1. Chapter 1 Introduction

2. February 2008Database System Concepts- Chapter1 Introduction -2 Main Parts in This Chapter Database System Applications Purpose of Database Systems View of Data Database Languages Relational Database Database Design Data Storage and Querying Transaction Management Database Architectures Database Users and Administrators History of Database Systems Appendix: Data, Information, Knowledge, etc.

3. February 2008Database System Concepts- Chapter1 Introduction -3 §1.0 DB, DBMS, DBS Definitions in the textbook Database (DB) — a collection of interrelated data, stored in systems as files Database management system (DBMS) — DB, or a collection of interrelated data — set of programs to access the data in DB Database system (DBS) having the same definition as DBMS in the textbook the term DBS and DBMS are used interchangeably in the textbook

4. February 2008Database System Concepts- Chapter1 Introduction -4 §1.0 DB, DBMS, DBS(cont.) DBMS provides an environment that is both convenient and efficient for store and retrieve information definition of structures for storage of information data manipulation mechanisms data safety mechanisms Definitions in some other textbooks Fig. 1.0.1 Database(DB) — a collection of interrelated data, stored in systems as files

5. February 2008Database System Concepts- Chapter1 Introduction -5 §1.0 DB, DBMS, DBS(cont.) Definitions in some other textbooks (cont.) Database management system (DBMS) — a system/mechanism to manage data in DB — or: set of programs to access the data in DB Database system(DBS) — DB + DBMS + Users/Administers Database application system — DB + DBMS + Application programs + Users/Administers

6. DBMS Application program 1 DB file … DB query language e.g. SQL API, e.g.ODBC, JDBC UsersDBMSDB DBS/DBAS Fig.1.0.1 DBS and DBAS Application program 1

7. February 2008Database System Concepts- Chapter1 Introduction -7 Databases and DBS touch all aspects of our lives Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions §1.2 Purpose of Database Systems

8. February 2008Database System Concepts- Chapter1 Introduction -8 In the early days, database applications were built on top of file systems E.g. Saving-bank enterprise a number of application programs to access data files A program to debit （将.. 记入借方） or credit （将.. 记 入贷方） an account( 帐户） A program to add a new account A program to find the balance （收付差额，余额） of an account A program to generate monthly statements §1.2 Purpose of Database Systems (cont.)

9. February 2008Database System Concepts- Chapter1 Introduction -9 Data management on the basis of file systems Example — customer_record= in Customer_File FS access need — file name, item name, length of record, length of item, position of item in the record, storage structure, access method, …. Demerit — application programs are not independent of the file system ( or operating system) — dependency among application programs and data ( 程序与 数据的非独立 / 依存性） §1.2 Purpose of Database Systems (cont.)

10. Fig. 1.0.2 Why DBS needed secondary storage (e.g. disk, tape) and data on it (address: cylinder, track, sector) memory controllers (i.e. disk controller), on the basis of secondary storage’s physical structures, such as storage structures, access method access programs (I) direct access through disk controller (I) access through OS’ file system (II) access through data base system (DBS) (III) access programs (II) access programs (III) I/O system : drivers file system: file’s logical structures and access methods DBMS: relational tables’ logical structures and access methods system calls related to file management DBS API

11. Select * From Student Where S#=100 DBS logical structures: relations/ tuples DBMSDB user Logical address : #Record Record1 Record k … block1 OS: Logical file … Record i Record m … Block n Physical address ： platter/track /sector block1 Block i Block k … … Physical File on disk DB files block OS ： file system and I/O subsystem view of data model view of file Fig. 1.0.3 Database access

12. February 2008Database System Concepts- Chapter1 Introduction -12 Drawbacks of using file systems to store data data redundancy （冗余） and inconsistency （不一致性） multiple file formats, duplication （副本） of information in different files difficulty in accessing data need to write a new program to carry out each new task data isolation （独立性） multiple files and formats §1.2 Purpose of Database Systems (cont.)

13. February 2008Database System Concepts- Chapter1 Introduction -13 integrity （完整性） problems data values should satisfy consistency constraints integrity constraints (e.g. account balance > 0) become part of program code hard to add new constraints or change existing ones atomicity problems failures may leave database in an inconsistent state with partial updates carried out e.g. transfer of funds from one account to another should either complete or not happen at all §1.2 Purpose of Database Systems (cont.)

