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1 Chapter 1 Introduction to Databases Transparencies
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2 Examples of Database Applications u Purchases from the supermarket u Purchases using your credit card u Booking a holiday at the travel agents u Using the local library u Taking out insurance u Using the Internet u Studying at university
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3 File-Based Systems u Collection of application programs that perform services for the end users (e.g. reports). u Each program defines and manages its own data.
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4 File-Based Processing
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5 Limitations of File-Based Approach u 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. u 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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6 Limitations of File-Based Approach u Data dependence –File structure is defined in the program code. u Incompatible file formats –Programs are written in different languages, and so cannot easily access each other’s files. u Fixed Queries/Proliferation of application programs –Programs are written to satisfy particular functions. –Any new requirement needs a new program.
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7 Database Approach u 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. u Result: –the database and Database Management System (DBMS).
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8 Database u Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization. u System catalog (metadata) provides description of data to enable program–data independence. u Logically related data comprises entities, attributes, and relationships of an organization’s information.
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9 Database Management System (DBMS) u A software system that enables users to define, create, and maintain the database and that provides controlled access to this database.
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10 Database Management System (DBMS)
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11 Database Approach u Data definition language (DDL). –Permits specification of data types, structures and any data constraints. –All specifications are stored in the database. u Data manipulation language (DML). –General enquiry facility (query language) of the data.
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12 Database Approach u Controlled access to database may include: –A security system. –An integrity system. –A concurrency control system. –A recovery control system. –A user-accessible catalog. u A view mechanism. –Provides users with only the data they want or need to use.
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13 Views u Allows each user to have his or her own view of the database. u A view is essentially some subset of the database.
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14 Views u Benefits include: –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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15 Components of DBMS Environment
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16 Components of DBMS Environment u Hardware –Can range from a PC to a network of computers. u Software –DBMS, operating system, network software (if necessary) and also the application programs. u Data –Used by the organization and a description of this data called the schema.
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17 Components of DBMS Environment u Procedures –Instructions and rules that should be applied to the design and use of the database and DBMS. u People
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18 Roles in the Database Environment u Data Administrator (DA) u Database Administrator (DBA) u Database Designers (Logical and Physical) u Application Programmers u End Users (naive and sophisticated)
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19 History of Database Systems u First-generation –Hierarchical and Network u Second generation –Relational u Third generation –Object Relational –Object-Oriented
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20 Advantages of DBMSs u Control of data redundancy u Data consistency u More information from the same amount of data u Sharing of data u Improved data integrity u Improved security u Enforcement of standards u Economy of scale
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21 Advantages of DBMSs u Balanced conflicting requirements u Improved data accessibility and responsiveness u Increased productivity u Improved maintenance through data independence u Increased concurrency u Improved backup and recovery services
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22 Disadvantages of DBMSs u Complexity u Size u Cost of DBMS u Additional hardware costs u Cost of conversion u Performance u Higher impact of a failure
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23 Chapter 2 - Objectives u Purpose of three-level database architecture. u Contents of external, conceptual, and internal levels. u Purpose of external/conceptual and conceptual/internal mappings. u Meaning of logical and physical data independence. u Distinction between DDL and DML. u A classification of data models.
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24 Chapter 2 - Objectives u Purpose/importance of conceptual modeling. u Typical functions and services a DBMS should provide. u Software components of a DBMS. u Meaning of client–server architecture and advantages of this type of architecture for a DBMS. u Function and uses of Transaction Processing Monitors. u Function and importance of the system catalog.
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25 Objectives of Three-Level Architecture u All users should be able to access same data. u A user’s view is immune to changes made in other views. u Users should not need to know physical database storage details.
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26 Objectives of Three-Level Architecture u DBA should be able to change database storage structures without affecting the users’ views. u Internal structure of database should be unaffected by changes to physical aspects of storage. u DBA should be able to change conceptual structure of database without affecting all users.
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27 ANSI-SPARC Three-Level Architecture
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28 ANSI-SPARC Three-Level Architecture u External Level –Users’ view of the database. –Describes that part of database that is relevant to a particular user. u Conceptual Level –Community view of the database. –Describes what data is stored in database and relationships among the data.
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29 ANSI-SPARC Three-Level Architecture u Internal Level –Physical representation of the database on the computer. –Describes how the data is stored in the database.
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30 Differences between Three Levels of ANSI- SPARC Architecture
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31 Data Independence u 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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32 Data Independence u 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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33 Data Independence and the ANSI-SPARC Three-Level Architecture
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34 Database Languages u Data Definition Language (DDL) –Allows the DBA or user to describe and name entities, attributes, and relationships required for the application –plus any associated integrity and security constraints.
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35 Database Languages u Data Manipulation Language (DML) –Provides basic data manipulation operations on data held in the database. u Procedural DML –allows user to tell system exactly how to manipulate data. u Non-Procedural DML –allows user to state what data is needed rather than how it is to be retrieved.
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36 Database Languages u Fourth Generation Language (4GL) –Query Languages –Forms Generators –Report Generators –Graphics Generators –Application Generators.
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37 Data Model Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization. u Data Model comprises: –a structural part; –a manipulative part; –possibly a set of integrity rules.
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38 Data Model u Purpose –To represent data in an understandable way. u Categories of data models include: –Object-based –Record-based –Physical.
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39 Data Models u Object-Based Data Models –Entity-Relationship –Semantic –Functional –Object-Oriented. u Record-Based Data Models –Relational Data Model –Network Data Model –Hierarchical Data Model. u Physical Data Models
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40 Conceptual Modeling u Conceptual schema is the core of a system supporting all user views. u Should be complete and accurate representation of an organization’s data requirements. u Conceptual modeling is process of developing a model of information use that is independent of implementation details. u Result is a conceptual data model.
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41 Functions of a DBMS u Data Storage, Retrieval, and Update. u A User-Accessible Catalog. u Transaction Support. u Concurrency Control Services. u Recovery Services.
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42 Functions of a DBMS u Authorization Services. u Support for Data Communication. u Integrity Services. u Services to Promote Data Independence. u Utility Services.
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43 Components of a DBMS
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44 Components of Database Manager (DM)
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45 Client-Server u Server holds the database and the DBMS. u Client manages user interface and runs applications. u Advantages include: –wider access to existing databases; –increased performance; –possible reduction in hardware costs; –reduction in communication costs; –increased consistency.
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46 Client-Server Architecture
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47 System Catalog u Repository of information (metadata) describing the data in the database. u Typically stores: –names of authorized users; –names of data items in the database; –constraints on each data item; –data items accessible by a user and the type of access. u Used by modules such as Authorization Control and Integrity Checker.
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48 Information Resource Dictionary System (IRDS) u Response to an attempt to standardize data dictionary interfaces. u Objectives: –extensibility of data; –integrity of data; –controlled access to data.
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