The Directory standard is a joint effort of the International Organization for Standardization / International Electrotechnical Commission (ISO/IEC) and The International Telephone and Telegraph Consultative Committee (CCITT). The standard is published jointly as ISO/IEC 9594 and as the CCITT X.500 series of recommendations. In general, the Directory adheres to a client/server paradigm, with the clients referred to as Directory User Agents (DUA) and the servers as Directory System Agents (DSA). This section provides a high-level overview of how the Directory is modeled in terms of architectural components and how the components relate to each other.