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.

RELATIONAL DATABASES.\ Relational databases have many advantages over network and hierarchical databases. They consist of one or more tables in which data are stored in the form of rows and columns. The main advantage is that relationships between the data can be established whenever you (the user) request information. For example, relation tables could be used to link a person with his/her NECs, duty assignments, and any special qualifications, as shown in figure 3-10. Many other relations are, of course, possible. Any relational database package normally uses an index of some sort for faster access to the data. Relational structures are a very popular database structuring approach for both mainframe and microcomputer database packages.