Database System Concepts Computer science and technology department

Database System Concepts Computer science and technology department Liping Zhang E-mail: Carolyn 321@163. com

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

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

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

Database system concepts Teaching outline: l 2. practice in the laboratory l 1. in the classroom l Requirement: Chapter 1 Introduction 1. preparation Chapter 2 Entity-Relationship Model 2. review Chapter 3 Relational Model 3. learn by yourself Chapter 4 SQL Delphi 7. 0 Chapter 5 Integrity and Security SQLServer 2000 Chapter 6 Relational-Database Design l Scores: Chapter 7 Query Optimization 70%+30% Chapter 8 Transactions absence -3 Chapter 9 Concurrency Control Chapter 10 Recovery System l

Chapter 1 introduction 1. 1 What is a database system? l l l 1. 2 What is a database? l 1. 3 Purpose of database systems. l l 1. 4 Database languages l l 1. 5 The three levels of the architecture 1. 5. 1 The three levels 1. 5. 2 Mappings 1. 5. 3 Instances and schemas l 1. 6 Transaction management 1. 7 The Database Management System 1. 8 Application Architectures 1. 9 Distributed processing

1. 1 What is a database system? l l l l l 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.

1. 1 What is a database system? v v 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

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

1. Data l. 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. l. 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.

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

3. Software USER 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, l the database management system(DBMS). … USER AS DBMS OS DATABASE l All requests for access to the database are handled by the DBMS. One general function provided by the DBMS is thus the shielding of database users from hardware—level details.

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

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.

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

1. Data redundancy and inconsistency name address department salary Hayes Round Hidd Account 500 Loan Johnson Perryridge employee Account 780 Hayes Loan Smith Perryridge Loan name course department Hayes OS Account Johnson DB Account Smith DS Loan ? inconsistency 1200 Hayes Account enrollment

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.

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

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

1. 3 Purpose of database system Benefits of the database approach: 1. The data can be shared 2. Redundancy can be reduced 3. Inconsistency can be avoided (to some extent) 4. Transaction support can be provided. 5. Integrity can be maintained 6. Security can be enforced 7. Conflicting requirements can be balanced 8. Standards can be enforced

1. 4 Database languages l 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

1. 5. 1 The three levels l. The ANSI/SPARC architecture is divided into three levels— internal, conceptual, and external l. The external level is the one closest to the users. it is consists of many occurrences of each of many types of external record. ( external schema) l. The conceptual level is a level of indirection between the other two. it is consists of many occurrences of each of many types of conceptual record. (conceptual schema) l. The internal level is the one closes to physical storage. it is consists of many occurrences of each of many types of internal record. (internal schema)

1. 5. 1 The three levels External level External schema (individual user views) Conceptual level (community user views) Internal level (storage views) Conceptual Schema Internal Schema Fig 1. 1 The three levels of the architecture

1. 5. 1 The three levels Example: External(PL/I) External(COBOL) DCL 1 EMPP, 01 EMPC. 2 EMP# CHAR(6), 02 EMPNO PIC X(6). 2 SAL FIXED BIN(31); 02 DEPTNO PIC X(4). Conceptual 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 Fig 1. 2 Detailed system architecture

1. 5. 2 Mappings l 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.

1. 5. 2 Mappings External schema external/conceptual Conceptual Schema conceptual/internal mapping Internal Schema External schema

1. 5. 2 Mappings l Data independence: 1. physical data independence is the ability to modify the physical schema without causing application programs to be rewritten. (conceptual/internal mapping) 2. logical data independence is the ability to modify the logical schema without causing application programs to be rewritten. (external/conceptual)

1. 5. 3 Instances and schemas The collection of information stored in the database at a particular moment is called an instance of the database. l The overall design of the database is called the database schema. l database schema instance of the database int i i=2 Student={sn, name, sex} sn 01 student 03 name carol bob sex female

1. 6 Transaction Management Atomicity Consistency Isolation Durability (ACID) l A transaction is a collection of operations that performs a single logical function in a database application. l Each transaction is a unit of both atomicity and consistency.

1. 7 The Database Management System l 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.

1. 7 The Database Management System l The functions of the DBMS： v. Data definition v. Data manipulation v. Optimization and execution v. Data security and integrity v. Data recovery and concurrency v. Data dictionary v. Performance

Fig 1. 3 major DBMS functions and components

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.

1. 9 Distributed processing means that distinct machines can be connected together into a communication network such as internet , such that a single dataprocessing task can span several machines in the network.

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. P 23 : 1. 1 1. 3 1. 5 1. 8