Costing_Basic_Definitions_-_Dictionary
declarative_base参数
declarative_base参数declarative_base是SQLAlchemy中的一个函数,用于创建一个基类(Base class),以便后续的类可以继承该基类。
本文将介绍declarative_base函数的参数以及相关的参考内容。
1. cls:指定继承的基类。
默认情况下,指定为object。
很少需要手动指定。
2. metadata:绑定元数据。
元数据是数据库对象的描述信息,包括表名、列名、数据类型等。
默认为None,如果不指定,则需要在之后手动绑定元数据。
3. name:指定基类的名称。
默认为Base。
可以将其更改为其他名称,以适应项目的需求。
4. kwargs:可选的其他参数,可以用于传递一些配置选项。
在使用declarative_base函数时,可以根据实际需求来使用不同的参数配置。
下面是一些相关参考内容,可以帮助理解和使用declarative_base函数。
1. SQLAlchemy官方文档:SQLAlchemy官方文档对declarative_base函数进行了详细的介绍,包括参数的使用方法和作用。
可以查阅该文档以及示例代码,快速上手declarative_base函数的使用。
2. SQLAlchemy ORM Tutorial:这是一个关于SQLAlchemyORM的教程,对declarative_base函数进行了详细介绍,并提供了示例代码。
通过跟随该教程,可以了解如何使用declarative_base函数来定义ORM模型。
3. SQLAlchemy ORM Tutorial for Python Developers:这是另一个关于SQLAlchemy ORM的教程,对declarative_base函数进行了详细介绍,并提供了示例代码和解释。
通过阅读该教程,可以了解使用declarative_base函数来创建ORM模型的最佳实践。
4. Real Python - Object-Relational Mapping (ORM) in Pythonwith SQLAlchemy:这是一篇关于SQLAlchemy ORM的教程,其中提到了declarative_base函数的用法。
数据库原理基本概念英文解释
数据库原理基本概念英文解释Database principles refer to the fundamental concepts that define the structure, functionality, and management of adatabase system. These principles are essential for designing, implementing, and maintaining a reliable and efficient database. In this essay, I will discuss the basic concepts and principlesof databases in detail, including data modeling, data integrity, normalization, indexing, and database transactions.Data Modeling:Data modeling is the process of defining the structure and relationships of the data in a database. It involves identifying and organizing the various entities, attributes, andrelationships that exist within the domain of an application. There are different types of data models, such as the conceptual, logical, and physical data models. The conceptual data model describes the high-level view of the data, the logical datamodel represents the data structure using entities, attributes, and relationships, and the physical data model maps the logical data model to a specific database management system.Data Integrity:Data integrity ensures the accuracy, consistency, and reliability of data stored in a database. It ensures that the data values conform to defined rules or constraints. There arefour types of data integrity: entity integrity, referential integrity, domain integrity, and user-defined integrity. Entity integrity ensures that each row in a table has a unique identifier. Referential integrity ensures that relationships between tables are maintained. Domain integrity ensures that data values are within certain predefined ranges. User-defined integrity ensures that additional business rules or constraints are enforced.Normalization:Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity. It involves breaking down larger tables into smaller, more manageable entities and establishing relationships between them. The normalization process follows a series of normal forms, such as First Normal Form (1NF), Second Normal Form (2NF), Third Normal Form (3NF), etc. Each normal form has a set of rules that need to be satisfied to ensure data integrity and eliminate data anomalies, such as update, insertion, and deletion anomalies.Indexing:Indexing is a technique used to improve the efficiency of data retrieval operations in a database. It involves creating an index on one or more columns of a table, which allows the database system to locate specific rows quickly using the indexed column(s). Indexes are typically implemented as B-treesand provide a faster search mechanism by reducing the number of disk I/O operations required to locate data. Indexes should be carefully designed and maintained to balance the trade-off between query performance and the overhead of maintaining the index.Database Transactions:。
basic认证机制 -回复
basic认证机制-回复Basic认证机制(Basic Authentication)是一种用于身份验证的简单而常用的机制。
它的基本原理是,在每个HTTP请求中,通过在请求头中添加一个包含用户名和密码的Authorization字段,来进行用户身份验证。
本文将详细探讨Basic认证机制的工作原理,并介绍如何使用它进行身份验证。
第一步:了解Basic认证机制的原理Basic认证机制是基于HTTP协议的一种认证方式。
它的工作原理可以概括为以下几个步骤:1. 客户端向服务器发出请求。
2. 服务器返回状态码401(未授权)。
3. 服务器在响应头中添加一个WWW-Authenticate字段,指定使用Basic认证机制。
4. 客户端将用户名和密码进行Base64编码,并在请求头的Authorization字段中添加该编码字符串。
5. 服务器接收到请求后,对Authorization字段进行解码,并验证用户名和密码的正确性。
6. 如果验证通过,服务器会返回状态码200(成功)。
7. 客户端可以在接下来的请求中继续使用该用户名和密码进行认证,直到会话结束。
第二步:编写代码实现Basic认证机制在代码中实现Basic认证机制通常需要以下几个步骤:1. 创建一个HTTP请求对象,例如使用Java中的HttpURLConnection 或Python中的requests库。
2. 在请求头中添加一个Authorization字段,值为"Basic " + Base64编码的用户名和密码。
3. 发送请求,并接收服务器的响应。
4. 解析响应,根据状态码判断认证是否成功。
以下是使用Java语言实现Basic认证机制的示例代码:javaimport .HttpURLConnection;import .URL;import java.util.Base64;public class BasicAuthenticationExample {public static void main(String[] args) {try {创建URL对象URL url = new URL("创建HTTP连接HttpURLConnection connection = (HttpURLConnection) url.openConnection();设置请求方法为GETconnection.setRequestMethod("GET");添加Authorization头String username = "user";String password = "pass";String authString = username + ":" + password;String encodedAuthString =Base64.getEncoder().encodeToString(authString.getBytes());connection.setRequestProperty("Authorization", "Basic " + encodedAuthString);发送请求int responseCode = connection.getResponseCode();解析响应if (responseCode == HttpURLConnection.HTTP_OK) {认证成功,处理数据...} else {认证失败,处理错误...}} catch (Exception e) {e.printStackTrace();}}}第三步:使用Basic认证机制进行身份验证在实际应用中,我们通常会将用户名和密码存储在安全的数据库中,并在用户登录时进行身份验证。
dbaccess 参数
dbaccess 参数
当使用 dbaccess 时,你可以指定一系列参数来控制其行为。
这些参数可以影响与数据库的连接方式、执行的操作类型以及输出格式等。
以下是一些可能用到的参数,以及它们的简要说明(注意:这里的参数可能会因 Informix 版本的不同而有所变化):-d 数据库名:指定要连接的数据库名称。
-e:启动 dbaccess 时直接进入 SQL 编辑器模式。
-f 文件名:从指定的文件中读取 SQL 语句并执行。
-l:列出数据库中所有表的名称。
-m:允许在批处理模式下执行多个 SQL 语句。
-n:不提示用户输入,通常与 -f 参数一起使用,用于非交互式执行。
-o 输出文件:将执行结果输出到指定的文件。
-p:打印 SQL 语句的执行计划,而不实际执行语句。
-r:以只读模式打开数据库,不允许执行任何修改操作。
-s:在屏幕上显示 SQL 语句的执行结果。
-t:设置事务处理模式,如自动提交或手动控制。
-u 用户名:以指定用户的身份连接到数据库。
-v:显示详细的执行信息,包括每个 SQL 语句的执行时间等。
-z:在执行完 SQL 语句后退出 dbaccess。
此外,dbaccess 还支持许多其他选项和参数,可以通过在命令行中键入 dbaccess -? 或查阅 Informix 的官方文档来获取完整的参数列表和详细说明。
请注意,由于 dbaccess 是一个功能强大的工具,错误地使用某些参数可能会对数据库造成不可逆的损害。
因此,在使用前务必仔细阅读相关文档,并在生产环境中谨慎操作。
翻译
中国石油大学(华东)本科毕业设计(论文)外文翻译学生姓名:姜华学号:06083201专业班级:软件工程2006级2班指导教师:梁玉环2010年6月10日Database ManagementDatabase (sometimes spelled database) is also called an electronic database, referring to any collections of data, or information, that is specially organized for rapid search and retrieval by a computer. Databases are structured to facilitate the storage, retrieval modification and deletion of data in conjunction with various data-processing operations. Database can be stored on magnetic disk or tape, optical disk, or some other secondary storage device.A database consists of a file or a set of files. The information in the these files may be broken down into records, each of which consists of one or more fields are the basic units of data storage, and each field typically contains information pertaining to one aspect or attribute of the entity described by the database. Using keywords and various sorting commands, users can rapidly search, rearrange, group, and select the fields in many records to retrieve or create reports on particular aggregates of data.Database records and files must be organized to allow retrieval of the information. Early system were arranged sequentially (i.e., alphabetically, numerically, or chronologically); the development of direct-access storage devices made possible random access to data via indexes. Queries are the main way users retrieve database information. Typically the user provides a string of characters, and the computer searches the database for a corresponding sequence and provides the source materials in which those characters appear.A user can request, for example, all records in which the content of the field for a person’s last name is the word Smith.The many users of a large database must be able to manipulate the information within it quickly at any given time. Moreover, large business and other organizations tend to build up many independent files containing related and even overlapping data, and their data, processing activities often require the linking of data from several files. Several different types of database management systems have been developed to support these requirements: flat, hierarchical, network, relational, and object-oriented.In flat databases, records are organized according to a simple list of entities; many simple databases for personal computers are flat in structure. The records in hierarchical databases are organized in a treelike structure, with each level of records branching off into a set of smaller categories. Unlike hierarchical databases, which provide single links between sets of records at different levels, network databases create multiple linkages between sets by placing links, or pointers, to one set of records in another; the speed and versatility of network databases have led to their wide use in business. Relational databases are used where associations among files or records cannot be expressed by links; a simple flat list becomes one table, or “relation”, and multiple relations can be mathematically as sociated toyield desired information. Object-oriented databases store and manipulate more complex data structures, called “objects”, which are organized into hierarchical classes that may inherit properties from classes higher in the chain; this database structure is the most flexible and adaptable.The information in many databases consists of natural-language texts of documents; number-oriented database primarily contain information such as statistics, tables, financial data, and raw scientific and technical data. Small databases can be maintained on personal-computer systems and may be used by individuals at home. These and larger databases have become increasingly important in business life. Typical commercial applications include airline reservations, production management, medical records in hospitals, and legal records of insurance companies. The largest databases are usually maintained by governmental agencies, business organizations, and universities. These databases may contain texts of such materials as catalogs of various kinds. Reference databases contain bibliographies or indexes that serve as guides to the location of information in books, periodicals, and other published literature. Thousands of these publicly accessible databases now exist, covering topics ranging from law, medicine, and engineering to news and current events, games, classified advertisements, and instructional courses. Professionals such as scientists, doctors, lawyers, financial analysts, stockbrokers, and researchers of all types increasingly rely on these databases for quick, selective access to large volumes of information.DBMS Structuring TechniquesSequential, direct, and