The rise of smart applications has drawn interest to logical reasoning over data streams. Recently, different query languages and stream processing reasoning engines were proposed in different communities. However, due to a lack of theoretical foundations, the expressivity and semantics of these diverse approaches are given only informally. Towards clear specifications and means for analytic study, a formal framework is needed to define their semantics in precise terms. To this end, we present a first step towards an ideal semantics that allows for exact descriptions and comparisons of stream reasoning systems.
ETALIS The ETALIS system @cite_16 aims at adding expressiveness to Complex Event Processing (CEP). It provides a rule-based language for pattern matching over event streams with . Simultaneous events are not allowed and windows are not regarded as first-class objects in the semantics, but they are available at the system implementation level. Tuple-based windows are also not directly supported. Furthermore, nesting of windows is not possible within the language, but it can be emulated with multiple rules as in CQL. On the other hand, ETALIS models complex events with time intervals and has operators to express temporal relationships between events.
@cite_16
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Addressing dynamics and notifications in the Semantic Web realm has recently become an important area of research. Run time data is continuously generated by multiple social networks, sensor networks, various on-line services and so forth. How to get advantage of this continuously arriving data events remains a challenge --that is, how to integrate heterogeneous event streams, combine them with background knowledge e.g., an ontology, and perform event processing and stream reasoning. In this paper we describe ETALIS --a system which enables specification and monitoring of changes in near real time. Changes can be specified as complex event patterns, and ETALIS can detect them in real time. Moreover the system can perform reasoning over streaming events with respect to background knowledge. ETALIS implements two languages for specification of event patterns: ETALIS Language for Events, and Event Processing SPARQL. ETALIS has various applicabilities in capturing changes in semantic networks, broadcasting notifications to interested parties, and creating further changes based on processing of the temporal, static, or slowly evolving knowledge.