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. A concrete instance assigned to an attribute is called an attribute value. A class of qualities being used to describe various operational units used by the CASE system to express data. Dialog element preferably used to display the fields or attributes to which the data element is assigned for editing purposes Message which is to be given by the application system when an input value for a field or attribute does not belong to the value range specified for the corresponding data element.
Data integrity rules Semantic rules for the creation, deletion, or modification of records.
These usually have to be enforced by the database management program rather than the database management system. Data items may be data fields, attribute fields, parts, or entities. A diagram may consist of several pages. Small numbers above the first data item point to the higher page, small numbers below point to the page where the respective data item is subdivided in more detail. The name of the entity is given in parenthesis in the box.