第七章Database

Difference between file system and DBMS
Look at Fig. 7-1 and pay attention to two different
Learn alternative ways for users to query information from database :
Keywords: MIS
an MIS can be defined as a network of
computer-based data processing procedures developed for the purpose of providing timely and effective information to support decision making and other necessary management functions. An information system that integrates data from all the departments it serves and provides operations and management with the information they require.

Databases 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
What is the advantage of DBMS compared with file-
oriented system? What is MIS?



The essence of MIS Who developed it? For what purpose The model of MIS Where does the information needed by managers come from?
information flowing path (the direction of arrowhead) Using DBMS

In a file-oriented system

Manager uses the DBMS to query database contents DBMS CPU Database Assemble the needed information in a few minutes Manager has need for special information Communicating information need to a programmer Application program to meet user needs CPU Database Output information received days later.
Outline
Keywords Features of DBMS Difference between file system and DBMS
Drawbacks of file system compared with
DBMS Features of MIS
Keywords: database
Major Features of a DBMS
Data Independence
With DBMS, the details of the data structure are not stated in each application program. The program asks the DBMS for data by field name; for example, a coded equivalent of "give me customer name " would be sent to the DBMS. Without a DBMS, the programmer must reserve space for the full structure of the record in the program. Any change in data structure requires changing all application programs.
Major Features of a DBMS
Data Security
The DBMS can prevent unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database or a subset of it known as a "subschema." For example, in an employee database, some users may be able to view salaries while others may view only work history and medical data.
Keywords: DBMS
The system software package that handles the
difficult tasks associated with creating, accessing, and maintaining database records is called a database management system(DBMS). The programs in a DBMS package establish an interface between the database itself and the users of the database. Software that controls the organization, storage, retrieval, security and integrity of data in a database. It accepts requests from the application and instructs the operating system to transfer the appropriate data.
A database is a collection of logically
related data elements that may be structured in various ways to meet the multiple processing and retrieval needs of organizations and individuals. A set of related files that is created and managed by a database management system (DBMS).
SUMMARY sentence
In short, the DBMS will “manage” the
stored data items and assemble the needed items from the common database in response to the queries of those who are not programmers. The availability of a DBMS, however, offers users a much faster alternative communication path.
Major Features of a DBMS
Interactive Data Entry and Updating
Many DBMS provide a way to interactively enter and edit data, allowing you to manage your own files and databases.
Section 7.1: Database management systems(DBMS) and Management Information System(MIS) Guidance and questions:
What is database? What is DBMS?
What can a DBMS do?
DBMS
Collection of interrelated data Set of programs to access the data DBMS contains information about a particular
enterprise DBMS provides an environment that is both convenient and efficient to use. Database Applications:
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Major Features of a DBMS
Data Integrity
The DBMS can ensure that no more than one user can update the same record at the same time. Interactive Query Most DBMS provide query languages and report writers that let users interactively interrogate the database and analyze its data. This important feature gives users access to all management information as needed.

Drawbacks of using file systems to store data
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files Difficulty in accessing data Need to write a new program to carry out each new task Data isolation — multiple files and formats Integrity problems Integrity constraints (e.g. account balance > 0) become part of program code Hard to add new constraints or change existing ones Concurrent access by multiple users Concurrent accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies E.g. two people reading a balance and updating it at the same time Database systems offer solutions to all the above problems