1 Introduction to Database Systems

2 Database and Database System / A database is a shared collection of logically related data designed to meet the information needs of an organization. / Components of a Database Systems 4Database 4Hardware 4Software - DBMS 4Users

3 Database / The data in the database will be expected to be both integrated and shared particularly on multi-user systems / Integration - The database may be thought of as a unification of several otherwise distinct files, with any redundancy among these files eliminated / Shared - individual pieces of data in the database may be shared among several different users

4 Hardware / These are secondary storage on which the database physically resides, together with the associated I/O devices, device controllers etc.

5 DBMS 2 Examples of DBMS Products l Oracle l Informix l Access l DB2 l Fox pro l dBase l SQL Server l My SQL

6 Typical Function of DBMS Data storage, retrieval and update A user-accessible catalog Transaction support Concurrency and control services Recovery services Authorization services Support of data communication Integrity Services Services to promote data independence Utility services

7 Users 2 Application Programmer - writes programs that use the database 2 Database Designers - designs conceptual and logical database 2 Database Administrator (DBA) 2 Data Administrator 2 End - user - interacts with the system from an on-line terminal by using Query Languages etc.

8 Data & Database Administration 2 Data Administrator – a business manager responsible for controlling the overall corporate data resources 2 Database Administrator (DBA) - a technical person responsible for development of the total system

9 Sample Applications  Student Records  Banking  Insurance  Billing Systems e.g. Electricity, Phone  ISPs  Personnel Records  Accounting Systems  Reservation Systems e.g. Airline, Hotel  Medical Records

10 Advantages  Control of data redundancy  Data consistency  Multipurpose use of data  Sharing of data,  Enforcement of standards  Economy of scale  Balance conflicting user requirement  Improved data accessibility and responsiveness  Increased productivity  Improved maintenance through data independence  Increased concurrency  Improved backup and recovery services.

11 Disadvantages  Complexity  Size  Cost of DBMS  Additional hardware costs  Cost of conversion

12 Database Architecture External Level – concerned with the way users perceive the database Conceptual Level – concerned with abstract representation of the database in its entirety Internal Level – concerned with the way data is actually stored

13 Architecture of Db System DBMS Application 2Application 1Application 3 Database Conceptual Level Internal Level External Level Logical Data Independence Physical Data Independence

14 Data Independence 2 Logical Data Independence – users and user programs are independent of logical structure of the database 2 Physical Data Independence – the separation of structural information about the data from the programs that manipulate and use the data i.e. the immunity of application programs to changes in the storage structure and access strategy

15 Data Independence 2 Different applications will need different views of the same data, so that if they are not interested in a part of the database, that part need not be included in their view. This feature is also important for controlling access to parts of database 2 The DBA must have the freedom to change the storage structure or access strategy in response to changing requirements, without having to modify the existing applications

16 Db Development Life Cycle  Database planning  System definition  Requirement collection and analysis  Database design  DBMS selection  Application design  Prototyping  Implementation  Data conversion and loading  Testing  Operational maintenance

17 Database Design l Conceptual database design - the process of constructing a model of the information used in an organization, independent of all physical considerations Step 1 Build local conceptual data model for each user view

18 Database Design l Logical database design for the relational model - the process of constructing a model of the info used in an organization based on a specific data model, but independent of a particular DBMS and other physical considerations Step 2 Build and validate local data model for each user view Step 3 Build and validate global logical data model

19 Database Design Physical database design for relational databases - the process of producing a description of the implementation of the database on secondary storage. Step 4 Translate global data model for target DBMS Step 5 Design physical representation Step 6 Design security mechanisms Step 7 Monitor and tune the operational system

20 Conceptual Database Design Step 1 Build local conceptual data model for each user view  Identify entity types  Identify relationship types  Identify and associate attributes with entity or relationship  Determine attributes domains  Determine candidate and primary key attributes  Specialize/generalize entity types (optional step)  Draw Entity-Relationship diagram  Review local conceptual data model with user

21 Logical Database Design for the Relational Model Step 2 Build and validate local data model for each user view  Map local conceptual data model to local logical data model  Derive relations from local logical data model  Validate model using normalization  Validate model against user transactions  Draw Entity-Relationship diagram  Define integrity constraints  Review local logical data model with user

22 Logical Database Design for the Relational Model Step 3 Build and validate global logical data model  Merge local logical data models into global model  Validate global data model  Check for future growth  Draw final Entity-Relationship diagram  Review global logical data model with users

23 Physical Database Design for Relational Databases Step 4 Translate global data model for target DBMS  Design base relations  Design enterprise constraints for target DBMS Step 5 Design physical representation  Analyze transactions  Choose file organizations  Choose secondary indexes  Consider the introduction of controlled redundancy  Estimate disk space requirements

24 Physical Database Design for Relational Databases Step 6 Design security mechanisms  Design user views  Design access rules Step 7 Monitor and tune the operational system