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The Advanced Applications Database: Logical Model

The database design problem can be stated very simply, as follows: Given some body of data to be represented in a database, how do we decide on a suitable logical structure for that data?. In other words, how do we decide what relations should exist and what attributes they should have?.

We are concerned here with the logical design problem only, not the physical design problem. We are trying to produce a hardware-independent, operating-system independent, DBMS-independent - etc., etc. - abstract logical design.

We are concerned primarily with relational design for several reasons:

  • It is one of the most widely used.
  • It is our belief that to do a nonrelational design, the relational design can be maped into whatever nonrelational structures (hierarchies, etc.) the target DBMS happens to support.
  • At the end, a specific relational system, Sybase SQL Server, will be used to implement the logical design.

A relational database is a database that is perceived by its users as a collection of tables (and nothing but tables). Relations in a relational database are always normalized, in the sense that the underlying simple domains contain atomic values only. The normalization procedure can be characterized as the successive reduction of a given collection of relations to some more desirable form.

The following logical model is obtained after the normalization procedure as a representation of the relational database content. Each square would represent a table with its respective attributes. The red attributes represent a unique identifier field or field combination of the table. Finally, the table where the arrows point is a table, or relation, where its unique identifier has a corresponding value in the tables where the arrows emerge.

The AAD data model view shown here is presented in IDEF1X modeling notation (the standard notation defined in DoD Directive 8320.1).

 

Advanced Applications Database || Logical Model || Query/Search

Contact DASTBlank Space Last reviewed: December 31, 1969
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