Introduction to Database Management Systems www.AssignmentPoint.com www.assignmentpoint.com

Motivation Organisations are increasingly aware of the importance of information in the solution of their problems. Because of decreasing cost of data storage, organisations store increasing quantities of data. This data must be managed in the most efficient and effective manner. www.assignmentpoint.com

The Database Approach Organizations must have access to operational data that is accurate timely convenient up-to-date secure but available As control decentralizes in an organization, there is a danger that data management decentralizes as well. www.assignmentpoint.com

Dangers of Decentralized Data Management Redundancy Inconsistency Incompatibility Different formats Different constraints Different models of the data Inaccuracy Insecurity Non-accountability Inflexibility www.assignmentpoint.com

Integration and Sharing Data should be integrated the database can be regarded as a unification of several otherwise distinct data files shared individual pieces of data in the database can be shared among several different users www.assignmentpoint.com

Data Management Objective Requirements Model a part of the world of the real world accurately and efficiently to give user useful data Requirements Flexibility Accuracy Reliability Accessibility Efficiency www.assignmentpoint.com

Data Modelling: Abstraction Again In modelling the data, we again use abstraction. We hide (irrelevant) detail and concentrate on the general and common attributes of a set of objects Example: Real world: Student Model: ST(id, name, dob, grade history) www.assignmentpoint.com

Definition of a Database A database (DB) is a collection of interrelated computer files, whose data contents and structure are described in a data dictionary and which is under the control of a database management system (DBMS) www.assignmentpoint.com

Database Management Systems A database management system is a collection of programs that carry out activities on a database, including setting up storage structures loading data accepting and performing updates accepting data requests from users and programs. www.assignmentpoint.com

Functions of a DBMS A good DBMS performs the following functions maintain data dictionary support multiple views of data enforce integrity constraints enforce access constraints support concurrency control support backup and recovery procedures support logical transactions www.assignmentpoint.com

Advantages of Using a DBMS All applications access a common DB. So, details related to data storage and access are removed from programs and users. Hence less redundancy less risk of inconsistency maintenance of data integrity application of access restrictions balance between different requirements data independence www.assignmentpoint.com

Layered Structure of a Database We can regard a database as having a layered structure ------------------------------ External Schema Conceptual Schema Internal Schema www.assignmentpoint.com

Schemas and Instances A schema is the overall design of the database. It describes the data contents, structure and some other aspects of the database also called the intension of the database The instance is the collection of data stored in the database at a particular time, also called the extension of the database. www.assignmentpoint.com

Data Independence: External schema Different users often need different views of the data. Example: Bursar needs to have access to financial information on a student Head of Department needs access to academic information. An external schema is a description of part of the DB as seen by an application programmer or a user www.assignmentpoint.com

Conceptual Schema Representation of the logical structure of the information content of the DB. Abstracts away from the actual physical storage. The data “as it really is”. It is, in a sense, a composite of all the external schemata. www.assignmentpoint.com

Internal Schema The internal schema describes the data as it is physically stored. For example, record structure types of fields in a record existence of primary and secondary indexes www.assignmentpoint.com

Data Independence Higher levels should be immune to changes at the lower level. Physical data independence: changes at the internal schema (e.g., changes in record structure or indexes) do not affect the conceptual schema Logical data independence changes at the conceptual schema (e.g., addition of further fields in a record) do not affect the external schema. www.assignmentpoint.com

Importance of Data Independence Similarity between data independence and the use of abstract data types. Immunity to lower-level implementation details. Possibility of adding new applications without having to restructure the data base. www.assignmentpoint.com