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Graph patterns

<!-- ##### SECTION Short_Description ##### -->
Collections of triple patterns, sub-graph patterns with operators.

<!-- ##### SECTION Long_Description ##### -->
<para>
Graph patterns form a a tree structure that build a #rasqal_query
top-level graph pattern (see rasqal_query_get_query_graph_pattern())
which may have sub-graph patterns.  Graph patterns at the leaf of the
tree operate over triple patterns (#rasqal_triple) matching the
RDF triples in the data sources for %RASQAL_GRAPH_PATTERN_OPERATOR_BASIC
or %RASQAL_GRAPH_PATTERN_OPERATOR_OPTIONAL.  Other graph patterns
operators operate over sub graph patterns and group them, union them
or apply a GRAPH matching keyword (%RASQAL_GRAPH_PATTERN_OPERATOR_GRAPH).
</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### SECTION Stability_Level ##### -->


<!-- ##### TYPEDEF rasqal_graph_pattern ##### -->
<para>

</para>


<!-- ##### FUNCTION rasqal_graph_pattern_add_constraint ##### -->
<para>

</para>

@gp: 
@expr: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_add_sub_graph_pattern ##### -->
<para>

</para>

@graph_pattern: 
@sub_graph_pattern: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_get_constraint ##### -->
<para>

</para>

@gp: 
@idx: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_get_constraint_sequence ##### -->
<para>

</para>

@gp: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_get_index ##### -->
<para>

</para>

@gp: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_get_operator ##### -->
<para>

</para>

@graph_pattern: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_get_sub_graph_pattern ##### -->
<para>

</para>

@graph_pattern: 
@idx: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_get_sub_graph_pattern_sequence ##### -->
<para>

</para>

@graph_pattern: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_get_triple ##### -->
<para>

</para>

@graph_pattern: 
@idx: 
@Returns: 


<!-- ##### ENUM rasqal_graph_pattern_operator ##### -->
<para>

</para>

@RASQAL_GRAPH_PATTERN_OPERATOR_UNKNOWN: 
@RASQAL_GRAPH_PATTERN_OPERATOR_BASIC: 
@RASQAL_GRAPH_PATTERN_OPERATOR_OPTIONAL: 
@RASQAL_GRAPH_PATTERN_OPERATOR_UNION: 
@RASQAL_GRAPH_PATTERN_OPERATOR_GROUP: 
@RASQAL_GRAPH_PATTERN_OPERATOR_GRAPH: 
@RASQAL_GRAPH_PATTERN_OPERATOR_LAST: 

<!-- ##### FUNCTION rasqal_graph_pattern_operator_as_string ##### -->
<para>

</para>

@op: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_print ##### -->
<para>

</para>

@gp: 
@fh: 


<!-- ##### USER_FUNCTION rasqal_graph_pattern_visit_fn ##### -->
<para>

</para>

@query: 
@gp: 
@user_data: 
@Returns: 


<!-- ##### FUNCTION rasqal_graph_pattern_visit ##### -->
<para>

</para>

@query: 
@gp: 
@fn: 
@user_data: 
@Returns: 