14. February 2008Database System Concepts- Chapter1 Introduction -14 concurrent access anomalies 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 security problems Database systems offer solutions to all the above problems §1.2 Purpose of Database Systems(cont.)

15. February 2008Database System Concepts- Chapter1 Introduction -15 §1.3 View of Data Basic concepts in DBS theory view of data ( 数据视图 ), data abstract data model, data schema ( 模式 ), schema instance logical /physical isolation 1.3.1 Data abstraction To simplify and “ divide and conquer ” the design of complex data application systems describes/design application data in three levels, and obtains three types of schema Fig. 1.1

16. Fig.1.1 The three levels of data abstraction

17. February 2008Database System Concepts- Chapter1 Introduction -17 View level describes data from different view of data in application areas, data item and associations among them several views for one datum description results external schema ( 外模式） ={view}, set of views description procedure/Logical DB design view abstraction merits: application programs are programmed according to views, hiding details of data types. Views can also hide information (e.g., salary) for security purposes. 1.3.1 Data abstraction (cont.)

18. February 2008Database System Concepts- Chapter1 Introduction -18 E.g. Banking Application Areas in Fig. 6.25 in page 240 in view-level, finding objects, object’s features, and associations among objects from more than one viewpoints, view integration view1: customer view2: loan view3: account view4: customer view5: customer view6: …. ……. be represented as relational views 1.3.1 Data abstraction (cont.)

19. February 2008Database System Concepts- Chapter1 Introduction -19 Logical level implementation-oriented, describes how data are stored in DBS as relational tables: table customer name : string; street : string; city : integer; description results logical schema ( 逻辑模式）, e.g. relational tables description procedure/Logical DB design logical abstraction Merits: hiding physical implementation details 1.3.1 Data abstraction (cont.)

20. February 2008Database System Concepts- Chapter1 Introduction -20 Physical level describes how the data (e.g., customer record/table) are actually stored in files ( or in secondary storage) description results physical/internal schema ( 物理模式，内模式） i.e. storage structure and access methods, such as index, physical blocks, access methods for secondary memory, etc. description procedure/Physical DB design physical abstraction 1.3.1 Data abstraction (cont.)

21. February 2008Database System Concepts- Chapter1 Introduction -21 An instance of the database the collection of information stored in the database at a particular moment (P7 in the textbook) the actual content of the database at a particular point in time Schema the structure of the database overall design of the database??? (P7 in the textbook) physical schema database design at the physical level logical schema database design at the logical level 1.3.2 Instances and Schemas

22. February 2008Database System Concepts- Chapter1 Introduction -22 Data model, data schema (of data model), instance of schema E.g. relational data model : R={ } relational data schema : customer= instance of schema : similar to data types declaration, variables of data types, and values of variables e.g. Fig.1.2 1.3.2 Instances and Schemas (cont.)

23. February 2008Database System Concepts- Chapter1 Introduction -23 Data descriptions/abstractions in three levels must obey three types of specification, i.e. three types of data models Definition of data model (P8) a collection of conceptual tools for describing data data relationships data semantics data constraints 程序 = 数据结构 + 算法 integrity constraints 1.3.3 Data Model

24. February 2008Database System Concepts- Chapter1 Introduction -24 Another definition of data model DBS 中对数据组织与管理 / 使用方式的抽象描述，包括 数据组织的语法定义，如数据项、数据项间的联系 数据组织的语义定义，如完整性约束 数据操作 (note: only in some data models, e.g. relational data model) Relational model ( 关系模型 ) using a collection of tables to represent both data and the relationships among those data a set of operations on tables are also defined (§2.2/ 2.3/2.4) e.g. Fig.1.4 1.3.3 Data Model (cont.)

25. February 2008Database System Concepts- Chapter1 Introduction -25 Entity-Relationship model ( 实体 - 联系模型 ) using the entity and the relationship to model the object and the association among objects e.g. Fig.1.3 Network model and hierarchical model only used for early DBS Other models object-oriented model (Chapter 9) semi-structured data models (Chapter 10) 1.3.3 Data Model (cont.)

