Abstract
Semantic interoperability for the Internet of Things (IoT) is enabled by standards and technologies from the Semantic Web. As recent research suggests a move towards decentralised IoT architectures, we have investigated the scalability and robustness of RDF (Resource Description Framework)engines that can be embedded throughout the architecture, in particular at edge nodes. RDF processing at the edge facilitates the deployment of semantic integration gateways closer to low-level devices. Our focus is on how to enable scalable and robust RDF engines that can operate on lightweight devices. In this paper, we have first carried out an empirical study of the scalability and behaviour of solutions for RDF data management on standard computing hardware that have been ported to run on lightweight devices at the network edge. The findings of our study shows that these RDF store solutions have several shortcomings on commodity ARM (Advanced RISC Machine) boards that are representative of IoT edge node hardware. Consequently, this has inspired us to introduce a lightweight RDF engine, which comprises an RDF storage and a SPARQL processor for lightweight edge devices, called RDF4Led. RDF4Led follows the RISC-style (Reduce Instruction Set Computer) design philosophy. The design constitutes a flash-aware storage structure, an indexing scheme, an alternative buffer management technique and a low-memory-footprint join algorithm that demonstrates improved scalability and robustness over competing solutions. With a significantly smaller memory footprint, we show that RDF4Led can handle 2 to 5 times more data than popular RDF engines such as Jena TDB (Tuple Database) and RDF4J, while consuming the same amount of memory. In particular, RDF4Led requires 10%–30% memory of its competitors to operate on datasets of up to 50 million triples. On memory-constrained ARM boards, it can perform faster updates and can scale better than Jena TDB and Virtuoso. Furthermore, we demonstrate considerably faster query operations than Jena TDB and RDF4J.
Highlights
IntroductionThe Internet of Things (IoT) proposes to connect a vast amount of everyday devices (“things”)
The Internet of Things (IoT) proposes to connect a vast amount of everyday devices (“things”)to the Internet to enable innovative and smarter domestic and commercial services [1]
We introduce a RISC-Style Resource Description Framework (RDF) engine design based on observations drawn from an empirical study of the performance of PC-based RDF engines running on lightweight edge devices
Summary
The Internet of Things (IoT) proposes to connect a vast amount of everyday devices (“things”). Such devices are powerful enough to run a fully-functional Linux distribution that are efficient in power consumption Their small size makes them easier to deploy or embed in other IoT devices (e.g., sensors and actuators), which provides reasonable computing resources. They can be placed on the network edge, as edge devices, i.e., data-processing gateways that interface with outer networks. This gateway can be fitted into a lamp pole on a street or at a traffic junction, sharing a power source powered by a small solar panel Despite their advantages in power consumption, size and cost-effectiveness, lightweight edge devices are significantly under-equipped in terms of the memory and CPU for supporting regular RDF engines.
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