Short Question Answers

Q What do you mean by data dictionary ?
A  A data dictionary is a file that contains "meta data" i.e data about data.


Q What are the main classification of SQL statements ? 
A SQL commands are classifieds as follows

  1. Data Defination Language (DDL) - allows you to perform tasks related to data defination eg CREATE, ALTER, DROP
  2. Data Manipulation Langugae (DML)- enables users to access or manipulate data as organized by appropriate data model eg SELECT, INSERT, UPDATE
  3. Transaction Control Languages(TCL)- To manage and control transactions Transaction Control Language is used eg COMMIT, ROLLBACK, SAVEPOINT.

Q What do you mean by schema ?
A A schema refers to collection of logical structures of data. Schema objects are logical structures that directly refer to the database's data.



Q Name some schema objects ?
A  Some of the schema objetcs are:-




  1. Clusters - These are storage areas storing related tables and indexes.
  2. Database Triggers- These are stored subprograms associated with tables which are executed automatically .
  3. Indexes- An index contains an entry for each value that appears in the indexed column(s) of table or cluster. Index provides fast access to rows.
  4. Packages- A package is a collection of related procedures, functions and other program objetcs stored in the database.
  5. Stored Procedures- a group of PL/SQL statements that can be invoked or called from SQL or PL/SQL 
  6. Tables - A table is a collection of related data.
  7. Views- a virtual table that draws data from existing table, but actually doesn't contain data , only maintains pointers.