For many RDF applications, the formulation of constraints and the automatic validation of data according to these constraints is a much sought-after feature. In 2013, the W3C invited experts from industry, government and academia to the RDF Validation Workshop, where first use cases have been presented and discussed. In collaboration with the W3C, a working group on RDF Application Profiles (RDFAP) is currently established in the Dublin Core Metadata Initiative that follows up on this workshop and addresses among others RDF constraint formulation and validation. In this paper, we present a database of requirements obtained from various sources, including the use cases presented at the workshop as well as in the RDF-AP WG. The database, which is openly available and extensible, is used to evaluate and compare several existing approaches for constraint formulation and validation. We present a classification and analysis of the requirements, show that none of the approaches satisfy all requirements and aim at laying the ground for future work, as well as fostering discussions how to close existing gaps.