other file processing approaches are used to organize and structure data in single files. But a DBMS is able to integrate data elements from several files to answer specific user inquiries for information. That is, the DBMS is able to structure and tie together the logically related data from several large files.Logical Structures. Identifying these logical relationships is a job of the data administrator. A data definition language is used for this purpose. The DBMS may then employ one of the following logical structuring techniques during storage access, and retrieval operations.List structures. In this logical approach, records are linked together by the use of pointers. A pointer is a data item in one record that identifies the storage location of another logically related record. Records in a customer master file, for example, will contain the name and address of each customer, and each record in this file is identified by an account number. During an accounting period, a customer may buy a number of items on different days. Thus, the company may maintain an invoice file to reflect these transactions. A list structure could be used in this situation to show the unpaid invoices at any given time. Each record in the customer in the invoice file. This invoice record, in turn, would be linked to later invoices for the customer. The last invoice in the chain would be identified by the useof a special character as a pointer.Hierarchical (tree) structures. In this logical approach, data units are structured in multiple levels that graphically resemble an “upside down” tree with the root at the top and the branches formed below. There’s a superior-subordinate relationship in a hierarchical (tree) structure. Below the single-root data component are subordinate elements or nodes, each of which, in turn, “own” one or more other elements (or none). Each element or branch in this structure below the root has only a single owner. Thus, a customer owns an invoice, and the invoice has subordinate items. The branches in a tree structure are not connected.Network Structures. Unlike the tree approach, which does not permit the connection of branches, the network structure permits the connection of the nodes in a multidirectional manner. Thus, each node may have several owners and may, in turn, own any number of other data units. Data management software permits the extraction of the needed information from such a structure by beginning with any record in a file.Relational structures. A relational structure is made up of many tables. The data are stored in the form of “relations” in these tables. For example, relation t ables could be established to link a college course with the instructor of the course, and with the location of the class.To find the name of the instructor and the location of the English class, the course/instructor relation is searched to get the name (“Fitt”), and the course/location relation is a relatively new database structuring approach that’s expected to be widely implemented in the future.Physical Structures. People visualize or structure data in logical ways for their own purposes. Thus, records R1 and R2 may always be logically linked and processed in sequence in one particular application. However, in a computer system it’s quite possible that these records that are logically contiguous in one application are not physically stored together. Rather, the physical structure of the records in media and hardware may depend not only on the I/O and storage devices and techniques used, but also on the different logical relationships that users may assign to the data found in R1and R2. For example, R1 and R2 may be records of credit customers who have shipments send to the same block in the same city every 2 weeks. From the shipping department manager’s perspective, then, R1 and R2 are sequential entries on a geographically organized shipping report. But in the A/R application, the customers represented by R1 and R2 may be identified, and their accounts may be processed, according to their account numbers which are widely separated. In short, then, the physical location of the stored records in many computer-based information systems is invisible to users.Database Management Features of OracleOracle includes many features that make the database easier to manage. We’ve divided the discussion in this section into three categories: Oracle Enterprise Manager, add-on packs,backup and recovery.1. Oracle Enterprise ManagerAs part of every Database Server, Oracle provides the Oracle Enterprise Manager (EM), a database management tool framework with a graphical interface used to manage database users, instances, and features (such as replication) that can provide additional information about the Oracle environment.Prior to the Oracle8i database, the EM software had to be installed on Windows 95/98 or NT-based systems and each repository could be accessed by only a single database manager at a time. Now you can use EM from a browser or load it onto Windows 95/98/2000 or NT-based systems. Multiple database administrators can access the EM repository at the same time. In the EM repository for Oracle9i, the super administrator can define services that should be displayed on other administrators’ consoles, and management regions can be set up.2. Add-on packsSeveral optional add-on packs are available for Oracle, as described in the following sections. In addition to these database-management packs, management packs are available for Oracle Applications and for SAP R/3.(1)standard Management PackThe Standard Management Pack for Oracle provides tools for the management of small Oracle databases (e.g., Oracle Server/Standard Edition). Features include support for performance monitoring of database contention, I/O, load, memory use and instance metrics, session analysis, index tuning, and change investigation and tracking.(2)Diagnostics PackYou can use the Diagnostic Pack to monitor, diagnose, and maintain the health of Enterprise Edition databases, operating systems, and applications. With both historical and real-time analysis, you can automatically avoid problems before they occur. The pack also provides capacity planning features that help you plan and track future system-resource requirements.(3)Tuning PackWith the Tuning Pack, you can optimise system performance by identifying and tuning Enterprise Edition databases and application bottlenecks such as inefficient SQL, poor data design, and the improper use of system resources. The pack can proactively discover tuning opportunities and automatically generate the analysis and required changes to tune the systems.(4)Change Management PackThe Change Management Pack helps eliminate errors and loss of data when upgrading Enterprise Edition databases to support new applications. It impact and complex dependencies associated with application changes and automatically perform databaseupgrades. Users can initiate changes with easy-to-use wizards that teach the systematic steps necessary to upgrade.(5)AvailabilityOracle Enterprise Manager can be used for managing Oracle Standard Edition and/or Enterprise Edition. Additional functionality is provided by separate Diagnostics, Tuning, and Change Management Packs.3. Backup and RecoveryAs every database administrator knows, backing up a database is a rather mundane but necessary task. An improper backup makes recovery difficult, if not impossible. Unfortunately, people often realize the extreme importance of this everyday task only when it is too late –usually after losing business-critical data due to a failure of a related system.The following sections describe some products and techniques for performing database backup operations.(1)Recovery ManagerTypical backups include complete database backups (the most common type), database backups, control file backups, and recovery of the database. Previously, Oracle’s Enterprise Backup Utility (EBU) provided a similar solution on some platforms. However, RMAN, with its Recovery Catalog stored in an Oracle database, provides a much more complete solution. RMAN can automatically locate, back up, restore, and recover databases, control files, and archived redo logs. RMAN for Oracle9i can restart backups and restores and implement recovery window policies when backups expire. The Oracle Enterprise Manager Backup Manager provides a GUI-based interface to RMAN.(2)Incremental backup and recoveryRMAN can perform incremental backups of Enterprise Edition databases. Incremental backups back up only the blocks modified since the last backup of a datafile, tablespace, or database; thus, they’re smaller and faster than complete backups. RMAN can also perform point-in-time recovery, which allows the recovery of data until just prior to a undesirable event.(3)Legato Storage ManagerVarious media-management software vendors support RMAN. Oracle bundles Legato Storage Manager with Oracle to provide media-management services, including the tracking of tape volumes, for up to four devices. RMAN interfaces automatically with the media-management software to request the mounting of tapes as needed for backup and recovery operations.