Exploratory search is about browsing and understanding an information base. It requires a more interactive process than retrieval search, where the user sends a query and the system returns answers. Logical Information Systems (LIS) support exploratory search by guiding users in the construction of queries, and by giving summaries of query results. The contribution of this paper is to adapt and extend LIS to the Semantic Web. We define a summarization and navigation data structure that provides rich views over data, and guides users from view to view. This guiding is proved consistent (i.e., never leads to an empty result set), and complete (i.e., every query can be reached by navigation only). The query language covers a large fragment of SPARQL, and is more concise by using a syntax close to description logics. Our approach could be implemented on top of existing tools for storing, reasoning and querying.