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A MOF meta-model is an abstract language for defining the types of meta-data. The M2-level constructs used in a metamodel
map onto M1-level representations as MOF values. The types of these M1-level values can be defined using either M2-level Classes
or M2-level DataTypes.
An M2-level Class defines an M1-level Instance type with the following properties:
• Instance typed objects have full object identity; that is, it is always possible to reliably distinguish one instance (object) from another. Object identity is intrinsic and permanent, and is not dependent on other properties such as attribute values.
• Instance typed objects can be linked via an Association.
• Null is a valid instance of an M2-level Class, though there are limitations on its use. By contrast, an M2-level DataType
defines a type with the following properties:
• Data typed values do not have full object identity; see below.
• Data typed values cannot be linked via an Association.
• Null is not a valid instance of an M2-level DataType.