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Further reading □ OverviewCAD*IExpressCAD*I WG3 October 1988CAD*I status March 1989STEP (STandard for Exchange of Product Information)STEP implementationCAD*I status March 1989 □ RAL Reports □ RAL-TR-96-043RAL-TR-96-054RAL-TR-96-072RAL-TR-96-087RAL-TR-96-098
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Further reading

Overview
CAD*I
Express
CAD*I WG3 October 1988
CAD*I status March 1989
STEP (STandard for Exchange of Product Information)
STEP implementation
CAD*I status March 1989
RAL Reports
RAL-TR-96-043
RAL-TR-96-054
RAL-TR-96-072
RAL-TR-96-087
RAL-TR-96-098

Express

EXPRESS was a textual conceptual schema language based on the entity-attribute-relationship model developed in CAD*I with both generalization and constraint-specification constructs. It was used to specify the normative part of all the information models in CAD*I and later STEP. It needed to be human readable and computer-processable.

EXPRESS had the following declarative constructs:

A simple example might be:

ENTITY point ;
  x : REAL ;
  y : REAL ;
END-ENTITY
ENTITY line ;
 p0 : point ;
 p1 : point ;
 END-ENTITY
 

The first entity point is used as an attribute type in the second entity line.

Inheritance allowed constraints on a parent to be inherited by the child. Multiple inheritances were allowed. The file reader and parser implemented at RAL originally for the CAD*I project were successfully converted to deal with STEP exchange files. A back-end to the file reader was written which provided an interface to the Nastran Finite Element program.

The Express compiler was originally written for CAD*I and then upgraded for STEP. Many utilities such as pretty printers were also added. The software was distributed to a number of academic and industrial organisations, both in the UK and overseas. A neutral database for electromagnetic and semiconductor modelling data was created based on an EXPRESS schema and a mapping from EXPRESS to SQL. Genera1ised subroutines to access the database were developed.

Many UK universities, both in the UK and world-wide, and industry were supplied with the Express compiler and/or the physical file reader RAL retained the Intellectual Property Rights for the software.

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