The ServiceID is an urn in the format urn:etoegang:DV:<OIN>:services:<index> where <OIN> represents the OIN of the service provider.
Registered services MUST have an index of 1 or higher. A portal function is specified (in messages and in the Service catalog) by the reserved index with value '0'. When an index with value '0' is used in a request, then a multivalued ServiceID MAY be returned in the response, representing all ServiceID's for which the subject has a registered authorization.
Although they look similar, EntityID's are not to be confused with ServiceID's. There is an n:n relationship between EntityID's and ServiceID's. One system may offer more than one service, or the other way around: more systems can offer the same service.