5.1.6.1 Levels of Data
For example, in a customer file for a department store, one complete record could contain all data pertaining to one customer. Subdivisions within that record could be: customer name, customer address, account number, department number of sale, unit amount of sale, dollar amount of sale, previous balance, plus other pertinent information.
After a record has been defined, it can be subdivided to provide more detailed data references.
The basic subdivisions of a record (that is, those fields not further subdivided) are called elementary items. Thus, a record can be made up of a series of elementary items, or it can itself be an elementary item.
It might be necessary to refer to a set of elementary items; thus, elementary items can be combined into group items. Groups themselves can be combined into a more inclusive group that contains one or more subgroups. Thus, within one hierarchy of data items, an elementary item can belong to more than one group item.
A system of level-numbers specifies the organization of elementary and group items into records. Special level-numbers are also used; they identify data items used for special purposes.
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