int survey #6..

**CHOOSE ONE DBMS SOFTWARE AND DISCUSS IT'S STRUCTURE AND HOW ITS DATA ENTRY FORMS ARE CREATED.

ORACLE


The Oracle RDBMS stores data logically in the form of table spaces and physically in the form of data files. Table spaces can contain various types of memory segments; for example, Data Segments, Index Segments etc. Segments in turn comprise one or more extents. Extents comprise groups of contiguous data blocks. Data blocks form the basic units of data storage. At the physical level, data-files comprise one or more data blocks, where the block size can vary between data-files.

Oracle database management tracks its computer data storage with the help of information stored in the SYSTEM table space. The SYSTEM table space contains the data dictionary — and often (by default) indexes and clusters. (A data dictionary consists of a special collection of tables that contains information about all user-objects in the database). Since version 8i, the Oracle RDBMS also supports "locally managed" table spaces which can store space management information in bitmaps in their own headers rather than in the SYSTEM table space (as happens with the default "dictionary-managed" table spaces).

If the Oracle database administrator has instituted Oracle RAC (Real Application Clusters), then multiple instances, usually on different servers, attach to a central storage array. This scenario offers numerous advantages, most importantly performance, scalability and redundancy. However, support becomes more complex, and many sites do not use RAC. In version 10g, grid computing has introduced shared resources where an instance can use (for example) CPU resources from another node (computer) in the grid.

The Oracle DBMS can store and execute stored procedures and functions within itself. PL/SQL (Oracle Corporation's proprietary procedural extension to SQL), or the object-oriented language Java can invoke such code objects and/or provide the programming structures for writing them.