Exploring an appropriate business application published as a Web Service in the UDDI registry is a critical issue. Search for such an application should be effective in terms of time and uniformed in terms interfaces. In this paper, an XML-based UDDI exploring engine that provides developers with standard interfaces for efficiently searching business and service information in single or multiple UDDI registries is proposed. We refer this engine as “Business Explorer for Web Services” (BE4WS). It is based on the proposed UDDI Search Markup Language (USML) for carrying a search request including multiple queries, key words, UDDI sources, and aggregation operators. The Advanced UDDI Search Engine (AUSE), a core component of BE4WS, processes the USML request and performs advanced exploring. The basic idea of an AUSE is to aggregate search results from different UDDI registries based on the USML request and its supporting intelligent search facilities. Examples of these facilities are ...