IMPLEMENTATION OF A DATA DEFINITION LANGUAGE FOR RELATIONAL DATABASE SYSTEMS

Abstract

A Data Definition Language (DDL) for a relational database has been implemented in this thesis. A relational model was adopted because it is easy to install and use. The developed system also supports the data security and integrity facilities. The DDL facilitates the users to describe both the data elements and their relationships. This also provides the facility of extending and dropping the existing relations. It is assumed that these descriptions are in fully normalized form. The basic unit of storage in this system is a record. Each record represents some fact about the real world. A record represents one taple of the relation and its fields correspond to the attributes of the relation. Database management systems differ in the way they organize records. This system organizesdata into tables. It considers the relational model as an organization which collects data into uniform tables, with each table corresponding to one relation. To improve the response in answering certain type of queries which need information from records that are identified by values in a field or fields that don't form key, the system provides for secondary indices. A security facility has been provided which protects the data from unauthorized access, insertion or deletion. This system divides the user community into five groups. Each group is characterized by default access rights to the data. The integrity facility prevents inconsistent data from being stored. The major commands that the system supports are DECLARE, LOAD, APPEND, DELETE, INDEX, ADD, RESTRICT, LIMIT, PRINT, HELP. This DDL has been implemented on DEC-2050 and tested.