The university library of Erlangen-Nürnberg harbors not only historic manuscripts and monographs but also valuable paintings, graphics, coins, etc. These cultural objects form part of the university’s rich and heterogeneous collections, ranging from anatomy and archaeology to school history and zoology. Embedded in a broader digitization strategy, the project "Objekte im Netz” develops a documentation and research platform together with a data model based on semantic web technologies and guidelines to provide means to ensure homogeneous data modelling and minimum data quality across the collections. Eventually, they shall provide scholars the means to work on transdisciplinary research questions, too. The tool builds upon the open source WissKI software, a virtual research environment for cultural heritage that natively stores data using RDF. The common data model is implemented as an OWL ontology that extends the CIDOC CRM and acts as the integrating link between the collections, and also to external sources. This presentation will focus on the integration of the university library's metadata of historic graphics: The metadata can be harvested as MARCXML from different systems and has to be transformed into RDF data aligned with the CIDOC CRM. Following a sketch of the general set-up, an outline of the practical integration steps will be given with a discussion of different technical and data mapping approaches, among others a mapping from BIBFRAME to CIDOC CRM. The discussion is accompanied by remarks on challenges and hindrances met so far, like the lack of officially coined URIs and ontology mismatches.