DSCEP: An Infrastructure for Decentralized Semantic Complex Event Processing
Many applications require the processing of event streams from different sources in combination with large amounts of background knowledge. Semantic CEP is a paradigm designed specifically for that. It extends complex event processing (CEP) with RDF support and uses a network of operators to process RDF streams in combination with RDF knowledge bases. Another popular class of systems designed for a similar purpose are the RDF stream processors (RSPs). These are systems that extend SPARQL (the RDF query language) with stream processing capabilities. Semantic CEP and RSPs have similar purposes but focus on different things. The former focuses on scalability and distributed processing while the latter tend to focus on the intricacies of RDF stream processing per se. In this paper we propose the use of RSP engines as building blocks for Semantic CEP. We present an infrastructure, called DSCEP, that allows the encapsulation of existing RSP engines into CEP-like operators so that these can be seamlessly interconnected in a distributed, decentralized operator network. DSCEP handles the hurdles of such interconnection, such as reliable communication, stream aggregation and slicing, event identification and time-stamping, etc., allowing users to concentrate on the queries. We also discuss in the paper how DSCEP can be used to speedup monolithic SPARQL queries by splitting them into parallel subqueries operating over restricted parts of the knowledge base.