Database Systems - Chapter 1: Database System Concepts & Architecture - Trương Quỳnh Chi

Nội dung text: Database Systems - Chapter 1: Database System Concepts & Architecture - Trương Quỳnh Chi

1. Contents 1 Introduction 2 File-based Approach and Database Approach 3 Three-Schema Architecture and Data Independence 4 Database Languages 5 Data Models, Database Schema, Database State 6 Data Management Systems Framework 2
2. Introduction  Collection of related data with an implicit meaning  Represents some aspect of the real world  Designed, built, and populated with data for a specific purpose.  UNIVERSITY database  Information concerning students, courses, and grades in a university environment Data records: STUDENT, COURSE, SECTION, GRADE_REPORT, LECTURER 4
3. Introduction  Traditional database: textual or numeric information  Multimedia database: images, audio clips, and video streams  Spatial database: Store and analyze maps, weather data, and satellite images  Temporal database: historical data 6
4. File-based Approach  Data is stored in one or more separate computer files  Data is then processed by computer programs - applications 8
5. File-based Approach  Problems:  Data Redundancy  The same information being kept in several different places (files)  Wastes storage space and duplicates effort  Data Inconsistency  Various copies of the same data are conflicting  Inconsistency in data format 10
6. Shared File Approach PrivateOwner File Data entry File handling and routines Reports File definition PropertyForRent Sales Department Sales Application Programs File Client File Data entry File handling and routines Reports File definition Lease File Contract Department Contract Application Programs 12
7. File-based Approach  Shared File Approach  Other problems:  Rigid data structure: If applications have to share files, the file structure that suits one application might not suit another  Physical data dependency: If the structure of the data file needs to be changed in some way, this alteration will need to be reflected in all application programs that use that data file  No support of concurrency control: While a data file is being processed by one application, the file will not be available for other applications or for ad hoc queries 14
8. Database Approach 16
9. A Simplified Database System Environment 18
10. Database Approach  Database System = Database + DBMS software  Database approach allows user:  Specify data types, structures and any data constraints to be stored in the database. All specifications are stored in the database  Query data: retrieve (query), update (insert, delete, modify)  Control access to database:  a security system  an integrity system  a concurrency control system  a recovery control system  a user-accessible catalog 20
11. Database Approach  Database administrators (DBA) are responsible for:  Authorizing access to the database  Coordinating and monitoring its use  Acquiring software and hardware resources  Database designers are responsible for:  Identifying the data to be stored  Choosing appropriate structures to represent and store this data 22
12. Database Approach  Workers behind the Scene  DBMS system designers and implementers  Design and implement the DBMS modules and interfaces as a software package  Tool developers  Design and implement tools  Operators and maintenance personnel  Responsible for running and maintenance of hardware and software environment for database system 24
13. Database Approach  Characteristics of the Database Approach  Self-describing nature of a database system  Insulation between programs and data, and data abstraction  Program-data independence + Program-operation independence = Data abstraction  A data model is a type of data abstraction  Support of multiple views of the data  Sharing of data and multi-user transaction processing 26
14. Database Approach  History of database systems  First generation: Hierarchical and Network  Second generation: Relational  Third generation: Object-Relational, Object-Oriented 28
15. Example of Relational Model Schema 30
16. Three-Schema Architecture and Data Independence  Objectives of Three-Schema Architecture  All users should be able to access same data  Users should not need to know physical database storage details  DBA should be able to change database storage structures without affecting the users’ views  Internal structure of database should be unaffected by changes to physical aspects of storage  DBA should be able to change conceptual structure of database without affecting all users 32
17. Three-Schema Architecture and Data Independence  External Level  Users’ view of the database  Describes that part of database that is relevant to a particular user  Conceptual Level  Community view of the database  Describes what data is stored in database and relationships among the data  Internal Level  Physical representation of the database on the computer.  Describes how the data is stored in the database 34
18. Three-Schema Architecture and Data Independence  Data Independence: is the capacity to change the schema at one level of a database system without having to change the schema at the next higher levels  Logical Data Independence:  Conceptual schema changes (e.g. addition/removal of entities) should not require changes to external schema or rewrites of application programs  Physical Data Independence:  Internal schema changes (e.g. using different file organizations, storage structures/devices) should not require changes to conceptual or external schemas 36
19. Contents 1 Introduction 2 File-based Approach and Database Approach 3 Three-Schema Architecture and Data Independence 4 Database Languages 5 Data Models, Database Schema, Database State 6 Data Management Systems Framework 38
20. Database Languages  Procedural DML allows user to tell system exactly how to manipulate data (e.g., Network and hierarchical DMLs)  Non-Procedural DML (declarative language) allows user to state what data is needed rather than how it is to be retrieved (e.g., SQL, QBE)  Fourth Generation Languages (4GLs)  Non-procedural languages: SQL, QBE, etc.  Application generators, report generators, etc. (see [2]) 40
21. Data Models, Database Schema and Database State  Data Model: An integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization  Categories of data models include:  Object-based (Conceptual)  ER, Object-Oriented, Describe data at the conceptual &  Record-based (Representational) external levels  Relational, Network, Hierarchical  Physical: used to describe data at the internal level 42
22. Relational Database Schema 44
23. Contents 1 Introduction 2 File-based Approach and Database Approach 3 Three-Schema Architecture and Data Independence 4 Database Languages 5 Data Models, Database Schema, Database State 6 Data Management Systems Framework 46
24. Data Management Systems Framework  Extending database capabilities for new applications  Example applications: storage and retrieval of images, videos, data mining (large amounts of data need to be stored and analyzed), spatial databases, time series applications,  More complex data structures than relational representation  New data types except for the basic numeric and character string types  New operations and query languages for new data types  New storage and retrieval methods  New security mechanisms  48