A comparison of BIBFRAME and RDA in RDF (referred to below as RDA), in an attempt to map RDA to BIBFRAME, raised the issue of constrained vs unconstrained schemas. The full set of RDA properties is constrained by the RDA classes of Agent, Work, Expression, Manifestation and Item. That is, each property is related to a specific class when appropriate: e.g. abridgementOfExpression and abridgementOfWork. A parallel set of properties has been created where the constraints of class are lifted: e.g. abridgementOf. This unconstrained version of RDA loses the context of some properties but is intended to facilitate mapping to schemas that do not use the FRBR model underlying RDA. BIBFRAME is a constrained schema, but constrained by different classes: Agent, Work, and Instance. There is no unconstrained version of BIBFRAME. A mapping of RDA to BIBFRAME presents choices and challenges. Is it better to use constrained RDA, which causes explicit conflicts of domain: e.g. mapping rdam:reproductionOfManifestation to bf:reproduction and rdai:reproductionOfItem to bf:reproduction? Or is it better to use unconstrained RDA, which still has conflicts (an unconstrained domain vs a constrained one in BIBFRAME): e.g. mapping rdau:reproductionOf to bf:reproduction? It is not obvious which is the better choice. Although perhaps we need both mappings, each with its own problems regarding original and destination domains. A corollary of the question is that any roundtrip RDA -> BF -> RDA is lossy. If constrained RDA is used as a starting point, RDA classes are lost in the mapping itself, and if unconstrained RDA is used, classes are lost prior to mapping. Either way, RDA classes cannot be recovered in a BF -> constrained RDA mapping.