26. February 2008Database System Concepts- Chapter1 Introduction -26 Data models can be classified as object-based model ( 基于对象的模型 ) record-based model ( 基于记录的模型 ) physical data model ( 物理数据模型 ) For more details about category of data models, refer to Appendix B 1.3.3 Data Model (cont.)

27. February 2008Database System Concepts- Chapter1 Introduction -27 3 种数据抽象、 3 种模式 →DBS 中 2 种数据独立性 概念 / 逻辑模式 → 内模式间的映射 与 physical data independence 外模式 → 概念模式间的映射 与 logical data independence refer to Fig.1.0.4 1.3.4 Data Independence Logical data independence when DBS’s logical schemas at logical level (DBMS- oriented) change, application-oriented external schema or application programs do not change e.g. customer= is extended into customer=

28. 用户 A1 宿主语言 + DML 用户 A2 用户 B1 用户 B2 外部视图 A 外部视图 B 概念 / 逻辑视图 外模式 概念 / 逻辑模式 内模式 DBMS 外模式 / 概念 模式映射 A 外模式 / 概念 模式映射 B 概念模式 / 内 模式映射 宿主语言 + DML 宿主语言 + DML 宿主语言 + DML Fig. 1.0.4

29. February 2008Database System Concepts- Chapter1 Introduction -29 Physical data independence (P7) application programs do not depend on DBS’s physical schema, i.e. when physical schema (e.g. index, block-size) change, application programs remain unchanged the ability to modify the physical schema without changing the external/logical schemas, on which application programs depend 1.3.4 Data Independence (cont.)

30. February 2008Database System Concepts- Chapter1 Introduction -30 §1.4 Database Language Database Languages as human-machine interfaces data manipulation language, DML data definition language, DDL 1.4.1 Data manipulation language DML is the language that enables users to access or manipulate the data as organized by the appropriate data model Types of DBS access retrieve, insert, delete, modify

31. February 2008Database System Concepts- Chapter1 Introduction -31 Two types of DML procedural ( 过程性 ) – user specifies what data is required and how to get those data nonprocedural ( 说明性， declarative) – user specifies what data is required without specifying how to get those data Query( 查询） a statement requesting the retrieval of information DML also known as query language 1.4.1 Database Manipulation Language (cont.)

32. February 2008Database System Concepts- Chapter1 Introduction -32 SQL is the most widely used non-procedural query language, others are QE, Datalog Example find the name of the customer with customer-id 192-83-7465 select customer.customer-name from customer where customer.customer-id = ‘192-83-7465’ 1.4.1 Database Manipulation Language (cont.)

33. February 2008Database System Concepts- Chapter1 Introduction -33 DDL is used for specifying the database schema and additional properties of the data E.g. create table account ( account-number char(10), balance integer) DDL can also be used to define integrity constraints in DB domain integrity, referential integrity, assertions, authorization, etc. The structures /schemas of the database defined by DDL is stored in the data dictionary/directory meta data, i.e., data about data, is stored 1.4.2 Database Definition Language

34. February 2008Database System Concepts- Chapter1 Introduction -34 Data storage and definition language a subset of DDL, defining physical schemas, i.e., storage structure and access methods, which are usually hidden form users 1.4.2 Database Definition Language (cont.)

35. February 2008Database System Concepts- Chapter1 Introduction -35 Application programs generally access databases in two methods application program interfaces (API, e.g. ODBC/JDBC) which allow SQL queries to be sent to a database Fig. 1.0.5 embed DML call within host language ( 宿主语言, such as C and Java) 1.4.3 DB Access for Application Programs

36. February 2008Database System Concepts- Chapter1 Introduction -36 C application programs Java application programs Other language application programs ODBCJDBC DBS DDL+ DML API Fig.1.0.5 DBS access interfaces 1.4.3 DB Access for Application Programs (cont.)