(4)AvailabilityWhile basic recovery facilities are available for both Oracle Standard Edition and Enterprise Edition, incremental backups have typically been limited to Enterprise Edition. Choosing between Oracle and SQL ServerI have to decide between using the Oracle database and WebDB vs. Microsoft SQL Server with Visual Studio. This choice will guide our future Web projects. What are the strong points of each of these combinations and what are the negatives?Lori: Making your decision will depend on what you already have. For instance, if you want to implement a Web-based database application and you are a Windows-only shop, SQL Server and the Visual Studio package would be fine. But the Oracle solution would be better with mixed platforms.There are other things to consider, such as what extras you get and what skills are required. WebDB is a content management and development tool that can be used by content creators, database administrators, and developers without any programming experience. WebDB is a browser-based tool that helps ease content creation and provides monitoring and maintenance tools. This is a good solution for organizations already using Oracle. Oracle also scales better than SQL Server, but you will need to have a competent Oracle administrator on hand.The SQL Sever/Visual Studio approach is more difficult to use and requires an experienced object-oriented programmer or some extensive training. However, you do get a fistful of development tools with Visual Studio: Visual Basic, Visual C++, and Visual InterDev for only $1,619. Plus, you will have to add the cost of the SQL Server, which will run you $1,999 for 10 clients or $3,999 for 25 clients-a less expensive solution than Oracle’s.Oracle also has a package solution that starts at $6,767, depending on the platform selected. The suite includes not only WebDB and Oracle8i but also other tools for development such as the Oracle application server, JDeveloper, and Workplace Templates, and the suite runs on more platforms than the Microsoft solution does. This can be a good solution if you are a start-up or a small to midsize business. Buying these tools in a package is less costly than purchasing them individually.Much depends on your skill level, hardware resources, and budget. I hope this helps in your decision-making.Brooks: I totally agree that this decision depends in large part on what infrastructure and expertise you already have. If the decision is close, you need to figure out who’s going to be doing the work and what your priorities are.These two products have different approaches, and they reflect the different personalities of the two vendors. In general, Oracle products are designed for very professional development efforts by top-notch programmers and project leaders. The learning period is fairly long, and the solution is pricey; but if you stick it out you will ultimately have greater scalability and greater reliability.If your project has tight deadlines and you don’t have the time and/or money to hire a team of very expensive, very experienced developers, you may find that the Oracle solutioni s an easy way to get yourself in trouble. There’s nothing worse than a poorly developed Oracle application.What Microsoft offers is a solution that’s aimed at rapid development and low-cost implementation. The tools are cheaper, the servers you’ll run it on are cheaper, and the developers you need will be cheaper. Choosing SQL Sever and Visual Studio is an excellent way to start fast.Of course, there are trade-offs. The key problem I have with Visual Studio and SQL Server is that you’ll be tied to Microso ft operating systems and Intel hardware. If the day comes when you need to support hundreds of thousands of users, you really don’t have anywhere to go other than buying hundreds of servers, which is a management nightmare.If you go with the Microsoft approach, it sounds like you may not need more than Visual Interdev. If you already know that you’re going to be developing ActiveX components in Visual Basic or Visual C++, that’s warning sign that maybe you should look at the Oracle solution more closely.I want to emphasize that, although these platforms have their relative strengths and weaknesses, if you do it right you can build a world-class application on either one. So if you have an organizational bias toward one of the vendors, by all means go with it. If you’re starting out from scratch, you’re going to have to ask yourself whether your organization leans more toward perfectionism or pragmatism, and realize that both “isms” have their faults.数据库管理数据库(有时拼成Database)也称为电子数据库,是指由计算机特别组织的快速查找和检索的任意的数据或信息集合。
数据库专业英语
数据库专业英语文章摘要:数据库专业英语是指与数据库相关的专业术语和表达方式,它涉及到数据库的基本概念、结构、设计、操作、管理、应用等方面。
掌握数据库专业英语对于学习和使用数据库技术是非常有益的,可以提高沟通和理解的效率,也可以拓展知识和视野。
本文将介绍一些常用的数据库专业英语,包括数据模型、数据操作、数据分析、数据安全等,并给出中英文对照的表格,以便于读者参考和学习。
1. 数据模型数据模型(Data Model)是对现实世界特征的数字化的模拟和抽象,它描述了数据的结构、属性、联系和约束。
不同的数据模型有不同的特点和适用范围,常见的数据模型有层次模型(Hierarchical Model)、网状模型(Network Model)、关系模型(Relational Model)、对象模型(Object Model)等。
下表列出了一些与数据模型相关的专业英语:中文英文数据Data数据库Database数据库管理系统Database Management System (DBMS)数据字典Data Dictionary数据仓库Data Warehouse数据湖Data Lake实体Entity属性Attribute域Domain关系Relation元组Tuple主键Primary Key外键Foreign Key视图View索引Index约束Constraint2. 数据操作数据操作(Data Manipulation)是指对数据库中的数据进行增加、删除、修改和查询等操作,通常使用一种称为结构化查询语言(Structured Query Language,简称SQL)的标准语言。
SQL语言分为数据定义语言(Data Definition Language,简称DDL)、数据操纵语言(Data Manipulation Language,简称DML)、数据控制语言(Data Control Language,简称DCL)等部分。
NIIT练习题及答案
NIIT练习题及答案1.如果要将事务的相关详细资料写入日志文件,那么应该使用以下哪个?DA.资源管理器B. 资源分配器C. CRM补偿器D. CRM工作器2.TechnoSoft Pvt需要采用一个应用程序来显示职员的详细资料。
公司的(clerk)应该只能访问职员的姓名和地址,而总经理那么应该能访问包括职员领取的薪水在内的所有详细资料。
为此,可以使用+所提供的以下哪些效劳?BA.资源管理器B.基于角色的平安性C.+事件D.对象池3.考虑以下陈述:陈述A:+从MTS继承了Just-in-time激活功能。
陈述B:通过使用Just-in-time激活来预留效劳器内存。
关于给定的陈述,以下哪个是正确的?CA.陈述A是正确的,陈述B是错误的。
B.陈述A是错误的,陈述B是正确的。
C.两个陈述都是正确的。
D.两个陈述都是错误的。
4.从以下关于.NET程序集的陈述中,找出正确的一项。
BA.创立程序集时,它会默认共享。
B.对于允许多个应用程序访问的私有程序集而言,必须将它的文件分别放在其它应用程序所在的文件平下。
C.私有程序集是到全局程序集缓存(GAC)中的程序集。
D.在共享系统中,程序集的名称不必是唯一的,这是因为系统中的所有应用程序都可以从全局程序集缓存(GAC)中访问它。
5.版本号的各组成部分是A:Revision号B:Major版本号C:Minor版本号D:Build版本号辩别版本号各部分的正确顺序?DA.C=》B=》D=》AB.B=》A=》C=》DC.B=》D=》C=》AD.B=》C=》D=》A6.以下哪个类包含了.NET框架的所有类和远程对象的接口方法?AA.TransparentProxyB.ReadProxyC.ObjRefD.RegisterWellKnownServiceType7.要将管道作为众所周知的效劳,需要以下哪个类?A.RealProxyB.ObjRefC.TransparentProxyD.RemotingConfiguration8.考虑以下陈述:陈述A:通道可以使用SOAP格式化程序(fomatter)和二进制格式化程序。
declarative_base参数
declarative_base参数SQLAlchemy是一个用Python编写的开源SQL工具和对象关系映射(ORM)库。
在使用SQLAlchemy进行数据库操作时,我们经常会使用`declarative_base`函数来定义ORM类。
`declarative_base`函数是SQLAlchemy提供的一个将类与表关联起来的基础工具。
在使用`declarative_base`函数时,可以给它传递一些参数来定制生成的ORM基类。
本文将详细介绍`declarative_base`函数的参数及其功能。
1. `metadata`参数`metadata`参数是`declarative_base`的第一个参数,默认值为`None`。
它可以用来指定一个`MetaData`实例,用于管理表和类之间的映射关系。
```pythonfrom sqlalchemy import MetaData, create_enginefrom sqlalchemy.ext.declarative import declarative_baseengine = create_engine('sqlite:///example.db')metadata = MetaData(bind=engine)Base = declarative_base(metadata=metadata)```在上面的例子中,我们创建了一个名为`example.db`的SQLite数据库,并创建了一个`MetaData`实例`metadata`。
然后,我们将`metadata`实例传递给`declarative_base`函数,使生成的基类`Base`使用这个`metadata`实例进行表和类的映射管理。
2. `name`参数`name`参数用于指定生成的基类的名称,默认为`Base`。
我们可以根据自己的需要来设置这个名称。
```pythonfrom sqlalchemy.ext.declarative import declarative_baseBase = declarative_base(name='MyBase')```上述例子中,我们将生成的基类命名为`MyBase`,而不是默认的`Base`。
Adobe Acrobat SDK 开发者指南说明书
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计算机专业英语试题及答案
计算机专业英语试题及答案1. 选择题1. Which of the following is not a programming language?a) Javab) HTMLc) Pythond) CSS答案: b) HTML2. Which protocol is used for sending and receiving email?a) HTTPSb) FTPc) SMTPd) DNS答案: c) SMTP3. What does the acronym CPU stand for?a) Central Processing Unitb) Computer Processing Unitc) Control Processing Unitd) Central Power Unit答案: a) Central Processing Unit4. Which programming language is commonly used for web development?a) C++b) Javac) JavaScriptd) Swift答案: c) JavaScript5. What does HTML stand for?a) Hyperlinks and Text Markup Languageb) Hyper Text Markup Languagec) Home Tool Markup Languaged) Hyper Text Modeling Language答案: b) Hyper Text Markup Language2. 填空题1. The process of converting high-level programming code into machine code is called ___________.答案: compilation2. HTTP stands for ___________ Transfer Protocol.答案: Hyper Text3. The process of testing software by executing it is called ___________.答案: debugging4. Java is an object-_____________ programming language.答案: oriented5. DNS stands for Domain Name ___________.答案: System3. 简答题1. What is the difference between TCP and UDP?答案: TCP (Transmission Control Protocol) is a connection-oriented protocol, which means it establishes a connection between the sender and receiver before transferring data. It ensures that all packets are received in the correct order and provides error checking. UDP (User Datagram Protocol), on the other hand, is a connectionless protocol that does not establish a direct connection before transmitting data. It does not guarantee packet delivery or order but is faster and more efficient for time-sensitive applications.2. What is the purpose of an operating system?答案: An operating system (OS) is a software that manages computer hardware and software resources and provides common services forcomputer programs. Its primary purpose is to enable the user to interact with the computer and provide a platform for running applications. It manages memory, file systems, input/output devices, and multitasking. The OS also handles system security and resource allocation to ensure optimal performance.4. 解答题请参考下文并给出自己的解答。
answer
Computer Systems:A Programmer’s PerspectiveInstructor’s Solution Manual1Randal E.BryantDavid R.O’HallaronDecember4,20031Copyright c2003,R.E.Bryant,D.R.O’Hallaron.All rights reserved.2Chapter1Solutions to Homework ProblemsThe text uses two different kinds of exercises:Practice Problems.These are problems that are incorporated directly into the text,with explanatory solutions at the end of each chapter.Our intention is that students will work on these problems as they read the book.Each one highlights some particular concept.Homework Problems.These are found at the end of each chapter.They vary in complexity from simple drills to multi-week labs and are designed for instructors to give as assignments or to use as recitation examples.This document gives the solutions to the homework problems.1.1Chapter1:A Tour of Computer Systems1.2Chapter2:Representing and Manipulating InformationProblem2.40Solution:This exercise should be a straightforward variation on the existing code.2CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS1011void show_double(double x)12{13show_bytes((byte_pointer)&x,sizeof(double));14}code/data/show-ans.c 1int is_little_endian(void)2{3/*MSB=0,LSB=1*/4int x=1;56/*Return MSB when big-endian,LSB when little-endian*/7return(int)(*(char*)&x);8}1.2.CHAPTER2:REPRESENTING AND MANIPULATING INFORMATION3 There are many solutions to this problem,but it is a little bit tricky to write one that works for any word size.Here is our solution:code/data/shift-ans.c The above code peforms a right shift of a word in which all bits are set to1.If the shift is arithmetic,the resulting word will still have all bits set to1.Problem2.45Solution:This problem illustrates some of the challenges of writing portable code.The fact that1<<32yields0on some32-bit machines and1on others is common source of bugs.A.The C standard does not define the effect of a shift by32of a32-bit datum.On the SPARC(andmany other machines),the expression x<<k shifts by,i.e.,it ignores all but the least significant5bits of the shift amount.Thus,the expression1<<32yields1.pute beyond_msb as2<<31.C.We cannot shift by more than15bits at a time,but we can compose multiple shifts to get thedesired effect.Thus,we can compute set_msb as2<<15<<15,and beyond_msb as set_msb<<1.Problem2.46Solution:This problem highlights the difference between zero extension and sign extension.It also provides an excuse to show an interesting trick that compilers often use to use shifting to perform masking and sign extension.A.The function does not perform any sign extension.For example,if we attempt to extract byte0fromword0xFF,we will get255,rather than.B.The following code uses a well-known trick for using shifts to isolate a