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Database System Concepts

Database System Concepts. Computer science and technology department. Liping Zhang E-mail: Carolyn321@163.com. Textbook：. Book name: Database System Concepts ,Fourth Edition Author: Abraham Silberschatz,Henry E Korth,S.Sudarshan Press: China Machine Press. References book：.

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Database System Concepts

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  1. Database System Concepts Computer science and technology department Liping Zhang E-mail: Carolyn321@163.com

  2. Textbook： Book name: Database System Concepts,Fourth Edition Author: Abraham Silberschatz,Henry E Korth,S.Sudarshan Press: China Machine Press

  3. References book： • Book name: An Introduction to Database Systems Author: C. J.Date Press: China Machine Press • Book name: A First Course in Database Systems Author: Jeffrey D.ullman Jennifer Widom Press: China Machine Press

  4. References book： • Book name :数据库系统概念（第三版） Author :萨师煊 王珊 Press:Higher Education Press • Book name :数据库系统教程 Author :王能斌 Press:Electronics industry • Book name : 数据库系统基础 Author : 冯玉才 Press:华中科技大学

  5. Teaching outline: 1. in the classroom Chapter 1 Introduction Chapter 2 Entity-Relationship Model Chapter 3 Relational Model Chapter 4 SQL Chapter 5 Integrity and Security Chapter 6 Relational-Database Design Chapter 7 Query Optimization Chapter 8 Transactions Chapter 9 Concurrency Control Chapter 10 Recovery System 2.practice in the laboratory Requirement: 1.preparation 2.review 3.learn by yourself Delphi7.0 SQLServer2000 Scores: 70%+30% absence -3 Database system concepts

  6. 1.1 What is a database system? 1.2 What is a database? 1.3 Purpose of database systems. 1.4 Database languages 1.5 The three levels of the architecture 1.5.1 The three levels 1.5.2 Mappings 1.5.3 Instances and schemas 1.6 Transaction management 1.7 The Database Management System 1.8 Application Architectures 1.9 Distributed processing Chapter 1 introduction

  7. 1.1What is a database system? • Banking:accounts, loans,baking transactions. • Airlines: reservations ,schedule information. • Universities:, student information,course registration, grades. • Credit card transactions: purchases on credit cards, generation of monthly statements. • Telecommunication: keeping records of calls made. • Finance • Sales:customer,product,purchase information. • Manufacturing:management of supply chain. • Human resources:employees,salaries.

  8. 1.1What is a database system? • A database system is basically a computerized record-keeping system; i.e.,it is a computerized system whose overall purpose is to store information and to allow users to retrieve and update that information on demand. • A database system involves four major components: data hardware software users DBS=DB+DBMS+APPLICATION+DBA+USER

  9. employee enrollment Personnel Department employee Education Department 1.Data The data in the database—at least in a large system—will be both integrated and shared. Example: ? Use the employee information for different purpose

  10. 1.Data • By integrated: we mean that the database can be thought of as a unification of several otherwise distinct files, with any redundancy among those files at least partly eliminated. • By shared:we mean that individual pieces of data in the database can be shared among different users, in the sense that each of those users can have access to the same piece of data, possibly for different purpose.

  11. 2.Hardware • The hardware components of the system consist of: 1.The secondary storage volumes, device controllers, I/o channels, and so forth;and 2.The hardware processor(s) and associated main memory

  12. USER … USER AS OS DATABASE 3.Software • Between the physical database itself—i.e., the data as physically stored—and the users of the system is a layer of software, know variously as the database manger or database server or, most commonly, the database management system(DBMS). DBMS • All requests for access to the database are handled by theDBMS. One general function provided by the DBMS is thus the shielding of database users from hardware—level details.

  13. 4.Users ①Application programmers:responsible writing database application programs in some programming language. ②End users:end users interact with the system from online workstations or terminals. ③Database administrator(DBA): Schema definition storage Structure and access-method definition Schema and physical-organization modification Granting of authorization for data access Routine maintenance

  14. 1.2 What is a database It is customary to refer to the data in a database as “persistent”. We say that data in the database “persists” because, once it has been accepted by the DBMS for entry into the database in the first place, it can subsequently be removed from the database only by some explicit request to the DBMS,not as a mere side effect of some program completing execution. A database is a collection of persistent data that is used by the application systems of some given enterprise.

  15. 1.3 Purpose of database system • Keeping organizational information in a file—processing system has a number of major disadvantages. 1. Data redundancy and inconsistency Data are scattered in various files&files may be in different formats 2. Difficulty in accessing data 3. Data isolation 4. Integrity problems Consistency constraints 5. Atomicity problems Example:balance of bank>=$25 6. Concurrent—access anomalies 7. Security problems

  16. 1. Data redundancy and inconsistency employee Loan Hayes Loan ? inconsistency Hayes Account enrollment

  17. 2. Difficulty in accessing data Requirement: Find out the names of all customers who live within wuhan.(the list of all customers) resolves Extract the needed information form the list of all customers Write a new necessary application program Find out the names of all customers who live within wuhan and have an account balance of $1000 or more.

