Database Reference
In-Depth Information
in the design process or, more disturbingly, well after the database has been put into opera-
tion.
The hierarchical database lent itself well to the tape storage systems used by mainframes
in the 1970s and was very popular in companies that used those systems. But, despite the
fact that the hierarchical database provided fast and direct access to data and was useful in
a number of circumstances, it was clear that a new database model was needed to address
the growing problems of data redundancy and complex relationships among data.
The Network Database Model
The network database was, for the most part, developed as an attempt to address some of
the problems of the hierarchical database. The structure of a network database is represen-
ted in terms of
nodes
and
set structures.
Figure 1.3
shows a diagram of a typical network
database.
Figure 1.3. Diagram of a typical network database
Anoderepresentsacollectionofrecords,andasetstructureestablishesandrepresentsare-
lationship in a network database. It is a transparent construction that relates a pair of nodes
togetherbyusingonenodeasanownerandtheothernodeasamember.(Thisisavaluable
improvementontheparent/childrelationship.)Asetstructuresupportsaone-to-manyrela-
tionship,whichmeansthatarecordintheownernodecanberelatedtooneormorerecords
in the member node, but a single record in the member node is related to only one record
