1 Database Management Systems (DBMS)

2 Database Management Systems (DBMS) n Overview of: ä Database Management Components ä Database Systems Architecture (DSA) ä DBMS Functions ä The Database Approach

3 Database Management Overview n A database system is comprised of four major components: n Data, Hardware, Software and Users. n Data in a database is both: ä Integrated –The database is a unification of several files, with redundancy eliminated. ä Shared –Individual pieces of data can be shared amongst different users. Different users can access the data at the same time (concurrent access).

4 Main Advantages of a DBMS n scalability – Expanded, Modified or downsized n Support for client/server systems n Economy of Scale- better utilization of hardware. n Sharing of data

5 Main Advantages of a DBMS n Balancing Conflicting requirements.- typically a DBMS is managed by a person called a database administrator(DBA) n Controlled Redundancy n Security-The DBA can define authorization procedures to ensure only legitimate users can access the database.

6 DBMS n DBMS require more expensive ä Hardware ä Software ä Data networks capable of supporting a multi-user environment

7 DBMS n DBMS is more complex than a file processing system. ä Learning curve for systems analysts, database administrators and users is usually steeper n This increase total cost of ownership (TCO)

8 DBMS Components n Provides an interface between a database and the users n Data manipulation language a schema and a physical data repository

9 DATABASE Data manipulation language Schema and subschema's Physical data repository Users Database Administrators Related Information Systems

10 Users n Users. Users typically work with predefined queries, forms, reports and switchboards, but can also use query languages to access stored data.

11 Data Manipulation Language n Controls database operations ä Storing ä Retrieving ä Updating ä Deleting data

12 Data Manipulation Language n Commercial DBMS ä Oracle and IBM’S DB/2 Use a DML

13 Schema n The complete definition of a database including descriptions of all fields, records and relationships.

14 Database System Architecture n Three Levels of the ANSI/SPARC architecture: n Internal (Physical) ä Low level representation of the database, i.e. indexes. n External (User Logical) ä The individual user level n Conceptual (Community logical) ä A view of the total database contents, definitions, security, integrity constraints

15 DBMS n The DBMS handles all access to the database. ä User issues an access request. ä DBMS intercepts request and analyses it. ä DBMS inspects, the external schema for the user, the conceptual scheme and storage structure definition. ä DBMS executes the operations on the stored database.

16 DBMS Functions: n Data Definition (DDL compiler or processor) n Data Manipulation (DML compiler or processor) n Optimisation and Execution (run-time manager) n Data Security and Integrity n Data Recovery and Concurrency (transaction manager) n Data Dictionary (metadata) n Performance

17 Client/Server Architecture n In this context the DBMS is the server as it supports all the basic functions, data definition, data manipulation, data security and integrity.

18 Client/Server Architecture n Clients: the applications that run on top of the DBMS. Applications DBMS End users Clients Server Database

19 Distributed Database System n When a system provides total transparency, i.e. each client behaves as if it was dealing with a single server on a single machine = distributed database system.

20 The Database Approach: Advantages n Centralised Control n Standardisation n Balancing n Visibility n Integrated Processing n Controlled redundancy of data n Data independence

21 The Database Approach: Disadvantages n Cost of Initial Conversion ä Purchase ä Installation ä Training ä New applications ä Data entry n Operating Costs – DBMS are resource hungry. n Success – performance degradation n Politics (naming conventions)