A subschema is the applications programmer's view of the data within the database pertinent to the specific application. A subschema has access to those areas, set types, reco
…rd types, data items, and data aggregates of interest in the pertinent application to which it was designed. Naturally, a software system usually has more than one programmer assigned and includes more than one application. This means there are usually many different subschemas for each schema. The following are a few of the many reasons subschemas are used: 1 Subschemas provide different views of the data to the user and the programmer, who do not need to know all the data contained in the entire database. 2. Subschemas enhance security factors and prohibit data compromise. 3. Subschemas aid the DBA while assuring data integrity. Each data item included in the subschema will be assigned a location in the user working area (UWA).The UWA is conceptually a loading and unloading zone,where all data provided by the DBMS in response to a CALL for data is delivered. It is also where all data to be picked up by the DBMS must be placed. Schema Data Definition Language (DDL) The schema data definition language (DDL) is used for describing a database, which maybe shared by many programs written in many languages. This description is in terms of the names and characteristics of the data items, data aggregates, records, areas, and sets included in the database, and the relationships that exist and must be maintained between occurrences of those elements in the database.l Data item. A data item is an occurrence of the smallest unit of named data. It is represented in a database by a value.l Data aggregate. A data aggregate is an occurrence of a named collection of data items within a record. There are two kinds-vectors and repeating groups. A vector is a one-dimensional sequence of data items, all of which have identical characteristics. A repeating group is a collection of data that occurs a number of times within a record occurrence collection may consist of data items, vectors.repeating groups (MORE) 
