ANSI-SPARC Architecture
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the ANSI-SPARC Architecture is an abstract design standard for a DBMS. Most commercial DBMS's are based on it.
ANSI-SPARC, stands for American National Standards Institute - Standards Planning And Requirements Committee
the ANSI-SPARC Architecture was first proposed in 1975.
- Note. ANSI-SPARC never became a formal standard, and is more for understanding the functionality of a typical DBMS.
the ANSI-SPARC model of a database identifies three distinct levels at which data items can be described.
These levels form a three-level architecture comprising:
- an external level,
- a conceptual level, and
- an internal level.
The objective of the three-level architecture is to separate the users’ view(s) of the database from the way that it is physically represented. This is desirable for the following reasons:
- It allows independent customised user views.
– Each user should be able to access the same data, but have a different customised view of the data. These should be independent: changes to one view should not affect others. - It hides the physical storage details from users.
– Users should not have to deal with physical database storage details. They should be allowed to work with the data itself, without concern for how it is physically stored. - The database administrator should be able to change the database storage structures without affecting the users’ views.
– From time to time rationalisations or otherchanges to the structure of an organisation’s data will be required. - The internal structure of the database should be unaffected by changes to the physical aspects of the storage.
– For example, a changeover to a new disk. - The database administrator should be able to change the conceptual or global structure of the database without affecting the users.
– This should be possible while still maintaining the desired individual users’ views.
