Developers can define different kinds on constraints on model attributes. The general grammar of constraints are defined in the TQL Model grammar There are two types of references

Simple Reference

Simple reference is defined using name and type modifier. The data associations between two models is automatically done via SID. 

<Reference cardinality="1..1" name="reference name" type="name of model/def"/>

In this example thingCat is a reference attribute of VendorInfo. thingCat References 1 (cardinality is 1) instance of ThingCategory. The value of thingCat must be the SID of the ThingCategory instance.

<DataModel Name="VendorInfo">
      <Sid Name="vendorId"/>
      <String Name="vendorName"/>
      <String Name="vendorCity"/>
      <Reference cardinality="1..1" name="thingCat" type="ThingCategory"/>
</DataModel>
<DataModel Name="ThingCategory">
      <Sid Name="thingCatID"/>
      <String Name="catList" cardinality="1..n"/>
</DataModel>


<!-- Let's Create few Thing Categories. -->
<Query>
  <DeleteAll>
    <ThingCategory>
      <thingCatID ne=""/>
    </ThingCategory>
  </DeleteAll>
  <Create>
    <ThingCategory>
      <catList>
        Sensors
      </catList>
    </ThingCategory>
  </Create>
  <Create>
    <ThingCategory>
      <catList>
        Actuators
      </catList>
    </ThingCategory>
  </Create>
  <Create>
    <ThingCategory>
      <catList>
        Sensors
      </catList>
      <catList>
        Actuators
      </catList>
      <catList>
        Gateways
      </catList>
    </ThingCategory>
  </Create>
</Query>


<!-- Now create VendorInfo with ThingCategory SID Value -->
<Query>
  <Create>
    <VendorInfo>
      <vendorId>
        vendorA
      </vendorId>
      <vendorName>
        Phidget
      </vendorName>
      <vendorCity>
        Calgary
      </vendorCity>
      <thingCat>
        LOBF4FOGAAAX6AAAAGEWWHEH
      </thingCat>
    </VendorInfo>
  </Create>
</Query>


<!-- Let's do a Find on VendorInfo with nested * -->
<Query>
  <Find format="all" nested="*">
    <VendorInfo>
      <vendorId ne=""/>
    </VendorInfo>
  </Find>
</Query>

Smart Reference