Describe the Three-Schema Architecture of DBMS. Distinguish Physical Data Independence and Logical Independence.
The Three-Schema Architecture:
The goal of the three-schema architecture is to separate the user applications and the physical database. In this architecture, schemas can be defined at 3 levels:
DATA INDEPENDENCE
The disjointing of data descriptions from the application programs (or user-interfaces) that uses the data is called data independence. Data independence is one of the main advantages of DBMS. The three-schema architecture provides the concept of data independence, which means that upper-levels are unaffected by changes to lower-levels. The three schemas architecture makes it easier to achieve true data independence. There are two kinds of data independence.
Logical data independence is harder to achieve as the application programs are usually heavily dependent on the logical structure of the data. An analogy is made to abstract data types in programming languages.
Define a Foreign key. Why is the concept needed? How does it play a role in the join operation?
State the advantages of using database system over file-based information system.
Explain the LOC, Function point and Feature point?
Short Notes : UML
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