The present document analyses and evaluates the definition of a Reference Data Model (RDM) for Ud interface between Front-Ends (FEs) for the HSS application and the User Data Repository (UDR). The stage 3 of the Ud interface in the User Data Convergence (UDC architecture) is defined in TS 29.335. The Reference Data Model (RDM) shall comply with the Common Baseline Information Model for UDC as defined in TS 32.182 and it shall follow the concepts of the Framework for Model Handling and Management as defined in TS 32.181. The analysis will comprise the general considerations impacting the RDM for HSS. The analysis will comprise the following topics:

• The general considerations impacting the RDM for HSS;
• Attributes definition: names, syntax, semantics;
• Object classes & Directory Information Tree: object classes names, attributes grouping, LDAP entries, Distinguished Names and Relative Distinguished Names.

Directory information trees, object classes and attributes in this report should be considered informative since they are subject to additions and/or modification depending on the specific implementation as illustrated in the presented alternatives in this technical report. Even the assignment of attributes to object classes may be redistributed, for example,because the normalization of object classes across different domains may result in attributes being moved to a superclass. Naming is provisional. Diagrams used and naming convention are not standardized.