37. February 2008Database System Concepts- Chapter1 Introduction -37 §1.5 Relational Database Refer to chapter 2

38. February 2008Database System Concepts- Chapter1 Introduction -38 §1.6 Database Design 1.6.1 Design process 从保持 data independence （数据无关性 / 独立性）角度出发， 根据 data models 所定义的数据规范形式，在 view 、 logical 、 physical 三个层次，采用三种 data abstraction 方法，通过 DB 概念设计、 DBS 逻辑设计、 DBS 物理设计三个阶段，构造 面向具体应用领域的 DBS 的 external schema 、 logical schema 、 internal schema 的集合, 从而得到 conceptual DBS 、 logical DBS 、 physical DBS 的设计结果 As described in Fig.1.0.6 conceptual design logical design physical design

39. Fig. 1.0.6 Data abstraction and Schema

40. February 2008Database System Concepts- Chapter1 Introduction -40 Banking Enterprise the bank is organized into branches each branch is described by the city is located in, the name and the assets a bank customer is illustrated by his customer_id and name, the street and city the bank offers two types of accounts, which are depicted by account_number and balance — the savings account: an interest rate — the checking account: overdraft 1.6.2-1.6.4 An Example

41. February 2008Database System Concepts- Chapter1 Introduction -41 the bank provides its customers with loans, which are depicted by loan_number, balance_name, and amount Bank employees are identified by their employee_id, telephone_number, employee_ street, employee_ city Conceptual DB design E-R diagram e.g. Fig.1.3 1.6.2-1.6.4 An Example (cont.)

42. February 2008Database System Concepts- Chapter1 Introduction -42 Fig.1.3 A sample entity-relationship model 1.6.2-1.6.4 An Example (cont.)

43. February 2008Database System Concepts- Chapter1 Introduction -43 Logical DB design database design in E-R model usually converted to design in the relational model, i.e the relational tables and views the converted relational tables are then normalized ( 规范化 ) e.g. Fig.1.4 and Fig.1.5 1.6.2-1.6.4 An Example (cont.)

44. February 2008Database System Concepts- Chapter1 Introduction -44 Attributes (a)The customer table Fig.1.4 A Sample Relational Database schema instances 1.6.2-1.6.4 An Example (cont.)

45. February 2008Database System Concepts- Chapter1 Introduction -45 Fig.1.4 A Sample Relational Database 1.6.2-1.6.4 An Example (cont.)

46. February 2008Database System Concepts- Chapter1 Introduction -46 Fig 1.6 DBS = User/DBA + DBMS + DB DBMS query processing storage manager DB files application data data dictionary/directory indices statistic data §1.11 DBS Architecture

47. Fig. 1.6 DBS Architecture user DBMS DB

48. February 2008Database System Concepts- Chapter1 Introduction -48 DBAS DB + DBMS + Application programs + Users/DBA 实现数据处理功能 DBS DB + DBMS + User/DBA 实现数据管理功能 信息 / 数据管理（ management ） 数据的分类、收集、组织、编码、存储、检索和维护 信息 / 数据处理（ processing ） 对数据进行分类、收集、组织、存储，进而从已有数据出 发，抽取或推导出新的数据 / 信息 1.11 Database Application System

49. February 2008Database System Concepts- Chapter1 Introduction -49 信息 / 数据处理与信息 / 数据管理的区别 数据管理侧重于对数据如何进行组织和存储，并根据用 户需要提供对数据的访问支持 数据处理除了具有数据管理功能外，还可以对通过数据 管理得到的数据进行进一步深加工，从中获取新的数据、 信息 例如，在一个商品零售系统中，可以利用数据库系统的数据 管理功能存储各种商品基本信息（如商品数量、销售额等） 并为各类用户提供对各类商品信息的查询功能。当从数据库 系统中得到这些商品信息后，可以采用一些统计分析工具、 数据挖掘（ Data Mining ）工具进一步进行分析处理，得到 有关那些商品属于热销商品、热销商品销售销售额等新信息。 这种统计分析属于数据处理范畴 1.11 Database Application System (cont.)

50. February 2008Database System Concepts- Chapter1 Introduction -50 1.11 Database Application System Architecture Fig.1.7 In DBAS, the application programs are responsible for information or data processing, e.g. data mining Two-tier architecture e.g. client programs using ODBC/JDBC to communicate with a database  Three-tier architecture e.g. web-based applications, and applications built using “middleware”

51. February 2008Database System Concepts- Chapter1 Introduction -51 Fig.1.7 Two-tier and three-tier architectures 1.11 Database Application System Architecture (cont.)

