identification of the primary key of a weak entity cannot be made until after all the relationships with the owner entities have been mapped. (3) One-to-many (1:*) binary relationship types – For each 1:* binary relationship, the entity on the ‘one side’ of the relationship is designated as the parent entity and the entity on the ‘many side’ is designated as the child entity. To represent this relationship, post a copy of the primary key attribute(s) of parent entity into the relation representing the child entity, to act as a foreign key.
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Step 2.1 Derive relations for logical data model
(4) One-to-one (1:1) binary relationship types – Creating relations to represent a 1:1 relationship is more complex as the cardinality cannot be used to identify the parent and child entities in a relationship. Instead, the participation constraints are used to decide whether it is best to represent the relationship by combining the entities involved into one relation or by creating two relations and posting a copy of the primary key from one relation to the other. – Consider the following » (a) mandatory participation on both sides of 1:1 relationship; » (b) mandatory participation on one side of 1:1 relationship; » (c) optional participation on both sides of 1:1 relationship.
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Step 2.1 Derive relations for logical data model
(6) Superclass/subclass relationship types – Identify superclass entity as parent entity and subclass entity as the child entity. There are various options on how to represent such a relationship as one or more relations. – The selection of the most appropriate option is dependent on a number of factors such as the disjointness and participation constraints on the superclass/subclass relationship, whether the subclasses are involved in distinct relationships, and the number of participants in the superclass/subclass relationship.
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Step 2 Build and Validate Logical Data Model