The need for descriptive information, i.e., metadata, about Web resources has been recognized in several application contexts (e.g., digital libraries, portals). The Resource Description Framework (RDF) aims at facilitating the creation and exchange of metadata, as directed labeled graphs serialized in XML. In particular, the definition of schema vocabularies enables the interpretation of semistructured RDF descriptions using taxonomies of node and edge labels. In this paper, we propose (i) a formal model capturing RDF schema constructs; (ii) a declarative query language featuring generalized path expressions for taxonomies of labels (iii) a metadata management architecture for efficient storage and querying of RDF descriptions and schemas.