particular range of bits and toperform sign extension at the same time.First,we perform a left shift so that the most significant bit of the desired byte is at bit position31.Then we right shift by24,moving the byte into the proper position and peforming sign extension at the same time.4CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS 3int left=word<<((3-bytenum)<<3);4return left>>24;5}Problem2.48Solution:This problem lets students rework the proof that complement plus increment performs negation.We make use of the property that two’s complement addition is associative,commutative,and has additive ing C notation,if we define y to be x-1,then we have˜y+1equal to-y,and hence˜y equals -y+1.Substituting gives the expression-(x-1)+1,which equals-x.Problem2.49Solution:This problem requires a fairly deep understanding of two’s complement arithmetic.Some machines only provide one form of multiplication,and hence the trick shown in the code here is actually required to perform that actual form.As seen in Equation2.16we have.Thefinal term has no effect on the-bit representation of,but the middle term represents a correction factor that must be added to the high order bits.This is implemented as follows:code/data/uhp-ans.c Problem2.50Solution:Patterns of the kind shown here frequently appear in compiled code.1.2.CHAPTER2:REPRESENTING AND MANIPULATING INFORMATION5A.:x+(x<<2)B.:x+(x<<3)C.:(x<<4)-(x<<1)D.:(x<<3)-(x<<6)Problem2.51Solution:Bit patterns similar to these arise in many applications.Many programmers provide them directly in hex-adecimal,but it would be better if they could express them in more abstract ways.A..˜((1<<k)-1)B..((1<<k)-1)<<jProblem2.52Solution:Byte extraction and insertion code is useful in many contexts.Being able to write this sort of code is an important skill to foster.code/data/rbyte-ans.c Problem2.53Solution:These problems are fairly tricky.They require generating masks based on the shift amounts.Shift value k equal to0must be handled as a special case,since otherwise we would be generating the mask by performing a left shift by32.6CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS 1unsigned srl(unsigned x,int k)2{3/*Perform shift arithmetically*/4unsigned xsra=(int)x>>k;5/*Make mask of low order32-k bits*/6unsigned mask=k?((1<<(32-k))-1):˜0;78return xsra&mask;9}code/data/rshift-ans.c 1int sra(int x,int k)2{3/*Perform shift logically*/4int xsrl=(unsigned)x>>k;5/*Make mask of high order k bits*/6unsigned mask=k?˜((1<<(32-k))-1):0;78return(x<0)?mask|xsrl:xsrl;9}.1.2.CHAPTER2:REPRESENTING AND MANIPULATING INFORMATION7B.(a)For,we have,,code/data/floatge-ans.c 1int float_ge(float x,float y)2{3unsigned ux=f2u(x);4unsigned uy=f2u(y);5unsigned sx=ux>>31;6unsigned sy=uy>>31;78return9(ux<<1==0&&uy<<1==0)||/*Both are zero*/10(!sx&&sy)||/*x>=0,y<0*/11(!sx&&!sy&&ux>=uy)||/*x>=0,y>=0*/12(sx&&sy&&ux<=uy);/*x<0,y<0*/13},8CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS This exercise is of practical value,since Intel-compatible processors perform all of their arithmetic in ex-tended precision.It is interesting to see how adding a few more bits to the exponent greatly increases the range of values that can be represented.Description Extended precisionValueSmallest denorm.Largest norm.Problem2.59Solution:We have found that working throughfloating point representations for small word sizes is very instructive. Problems such as this one help make the description of IEEEfloating point more concrete.Description8000Smallest value4700Largest denormalized———code/data/fpwr2-ans.c1.3.CHAPTER3:MACHINE LEVEL REPRESENTATION OF C PROGRAMS91/*Compute2**x*/2float fpwr2(int x){34unsigned exp,sig;5unsigned u;67if(x<-149){8/*Too small.Return0.0*/9exp=0;10sig=0;11}else if(x<-126){12/*Denormalized result*/13exp=0;14sig=1<<(x+149);15}else if(x<128){16/*Normalized result.*/17exp=x+127;18sig=0;19}else{20/*Too big.Return+oo*/21exp=255;22sig=0;23}24u=exp<<23|sig;25return u2f(u);26}10CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS int decode2(int x,int y,int z){int t1=y-z;int t2=x*t1;int t3=(t1<<31)>>31;int t4=t3ˆt2;return t4;}Problem3.32Solution:This code example demonstrates one of the pedagogical challenges of using a compiler to generate assembly code examples.Seemingly insignificant changes in the C code can yield very different results.Of course, students will have to contend with this property as work with machine-generated assembly code anyhow. They will need to be able to decipher many different code patterns.This problem encourages them to think in abstract terms about one such pattern.The following is an annotated version of the assembly code:1movl8(%ebp),%edx x2movl12(%ebp),%ecx y3movl%edx,%eax4subl%ecx,%eax result=x-y5cmpl%ecx,%edx Compare x:y6jge.L3if>=goto done:7movl%ecx,%eax8subl%edx,%eax result=y-x9.L3:done:A.When,it will computefirst and then.When it just computes.B.The code for then-statement gets executed unconditionally.It then jumps over the code for else-statement if the test is false.C.then-statementt=test-expr;if(t)goto done;else-statementdone:D.The code in then-statement must not have any side effects,other than to set variables that are also setin else-statement.1.3.CHAPTER3:MACHINE LEVEL REPRESENTATION OF C PROGRAMS11Problem3.33Solution:This problem requires students to reason about the code fragments that implement the different branches of a switch statement.For this code,it also requires understanding different forms of pointer dereferencing.A.In line29,register%edx is copied to register%eax as the return value.From this,we can infer that%edx holds result.B.The original C code for the function is as follows:1/*Enumerated type creates set of constants numbered0and upward*/2typedef enum{MODE_A,MODE_B,MODE_C,MODE_D,MODE_E}mode_t;34int switch3(int*p1,int*p2,mode_t action)5{6int result=0;7switch(action){8case MODE_A:9result=*p1;10*p1=*p2;11break;12case MODE_B:13*p2+=*p1;14result=*p2;15break;16case MODE_C:17*p2=15;18result=*p1;19break;20case MODE_D:21*p2=*p1;22/*Fall Through*/23case MODE_E:24result=17;25break;26default:27result=-1;28}29return result;30}Problem3.34Solution:This problem gives students practice analyzing disassembled code.The switch statement contains all the features one can imagine—cases with multiple labels,holes in the range of possible case values,and cases that fall through.12CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS 1int switch_prob(int x)2{3int result=x;45switch(x){6case50:7case52:8result<<=2;9break;10case53:11result>>=2;12break;13case54:14result*=3;15/*Fall through*/16case55:17result*=result;18/*Fall through*/19default:20result+=10;21}2223return result;24}code/asm/varprod-ans.c 1int var_prod_ele_opt(var_matrix A,var_matrix B,int i,int k,int n) 2{3int*Aptr=&A[i*n];4int*Bptr=&B[k];5int result=0;6int cnt=n;78if(n<=0)9return result;1011do{12result+=(*Aptr)*(*Bptr);13Aptr+=1;14Bptr+=n;15cnt--;1.3.CHAPTER3:MACHINE LEVEL REPRESENTATION OF C PROGRAMS13 16}while(cnt);1718return result;19}code/asm/structprob-ans.c 1typedef struct{2int idx;3int x[4];4}a_struct;14CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS 1/*Read input line and write it back*/2/*Code will work for any buffer size.Bigger is more time-efficient*/ 3#define BUFSIZE644void good_echo()5{6char buf[BUFSIZE];7int i;8while(1){9if(!fgets(buf,BUFSIZE,stdin))10return;/*End of file or error*/11/*Print characters in buffer*/12for(i=0;buf[i]&&buf[i]!=’\n’;i++)13if(putchar(buf[i])==EOF)14return;/*Error*/15if(buf[i]==’\n’){16/*Reached terminating newline*/17putchar(’\n’);18return;19}20}21}An alternative implementation is to use getchar to read the characters one at a time.Problem3.38Solution:Successfully mounting a buffer overflow attack requires understanding many aspects of machine-level pro-grams.It is quite intriguing that by supplying a string to one function,we can alter the behavior of another function that should always return afixed value.In assigning this problem,you should also give students a stern lecture about ethical computing practices and dispell any notion that hacking into systems is a desirable or even acceptable thing to do.Our solution starts by disassembling bufbomb,giving the following code for getbuf: 1080484f4<getbuf>:280484f4:55push%ebp380484f5:89e5mov%esp,%ebp480484f7:83ec18sub$0x18,%esp580484fa:83c4f4add$0xfffffff4,%esp680484fd:8d45f4lea0xfffffff4(%ebp),%eax78048500:50push%eax88048501:e86a ff ff ff call8048470<getxs>98048506:b801000000mov$0x1,%eax10804850b:89ec mov%ebp,%esp11804850d:5d pop%ebp12804850e:c3ret13804850f:90nopWe can see on line6that the address of buf is12bytes below the saved value of%ebp,which is4bytes below the return address.Our strategy then is to push a string that contains12bytes of code,the saved value1.3.CHAPTER3:MACHINE LEVEL REPRESENTATION OF C PROGRAMS15 of%ebp,and the address of the start of the buffer.To determine the relevant values,we run GDB as follows:1.First,we set a breakpoint in getbuf and run the program to that point:(gdb)break getbuf(gdb)runComparing the stopping point to the disassembly,we see that it has already set up the stack frame.2.We get the value of buf by computing a value relative to%ebp:(gdb)print/x(%ebp+12)This gives0xbfffefbc.3.Wefind the saved value of register%ebp by dereferencing the current value of this register:(gdb)print/x*$ebpThis gives0xbfffefe8.4.Wefind the value of the return pointer on the stack,at offset4relative to%ebp:(gdb)print/x*((int*)$ebp+1)This gives0x8048528We can now put this information together to generate assembly code for our attack:1pushl$0x8048528Put correct return pointer back on stack2movl$0xdeadbeef,%eax Alter return value3ret Re-execute return4.align4Round up to125.long0xbfffefe8Saved value of%ebp6.long0xbfffefbc Location of buf7.long0x00000000PaddingNote that we have used the.align statement to get the assembler to insert enough extra bytes to use up twelve bytes for the code.We added an extra4bytes of0s at the end,because in some cases OBJDUMP would not generate the complete byte pattern for the data.These extra bytes(plus the termininating null byte)will overflow into the stack frame for test,but they will not affect the program behavior. Assembling this code and disassembling the object code gives us the following:10:6828850408push$0x804852825:b8ef be ad de mov$0xdeadbeef,%eax3a:c3ret4b:90nop Byte inserted for alignment.5c:e8ef ff bf bc call0xbcc00000Invalid disassembly.611:ef out%eax,(%dx)Trying to diassemble712:ff(bad)data813:bf00000000mov$0x0,%edi16CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS From this we can read off the byte sequence:6828850408b8ef be ad de c390e8ef ff bf bc ef ff bf00000000Problem3.39Solution:This problem is a variant on the asm examples in the text.The code is actually fairly simple.It relies on the fact that asm outputs