  18. 5. Atomicity problems Account A $500 (1) $50 $50 $50 $50 $50 $50 Account B $100 x $50 $50 $50 (2) $100 $500-$50=$450 ? $50

  19. 6. Concurrent—access anomalies Account A $500 Husband $100 Wife $50 Read $500 $500-$50=$450 Write $450 Read $500 $500-$100=$400 Write $400 Read $400 $400-$50=$350 Write $350 Read $450 $450-$100=$350 Write $350 X $400 / $450

  20. 1.3 Purpose of database system Benefits of the database approach: 1. The data can beshared 2.Redundancycan be reduced 3.Inconsistencycan be avoided (to some extent) 4. Transaction support canbe provided. 5.Integritycan be maintained 6.Securitycan be enforced 7. Conflicting requirements can be balanced 8. Standards can be enforced

  21. 1.4 Database languages • A database system provides two different types of languages: one to specify the database schema, and the other to express database queries and updates. Database Language Data-Definition Language Data-Manipulation Language Procedural DMLs Declarative DMLs

  22. 1.5.1 The three levels • The ANSI/SPARC architecture is divided into three levels—internal, conceptual, and external • The external levelis the one closest to the users. it is consists of many occurrences of each of many types of external record. ( external schema) • The conceptual levelis a level of indirection between the other two. it is consists of many occurrences of each of many types of conceptual record.(conceptual schema) • The internal levelis the one closes to physical storage. it is consists of many occurrences of each of many types of internal record.(internal schema)

  23. External schema External schema External schema Conceptual Schema Internal Schema 1.5.1 The three levels External level (individual user views) Conceptual level (community user views) Internal level (storage views) Fig 1.1 The three levels of the architecture

  24. External(PL/I) External(COBOL) DCL 1 EMPP, 2 EMP# CHAR(6), 2 SAL FIXED BIN(31); 01 EMPC. 02 EMPNO PIC X(6). 02 DEPTNO PIC X(4). Conceptual EMPLOYEE EMPLOYEE NUMBER CHARACTER (6) DEPARTMENT_NUMBER CHARACTER (4) SALARY Internal STORED EMP BYTES=20 PREFIX TYPE=BYTE(6), OFFSET=0 EMP# TYPE=BYTE(6), OFFSET=6, INDEX=EMPX DEPT# TYPE=BYTE(4), OFFSET=12 PAY TYPE=FULLWORD, OFFSET=16 1.5.1 The three levels Example:

  25. 1.5.1 The three levels Fig 1.2 Detailed system architecture

  26. 1.5.2 Mappings • conceptual/internal mapping and several external/conceptual mappings： 1.the conceptual/internal mapping defines the correspondence between the conceptual view and the stored database; it specifies how conceptual records and fields are represented and the internal level. 2.an external/conceptual mapping defines the correspondence between a particular external view and the conceptual view.

  27. External schema External schema External schema external/conceptual Conceptual Schema conceptual/internal mapping Internal Schema 1.5.2 Mappings

  28. 1.5.2 Mappings • Data independence: 1.physical data independenceis the ability to modify the physical schema without causing application programs to be rewritten. (conceptual/internal mapping) 2.logical data independenceis the ability to modify the logical schema without causing application programs to be rewritten. (external/conceptual)

  29. 1.5.3 Instances and schemas • The collection of information stored in the database at a particular moment is called aninstance of the database. • The overall design of the database is called thedatabase schema. database schema instance of the database int i i=2 Student={sn,name,sex} student

  30. 1.6 Transaction Management • A transaction is a collection of operations that performs a single logical function in a database application. • Each transaction is a unit of both atomicity and consistency. Atomicity Consistency Isolation Durability(ACID)

  31. 1.7 The Database Management System • DBMS is the software that handles all access to the database. 1.A user issues an access request, using some particular data sublanguage (SQL) 2.The DBMS intercepts that request and analyzes it 3.The DBMS inspects, in turn, the external schema for that user, the corresponding external/conceptual mapping, the conceptual schema,the conceptual/internal mapping,and the storage structure definition. 4.The DBMS execute the necessary operations on the stored database.

  32. 1.7 The Database Management System • The functions of the DBMS： • Data definition • Data manipulation • Optimization and execution • Data security and integrity • Data recovery and concurrency • Data dictionary • Performance

  33. Fig 1.3 major DBMS functions and components

  34. 1.8 Application Architectures A database system can be regarded as having a very simple two-part structure consisting of a server and a set of clients. The server is just the DBMS itself. The clients are various applications that run on top of the DBMS.

  35. 1.9 Distributed processing Distributed processing means that distinct machines can be connected together into a communication network such as internet ,such that a single data-processing task can span several machines in the network.

  36. Exercises: 1.Explain the following terms: DBMS Data inconsistency Data view Data instance Database schema Physical schema Logical schema Physical data independence Logical data independence 2. P23 : 1.1 1.3 1.5 1.8

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