An apparatus comprising a processor, a memory, and communication circuitry, the apparatus being connected to a network via its communication circuitry, the apparatus further comprising computer-executable instructions stored in the memory of the apparatus which, when executed by the processor of the apparatus, cause the apparatus to perform operations comprising: receiving, at a service layer, a request to register information, the information defining a new custom resource type comprising one or more custom resource attributes, wherein the request comprises a resource definition for defining the new custom resource type; integrating the information into operations of the service layer; and exposing the information for discovery by other network apparatuses communicating on the network; wherein the information comprises an XML or JSON Schema Definition of the new resource type located at a Uniform Resource Identifier, URI; characterized in that the apparatus is caused to further perform operations comprising: receiving a request to create a data model mapping for the one or more custom resource attributes, the data model mapping providing one or more URIs of interworked resources and retargeting indicators for indicating when to retarget a retrieve request targeting the interworked resources, the retargeting indicators comprising one of one-time retarget, always retarget, retarget on change and periodic retarget, and the retargeting indicators being independent for resource instances of the new custom resource type; creating the data model mapping at the service layer; receiving, at the service layer, a retrieve request targeting one of the interworked resources; and determining whether to retarget the retrieve request based on the retargeting indicators. receiving, at a service layer, a request to register information, the information defining a new custom resource type comprising one or more custom resource attributes, wherein the request comprises a resource definition for defining the new custom resource type; integrating the information into operations of the service layer; and exposing the information for discovery by other network apparatuses communicating on the network; wherein the information comprises an XML or JSON Schema Definition of the new resource type located at a Uniform Resource Identifier, URI; characterized in that the apparatus is caused to further perform operations comprising: receiving a request to create a data model mapping for the one or more custom resource attributes, the data model mapping providing one or more URIs of interworked resources and retargeting indicators for indicating when to retarget a retrieve request targeting the interworked resources, the retargeting indicators comprising one of one-time retarget, always retarget, retarget on change and periodic retarget, and the retargeting indicators being independent for resource instances of the new custom resource type; creating the data model mapping at the service layer; receiving, at the service layer, a retrieve request targeting one of the interworked resources; and determining whether to retarget the retrieve request based on the retargeting indicators. receiving a request to create a data model mapping for the one or more custom resource attributes, the data model mapping providing one or more URIs of interworked resources and retargeting indicators for indicating when to retarget a retrieve request targeting the interworked resources, the retargeting indicators comprising one of one-time retarget, always retarget, retarget on change and periodic retarget, and the retargeting indicators being independent for resource instances of the new custom resource type; creating the data model mapping at the service layer; receiving, at the service layer, a retrieve request targeting one of the interworked resources; and determining whether to retarget the retrieve request based on the retargeting indicators.