Syntax

   FACTORY_DEF <ReaderKeyword> SharedObjectFactory
   [FACTORY_NAME <factory name>] 
   [INPUT (DEFINITION|DEFINITION_FRONT|DEFINITION_BACK|REFERENCER) 
      FEATURE_TYPE <feature type>
      [<attribute name> <attribute value>]*
      [<feature function>]*]*
   [MODE (ADD|REMOVE|EXTRACT)]
   [SHARED_OBJECT_TYPE (APPEARANCE|GEOMETRY_DEFINITION)]
   [ADDITIONAL_NECESSARY_DEFINITION_TAGS tag1 | tag2 | ...] //correct?
   [GROUP_BY [<attribute_name>]+]*
   [UNIQUE_DEFINITIONS [(YES|NO)]]
   [RECURSIVE [(YES|NO)]]
   [OUTPUT (SUCCESSFUL|INVALID_GEOMETRY|INVALID_DEFINITION|EXTRA_DEFINITION) 
      FEATURE_TYPE <feature type>
      [<attribute name> <attribute value>]*
      [<feature function>]*]*

Overview

   To be documented.
   
Clauses

   The SharedObjectFactory supports the following clauses.

      MODE
      
         ADD - create a shared object of type SHARED_OBJECT_TYPE using 
         properties from the definition feature, add it to the library and set 
         the REFERENCER features to reference the new shared object.
            
         REMOVE - remove reference from REFERENCER feature.
         
         EXTRACT - extract DEFINITION associated with shared object referenced 
         by REFERENCER feature.
         
      
      SHARED_OBJECT_TYPE
      
         Type of shared object we are interested in and which definition tags will be processed. 
         
      ADDITIONAL_NECESSARY_DEFINITION_TAGS
      
         Additional definition tags that we are interested in processing. An example when this is
         needed is when we are extracting an appearance. there will be no DEFINITION_* input tags
         but we still need to process either or both front and back faces.

      GROUP_BY
      
         Which attributes to group referenceres/definitions by.

      UNIQUE_DEFINITIONS
      
         Whether to output only unique definitons in extract mode.

      RECURSIVE 
      
         Whether we want to remove or extract recursively (it might or might not 
         apply depending on the SHARED_OBJECT_TYPE).
   
Input Tags

   The SharedObjectFactory supports the following input tags.
   
   DEFINITION, DEFINITION_FRONT, DEFINITION_BACK

      Feature that contains information about the shared object which will be 
      created. When multiple definitions are required on a dynamic basis, they 
      are given different tags. As in the instance when we need definitions for 
      either or both the front and the back faces of a surface.
   
   REFERENCER

      Feature which references or will reference a shared object.

Output Tags

   The SharedObjectFactory supports the following output tags.

      SUCCESSFUL

         Features going out here depend on MODE.

      INVALID_GEOMETRY

         Input features with invalid geometry.

      INVALID_DEFINITION

         Invalid DEFINITION features (missing attributes, wrong attribute 
         values, etc.)  

      EXTRA_DEFINITION

         Extra definition features. Only 1 definition per tag per group is 
         allowed. 

TO BE RESOLVED

   Overview section needs to be documented.