Chapter 1 Introduction to Databases Transparencies 1 Chapter

Chapter 1 Introduction to Databases Transparencies 1

Chapter 1 Objectives u Some common uses of database systems. u Characteristics of file-based systems. u Problems with file-based approach. u Meaning of the term database. u Meaning of the term Database Management System (DBMS). 2

Chapter 1 Objectives u Typical functions of a DBMS. u Major components of the DBMS environment. u Personnel involved in the DBMS environment. u History of the development of DBMSs. u Advantages and disadvantages of DBMSs. 3

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 4

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. 5

File-based Processing 6

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. 7

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 others files. u Fixed Queries/Proliferation of application programs – Programs are written to satisfy particular functions. Any new requirement needs a new program. 8

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). 9

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. 10

Database Management System (DBMS) u. A software system that enables users to define, create, and maintain the database and which provides controlled access to this database. 11

Database Management System (DBMS) 12

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. 13

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. 14

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. 15

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. 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. 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 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) 19

History of Database Systems u First-generation – Hierarchical and Network u Second generation – Relational u Third generation – Object Relational – Object-Oriented 20

Advantages of DBMS 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 21

Advantages of DBMS 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 22

Disadvantages of DBMS u Complexity u Size u Cost of DBMS u Additional hardware costs u Cost of conversion u Performance u Higher impact of a failure 23