Implementing an included odata service

Hi experts, I included an OData service into a standard SAP OData service. The association I want to create is from standard SAP entity Contact to custom developped AttributeName and should be addressable by this URI /ContactCollection(contactID='2000000165',accountID='41000104')/Attributes. After importing my Odata service, I created an association, associationset and navigation property (Attributes). My navigation works and I can implement the get_entityset in my included OData service. However at runtime I do not receive the necessary contactID and accountID in my IT_KEY_TAB or any other variable. How can I know the contactID and accountID???

Your help is appreciated. Kind regards