XMI21 — How to serialize values of the PrimitiveType UnlimitedNatural

The XMI is not explicit as to how to serialize values of the PrimitiveType UnlimitedNatural. In practice, and in the normative metamodels for UML as well as MOF, the value ‘’ has been used to represent ‘unlimited’ (as opposed to the value ‘-1’ which was used at UML/MOF 1.x). Rule 2i in section 6.3 states: Use this production rule to serialize an attribute whose type is not an object and whose value can be represented by a string. Multi-valued attributes cannot be serialized as XML attributes. If the attribute’s type is one of the types defined by the XML Schema Part 2: Datatypes specification, serialize the value as specified in that specification. PROPOSED RESOLUTION Add the following sentence to the end of the above paragraph: “Unless specified otherwise, values of other types may be serialized as strings using any permitted visual notation for that type. This applies to values for the Primitive Type UnlimitedNatural, where unlimited is serialized, as well as displayed, as ‘’.