Notes > Database Systems > ANSI SPARC 3 Level Database Architecture
ANSI SPARC is an acronym for the American National Standard Institute Standard Planning and Requirements Committee. A standard three level approach to database design has been agreed.
- External level
- Conceptual level
- Internal level (includes physical data storage)
The 3 Level Architecture has the aim of enabling users to access the same data but with a personalised view of it. The distancing of the internal level from the external level means that users do not need to know how the data is physically stored in the database. This level separation also allows the Database Administrator (DBA) to change the database storage structures without affecting the users' views.
External Level (User Views)
A user's view of the database describes a part of the database that is relevant to a particular user. It excludes irrelevant data as well as data which the user is not authorised to access.
The conceptual level is a way of describing what data is stored within the whole database and how the data is inter-related. The conceptual level does not specify how the data is physically stored.
The internal level involves how the database is physically represented on the computer system. It describes how the data is actually stored in the database and on the computer hardware.
The database schema provide an overall description of the database structure (not actual data). There are three types of schema which relate to the 3 Level Database Architecture.
External Schemas or subschemas relate to the user views. The Conceptual Schema describes all the types of data that appear in the database and the relationships between data items. Integrity constraints are also specified in the conceptual schema. The Internal Schema provides definitions for stored records, methods of representation, data fields, indexes, and hashing schemes etc...
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