ISO 10303-108:2005 specifies the resource constructs for the representation of model parameters and constraints in CAD or other kinds of models, together with the mechanisms necessary for associating them with geometric or other elements of transferred models. The use of these capabilities potentially allows certain aspects of the behaviour of a model in its originating system to be conveyed together with the basic model itself. The intention in transferring this additional information is to provide the receiving system with data that will enable it to reconstruct corresponding behavioural characteristics in the model following the transfer. Ideally, this will enable the model to be edited in the receiving system just as as though it had been created there. That would not be possible without the exchange of what is known as design intent information. ISO 10303-108:2005 enables the capture and transfer of an important aspect of design intent.
The following are within the scope of ISO 10303-108:2005:
- parameterization of models through the association of variables with quantities occurring in them, including dimensional values;
- constraints defining mathematical relationships between variable parameters;
- constraints on models expressed as descriptive relationships between their constituent elements or attributes of those elements;
- specialized descriptive constraints corresponding to the geometric constraints commonly used in product shape modelling (e.g., parallelism or tangency between geometric elements);
- applications of parameterization and constraints to two- and three-dimensional shape models;
- specialized representations for two-dimensional geometric sketches or profiles;
- representation of models that are incompletely defined in the sense that certain values in the model may be regarded as not fully constrained.
The following are outside the scope of ISO 10303-108:2005:
- procedural or history-based model representations, expressed in terms of sequences of constructional operations;
- implicit or procedurally defined constraints, inherent in the operation of constructional operations;
- solution methods for systems of constraint equations;
- form features of shape models;
- behaviour of a system in which a variational model is edited following a transfer;
- considerations of accuracy in constraint satisfaction.
The following notes apply to the excluded capabilities.
- Procedural or history-based representations are the subject of ISO 10303-55.
- Methods of solving constraint equations are the responsibility of the application systems involved in the exchange. ISO 10303-108:2005 merely transfers the constraint relationships that need to be solved.
- Various other parts of ISO 10303 provide representations for different application-oriented views of form features.
- The information transmitted by the use of ISO 10303-108:2005 is intended to allow implementers to provide 'reasonable' or 'intuitive' behaviour by receiving systems following the transfer of a model in the circumstances mentioned above, but ISO 10303-108:2005 does not prescribe the detailed nature of such behaviour or of its presentation to the system user.
- Accuracy considerations are essentially the same in the ISO 10303-108:2005 context as those arising generally in the geometric modelling of product shape. Means are provided elsewhere in ISO 10303 for addressing accuracy issues.