Database Reference
In-Depth Information
Figure 1.3
The Network Data
Model.
Network
. Refinement of the hierarchical model where many-to-
many relationships are permitted because child tables can have more
than a single parent table. This creates a “networked” structure of
tables as shown in Figure 1.3. A network structure is an improved
hierarchical or branch-leaf tree structure where many-to-many enti-
ties can be accessed, but access to a node still requires access to all par-
ent nodes from the root node.
Relational
. Any two tables can be linked irrespective of hierarchical
placement. Therefore, any table can be accessed directly without hav-
ing to access child tables through a hierarchy or network of parent
tables. Relatively complex and efficient data structures can be created
with the relational data model. The operative phrase for use of rela-
tional tables is rapid selection of groups of data rather than single
items. Relational databases are most effective for reporting. An exam-
ple relational structure is shown in Figure 1.4 where any table can be
retrieved from based on key values. Tables or entities are built from
those keys.
Object
. Directly addressed hierarchies of collections to any data item
within a structure. This assumes that the direct address or pointer is a
known value. The relational data model is most efficient for accessing
groups of data at once, such as in reporting. On the contrary, the
object data model is excellent for access to unique data items within
large, highly complex data sets or groups of interlinked objects. In
other words, the object data model is much more effective than the
