Properties whose values are bound to a select list are annotated with the Com.Ingr.Vocabularies.Core.V1.SelectListId term.
If you inspect the annotations metadata document for the SampleService at the following URL, you will discover two Pipe properties that derive values from select lists:
https://sam.spclouddave.com/SampleService/Sppid/V2/Annotations/$metadata
<Annotations Target="Com.Ingr.Sppid.V1.Pipe/InsulPurpose">
<Annotation Term="Com.Ingr.Vocabularies.Core.V1.SelectListId" String="InsulPurpose"/>
.
</Annotations>
<Annotations Target="Com.Ingr.Sppid.V1.Pipe/InsulSpec">
<Annotation Term="Com.Ingr.Core.V1.DependsOn" PropertyPath="InsulPurpose" />
<Annotation Term="Com.Ingr.Vocabularies.Core.V1.SelectListId" String="InsulSpec"/>
.
</Annotations>