ANSI-SPARC Architecture
the ANSI-SPARC Architecture is an abstract design witch most commercial DBMSs is based on.
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:
• 1. 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.
• 2. 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.
• 3. 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.
• 4. 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.
• 5. 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