can be arbitrary lvalues,and hence we can use dest[0]and dest[1]directly in the output list.code/asm/asmprobs-ans.c Problem3.40Solution:For this example,students essentially have to write the entire function in assembly.There is no(apparent) way to interface between thefloating point registers and the C code using extended asm.code/asm/fscale.c1.4.CHAPTER4:PROCESSOR ARCHITECTURE17 1.4Chapter4:Processor ArchitectureProblem4.32Solution:This problem makes students carefully examine the tables showing the computation stages for the different instructions.The steps for iaddl are a hybrid of those for irmovl and OPl.StageFetchrA:rB M PCvalP PCExecuteR rB valEPC updateleaveicode:ifun M PCDecodevalB RvalE valBMemoryWrite backR valMPC valPProblem4.34Solution:The following HCL code includes implementations of both the iaddl instruction and the leave instruc-tions.The implementations are fairly straightforward given the computation steps listed in the solutions to problems4.32and4.33.You can test the solutions using the test code in the ptest subdirectory.Make sure you use command line argument‘-i.’18CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS 1####################################################################2#HCL Description of Control for Single Cycle Y86Processor SEQ#3#Copyright(C)Randal E.Bryant,David R.O’Hallaron,2002#4####################################################################56##This is the solution for the iaddl and leave problems78####################################################################9#C Include’s.Don’t alter these#10#################################################################### 1112quote’#include<stdio.h>’13quote’#include"isa.h"’14quote’#include"sim.h"’15quote’int sim_main(int argc,char*argv[]);’16quote’int gen_pc(){return0;}’17quote’int main(int argc,char*argv[])’18quote’{plusmode=0;return sim_main(argc,argv);}’1920####################################################################21#Declarations.Do not change/remove/delete any of these#22#################################################################### 2324#####Symbolic representation of Y86Instruction Codes#############25intsig INOP’I_NOP’26intsig IHALT’I_HALT’27intsig IRRMOVL’I_RRMOVL’28intsig IIRMOVL’I_IRMOVL’29intsig IRMMOVL’I_RMMOVL’30intsig IMRMOVL’I_MRMOVL’31intsig IOPL’I_ALU’32intsig IJXX’I_JMP’33intsig ICALL’I_CALL’34intsig IRET’I_RET’35intsig IPUSHL’I_PUSHL’36intsig IPOPL’I_POPL’37#Instruction code for iaddl instruction38intsig IIADDL’I_IADDL’39#Instruction code for leave instruction40intsig ILEAVE’I_LEAVE’4142#####Symbolic representation of Y86Registers referenced explicitly##### 43intsig RESP’REG_ESP’#Stack Pointer44intsig REBP’REG_EBP’#Frame Pointer45intsig RNONE’REG_NONE’#Special value indicating"no register"4647#####ALU Functions referenced explicitly##### 48intsig ALUADD’A_ADD’#ALU should add its arguments4950#####Signals that can be referenced by control logic####################1.4.CHAPTER4:PROCESSOR ARCHITECTURE195152#####Fetch stage inputs#####53intsig pc’pc’#Program counter54#####Fetch stage computations#####55intsig icode’icode’#Instruction control code56intsig ifun’ifun’#Instruction function57intsig rA’ra’#rA field from instruction58intsig rB’rb’#rB field from instruction59intsig valC’valc’#Constant from instruction60intsig valP’valp’#Address of following instruction 6162#####Decode stage computations#####63intsig valA’vala’#Value from register A port64intsig valB’valb’#Value from register B port 6566#####Execute stage computations#####67intsig valE’vale’#Value computed by ALU68boolsig Bch’bcond’#Branch test6970#####Memory stage computations#####71intsig valM’valm’#Value read from memory727374####################################################################75#Control Signal Definitions.#76#################################################################### 7778################Fetch Stage################################### 7980#Does fetched instruction require a regid byte?81bool need_regids=82icode in{IRRMOVL,IOPL,IPUSHL,IPOPL,83IIADDL,84IIRMOVL,IRMMOVL,IMRMOVL};8586#Does fetched instruction require a constant word?87bool need_valC=88icode in{IIRMOVL,IRMMOVL,IMRMOVL,IJXX,ICALL,IIADDL};8990bool instr_valid=icode in91{INOP,IHALT,IRRMOVL,IIRMOVL,IRMMOVL,IMRMOVL,92IIADDL,ILEAVE,93IOPL,IJXX,ICALL,IRET,IPUSHL,IPOPL};9495################Decode Stage################################### 9697##What register should be used as the A source?98int srcA=[99icode in{IRRMOVL,IRMMOVL,IOPL,IPUSHL}:rA;20CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS 101icode in{IPOPL,IRET}:RESP;1021:RNONE;#Don’t need register103];104105##What register should be used as the B source?106int srcB=[107icode in{IOPL,IRMMOVL,IMRMOVL}:rB;108icode in{IIADDL}:rB;109icode in{IPUSHL,IPOPL,ICALL,IRET}:RESP;110icode in{ILEAVE}:REBP;1111:RNONE;#Don’t need register112];113114##What register should be used as the E destination?115int dstE=[116icode in{IRRMOVL,IIRMOVL,IOPL}:rB;117icode in{IIADDL}:rB;118icode in{IPUSHL,IPOPL,ICALL,IRET}:RESP;119icode in{ILEAVE}:RESP;1201:RNONE;#Don’t need register121];122123##What register should be used as the M destination?124int dstM=[125icode in{IMRMOVL,IPOPL}:rA;126icode in{ILEAVE}:REBP;1271:RNONE;#Don’t need register128];129130################Execute Stage###################################131132##Select input A to ALU133int aluA=[134icode in{IRRMOVL,IOPL}:valA;135icode in{IIRMOVL,IRMMOVL,IMRMOVL}:valC;136icode in{IIADDL}:valC;137icode in{ICALL,IPUSHL}:-4;138icode in{IRET,IPOPL}:4;139icode in{ILEAVE}:4;140#Other instructions don’t need ALU141];142143##Select input B to ALU144int aluB=[145icode in{IRMMOVL,IMRMOVL,IOPL,ICALL,146IPUSHL,IRET,IPOPL}:valB;147icode in{IIADDL,ILEAVE}:valB;148icode in{IRRMOVL,IIRMOVL}:0;149#Other instructions don’t need ALU1.4.CHAPTER4:PROCESSOR ARCHITECTURE21151152##Set the ALU function153int alufun=[154icode==IOPL:ifun;1551:ALUADD;156];157158##Should the condition codes be updated?159bool set_cc=icode in{IOPL,IIADDL};160161################Memory Stage###################################162163##Set read control signal164bool mem_read=icode in{IMRMOVL,IPOPL,IRET,ILEAVE};165166##Set write control signal167bool mem_write=icode in{IRMMOVL,IPUSHL,ICALL};168169##Select memory address170int mem_addr=[171icode in{IRMMOVL,IPUSHL,ICALL,IMRMOVL}:valE;172icode in{IPOPL,IRET}:valA;173icode in{ILEAVE}:valA;174#Other instructions don’t need address175];176177##Select memory input data178int mem_data=[179#Value from register180icode in{IRMMOVL,IPUSHL}:valA;181#Return PC182icode==ICALL:valP;183#Default:Don’t write anything184];185186################Program Counter Update############################187188##What address should instruction be fetched at189190int new_pc=[191#e instruction constant192icode==ICALL:valC;193#Taken e instruction constant194icode==IJXX&&Bch:valC;195#Completion of RET e value from stack196icode==IRET:valM;197#Default:Use incremented PC1981:valP;199];22CHAPTER 1.SOLUTIONS TO HOMEWORK PROBLEMSME DMispredictE DM E DM M E D E DMGen./use 1W E DM Gen./use 2WE DM Gen./use 3W Figure 1.1:Pipeline states for special control conditions.The pairs connected by arrows can arisesimultaneously.code/arch/pipe-nobypass-ans.hcl1.4.CHAPTER4:PROCESSOR ARCHITECTURE232#At most one of these can be true.3bool F_bubble=0;4bool F_stall=5#Stall if either operand source is destination of6#instruction in execute,memory,or write-back stages7d_srcA!=RNONE&&d_srcA in8{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE}||9d_srcB!=RNONE&&d_srcB in10{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE}||11#Stalling at fetch while ret passes through pipeline12IRET in{D_icode,E_icode,M_icode};1314#Should I stall or inject a bubble into Pipeline Register D?15#At most one of these can be true.16bool D_stall=17#Stall if either operand source is destination of18#instruction in execute,memory,or write-back stages19#but not part of mispredicted branch20!(E_icode==IJXX&&!e_Bch)&&21(d_srcA!=RNONE&&d_srcA in22{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE}||23d_srcB!=RNONE&&d_srcB in24{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE});2526bool D_bubble=27#Mispredicted branch28(E_icode==IJXX&&!e_Bch)||29#Stalling at fetch while ret passes through pipeline30!(E_icode in{IMRMOVL,IPOPL}&&E_dstM in{d_srcA,d_srcB})&&31#but not condition for a generate/use hazard32!(d_srcA!=RNONE&&d_srcA in33{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE}||34d_srcB!=RNONE&&d_srcB in35{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE})&&36IRET in{D_icode,E_icode,M_icode};3738#Should I stall or inject a bubble into Pipeline Register E?39#At most one of these can be true.40bool E_stall=0;41bool E_bubble=42#Mispredicted branch43(E_icode==IJXX&&!e_Bch)||44#Inject bubble if either operand source is destination of45#instruction in execute,memory,or write back stages46d_srcA!=RNONE&&47d_srcA in{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE}|| 48d_srcB!=RNONE&&49d_srcB in{E_dstM,E_dstE,M_dstM,M_dstE,W_dstM,W_dstE};5024CHAPTER1.SOLUTIONS TO HOMEWORK PROBLEMS 52#At most one of these can be true.53bool M_stall=0;54bool M_bubble=0;code/arch/pipe-full-ans.hcl 1####################################################################2#HCL Description of Control for Pipelined Y86Processor#3#Copyright(C)Randal E.Bryant,David R.O’Hallaron,2002#4####################################################################56##This is the solution for the iaddl and leave problems78####################################################################9#C Include’s.Don’t alter these#10#################################################################### 1112quote’#include<stdio.h>’13quote’#include"isa.h"’14quote’#include"pipeline.h"’15quote’#include"stages.h"’16quote’#include"sim.h"’17quote’int sim_main(int argc,char*argv[]);’18quote’int main(int argc,char*argv[]){return sim_main(argc,argv);}’1920####################################################################21#Declarations.Do not change/remove/delete any of these#22#################################################################### 2324#####Symbolic representation of Y86Instruction Codes#############25intsig INOP’I_NOP’26intsig IHALT’I_HALT’27intsig IRRMOVL’I_RRMOVL’28intsig IIRMOVL’I_IRMOVL’29intsig IRMMOVL’I_RMMOVL’30intsig IMRMOVL’I_MRMOVL’31intsig IOPL’I_ALU’32intsig IJXX’I_JMP’33intsig ICALL’I_CALL’34intsig IRET’I_RET’1.4.CHAPTER4:PROCESSOR ARCHITECTURE25 36intsig IPOPL’I_POPL’37#Instruction code for iaddl instruction38intsig IIADDL’I_IADDL’39#Instruction code for leave instruction40intsig ILEAVE’I_LEAVE’4142#####Symbolic representation of Y86Registers referenced explicitly##### 43intsig RESP’REG_ESP’#Stack Pointer44intsig REBP’REG_EBP’#Frame Pointer45intsig RNONE’REG_NONE’#Special value indicating"no register"4647#####ALU Functions