Dbms

Data Bases
Data base approach focuses on data integration and data sharing, views data as an organizational resource

Data Base Management System (DBMS) refers to programs that control the data and interfaces between the data and application programs

The data based, DBMS, and the application programs together are termed as data base system

Data base administrator is the person responsible for the data base.

Data base systems separate logical and physical views of data, referred to as program-data independence
Logical view - how the user or programmer conceptually organizes and understands data
Physical view - how and where the data are physically arranged and stored on storage medium

Advantages of program-data independence
Application programmers can code application logic without concern for physical storage the logical view of the task can be changed without changing the physical data storage

Schema - logical structure of the data base
Conceptual level schema - organization wide view of entire data base
External level schema - individual user views of data, subschema
Internal level schema - low-level view of data based, how data are stored
DBMS translates user requests at logical level into physical actions
Accountants are involved with conceptual and external levels, rarely the internal level.

Data Dictionary - information on the structure of the data base
Each data element is described in detail.
Usually maintained automatically by DBMS
Output of data dictionary often includes
Programs where data items are used.
List of synonyms
Data elements used by a user
List of output reports where data element is used.

DBMS languages - functions of creating, changing and querying
Data definition language (DDL) - build data dictionary, initialize, describe logical views, specify security imposed on users.
Data manipulation language (DML) - data maintenance, updating, inserting and deleting, references