The following constraint selects on all documents whose Type property is equal to this document's referenced Service's Type. 

$<Type>=[${Service->Type}]

Here is a similar constraint, but this time the property may contain multiple services.

$<Type>~(${Services->Type})

In this case the type must match any one type value of the referenced services.

To match with deep linked values with the matching document, which is on the left side, the value is required to be materialized.

$<Type->Tags>=[${Tags}]

Again a similar constraint using lists.

$<Categories->Tags>=[${Tags}]

For these queries to work, the properties on the left side (Type->Tags respectively Categories->Tags) are required to be materialized.

Materialization can have three forms