All user-defined data used in a COBOL program belongs to one or more logical records. A logical record is defined by a record description entry. Logical records may correspond to actual disk records (by being defined in the File Section), or they may simply be areas of computer memory used by the program. A record description entry is itself composed of one or more data description entries. Each data description entry defines one COBOL data item.
Logical records can be divided into a hierarchy of individual data items. Subdivision can continue for each of the record's parts. The lowest level subdivision of a record is the elementary data item. Elementary data items are never subdivided. A logical record is either an elementary data item or a set of elementary data items.
A group item is a piece of data that contains other subordinate data items. These subordinate items may be either elementary data items or other group items. The lowest level group item is always a sequence of one or more elementary data items.