Introduction to Database Systems 1 Database and Database

Introduction to Database Systems 1

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 4 Database 4 Hardware 4 Software - DBMS 4 Users 2

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 3

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

DBMS 2 Examples of DBMS Products Oracle l Informix l Access l DB 2 l Fox pro l d. Base l SQL Server l My SQL l 5

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 to promote data independence Utility services 6

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. 7

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 8

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 9

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. 10

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

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 12

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

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 14

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 15

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 16

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 17

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 18

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 19

Conceptual Database Design Step 1 Build local conceptual data model for each user view 4 Identify entity types 4 Identify relationship types 4 Identify and associate attributes with entity or 4 4 4 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 20

Logical Database Design for the Relational Model Step 2 Build and validate local data model for each user view 4 Map local conceptual data model to local logical data model 4 Derive relations from local logical data model 4 Validate model using normalization 4 Validate model against user transactions 4 Draw Entity-Relationship diagram 4 Define integrity constraints 4 Review local logical data model with user 21

Logical Database Design for the Relational Model Step 3 Build and validate global logical data model 4 Merge local logical data models into global model 4 Validate global data model 4 Check for future growth 4 Draw final Entity-Relationship diagram 4 Review global logical data model with users 22

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

Physical Database Design for Relational Databases Step 6 Design security mechanisms 4 Design user views 4 Design access rules Step 7 Monitor and tune the operational system 24