Link services for linked data

Abstract

This thesis investigated the concept of building link services as an extension of Linked Data to improve its navigability (thus improving the linking of the Web of Linked Data). The study first considered the Semantic Web URI and how an agent understands what a URI refers to when dereferencing it. As a result, a generic URI dereferencing algorithm was designed which can be used by any agent to consume Linked Data. The navigability of the Web of Linked Data was then defined - how an agent can follow the links to discover more data. To understand how the Web of Linked Data is connected, this study found 425 million across-datasets URIs (URIs link two different datasets and enable discoverability between datasets) on the Linked Data cloud and only 7.5% of resources are linked to non-local datasets. To improve the navigability of the Web of Linked Data, a list of link services was built. These link services are RESTful services, and takes a link as input and provides a RDF document as output with linking information of the requested URIs. They are: resolution service (retrieves the RDF description of the requested URI for agents), Link extraction service (extracts URIs from a RDF), Linkbase service (third party hosting link relations between datasets, especially for those data which were not originally linked), Reasoning service (applies rules of reasoning to generate a new RDF), Composition service (compose multiple RDF documents into one documents), and Link injection service (inject extra links relations into the client requested RDF document). To use link services, it is almost always requires multiple requests from the clients. Thus, to make the service transparent to the clients and to enable clients to orchestrate link services easily, a link service proxy was built that can be used from the client side with any Linked Data application. When clients request a URI via HTTP, the proxy injects link relations to the requested RDF documents on the fly, hence augmenting Linked Data. The link service proxy was evaluated using four services we built during the enAKTing project: PSI backlink service, sameAs co-reference service, geo-reasoning services, and a link injection service. This work showed that these services alone added 373 million across datasets foreign URIs, which almost doubles the previously mentioned 7.5% across-datasets foreign URIs coverage to the 14%. We also demonstrated how the linked service proxy works dynamically with the Web browser to enrich the Web of Linked Data. As all link services can be easily reused, and programmed to navigate theWeb of Linked Data as well as generating new link services, we believe this provides a basis for agents to consume Linked Data. Following this trend, the Linked Data consumers will only need to orchestrate or create the link services to consume the Web of Linked Data. Any other Web-based Linked Data applications can be understood as specialised services to be built on top of the link services.

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Identifiers

ORCID for Nicholas Gibbins: orcid.org/0000-0002-6140-9956

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