Chapter 1 Introduction to Databases Transparencies 1 Examples
Chapter 1 Introduction to Databases Transparencies 1
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 2
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. 3
File-Based Processing 4
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. 5
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. 6
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). 7
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. 8
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. 9
Database Management System (DBMS) 10
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. 11
Database Approach u Controlled – – – u. A access to database may include: A security system. An integrity system. A concurrency control system. A recovery control system. A user-accessible catalog. view mechanism. – Provides users with only the data they want or need to use. 12
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. 13
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. 14
Components of DBMS Environment 15
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. 16
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 17
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) 18
History of Database Systems u First-generation – Hierarchical and Network u Second generation – Relational u Third generation – Object Relational – Object-Oriented 19
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 20
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 21
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 22
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. 23
Chapter 2 - Objectives 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. u 24
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. 25
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. 26
ANSI-SPARC Three-Level Architecture 27
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. 28
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. 29
Differences between Three Levels of ANSISPARC Architecture 30
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. 31
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. 32
Data Independence and the ANSI-SPARC Three-Level Architecture 33
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. 34
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. 35
Database Languages u Fourth Generation Language (4 GL) – Query Languages – Forms Generators – Report Generators – Graphics Generators – Application Generators. 36
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. 37
Data Model u Purpose – To represent data in an understandable way. u Categories of data models include: – Object-based – Record-based – Physical. 38
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 39
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. 40
Functions of a DBMS u Data u. A Storage, Retrieval, and Update. User-Accessible Catalog. u Transaction Support. u Concurrency u Recovery Control Services. 41
Functions of a DBMS u Authorization u Support for Data Communication. u Integrity u Services u Utility Services. to Promote Data Independence. Services. 42
Components of a DBMS 43
Components of Database Manager (DM) 44
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. 45
Client-Server Architecture 46
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. 47
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. 48
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