10,236 research outputs found
Marrying Big Data with Smart Data in Sensor Stream Processing
Widespread deployments of spatially distributed sensors are continuously generating data that require advanced analytical processing and interpretation by machines. Devising machine-interpretable descriptions of sensor data is a key issue in building a semantic stream processing engine. This paper proposes a semantic sensor stream processing pipeline using Apache Kafka to publish and subscribe semantic data streams in a scalable way. We use the Kafka Consumer API to annotate the sensor data using the Semantic Sensor Network ontology, then store the annotated output in an RDF triplestore for further reasoning or semantic integration with legacy information systems. We follow a Design Science approach addressing a Smart Airport scenario with geolocated audio sensors to evaluate the viability of the proposed pipeline under various Kafka-based configurations. Our experimental evaluations show that the multi-broker Kafka cluster setup supports read scalability thus facilitating the parallelization of the semantic enrichment of the sensor data
Multi-Shot Stream Reasoning in Answer Set Programming: A Preliminary Report
In the past, we presented a first approach for stream reasoning using Answer Set Programming (ASP). At the time, we implemented an exhaustive wrapper for our underlying ASP system, clingo, to enable reasoning over continuous data streams. Nowadays, clingo natively supports multi-shot solving: a technique for processing continuously changing logic programs. In the context of stream reasoning, this allows us to directly implement seamless sliding-window-based reasoning over emerging data. In this paper, we hence present an exhaustive update to our stream reasoning approach that leverages multi-shot solving. We describe the implementation of the stream reasoner's architecture, and illustrate its workflow via job shop scheduling as a running example
A Configurable Transport Layer for CAF
The message-driven nature of actors lays a foundation for developing scalable
and distributed software. While the actor itself has been thoroughly modeled,
the message passing layer lacks a common definition. Properties and guarantees
of message exchange often shift with implementations and contexts. This adds
complexity to the development process, limits portability, and removes
transparency from distributed actor systems.
In this work, we examine actor communication, focusing on the implementation
and runtime costs of reliable and ordered delivery. Both guarantees are often
based on TCP for remote messaging, which mixes network transport with the
semantics of messaging. However, the choice of transport may follow different
constraints and is often governed by deployment. As a first step towards
re-architecting actor-to-actor communication, we decouple the messaging
guarantees from the transport protocol. We validate our approach by redesigning
the network stack of the C++ Actor Framework (CAF) so that it allows to combine
an arbitrary transport protocol with additional functions for remote messaging.
An evaluation quantifies the cost of composability and the impact of individual
layers on the entire stack
Heterogeneous reasoning in dynamic environments
We would like to thank K. Schekotihin and the anonymous reviewers for their comments, which helped improving this paper. G. Brewka, S. Ellmauthaler, and J. Puhrer were partially supported by the German Research Foundation (DFG) under grants BR-1817/7-1/2 and FOR 1513. R. Goncalves, M. Knorr and J. Leite were partially supported by Fundacao para a Ciencia e a Tecnologia (FCT) under project NOVA LINCS (UID/CEC/04516/2013). Moreover, R. Goncalves was partially supported by FCT grant SFRH/BPD/100906/2014 and M. Knorr by FCT grant SFRH/BPD/86970/2012.Managed multi-context systems (mMCSs) allow for the integration of heterogeneous knowledge sources in a modular and very general way. They were, however, mainly designed for static scenarios and are therefore not well-suited for dynamic environments in which continuous reasoning over such heterogeneous knowledge with constantly arriving streams of data is necessary. In this paper, we introduce reactive multi-context systems (rMCSs), a framework for reactive reasoning in the presence of heterogeneous knowledge sources and data streams. We show that rMCSs are indeed well-suited for this purpose by illustrating how several typical problems arising in the context of stream reasoning can be handled using them, by showing how inconsistencies possibly occurring in the integration of multiple knowledge sources can be handled, and by arguing that the potential non-determinism of rMCSs can be avoided if needed using an alternative, more skeptical well-founded semantics instead with beneficial computational properties. We also investigate the computational complexity of various reasoning problems related to rMCSs. Finally, we discuss related work, and show that rMCSs do not only generalize mMCSs to dynamic settings, but also capture/extend relevant approaches w.r.t. dynamics in knowledge representation and stream reasoning.publishe
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