Collections, i. e., sets, bags, ordered sets and sequences, play a central role in UML and OCL models. Essential OCL operations like role navigation, object selection by stating properties and the first order logic universal and existential quantifiers base upon or result in collections. In this paper, we show a uniform representation of flat and nested, but typed OCL collections as well as strings in form of flat, untyped relations, i. e., sets of tuples, respecting the OCL particularities for

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... nesting, undefinedness and emptiness. Transforming collections and strings into relations is particularly needed in the context of automatic model validation on the basis of a UML and OCL model transformation into relational logic.