Syntax

   FACTORY_DEF <ReaderKeyword> CommonSegmentFactory
   [FACTORY_NAME <factory name>] 
   [INPUT (BASE|CANDIDATE) FEATURE_TYPE <feature type>
   [<attribute name> <attribute value>]*
   [<feature function>]*]*
   [GROUP_BY [<attribute name>]+]*
   [FLUSH_WHEN_GROUPS_CHANGE (Yes|No)]
   [OUTPUT (OVERLAP|NO_OVERLAP|BASE)
   FEATURE_TYPE <feature type>
   [<attribute name> <attribute value>]*
   [<feature function>]*]*

Overview

   This factory tests to see which of the features entering by the CANDIDATE 
   input clause have even one segment in common with any feature entering by way 
   of the BASE input clause. If a CANDIDATE feature does share one segment with 
   some BASE feature, then it is output with the OUTPUT OVERLAP clause. If the 
   candidate does not share any segment, then it is output via the OUTPUT 
   NO_OVERLAP clause. As the factory shuts down, all BASE features are output 
   unmodified through the BASE output clause.

   The GROUP_BY clause allows the candidates and base features to be clustered 
   on the basis of some set of attribute values. If FLUSH_WHEN_GROUPS_CHANGE is
   set to Yes, processing up to that point will be performed immediately upon 
   encountering a feature from a different group.

   All attributes present on any input feature when it enters the factory, will 
   be present when the feature leaves it. The factory makes no changes to any 
   features that flow through it.

   Whenever possible the BASE feature set should be kept as small as possible to 
   reduce the memory requirements of this factory.

Assumptions

   The only overlap that can be detected is one where at least one segment 
   connects precisely the same two vertices in both the BASE and CANDIDATE 
   features. 

Input Tags

   The CommonSegmentFactory supports the following input tags.

   BASE
   
      The set of features to be searched for a common segment by each candidate 
      feature.
   
   CANDIDATE
   
      The features to be categorized as either having a common segment with the 
      base set or not.
   
Output Tags

   The CommonSegmentFactory supports the following output tags.
   
   OVERLAP
   
      Any candidate feature that shares a common segment with some feature in 
      the base set.

   NO_OVERLAP

      Any candidate feature that does not share a common segment with some 
      feature in the base set.

   BASE
   
      The original, unchanged input base features.