A service-oriented system architecture includes a computer-implemented search method and computer-implemented agent system for enabling efficient information searches on, for example, on XML databases, relational databases, and files located on intranets, the Internet, or other computer network systems. Referred to as the Knowledge Sifter architecture, the architecture may comprise, in one embodiment, a community of cooperating agents. The system architecture may be employed using a variety of methodologies, such as a case-based framework, collaborative filtering, or hybrid filtering. The case-based framework may be configured to recommend query specifications and refinements based on previously-stored user-query cases. Collaborative filtering involves the architecture recommending a set of unseen items that are preferred by other users to the active user. Hybrid filtering combines collaborative filtering and content-based filtering.