Various versions of an ORM 1 metamodel have been published, e.g.
Cuyler, D. & Halpin, T. 2003, 'Metamodels for Object-Role Modeling', Proc. EMMSAD’03: 8th IFIP WG8.1 Int. Workshop on Evaluation of Modeling Methods in Systems Analysis and Design, Velden, Austria (June).
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