2 SET File Format

SET is a French standard to exchange and archive CAD data. It was developed as a neutral file format for exchanging data between different CAD systems at Aerospatiale in 1983. The aim was to develop a more reliable alternative to IGES. It became an official French standard, Afnor Z68-300, SET, in 1985. SET was revised and extended in 1989. The version (89-06) used in CADINT, supports wireframe, surface and solid entities. Entities for drafting and connectivity applications, as well as scientific data and FEM (Finite Element Method) modelling are also included. The philosophy behind the standard is that it should be able to handle the complete information that may occur. It is also considered to be important to have an unambiguously defined format, that is compact in size, and is flexible enough to handle future demands from the CAD/CAM industry.

The structure of SET is based upon a three level hierarchical structure, which consists of data assemblies, data blocks, and data sub-blocks. Information that is common to several blocks or assemblies, is stored in a so-called dictionary.

• Assembly: A SET data assembly is a collection of data defining a certain piece of information, such as a mechanical part. A SET file can contain one or more data assemblies;

• Block: In the nomenclature of the SET files, the blocks are identified by an @, followed by the number of the block identifying its type. This number is followed by the block's reference number in the file. (i.e. in a file with n blocks, the block sequence numbers will be from 0 to n.) After this, sub-blocks and dictionary entries used in the block follows. A SET data block is an elementary entity, which consists of definition or control data that are used in different applications. Such entities could be geometric objects as points or lines, or other entities like matrices, drawings and views or SET file identifiers;

• Sub-block: A sub-block consists of an identifier, and a list of data that contributes to the description of the entity defined by the data block. The different parameters inside a sub-block, such as coordinates, are represented by their values. A sub-block has the identifier ``#'', followed by its type number, possible references to the dictionary, and parameters applicable in the sub-block;

• Dictionary: The dictionary is a set of predefined parameters in the specifications of the standard. They are accessible as dictionary entries which are assigned an identifier (a colon `` :'' and the dictionary number), and a precise meaning given by authorised and/or default values.

References among entities in a SET file are made by using pointers, either directly from the blocks, or via sub-blocks or dictionary entries. Pointers to other blocks are identified by an `` !'', followed by the sequence numbers of the blocks. SET has no unique mapping of sub-block types and dictionary entries into blocks. Several combinations are allowed for each different block. Definitions of possible combinations and guidelines for implementation are given in the SET standard [1].