Event-based middleware is emerging as the major paradigm for large-scale and widely distributed systems, especially sensor-rich environments. Here, many primitive events are low-level and effort has been directed towards defining more meaningful composite events, which are typically recognised by finite-state machines. We argue that finite-state-machines (FSMs) are insufficient for meeting the requirements of users in Sentient Computing environments; user intuition may be concerned with notions such as state and negation which FSMs cannot support with reasonable efficiency. We aim to support querying and subscribing transparently to distributed state, which necessitates an alternative model for Sentient Computing. We propose a state-based, temporal first order logic (TFOL) model whose implementation is based on a deductive knowledgebase. Furthermore, we propose a generalised notion of an event, an abstract event, which we define as a notification of transparent changes in distributed state. An extension to the publish/subscribe protocol is discussed, in which a higher-order service (Abstract Event Detection Service) publishes its interface; this service takes a TFOL abstract event definition as an argument and in return publishes an interface to a further service (an abstract event detector) which notifies transitions between the values true and false of the formula, thus providing a more natural and efficient interface to applications.
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