52. February 2008Database System Concepts- Chapter1 Introduction -52 In DBS, DBMS provides data management mechanisms for users, that is data storage and data querying DBMS consists of two modules storage manager query processor Storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system The storage manager is responsible for translating DML statements into low-level file commands efficient storing, retrieving and updating of data §1.8 Data Storage and Querying

53. February 2008Database System Concepts- Chapter1 Introduction -53 The modules in the storage manager are authorization and integrity manager, transaction manager, file manager, and buffer manager The query processor includes DDL interpreter DML compiler Query optimization Query evaluation engine 1.8 Data Storage and Querying (cont.)

54. C, Pascal programs 词法 / 语法 / 语义分析 中间代码生成 ( 中间 ) 代码优化 目标代码生成 OS SQL query 扫描和语法 / 语义分析 查询优化 ( 优化后 ) 查询执行计划 查询代码生成 process / thread Chapter 13, 14 Chapter 15,16, 17 transaction 关系代数表达式 & 查询树 查询计划执行的代码目标程序代码 (§14) (§13) (§15)(§16) (§17)

55. February 2008Database System Concepts- Chapter1 Introduction -55 A transaction is a collection of operations that performs a single logical function in a database application E.g. Transaction T1: transfer $50 from account_A to account_B T1 : read ( account_A ); account_A := account_A -50; write (account_A ); read (account_ B ); account_ B := account_ B + 50; write (account_ B ); integrity constraint total amount of account_A and account_B remains unchanged before and after the transaction execution §1.9 Transaction Management

56. February 2008Database System Concepts- Chapter1 Introduction -56 Transaction properties atomicity ( 原子性 ), consistency ( 一致性 ), isolation ( 独立 性 ), durability( 持久性 ) Transaction-management component in DBMS ensures that the database remains in a consistent/correct state despite system failures (e.g., power failures and operating system crashes) and transaction failures, by means of concurrency and control failure recovery. controls the interaction among the concurrent transactions, to ensure the consistency of the database 1.9 Transaction Management

57. February 2008Database System Concepts- Chapter1 Introduction -57 §1.12 Database User and Administrators 1.12.1 Database users and user interfaces Users are differentiated by the way they expect to interact with the system, four categories of users, four categories of interfaces: Fig.1.6 naive users – invoke one of the permanent application programs that have been written previously e.g. people accessing database over the web, bank tellers, clerical staff application programmers – interact with system through DML calls sophisticated users – form requests in a database query language or tools, and submit these queries to the query processor

58. February 2008Database System Concepts- Chapter1 Introduction -58 specialized users – write specialized database applications that do not fit into the traditional data processing framework, 1.12.2 Database Administrator (DBA) The responsibilities of DBA include schema definition schema and physical organization modification granting of authorization for data access routine maintenance §1.12 Database User and Administrators (cont.)

59. February 2008Database System Concepts- Chapter1 Introduction -59 Appendix A Data, Information, Knowledge 1.0.1 Definitions in Microsoft Press Computer Dictionary data Plural of datum, an item of information Information: the meaning of the data as it is intended to be interpret by people. Data consist of facts, which become information as they are seen in context and convey meaning to people. Computer process data without any understanding of what the data represents

60. February 2008Database System Concepts- Chapter1 Introduction -60 Appendix A Data, Information, Knowledge (cont.) 1.0.2 Definitions in Longman Dictionary of Contemporary English data facts, information information in a form that can be processed and stored in computers Information knowledge in the form of facts and news

61. February 2008Database System Concepts- Chapter1 Introduction -61 knowledge what a person knows; the facts, information, skills and understanding that one has gained, esp. through learning or experience 1.0.3 Definitions in Cambridge International Dictionary of English Data information, esp. facts or numbers, collected for examination and used to help decision—making or, information in a electronic form that can be processed by computers Appendix A Data, Information, Knowledge (cont.)

62. February 2008Database System Concepts- Chapter1 Introduction -62 Information knowledge about something, esp. facts and news Knowledge information, esp. facts or numbers, collected for examination and used to help decision—making understanding of,or information about a subject which has been obtained by experience or study, and which is either in a person ’ s mind or possessed by people generally Appendix A Data, Information, Knowledge (cont.)

