Some users’ information needs are very targeted, especially in domain-specific settings. The semantic components model supplements traditional full text and keyword indexing with a semantic description of subdocument content that does not necessarily correspond to structural elements in a document. The model extends typical query languages by allowing user queries to address subdocument components in addition to the whole document. We have evidence from a large interactive user study showing that semantic components can enhance document retrieval in a domainspecific digital library. We now propose to adapt the semantic components approach to improve its scalability for use in large document collections by allowing user indexing, by allowing multiple indexing instances per document, and by introducing an open semantic component schema. The proposed research will examine design issues and implementation options and provide preliminary evaluations of the effect of these adaptations on retrieval performance.