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<Title>Property</Title>
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<H2><A NAME="concept:PropertyTag"></A>
PropertyTag
</H2>

A Property Tag is a type used to name or identify properties that are
attached to the vertices and edges of a graph. A Property type is not
the type of the actual property values. Objects of the Property type
are not used except to carry the type information which specifies the
property. See the section about <A
href="using_adjacency_list.html#sec:custom-edge-properties"> Custom
Edge Properties</a> for a description of how to define your own
property tags.


<h3>Associated Types</h3>

<table border>

<tr>
<td>Property Kind </td>
<td><TT>property_kind&lt;PropertyTag&gt;::type</TT> </td>
<td>

This specifies whether the property is a <a
name="VertexPropertyTag"><b>Vertex Property Tag</b></a>
(<tt>vertex_property_tag</tt>), an <a
name="EdgePropertyTag"><b>Edge Property Tag</b></a> (<tt>edge_property_tag</tt>), or
a <a name="GraphPropertyTag"><b>Graph Property Tag</b></a> which is attached to the
graph object itself (<tt>graph_property_tag</tt>). The tags are
defined in <a
href="../../../boost/graph/properties.hpp"><tt>boost/graph/properties.hpp</tt></a>. The <tt>property_kind</tt> traits class is defined in <a href="../../../boost/pending/property.hpp"><tt>boost/pending/property.hpp</tt></a>.

</td>
</tr>

<tr>
<td>Property ID Number </td>
<td><TT>property_num&lt;PropertyTag&gt;::value</TT> </td>
<td>
This is needed as a workaround when using compilers that do not
support partial specialization (and hence prevent us from using
<tt>boost::is_same</tt> to detect if two property tags are the same).
The <tt>property_num</tt> traits class is defined in <a
href="../../../boost/pending/property.hpp"><tt>boost/pending/property.hpp</tt></a>.
</td>
</tr>

</table>

<h3>Refinement of</h3>

<a
href="http://www.sgi.com/tech/stl/DefaultConstructible.html">Default Constructible</a> 


<h3>Models</h3>

The following models of the Property Tag concept are defined
in <a
href="../../../boost/graph/properties.hpp"><tt>boost/graph/properties.hpp</tt></a>.

<ul>
  <li><tt>vertex_index_t</tt></li>
  <li><tt>edge_index_t</tt></li>
  <li><tt>graph_name_t</tt></li>
  <li><tt>vertex_name_t</tt></li>
  <li><tt>edge_name_t</tt></li>
  <li><tt>edge_weight_t</tt></li>
  <li><tt>vertex_distance_t</tt></li>
  <li><tt>vertex_color_t</tt></li>
  <li><tt>vertex_degree_t</tt></li>
  <li><tt>vertex_out_degree_t</tt></li>
  <li><tt>vertex_in_degree_t</tt></li>
  <li><tt>vertex_discover_time_t</tt></li>
  <li><tt>vertex_finish_time_t</tt></li>
</ul>

<h3>See Also</h3>

<a href="./PropertyGraph.html">PropertyGraph</a>
and
<a href="../../property_map/doc/property_map.html">Property Map Concepts</a>

<h3>Notes</h3>

On compilers that do not support partial specialization, each Property
type is also required to specialize
<tt>property_num&lt;PropertyTag&gt;</tt> to contain an enum named
<tt>value</tt> which uniquely identifies the property type.

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<TD nowrap>Copyright &copy; 2000-2001</TD><TD>
<A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, Indiana University (<A HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)
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