63. February 2008Database System Concepts- Chapter1 Introduction -63 Appendix A Information Theory (cont.) 什么是信息？ 是一种人人皆知的抽象概念，无确切定义，具有两个 明显的特征：广泛性与抽象性。 广泛性可从以下三方面来理解 客观世界充满着信息： — 一切客观物质无不具有自己的特征信息。 人类离不开信息 — 人的五官在不停地感知、接收信息；人的神经系统在 不停地传递信息；人的大脑则在不停地处理与决策信 息；人与人之间又在不停地交流信息；人活在世上百 分之百时间都在自觉与不自觉地与信息打交道。

64. February 2008Database System Concepts- Chapter1 Introduction -64 Appendix A Information Theory (cont.) 知识、书本是有用信息的积累 抽象性则是指 信息是组成客观世界并促进社会发展的三大基本要素 之一 三大要素是：物质、能量与信息 物质是基础，是实体。 能量是物质运动的形式， E=mc2 ，物质可转换成能量， 而能量 又是改造客观世界的主要动力。

65. February 2008Database System Concepts- Chapter1 Introduction -65 Appendix A Information Theory (cont.) 信息：它依附于物质和能量，但又不同于物质和能量。 没有信息就不能更好地利用物质和能量，人类利用信 息和知识改造物质，创造新物质，提高能量利用效率， 发现新能量形式。信息也是客观存在的，它是人类认 识、改造客观世界的主要动力，是人类认识客观世界 的更高层次。 在通信中对信息的表达分为三个层次：信号、消息、信息 信号：是信息的物理表达层，是三个层次中最具体的 层次。它是一个物理量，是一个载荷信息的实体，可 测量、可描述、可显示。

66. February 2008Database System Concepts- Chapter1 Introduction -66 Appendix A Information Theory (cont.) 消息： ( 或称为符号 ) 是信息的数学表达层，它虽不是 一个物理量，但是可以定量地加以描述，它是具体物 理信号的进一步数学抽象，可将具体物理信号抽象为 两大类型：离散 ( 数字 ) 消息, 连续 ( 模拟 ) 消息， 信息：更高层次哲学上的抽象，是信号与消息的更高 表达层次。 三个层次中，信号最具体，信息最抽象。它们三者之间的 关系是哲学上的内涵与外延的关系 信息可以认为是具体的物理信号、数学描述的消息的 内涵，即信号具体载荷的内容、消息描述的含义

67. February 2008Database System Concepts- Chapter1 Introduction -67 Appendix A Information Theory (cont.) 信号是抽象信息在物理层表达的外延 消息是抽象信息在数学层表达的外延 同一信息，可以采用不同的信号形式 ( 比如文字、语言、 图象等 ) 来载荷；同一信息，也可以采用不同的数学表达 形式 ( 比如离散或连续 ) 来定量描述。同样，同一信号形式， 比如 “ 0 ” 与 “ 1 ” 可以表达不同形式的信息，比如无与有、断 与通、低与高 ( 电平 ) 等等。

68. February 2008Database System Concepts- Chapter1 Introduction -68 Data models can be classified as object-based data model( 基于对象的数据模型 ) record-based data model( 基于记录的数据模型 ) physical data model( 物理数据模型 ) 基于对象（ Object-based ）的数据模型 用处： DBS 概念设计阶段，在概念和视图级别上描述 数据，定义 DBS 概念 / 外模式，生成概念 DBS 包括：实体 — 联系模型、面向对象（ object-oriented ）数 据模型 面向对象模型 : 对象、对象类 ; 类 = 变量 / 属性 + 方 法 Appendix B Category of Data Model

69. February 2008Database System Concepts- Chapter1 Introduction -69 基于记录的数据模型 用处： DBS 逻辑设计阶段，生成数据库逻辑模式。与 DBMS 相关，决定了不同的 DBS 类型。 包括：关系数据模型、层次型数据模型、网状数据模型 物理数据模型 用处： DBS 物理设计阶段，定义 DBS 的 DBS 文件的物理 存储结构和存取方法，生成物理数据库模式。与 DBMS 和 DBS 的实现相关。 包括： Unifying Model 、 Frame Memory Model Appendix B Category of Data Model (cont.)

70. February 2008Database System Concepts- Chapter1 Introduction -70 Have a break