留学生辅导 Database Systems: A Practical Approach to Design, Implementation, and Mana

Database Systems: A Practical Approach to Design, Implementation, and Management Sixth Edition
Introduction to Databases
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Learning Objectives (1 of 2)
1.1 Some common uses of database systems. 1.2 Characteristics of file-based systems.
1.3 Problems with file-based approach.
1.4 Meaning of the term database.
1.5 Meaning of the term Database Management System (DBMS).
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Learning Objectives (2 of 2)
1.6 Typical functions of a DBMS.
1.7 Major components of the DBMS environment. 1.8 Personnel involved in the DBMS environment. 1.9 History of the development of DBMSs.
1.10 Advantages and disadvantages of DBMSs.
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Examples of Database Applications
• Purchases from the supermarket
• Purchases using your credit card
• Booking a holiday at the travel agents • Using the local library
• Taking out insurance
• Renting a video
• Using the Internet
• Studying at university
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File-Based Systems
• Collection of application programs that perform services for the end users (e.g. reports).
• Each program defines and manages its own data.
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File-Based Processing
Sales Files
PropertyForRent (propertyNo, street, city, postcode, type, rooms, rent, and ownerNo) PrivateOwner (ownerNo, fName, lName, address, telNo)
Client (clientNo, fName, lName, address, telNo, prefType, maxRent)
Contracts files
Lease (leaseNo, propertyNo, clientNo, rent, paymentMethod, deposit, paid, rentStart, rentFinish, duration)
PropertyForRent (propertyNo, street, city, postcode, rent)
Client (clientNo, fName, lName, address, telNo)
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Limitations of File-Based Approach (1 of 2)
• Separation and isolation of data
– Each program maintains its own set of data.
– Users of one program may be unaware of potentially useful data held by other programs.
• Duplication of data
– Same data is held by different programs.
– Wasted space and potentially different values and/or different formats for the same item.
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Limitations of File-Based Approach (2 of 2) • Data dependence
– File structure is defined in the program code. • Incompatible file formats
– Programs are written in different languages, and so cannot easily access each other’s files.
• Fixed Queries/Proliferation of application programs
– Programs are written to satisfy particular functions. – Any new requirement needs a new program.
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Database Approach (1 of 3) • Arose because:
– Definition of data was embedded in application programs, rather than being stored separately and independently.
– No control over access and manipulation of data beyond that imposed by application programs.
– the database and Database Management System
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• Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization.
• System catalog (metadata) provides description of data to enable program–data independence.
• Logically related data comprises entities, attributes, and relationships of an organization’s information.
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Database Management System (DBMS) (1 of 2)
• A software system that enables users to define, create,
maintain, and control access to the database.
• (Database) application program: a computer program that interacts with database by issuing an appropriate request (SQL statement) to the DBMS.
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Database Management System (DBMS) (2 of 2)
PropertyForRent (propertyNo, street, city, postcode, type, rooms, rent, ownerNo) PrivateOwner (ownerNo, fname, lName, address, telNo)
Client (clientNo, fName, lName, address, telNo, prefType, maxRent)
Lease (leaseNo, propertyNo, clientNo, paymentMethod, deposit, paid, rentStart, rentFinish)
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Database Approach (2 of 3) • Data definition language (DDL).
– Permits specification of data types, structures and any data constraints.
– All specifications are stored in the database. • Data manipulation language (DML).
– General enquiry facility (query language) of the data.
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Database Approach (3 of 3)
• Controlled access to database may include: – a security system
– an integrity system
– a concurrency control system
– a recovery control system – a user-accessible catalog.
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• Allows each user to have his or her own view of the database.
• A view is essentially some subset of the database.
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Views – Benefits
• Reduce complexity
• Provide a level of security
• Provide a mechanism to customize the appearance of the database
• Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed
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Components of DBMS Environment (1 of 3)
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Components of DBMS Environment (2 of 3) • Hardware
– Can range from a PC to a network of computers. • Software
– DBMS, operating system, network software (if necessary) and also the application programs.
– Used by the organization and a description of this
data called the schema.
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Components of DBMS Environment (3 of 3) • Procedures
– Instructions and rules that should be applied to the design and use of the database and DBMS.
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Roles in the Database Environment
• Data Administrator (DA)
• Database Administrator (DBA)
• Database Designers (Logical and Physical) • Application Programmers
• End Users (naive and sophisticated)
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History of Database Systems
• First-generation
– Hierarchical and Network
• Second generation – Relational
• Third generation
– Object-Relational – Object-Oriented
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Advantages of DBMSs (1 of 2)
• Control of data redundancy
• Data consistency
• More information from the same amount of data • Sharing of data
• Improved data integrity
• Improved security
• Enforcement of standards
• Economy of scale
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Advantages of DBMSs (2 of 2)
• Balance conflicting requirements
• Improved data accessibility and responsiveness
• Increased productivity
• Improved maintenance through data independence • Increased concurrency
• Improved backup and recovery services
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Disadvantages of DBMSs
• Complexity
• Cost of DBMS
• Additional hardware costs • Cost of conversion
• Performance
• Higher impact of a failure
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Database Systems: A Practical Approach to Design, Implementation, and Management Sixth Edition
Database Environment
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Learning Objectives (1 of 2)
2.1 Purpose of three-level database architecture.
2.2 Contents of external, conceptual, and internal levels.
2.3 Purpose of external/conceptual and conceptual/internal mappings.
2.4 Meaning of logical and physical data independence. 2.5 Distinction between DDL and DML.
2.6 A classification of data models.
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Learning Objectives (2 of 2)
2.7 Purpose/importance of conceptual modeling.
2.8 Typical functions and services a DBMS should provide.
2.9 Function and importance of system catalog.
2.10 Software components of a DBMS.
2.11 Meaning of client–server architecture and advantages of this type of architecture for a DBMS.
2.12 Function and uses of Transaction Processing Monitors.
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Objectives of Three-Level Architecture (1 of 2)
• All users should be able to access same data.