referenced explicitly##########################48intsig ALUADD’A_ADD’#ALU should add its arguments4950#####Signals that can be referenced by control logic##############5152#####Pipeline Register F##########################################5354intsig F_predPC’pc_curr->pc’#Predicted value of PC5556#####Intermediate Values in Fetch Stage###########################5758intsig f_icode’if_id_next->icode’#Fetched instruction code59intsig f_ifun’if_id_next->ifun’#Fetched instruction function60intsig f_valC’if_id_next->valc’#Constant data of fetched instruction 61intsig f_valP’if_id_next->valp’#Address of following instruction 6263#####Pipeline Register D##########################################64intsig D_icode’if_id_curr->icode’#Instruction code65intsig D_rA’if_id_curr->ra’#rA field from instruction66intsig D_rB’if_id_curr->rb’#rB field from instruction67intsig D_valP’if_id_curr->valp’#Incremented PC6869#####Intermediate Values in Decode Stage#########################7071intsig d_srcA’id_ex_next->srca’#srcA from decoded instruction72intsig d_srcB’id_ex_next->srcb’#srcB from decoded instruction73intsig d_rvalA’d_regvala’#valA read from register file74intsig d_rvalB’d_regvalb’#valB read from register file 7576#####Pipeline Register E##########################################77intsig E_icode’id_ex_curr->icode’#Instruction code78intsig E_ifun’id_ex_curr->ifun’#Instruction function79intsig E_valC’id_ex_curr->valc’#Constant data80intsig E_srcA’id_ex_curr->srca’#Source A register ID81intsig E_valA’id_ex_curr->vala’#Source A value82intsig E_srcB’id_ex_curr->srcb’#Source B register ID83intsig E_valB’id_ex_curr->valb’#Source B value84intsig E_dstE’id_ex_curr->deste’#Destination E register ID。
3GPP 5G基站(BS)R16版本一致性测试英文原版(3GPP TS 38.141-1)
4.2.2
BS type 1-H.................................................................................................................................................. 26
4.3
Base station classes............................................................................................................................................27
1 Scope.......................................................................................................................................................13
All rights reserved. UMTS™ is a Trade Mark of ETSI registered for the benefit of its members 3GPP™ is a Trade Mark of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners LTE™ is a Trade Mark of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners GSM® and the GSM logo are registered and owned by the GSM Association
IBM Cognos Transformer V11.0 用户指南说明书
Oracle数据库中有关CBO优化的三个问题
Oracle数据库中有关CBO优化的三个问题
一.如何使用CostBased优化器优化查询操作?
Oracle 提供了基于成本(CostBased)和基于规则(RuleBased)两种优化器,简称为CBO和RBO,用于确定查询操作的执行计划。
CostBased优化器将计算各种执行计划的开销,然后选出最低成本的执行计划。
可使用下列方法选择使用CBO:
1.在INIT.ORA文件中设置参数OPTIMIZER_MODE=choose;
2.在Session级设置OPTIMIZER_GOAL=FIRST_ROWS或ALL_ROWS。
3、在查询语句中使用Hint,包括CHOOSE、ALL_ROWS、FIRST_ROWS等。
二.为什么我的执行计划不是的?
CBO是依赖于表的一些统计信息来选择出最低成本的执行计划,当这些统计信息不准确时,产生的计划便可能不是的。
因而应使用ANALYZE命令及时对表进行分析统计。
三.我的查询上周的性能很好,为什么现在查询速度很慢?
这是由于执行计划被改变而造成的,下列因素将会改变一个执行计划:
1、INIT.ORA文件中的参数OPTIMIZER_MODE被改变;
2、表上定义或改变了并行查询度;
3、使用ANALYZE命令重新分析了表,而且使用了ESTIMATE方式,这种方式选择不同的百分比可产生不同的分析结果;
4、DB_FILE_MULTIBLOCK_READ_COUNT参数被修改;
5、SORT_AREA_SIZE参数被修改。
【。
dlbasics_utilities 用法
DLBasics是一种深度学习库,提供了各种用来搭建和训练深度学习模型的工具和资源。
在实际应用中,DLBasics可以用于进行图像识别、自然语言处理、语音识别等任务,因此它具有广泛的应用价值。
DLBasics提供了丰富的工具和实用的函数,可以方便地实现各种深度学习模型。
以下是DLBasics的一些常用功能和用法:1. 数据加载和预处理DLBasics提供了各种函数和类,用于加载和预处理数据。
用户可以方便地从文件、数据库或其它数据源中加载数据,并进行标准化、归一化、分割等预处理操作。
通过这些功能,用户可以快速地准备好用于训练的数据集。
2. 模型搭建DLBasics提供了各种函数和类,可以方便地搭建深度学习模型。
用户可以使用这些工具来定义各种类型的网络结构,包括卷积神经网络、循环神经网络等。
DLBasics还提供了各种常用的激活函数、损失函数和优化器,可以帮助用户快速地构建出一个完整的深度学习模型。
3. 模型训练和评估DLBasics提供了丰富的函数和类,可以用于模型的训练和评估。
用户可以方便地指定训练的超参数,如学习率、批大小等,同时还可以指定评估指标进行模型性能的评估。
通过这些功能,用户可以快速地训练出一个性能良好的深度学习模型,并进行全面的评估。
4. 模型保存和部署DLBasics还提供了函数和类,用于模型的保存和部署。
用户可以方便地将训练好的模型保存到文件中,并在实际应用中进行加载和部署。
通过这些功能,用户可以轻松地将训练好的深度学习模型应用到实际的生产环境中。
DLBasics是一款功能强大、易用便捷的深度学习库,具有广泛的应用价值。
无论是初学者还是专业人士,只要掌握了DLBasics的用法,都可以快速地实现各种复杂的深度学习任务。
希望以上介绍可以帮助大家更好地了解DLBasics的功能和用法,也希望更多的人能够利用DLBasics来进行深度学习模型的搭建和训练。
尊敬的读者,前面我们已经介绍了DLBasics的一些常用功能和用法,接下来我们将进一步探讨DLBasics在深度学习领域的具体应用,以及一些高级功能,帮助您更加深入地了解这一深度学习库。
云计算中英文术语
云计算中英文术语云计算中英文术语本文档旨在提供云计算中常见的中英文术语,方便读者查阅和使用。
以下是详细的分类和解释:1.云计算基础 (Cloud Computing Basics)1.1 云计算 (Cloud Computing)云计算是一种基于互联网的计算模式,通过共享大量的计算资源,提供灵活的计算能力和存储服务。
1.2 云服务提供商 (Cloud Service Provider)云服务提供商是指提供云计算服务的公司或组织,例如亚马逊云服务 (Amazon Web Services) 和微软 Azure。
1.3 虚拟化 (Virtualization)虚拟化是将物理计算资源虚拟化为多个虚拟资源的技术,通过隔离和共享资源,提高资源的利用率和灵活性。
1.4 弹性计算 (Elastic Computing)弹性计算是指根据实际需求动态调整计算资源的能力,使系统能够在负载波动时保持稳定。
2.云服务模型 (Cloud Service Models)2.1 基础设施即服务 (Infrastructure as a Service, IaaS)基础设施即服务是一种云计算模式,提供基础的计算、存储和网络资源,用户可根据需求自由配置运行环境。
2.2 平台即服务 (Platform as a Service, PaaS)平台即服务是一种云计算模式,提供开发和运行应用程序的平台环境,用户只需关注应用程序的开发和部署,无需关心底层基础设施。
2.3 软件即服务 (Software as a Service, SaaS)软件即服务是一种云计算模式,提供基于互联网的软件应用,用户无需安装和维护软件,只需通过浏览器访问即可使用。
3.云计算部署模型 (Cloud Deployment Models)3.1 公共云 (Public Cloud)公共云是由云服务提供商提供的在公共网络上访问的共享资源,多个客户共享同一组硬件设备和软件服务。
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Dictionary :AAbsorbed Overhead: Overheads which, by means of absorption rates, in included in costs of specific products or saleable services, in a given period of time.Absorption Cost:The procedure which charges fixed as will as variable overhead at a predetermined level of activity.Absorption Rate: A rate charged to a cost unit intended to account for the overhead at a predetermined level of activity.Activity-based Costing (ABC):Cost attribution to cost units on the basis of benefit received from indirect activities, e.g., ordering, setting-up-, assuring quality.Administration Cost: Cost of management, and of secretarial, accounting and administrative services, which cannot be directly related to the production, marketing, research or development functions of the enterprise.Attainable Standard :A standard which can be attained if a standard unit of work is carried out efficiently, a machine properly operated or a materiel properly used. Allowances are made for normal losses, waste and machine downtime.The standard represents future performance and objectives which are reasonably attainable. Besides having a desirable motivational impact on employees, attainable standards serve other purposes, e.g., cash budgeting, inventory valuation and budgeting departmental performance.BBasic Standard: A standard established for use over a long period from which a current standard can be developed.Bases of Apportionment:Formulae varying according to the nature of costs for the purpose of apportioning those costs among cost centres or products.Basic Costing Method:A method of costing which is devised to suit the methods by which goods are manufactured or services are provided.Batch Cost:Aggregated costs relative to a cost unit which consists of a group of similar articles which maintains its identity throughout one or more stages of productionBatch Costing:That form of specific order costing which applies where similar articles are manufactured in batches, either for sale or for use within the undertaking. In most cases the costing is similar to job costing.Breaking-down Time: The time required to return a work station to a standard condition after completion of an operation.Break-even Chart: A chart which indicates approximate profit or loss at different levels of sales volume within a limited range.Break-even Point :The level of activity at which there is neither profit or loss. It can beBudget :A plan expressed in money. It is prepared and approved prior to be budget period and may show income, expenditure and the capital to be employed.Budget Cost Allowance:The cost which a budget centre is expected to incur in a control period.At its simplest this usually comprises variable costs in direct proportion to the volume of production or service achieved, and fixed costs as a proportion of the annual budget.Budget Period: The period for which a budget is prepared and used, which may then by sub-divided into control periods.Budgetary Control: The establishment of budgets relating to responsibilities of executives to the requirements of a policy, and the continuous comparison of actual with budgeted results, either to secure by individual action the objective of that policy or to provide a basis for this revision.Budget Centre: A section of an entity for which control may be exercised and budgets prepared.By-product: A product which is recovered incidentally from the material used in the manufacture of recognised main products, such a by-product having either a net realisable value or a usable value which is relatively low in comparison with the saleable value of the main products. By-products may be further processed to increase their realisable value.CCapital Expenditure Budget: A plan for capital expenditure in monetary terms.Capital Expenditure:Expenditure on fixed assets or additions thereto intended to benefit future accounting periods (in contrast to revenue expenditure which benefits a current period) or expenditure which increases the capacity, efficiency, life span or economy of operation of an existing fixed asset.Cash Flow Budget: A detailed budget of income and cash expenditure incorporating both revenue and capital items.The cash flow budget should be prepared in the same format in which the actual position is to be presented. The year’s budget is usually phased into shorter periods for control, e.g. monthly or quarterly.Changeover Time:The time required to change a work station from a state of readiness for one operation to a state of readiness for another.Common Costs:Shared costs of more than one product or service, where the shared proportions are determined by management decision.Contribution Centre: A profit centre whose expenditure is reported on a marginal or direct cost basis.Continuous Operation/Process Costing:The basic costing method applicable where goods or services result from a sequence of continuous or repetitive operat ions or processes to which costs are charged before being averaged over the units produced during the period.Contract Cost:Aggregated costs relative to a single contract designated as cost unit. This usually applied to major long term contracts as distinct from short term job costs.Contract Costing: That form of specific order costing which applies where work is undertaken to customer’s special requirements and each order is of long duration (compared with those to which job costing applies) The work is usually constructional and in general the method is similar to job costing.Contribution:Sales value less variable cost of sales. It may be expressed as total contribution, contribution per unit or as a percentage of sales.Controllable or Managed Cost: A cost, chargeable to a budget or cost-centre, which can be influenced by the actions of the person in whom control of the centre is vested.It is not always possible to predetermine responsibility, because the reason for deviation from expected performance may only become evident later. For example, excessive scrap may arise from inadequate supervision or from latent defect in purchased material.Conversion Cost: Costs of converting material input into semi-finished or finished products, i.e. additional direct materials, direct wages, direct expenses and absorbed production overhead.Cost Centre: A production or service location, function activity or item of equipment whose cost may be attributed to cost units.Cost Accounting:The establishment of budgets, standard costs and actual costs of operations, processes activities or products and the analysis of variances, profitability or the social use of funds. The use of the term costing is not recommended except with a qualifying adjective e.g., standard costing.Cost (as a noun) : The amount of expenditure (actual or notional) incurred on, or attributable to, a specified thing or activity.