materials instances

Other Standards COLLADA
1

hy.
I have the attached file.
I have a doub on this mesh (mesh2):


 <node id="mesh2" name="mesh2">
                  <instance_geometry url="#mesh2-geometry">
                     <bind_material>
                        <technique_common>
                           <instance_material symbol="material_1_1_0" target="#material_1_1_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_5_4_0" target="#material_5_4_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_9_8_0" target="#material_9_8_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_3_16" target="#material_3_16ID"/>
                           <instance_material symbol="material_16_15_0" target="#material_16_15_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_7_6_0" target="#material_7_6_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_0_16" target="#material_0_16ID"/>
                           <instance_material symbol="material_11_19_0" target="#material_11_19_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_8_7_0" target="#material_8_7_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_11_10_0" target="#material_11_10_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_10_9_0" target="#material_10_9_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_12_11_0" target="#material_12_11_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_17_16_0" target="#material_17_16_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_18_17_0" target="#material_18_17_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_15_14_0" target="#material_15_14_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_4_3_0" target="#material_4_3_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_20_20_0" target="#material_20_20_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_2_2_0" target="#material_2_2_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_19_18_0" target="#material_19_18_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_13_12_0" target="#material_13_12_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_14_13_0" target="#material_14_13_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                           <instance_material symbol="material_21_21_0" target="#material_21_21_0ID">
                              <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0"/>
                           </instance_material>
                        </technique_common>
                     </bind_material>
                  </instance_geometry>
               </node>

why so many materials?
and What should I do in my collada importer?
my game engine only accept one effect at once.
What I doing with all those materials

2

Apparently you have a mesh with a lot of textures. The bind_material elements are providing the mapping to the appropriate texture coordinates for each material.