PDM-UG: Relating Externally Defined Part Shape to an External File
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This page belongs to the PDM Usage Guide.
The PDM Schema generally represents part master data. This part 'meta' data does not typically represent the detailed geometry of the part shape - this is the scope of CAD systems. Rather, the externally defined geometry is identified as an external representation of the part shape that is related to the part master data. Part geometry is identified in the PDM Schema as a representation of a property of a part definition - it is actually in externally referenced files. These files are often generated by CAD systems, and contain the detailed geometric shape representation with dedicated geometric elements.
The external part shape is an external geometric model related to the part master data and is referenced as an external CAD file. Specifics of external file identification are described in External Files. The external file that contains the detailed geometry is attached to the part master data in two ways:
- Related to the product identification data using applied_document_reference.
- Related to the shape_representation representing the external geometric model using the entities property_definition and property_definition_representation.
It is recommended that applied_document_reference be used, in general, to relate an external file representing the CAD model to the product_definition of a part identification (see Document and File Association with Product Data). If the external file representing the CAD model exists alone as an unmanaged external file reference, then the document_reference should be applied directly from the document_file (see External File Reference). If the external file representing the CAD model exists as a constituent file of a managed document (using the ‘Document as Product’ approach), the document_reference should be applied from the managed document via the document_product_equivalence (see Document Reference).
If the CAD file contains the definitional shape of the part, then an external geometric model should be represented (using shape_representation) and the external CAD file should also be related to this shape_representation using property_definition and property_definition_representation.
The Instance Model: EXPRESS entities and attributes
The EXPRESS entities and attributes used to support the requirements of relating part shape to the external CAD file is illustrated in Diagram 10.
The Instance Model: STEP exchange file format (ISO10303 Part 21 syntax)
/* Entities #370 to #497 define a managed document which */
/* contains a representation of the shape of 'part2' */
#370 = PRODUCT('p2_shape_doc', 'document reflecting
shape of part2', '', (#20));
#380 = PRODUCT_RELATED_PRODUCT_CATEGORY('document', '', (#370));
#390 = DOCUMENT_TYPE('configuration controlled document version');
#400 = DOCUMENT('', '', '', #390);
#410 = APPLIED_DOCUMENT_REFERENCE(#290, 'equivalence', (#400));
#420 = OBJECT_ROLE('mandatory', '');
#430 = ROLE_ASSOCIATION(#420, #410);
#440 = PRODUCT_DEFINITION_FORMATION('1', '', #370);
#450 = DOCUMENT_PRODUCT_EQUIVALENCE('equivalence', '', #400, #440);
#460 = PRODUCT_DEFINITION_CONTEXT('digital document definition', #10, '';
#470 = PRODUCT_DEFINITION_WITH_ASSOCIATED_DOCUMENTS('p2_shape_d',
'digital document for part2 shape', #440, #460,(#475));
#475 = DOCUMENT_FILE('p2_shape_file', '', '', #485, '', $);
#480 = DOCUMENT_REPRESENTATION_TYPE('digital',#475);
#485 = DOCUMENT_TYPE('');
#490 = IDENTIFICATION_ROLE('local node','access context');
#495 =APPLIED_EXTERNAL_IDENTIFICATION_ASSIGNMENT( 'part1_geometry.stp',#490, #497,(#475));
#497 = EXTERNAL_SOURCE('c:\part_dir');
/* Entities #600 to #660 define the geometric model for 'part2' */
#600 = PRODUCT_DEFINITION_SHAPE('shape_p2',$,#290);
#610 = SHAPE_DEFINITION_REPRESENTATION(#600,#620);
#620 = SHAPE_REPRESENTATION('sol2',(#670),#630);
#630 = GEOMETRIC_REPRESENTATION_CONTEXT('c2','external',3);
#640 = CARTESIAN_POINT('', (3.0E+001, 0.0E+000, 1.0E+001));
#650 = DIRECTION('', (0.0E+000, -1.0E+000, 0.0E+000));
#660 = DIRECTION('', (1.0E+000, 0.0E+000, 0.0E+000));
#670 = AXIS2_PLACEMENT_3D('', #640, #650, #660);
/* Entities #680 and #690 indicate that the shape_representation #620 /
/* is externally defined by the file represented by #475 */
#680 = PROPERTY_DEFINITION('external definition',$,#475);
#690 = PROPERTY_DEFINITION_REPRESENTATION(#680,#620);
/* Entities #500 to #560 define the geometric model for 'part1' */
#500 = PRODUCT_DEFINITION_SHAPE('shape_p1',$,#230);
#510 = SHAPE_DEFINITION_REPRESENTATION(#500,#520);
#520 = SHAPE_REPRESENTATION('sol1',(#570),#530);
#530 = GEOMETRIC_REPRESENTATION_CONTEXT('c1','external',3);
#540 = CARTESIAN_POINT('', (1.0E+001, 0.0E+000, 1.0E+001));
#550 = DIRECTION('', (0.0E+000, -1.0E+000, 0.0E+000));
#560 = DIRECTION('', (1.0E+000, 0.0E+000, 0.0E+000));
#570 = AXIS2_PLACEMENT_3D('', #540, #550, #560);
/* Entities #575 to #585 state that the shape_representation #520 */
/* is externally defined in a digital file with the location */
/* 'part2_geometry.stp' */
#575 = APPLIED_DOCUMENT_REFERENCE(#576,(#230));
#576 = DOCUMENT_FILE('p1_shape','',$,#577,'',$);
#577 = DOCUMENT_TYPE('geometry');
#578 = ROLE_ASSOCIATION(#579,#575);
#579 = OBJECT_ROLE('mandatory',$);
#580 = DOCUMENT_REPRESENTATION_TYPE('digital',#576);
#581 = IDENTIFICATION_ROLE('local node','access context');
#582 = APPLIED_EXTERNAL_IDENTIFICATION_ASSIGNMENT( 'part2_geometry.stp',#581,#583,(#576));
#583 = EXTERNAL_SOURCE('c:\part_dir');
#584 = PROPERTY_DEFINITION('external definition',$,#576);
#585 = PROPERTY_DEFINITION_REPRESENTATION(#584,#520);