(as a verb) : to ascertain the cost of a specified thing or activity.The word Cost can rarely stand alone and should be qualified as to its nature and limitations.Cost Allocation:That part of cost attribution which charges specific cost to a cost centre or cost unit.Cost Apportionment: That part of cost attribution which shares costs among two or more cost centres or cost units in proportion to the estimated benefit received using a proxy, e.g. square metres.Cost Ascertainment: The collection of costs attributable to cost centres and cost units using the costing methods, principles and techniques prescribed for a particular business entity.Cost Attribution:The process of relating cost to cost centres or cost units using cost allocation or cost apportionment.Cost of Sales:The sum of direct cost of sales plus factory overhead attributable to the turnover.In management accounts this may be referred to as production cost of sales, or cost of goods sold.Cost Unit: A unit of product or service in relation to which costs are ascertained.Cost Unit Rate: A rate calculated by dividing the budget or estimated overhead cost attributable to a cost centre by the amount of direct labour cost expected to be incurred (or which would relate to working at normal capacity) and expressing the result as a percentage.Current Standard : A standard established for use over a long period from which a current standard can be developed.DDepreciation:The measure of the wearing out, consumption or other loss of value of a fixed asset whether arising from use, defluxion of time or obsolescence through technology and market changes (SSAP 12).Development Cost:The cost of using scientific or technical knowledge in order to produce new or substantially improved materials, devices, products, processes, systems or services prior to the commencement of commercial production (SSAP 13)Direct Cost of Sales:The sum of direct materials consumed, direct wages, direct expenses and variable production overhead.In management accounting this may be referred to as direct production cost of sales.Direct Expenses: Costs other than materials or labour, which can be identified in a specified product or saleable service.Direct Labour Cost: The cost of remuneration for employees’ efforts and skills applied directly to a product or saleable service and which can be identified separately in product costs. Direct Materials Cost: The cost of materials entering into and becoming constituent elements of a product or saleable service and which can be identified separately in product costs.Distribution Cost: Cost incurred in warehousing saleable products and in delivering products to customers.Direct hours: The hours of employees applied directly to a product or service.Down time: The period of time for which a work station is not available for production due to a functional failure.Direct Labour Cost Percentage Rate: A rate calculated by dividing the budgeted or estimated overhead cost attributable to a cost centre by the appropriate number of direct labour hours. Hours may be either the number of hours expected to be worked, or the number of hours which would relate to working at normal capacity.Departmental/Functional Budget : A budget of income and/or expenditure applicable to a particular function.A function may refer to a department or a process.EEconomic Order Quantity: A quantity of materials to be ordered which takes into account the optimum combination of (i) bulk discounts from high volume purchases, (ii) usage rate, (iii) stock holding costs, (iv) storage capacity, (v) order delivery time, and (vi) cost of processing the order.Equivalent Units:A notional quantity of completed units substituted for an actual quantity of incomplete physical units in progress, when the aggregate work content of the incomplete units is deemed to be equivalent to that of the substituted quantity of completed units, e.g., 150 units 50 percent complete = 75 equivalent units.The principle applies when operation costs are being apportioned between work in progress and complete output.Employment Cost:A generic term given to costs attributable to an employee, in addition to gross wages/salaries.They usually include employers’ national health insurance and state pensions contributions, employers’ pension premiums, holidays with pay, employers’ contributions to sickness benefit schemes and other benefits, e.g. protective clothing and canteen subsidies.Exceptions Reporting: A system of reporting based on the exception principle which focuses attention on those items where performance differs significantly from standard or budget.FFixed Overhead Cost:The cost which accrues in relation to the passage of time and which, within certain output and turnover limits, tends to be unaffected by fluctuations in the levels of activity (output or turnover).Examples are rent, rates, insurance and executive salaries. Other terms used included period cost and policy cost.First in, First out Price (FIFO): A method of pricing material issues using the oldest purchase price first.Fixed Budget: A budget which is designed to remain unchanged irrespective of the volume of output or turnover attained.Flexible Budget: A budget which, by recognising different cost behaviour patterns, is designed to change as volume of output changes.IIncremental Costing : A technique used in the preparation of ad hoc information where consideration is given to a range of graduated or stepped changes in the level or nature of activity, and the additional costs and revenues likely to result from each degree of change are presented.Incremental Yield : A measure used in capital investment appraisal where a choice lies between two or more projects.The cash flows of project A are deducted from those of project B and the rate of return is calculated on the incremental cash flow.Incremental Rate of Return (IRR): A percentage discount rate used in capital investment appraisal which brings the cost of a project and its future cash inflows into equality.Idle Time:The period of time for which a work station is available for production but is not utilised due to shortage of tooling material, operations, etc.Ideal Standard:A standard which can be attained under the most favourable conditions withInvestment Centre: A profit centre whose performance is measured by its return on capital employed.Indirect Expenses:Expenses which are not charged directly to a product, e.g., buildings, insurance, water rates.Indirect Labour Cost:Labour Costs which are not charged directly to a product, e.g., supervision.Indirect Materials Cost:Materials costs which are not charged directly to a product, e.g. coolant, cleaning materials.JJob Cost: Aggregated costs relative to a cost unit which consists of a single specific customer order or specific task.Job Costing:That form of specific order costing which applies where work is undertaken to customers’ special requirements and each order is of comparatively short duration (compared with those to which contract costing applies).The work is usually carried out within a factory or workshop and moves through processes and operations as a continuously identifiable unit. The term may also be applied to work such as properly repairs and the method my be used in the costing of internal capital expenditure jobs.Joint Cost: The costs of providing two or more products or services whose production could not, for physical reasons, be segregated.Example, the cost of sheep rearing to produce both mutton and wool.Joint Products:Two or more products separated in the course of processing, each having a sufficiently high saleable value to merit recognition as a main product.LLimiting Factor or Key Factor: A factor which at any time or over a period may limit the activity of an entity, often one where there is shortage or difficulty of supply.Long-term Strategic Planning : The formulation, evaluation and selection of strategies involving a review of the objectives of an organisation, the environment in which it is to operate, and an assessment of its strengths, weaknesses, opportunities and threats for the purpose of preparing a long term strategic plan of action which will attain the objective set.Last in, First out Price (LIFO): A method of pricing material issues using the last purchase price first.Life cycle costing:The practice of obtaining, over their life-times, the best use of physical assets at the lowest total cost to the entity (terotechnology).This is achieved through a combination of management, financial, engineering and other disciples.Long Term Budget: A long term plan usually prepared in monetary terms.Management Audit: An objective and independent appraisal of the effectiveness of managers and the effectiveness of the corporate structure in the achievement of company objectives and policies.Its aim is to identify existing and potential management weaknesses within an organisation and to recommend ways to rectify these weaknesses.Margin of Safety: The excess of normal or actual sales over sales at break-even point Marketing Cost:The cost incurred in researching the potential markets and promoting products in suitably attractive forms and at acceptable prices.Master Budget: A budget which is prepared from, and summarises, the functional budgets. The term summary budget is synonymous.Machine Hour Rate : A rate calculated by dividing the budget or estimated overhead or labour and overhead cost attributable to a machine group of similar machines by the appropriate number of machine hours.The hours may be the number of hours for which the machine or group is expected