1. A method for data access, comprising: defining an ontology including a structured vocabulary of entities, types of the entities and relations between the entities, pertaining to a given sphere of knowledge; receiving in a computer a search query generated using the ontology; providing to a user of the computer at least one document in response to the query; receiving in the computer ontological tags, indicating for data elements in the document a semantic nature of the element, associated with data elements in the at least one document; and automatically updating the ontology, by the computer, responsively to the ontological tags.