In the case that an enumeration type is declared extensible it can be extended in other schemas.
An EXPRESS-G diagram for Family schemaĪ simple EXPRESS data model looks like fig 2, and the code like this:ĪBSTRACT SUPERTYPE OF (ONEOF (Male, Female)) The data model presented in figure could be used to specify the requirements of a database for an audio compact disc (CD) collection. A disadvantage of EXPRESS-G is that complex constraints cannot be formally specified. One of the advantages of using EXPRESS-G over EXPRESS is that the structure of a data model can be presented in a more understandable manner. This graphical notation supports a subset of the EXPRESS language. It is a companion to the EXPRESS language for displaying entity and type definitions, relationships and cardinality. A main feature of EXPRESS is the possibility to formally validate a population of datatypes - this is to check for all the structural and algorithmic rules.ĮXPRESS-G is a standard graphical notation for information models. Within a SCHEMA various datatypes can be defined together with structural constraints and algorithmic rules. The graphical representation, called EXPRESS-G, is not able to represent all details that can be formulated in the textual form.ĮXPRESS is similar to programming languages such as Pascal. The graphical representation on the other hand is often more suitable for human use such as explanation and tutorials.
For formal verification and as input for tools such as SDAI the textual representation within an ASCII file is the most important one. Īn EXPRESS data model can be defined in two ways, textually and graphically.
EXPRESS is a data modeling language defined in ISO 10303-11, the EXPRESS Language Reference Manual. Data models are specified in a data modeling language. Some typical applications of data models include supporting the development of databases and enabling the exchange of data for a particular area of interest. Data models formally define data objects and relationships among data objects for a domain of interest.