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ACIS patterns are designed to accommodate both tags and attributes (ACIS objects derived from the
ATTRIB class). The tags of all pattern elements are saved, even when their associated entities are not. Attributes, on the other hand, are considered either pattern-incompatible or pattern-compatible, depending upon whether or not they contain references to entities other than their owning entities.
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When the entities comprising a part contain one or more pattern-incompatible attributes, the pattern is removed prior to a save operation, causing all elements to be saved in their entirety. When all attributes are pattern-compatible, the pattern remains on the part, and the attributes are saved and restored independently of their owning entities (except for those attached to the seed entity).
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For safety, the
ATTRIB base class marks all attributes as pattern-incompatible, via a virtual function. When a class is derived from
ATTRIB, it is the developer's responsibility determine if the class is pattern-compatible, and if so, mark it as such.
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