The following definitions and concepts have been intentionally kept simple; for a detailed theoretical approach textbooks about database models and set theory should be consulted. With few exceptions, the definition of terms given follows Microtool (1995).
Attribute: Corresponds to the header of a column in a relational table (field name). A concrete instance assigned to an attribute is called an attribute value.
Data element: A class of qualities being used to describe various operational units used by the CASE system to express data. In the present model, a data element must be assigned to every attribute. Data elements are unique, but more than one attribute and/or data item may have the same data element assigned to it. The qualities which can be defined include semantics (description of its problem-domain meaning), technical type (e.g. "Integer", "Char(5)"), value range (a condition for, or an enumeration of the permitted values for the range), and default value.
Data integrity rules: Semantic rules for the creation, deletion, or modification of records. In contrast to the rules defined by relational integrity, data integrity rules usually have to be enforced by the functions specifically designed for the problem domain rather than being implemented in the underlying relational database system itself.
Entity: An abstract type of object, the instances of which can be mapped into a relational table, i.e. a table containing a header consisting of a set of attributes, and a body consisting of a variable set of tuples (rows with values for the attributes). Duplicate tuples or attributes are not allowed. The term Entity as used here corresponds to Entity-Set in Chen (1976) and to Entity-Type in MicroTool (1995).
Event: Entities bearing an "event" suffix contain or link data items which describe a particular action or incident taking place at a defined point in time. They should not be confused with events acting on these data in an object oriented information flow model.
Part: A separate data structure diagram referenced by another DSD. Indicated by a little arrow pointing to the bottom of a shaded data box.
Subtyping: Classification of some of the attributes of an entity (supertype) into several additional entities (subtypes). A subtype inherits all of the attributes of its supertype, but also has additional attributes (ASC 1992). Another way to express this is that the supertype set is the intersection of the attributes of all subtype sets.