Disclosed is a system architecture, components and a searching technique for an Unstructured Information Management System (UIMS). The UIMS may be provided as middleware for the effective management and interchange of unstructured information over a wide array of information sources. The architecture generally includes a search engine, data storage, analysis engines containing pipelined document annotators and various adapters. The searching technique makes use of a two-level searching technique. A search query includes a search operator containing of a plurality of search sub-expressions each having an associated weight value. The search engine returns a document or documents having a weight value sum that exceeds a threshold weight value sum. The search operator is implemented as a Boolean predicate that functions as a Weighted AND (WAND).