We believe that UN/CEFACT and ebXML use as a baseline UML (perhaps adapted to the specific purpose of EDI with the UN/CEFACT version UMM). We have difficulty in understanding how to apply the UML principles to the CCTS especially when we look at the core components. All our analysts use extensively UML and one of the prinicpal interests in ebXML and UN/CEFACT is the strong attachment to UML as it enables us to remain business orientated rather than syntax orientated. The standardisation of core components that can be used within UML seem to be extremely rich to us and we therefore want to align our basic constructs on their UN/CEFACT equivalents. The basic principle of UML is that a class is the description of a set of objects that share the same attributes, operations, methods, relationships and semantics. When one looks at the principles of the CCTS core components where a core component contains only the information pieces necessary to describe a specific concept, one expects a UML class and a core component to be very similar. However, one does not understand the requirement within the CCTS that obliges a basic core component only to be used in a aggregate core component. Why can't an atomic part such as an attribut (BCC) be used within any construct, as is possible in UML? Can one assume that an ASCC is merely an association between two UML classes? There appears to be an inconsistancy between the use of a BCC that can only be referenced through an ACC, however, in a message construct one can mix and mingle both ABIEs and BBIEs as appears in figure 4.2. Thus, since a BBIE is based on a BCC one can construct a structure that contains both ABIEs and BBIEs at the same hierarchical level. Is this correct? This does appear however to be illogical from a UML point of view since an attribute can't be a class. I would appreciate a definition and example of datatype as it appears to be used all over the place with different meanings. My understanding is that it is a set of values and thus only has significance if these values are restricted. Is that correct? My understanding of the CCT is that it corresponds to a UML attribute type and that a BCC corresponds to an UML attribute and finally that an ACC corresponds to a UML class? Is this correct? If this is so, then I assume that the ABIE simply inherits the ACC through a generalisation and that the generalisation itself provides the business context. Is this exact? However, if this is so I therefore have a problem with the BBIE, where does this fit into the UML picture? I assume that the datatype notion can be derived from a constraint on the type using a UML constraint built in OCL. Is this exact? I know I'm asking an awful lot of questions, but since you people have been working so long with the CCTs and UML you have certainly worked all this out already and thus will save me the time in trying to figure out the relationships. Thank you for you comprehension. Regards Michel Hunsicker.