database is it permits the maintenance of a related set of
files or tables that can provide information to several
different users. So how do these database structures
differ? you might ask. That’s a good question. Read on
and find out.
LIST DATABASES.— List databases link records
together through the use of pointers. The pointer is a
data element in one record (normally the master record)
that points to the actual disk location of another
logically related record, as illustrated in figure 3-7.
HIERARCHICAL DATABASES.— Hierarchical
databases consist of elements that act in a superior-
subordinate or parent-child relationship. What this
means is that one element is linked to another element in
the database. The superior element points to one or
more subordinate elements. There can also be a
subordinate of a subordinate, which will enable many
hundreds of elements to be connected. See figure 3-8.
NETWORK DATABASES.— Network databases
are very similar to hierarchical databases except that an
element can have one or more superiors. Network
structure permits the connection of the nodes
multidirectionally. Each node may have several owners
(or elements) and may own any number of other data
elements on the network (see figure 3-9). The database
management software permits the extraction of needed
information from such a structure to begin with any
record in the file. Although network databases are more
Figure 3-7.—Example of a list database structure.
Figure 3-8.—Example of a hierarchical database structure.
flexible than hierarchical databases, they still have
limitations. The networking scheme must be defined
when the database is initially created, and information
retrieval is based solely on the predefined scheme.
Figure 3-9.—Example of a network database structure.
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