• A user’s view is immune to changes made in other views.
• Users should not need to know physical database storage details.
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Objectives of Three-Level Architecture (2 of 2)
• 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.
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ANSI-SPARC Three-Level Architecture (1 of 3)
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ANSI-SPARC Three-Level Architecture (2 of 3)
• 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.
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ANSI-SPARC Three-Level Architecture (3 of 3) • Internal Level
– Physical representation of the database on the computer.
– Describes how the data is stored in the database.
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Differences Between Three Levels of ANSI- SPARC Architecture
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Data Independence (1 of 2) • Logical Data Independence
– Refers to immunity of external schemas to changes in conceptual schema.
– Conceptual schema changes (e.g. addition/removal of entities).
– Should not require changes to external schema or rewrites of application programs.
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Data Independence (2 of 2) • Physical Data Independence
– Refers to immunity of conceptual schema to changes in the internal schema.
– Internal schema changes (e.g. using different file organizations, storage structures/devices).
– Should not require change to conceptual or external schemas.
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Data Independence and the ANSI-SPARC Three-Level Architecture
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Database Languages (1 of 2) • Data Definition Language (DDL)
– Allows the DBA or user to describe and name entities, attributes, and relationships required for the application
– plus any associated integrit and security constraints.
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Database Languages (2 of 2)
• Data Manipulation Language (DML)
– Provides basic data manipulation operations on data held in the database.
• Procedural DML
– allows user to tell system exactly how to manipulate
• Non-Procedural DML
– allows user to state what data is needed rather than how it is to be retrieved.
• Fourth Generation Languages (4GLs)
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Data Model (1 of 2)
• Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization.
• Data Model comprises:
– a structural part;
– a manipulative part;
– possibly a set of integrity rules.
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Data Model (2 of 2) • Purpose
– To represent data in an understandable way.
• Categories of data models include: – Object-based
– Record-based
– Physical.
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Data Models
• Object-Based Data Models – Entity-Relationship
– Semantic
– Functional
– Object-Oriented.
• Record-Based Data Models – Relational Data Model
– Network Data Model
– Hierarchical Data Model.
• Physical Data Models
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Relational Data Model
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Supervisor

Network Data Model
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Hierarchical Data Model
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Conceptual Modeling
• Conceptual schema is the core of a system supporting all user views.
• Should be complete and accurate representation of an organization’s data requirements.
• Conceptual modeling is process of developing a model of information use that is independent of implementation details.
• Result is a conceptual data model.
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Functions of a DBMS (1 of 2)
• Data Storage, Retrieval, and Update. • A User-Accessible Catalog.
• Transaction Support.
• Concurrency Control Services.
• Recovery Services.
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Functions of a DBMS (2 of 2)
• Authorization Services.
• Support for Data Communication.
• Integrity Services.
• Services to Promote Data Independence. • Utility Services.
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System Catalog
• Repository of information (metadata) describing the data in the database.
• One of the fundamental components of DBMS.
• Typically stores:
– names, types, and sizes of data items;
– constraints on the data;
– names of authorized users;
– data items accessible by a user and the type of access;
– usage statistics.
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File-Server
• File-server is connected to several workstations across a network.
• Database resides on file-server.
• DBMS and applications run on each workstation.
• Disadvantages include:
– Significant network traffic.
– Copy of DBMS on each workstation.
– Concurrency, recovery and integrity control more complex.
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Traditional Two-Tier Client-Server (1 of 3) • Client (tier 1) manages user interface and runs
applications.
• Server (tier 2) holds database and DBMS.
• Advantages include:
– wider access to existing databases; – increased performance;
– possible reduction in hardware costs; – reduction in communication costs;
– increased consistency.
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Three-Tier Client-Server (1 of 3)
• Client side presented two problems preventing true
scalability:
– ‘Fat’ client, requiring considerable resources on client’s computer to run effectively.
– Significant client side administration overhead.
• By 1995, three layers proposed, each potentially running
on a different platform.
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Three-Tier Client-Server (2 of 3)
• Advantages:
– ‘Thin’ client, requiring less expensive hardware.
– Application maintenance centralized.
– Easier to modify or replace one tier without affecting others.
– Separating business logic from database functions makes it easier to implement load balancing.
– Maps quite naturally to Web environment.
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Transaction Processing Monitors
• Program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for Online Transaction Processing (OLTP).
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Database Systems: A Practical Approach to Design, Implementation, and Management Sixth Edition
Database Architectures and the Web Transparencies
Slides in this presentation contain hyperlinks. JAWS users should be able to get a list of links by using INSERT+F7
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Learning Objectives (1 of 2)
3.1 The meaning of the client–server architecture and the
advantages of this type of architecture for a DBMS.
3.2 The difference between two-tier, three-tier and n-tier client–server architectures.
3.3 About cloud computing and data as a service (DaaS) and database as a service (DBaaS).
3.4 Software components of a DBMS.
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Learning Objectives (2 of 2)
3.5 The purpose of a Web service and the technological
standards used to develop a Web service.
3.6 The meaning of service-oriented architecture (SOA).
3.7 The difference between distributed DBMSs, and distributed processing.
3.8 The architecture of a data warehouse.
3.9 About cloud computing and cloud databases. 3.10 The software components of a DBMS.
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Multi-User DBMS Architectures
• The common architectures that are used to implement multi-user database management systems:
– Teleprocessing – File-Server
– Client-Server
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