to be operated, the number of hours which would relate to normal working for the factory, or full capacity.Margin:Sales less the cost of sales expressed either as a value or a percentage. Since the margin may be calculated at different stages, the terms gross and net margin, also known as gross profit and et profit, are used to differentiate between the levels.Marginal Cost: The cost of one unit of product or service which would be avoided if that unit were not produced or provided.Note: In this context, a unit is usually either a single article or a standard measure such as the litre or kilogram, but may in certain circumstances be an operation, process or part of an organisation.Marginal Costing: The accounting system in which variable cost are charged to cost units and fixed costs of the period are written off in full against the aggregate contribution.NNon-controllable Cost (indirectly controlled cost) :A cost chargeable to a budget or cost centre which can only be influenced indirectly by the actions of the person in whom control of the centre is vested.Typically, these costs will be mainly an apportionment of overhead costs of the entity.Notional Cost: The value of a benefit where no actual cost is incurred.Operation Time:The period of time required to carry out an operation on a complete batch exclusive of set-up and breaking-down times.Opportunity Cost: The value of a benefit sacrificed in favour of an alternative course of action. Overhead Absorption Methods:The charging of overhead to cost units by means of rates separately calculated for each cost centre.In most cases the rates are predetermined.Overhead Cost: The total cost of indirect materials, indirect labour and indirect expenses.PPrime Cost: The total cost of direct materials, direct labour and direct expenses.The term prime cost is commonly restricted to direct production costs only and so does not customarily include direct production costs only and so does not customarily include direct costs of marketing or research and development.Production Cost: Prime cost plus absorbed production overhead.Policy Cost: Costs incurred as a result of taking a particular policy decision. For example, ownership of assets will create a charge for depreciation. Depreciation is, therefore, a policy cost.Product Cost : The cost of a finished product built up from its cost elements.An example of a product cost which provides for a first estimate, a subsequen t standard cost and for stock valuations at various work in progress stage.Perpetual Inventory :The recording as they occur of receipts, issues, and the resulting balances of individual items of stock in either quality or quantity and value.Physical Inventory: An inventory determined by actual count, weight or measurement. Process Time: The period of time which elapses between the start and finish of one process or stage of a process.Production Cost Centre: A cost in which production is carried on: this may embrace one specific operation, e.g., machine, or a continuous process, e.g., distillation.Profit Centre: A part of a business accountable for costs and revenues. It may be called a business centre, business unit, or strategic business unit.PERT (Project Evaluation and Review Technology) :A specification of all activities events and constraints relating to a project, from which a network is drawn which provides a model of the way the project should proceed.Product Life Cycle: The pattern of demand for a product or service over time.Principle Budget Factor: A factor which, at a particular time or over a period, will limit thePublicity Cost: (a) Cost incurred in advertising and promotion as aids to the eventual sales of goods or services.(b) Cost incurred in advertising and promotion of an entity as distinct from its products or services (public relations)RRaw Materials: Unprocessed stock awaiting conversion.Cost: Cost incurred in securing orders, usually including salesmen’s salaries, commissions and travelling expenses.Short term Budget: A budget established for use over a short period of time (usually one year but sometimes less) and which the person responsible is expected to achieve and use for control purposes.Standard: A Predetermined measurable quantity set in defined conditions against which actual performance can be compared, usually for an element of work, operation or activity.While standards may be based on unquestioned and immutable natural law or facts, they are finally set by human judgement and consequently are subject to the same fallibility which attends all human activity. Thus a standard for 100 percent machine output can be fixed by its geared input/output speeds, but the effective realisable output standard is one of judgement.Standard Cost: A standard expressed in money. It is built up from an assessment of the value of cost elements. Its main uses are providing bases for performance measurement, control by exception reporting, valuing stock and establishing selling prices.Standard Price:A predetermined price fixed on the basis of a specification of a product or service and of all factors affecting that price.Standard Production Cost—Total:The predetermined cost of producing or providing specified quantities of products or service at standard performance over a specified period. Standard Production Cost—Unit:The predetermined cost of producing or providing a specified quantity of a product or service at standard performance.Standard Profit—Total: The predetermined profit arising from the sale of actual quantities of products or services at standard selling prices, over a specified period.Standard profit may be at the level of net profit, gross profit, or contribution. Profit which relates only to trading activities is often referred to as operating profit.Standard Selling Price—Unit:A predetermined price for a specified unit to be sold. A unit may consist of a single item or a batch of processed output.Standard Unit of Work: A unit of work consisting of basic time plus relaxation allowance and contingency allowance where applicable.The unit of work may be for labour output only, a combination of machine and labour output, or for a machine only.Standard Time:The total time (hours and minutes) in which a task should be completed atStock Control:The systematic regulation of stock levels with respect to quantity, cost and lead time.The alternative term inventory control is common in the U.S.A.Stock Recorder Level:A quantity of materials fixed in advance at which level stocks should be reordered.Stocktaking: A process whereby stocks (which may comprise direct and indirect materials, work in progress and finished goods) are physically counted and are then valued item by item.This may be at a point in time (periodic) or by counting and valuing a number of items at different times (continuous)Service Cost Centre: A cost centre providing services to other cost centres. When the output of an organisation is a service, rather than goods, an alternative term is normally used, e.g., support cost centre or utility cost centre.Scrap: Discarded material which has some recovery value and which is usually either disposed of without further treatment (other than reclamation and handling), or reintroduced into the production process in place of raw material.Set-up Time:The time required to prepare a work station from a standard condition to readiness to commence a specified operation.Stock:Any current asset held for conversion into cash in the normal course of trading, e.g., raw materials, work-in progress, finished goods and goods in transit, or on consignment, or on sale or return.Sunk Cost:Shared costs of more than one product or service, where the shared proportions are determined by management decisions.Semi-Variable Cost/Semi-Fixed Cost: A cost containing both fixed and variable elements, and which is thus partly affected by fluctuation in the level of activity.Service/Function Costing:Cost accounting for services or functions, e.g., canteens, maintenance, personnel. These may be referred to as service centres, departments or functions.Specific Order Costing:The basic cost accounting method applicable where the work consists of separate contracts, jobs or batches.TTurnover:Amounts derived from the provision of goods and services falling within the company’s ordinary activities, after deduction of trade discounts, value added tax, and any other taxes based on the amounts so derived (Companies Act)This would normally be invoiced sales less returns and allowances.Tax Shield Education Pvt. Ltd. Cost Accounting- 11 Under-or-over-absorbed overhead:The difference between overhead cost incurred and overhead cost absorbed; it may be split into its tow constitute parts for control purposes.Uniform Costing:The use by several undertakings of the same costing systems, i.e., the same basic costing methods, principles and techniques.VValue Analysis: A systematic inter-disciplinary examination of factors affecting the cost of a product or service, in order to devise means of achieving the specified purpose most economically at the required standard of quality and reliability.Variance:The difference between planned, budgeted, or standard cost and actual costs (and similarly in respect of revenues)Note: This is not to be confused with the statistical variance which measures the dispersionof a statistical population.Variance Analysis: The analysis of variance arising in a standard costing system into their constituent parts.It is the analysis and comparison of the factors which have caused the difference between predetermined standards and actual results, with a view to eliminating inefficiencies.Variable Cost: Cost which tends to vary with the level of activity.Variable Overhead Cost:Overhead cost which tends to vary with changes in the level of activity.WWeighted Average Price: A method of pricing material issues using a price which is calculated by dividing the total cost of material in stock by the total quantity in stock.Waiting Time: The period of time for which an operator is available for production but is prevented from working by storage of material or tooling, machine breakdown.Waste: Discarded substances having no value (as distinct from scrap)Work in progress:Any material, component, product or contract at an intermediate stage of completion.ZZero Base Budgeting: A method of budgeting whereby all activities are re-evaluated each time a budget is set. Discrete levels of each activity are valued and a combination chosen to match funds available.Each functional budget starts with the assumption that the function does not exist and is at zero costs. Increments of cost are compared with increments of benefit, culminating in the planned maximum benefit for a given budget cost.。