03-06-2013, 04:25 PM
DATABASE THEORY
DATABASE.ppt (Size: 197.5 KB / Downloads: 22)
DBMS
A DATABASE MANAGEMENT SYSTEM (DBMS) CONSISTS OF A COLLECTION OF INTERRELATED DATA AND SET OF PROGRAMS TO ACCESS THOSE DATA.
THE PRIMARY GOAL OF A DBMS IS TO PROVIDE AN ENVIRONMENT THAT IS BOTH CONVENIENT AND EFFICIENT TO USE IN RETRIEVING AND STORING DATABASE INFORMATION.
PURPOSE OF DBMS
DEFINITION OF STRUCTURE FOR THE STORAGE OF INFO .
PROVISION OF MECHANISMS FOR THE MANIPULATION OF INFO.
SAFETY OF INFO.
ON A NETWORK, THE SYS MUST AVOID POSSIBLE ANOMALOUS RESULTS.
DATA ABSTRACTION
COLLECTION OF DATA FROM ANY PLACE OR STORAGE POINT
TO SIMPLIFY USER’S INTERACTIONS WITH THE SYS
A DBMS PROVIDE THREE LEVELS OF DATA ABSTRACTION.
IDENTIFYING RELATIONSHIP
IF THE PRIMARY KEY COLUMN IS CONTRIBUTED TO THE CHILD TABLE’S PRIMARY KEY, THEN THIS RELATIONSHIP IS KNOWN AS AN IDENTIFYING RELATIONSHIP.
IN THIS CASE, THE CHILD ENTITY IS KNOWN AS A DEPENDENT ENTITY BECAUSE ITS IDENTIFICATION DEPENDS ON THE PARENT ENTITY.
FOREIGN KEYS IN THIS RELATIONSHIPS CANNOT CONTAIN NULL VALUES