This part of ISO/IEC 10021 defines the overall system and service of EDI messaging. Other aspects of message handling systems and services are defined in other parts of ISO/IEC 10021. The layout of Standards / Recommendations defining the message handling system and services is showen in table 1 of ISO/IEC 10021-1 / ITU-T Recommendation X/F.400. The public services built on MHS, as well as access to and from the MHS for public services are defined in the ITU-T´s F.400-Series of Recommendations.