Abstract
Abstract. In this study, a prototype service to provide data from Web Feature Service (WFS) as linked data is implemented. At first, persistent and unique Uniform Resource Identifiers (URI) are created to all spatial objects in the dataset. The objects are available from those URIs in Resource Description Framework (RDF) data format. Next, a Web Ontology Language (OWL) ontology is created to describe the dataset information content using the Open Geospatial Consortium’s (OGC) GeoSPARQL vocabulary. The existing data model is modified in order to take into account the linked data principles. The implemented service produces an HTTP response dynamically. The data for the response is first fetched from existing WFS. Then the Geographic Markup Language (GML) format output of the WFS is transformed on-the-fly to the RDF format. Content Negotiation is used to serve the data in different RDF serialization formats. This solution facilitates the use of a dataset in different applications without replicating the whole dataset. In addition, individual spatial objects in the dataset can be referred with URIs. Furthermore, the needed information content of the objects can be easily extracted from the RDF serializations available from those URIs. A solution for linking data objects to the dataset URI is also introduced by using the Vocabulary of Interlinked Datasets (VoID). The dataset is divided to the subsets and each subset is given its persistent and unique URI. This enables the whole dataset to be explored with a web browser and all individual objects to be indexed by search engines.
Highlights
Many initiatives to facilitate the integration of spatial data to other available datasets have been introduced
Some prominent recent initiatives for geographic linked data are the collaboration of Open Geospatial Consortium (OGC) and World Wide Web Consortium (W3C) to improve interoperability and integration of geospatial information with data on the Web (W3C 2015) and OGC's GeoSPARQL standard, which provides spatial operations for SPARQL and a Resource Description Framework (RDF) vocabulary to describe geometries and topology (OGC 2012)
The service parses the Uniform Resource Identifiers (URI) and makes a Web Feature Service (WFS) Query according to the URI, sends the query to NLSF WFS, creates RDF according to the response and returns the RDF data to the client in desired serialization format
Summary
Many initiatives to facilitate the integration of spatial data to other available datasets have been introduced. Generic transformation from GML to RDF will lose the domain specific semantics defined in UML (Unified Modeling Language) model. These tools may provide a possibility for user to define the mappings from the GML schema to existing Web Ontology Language (OWL) vocabularies The OWL ontology is created according to the improved UML/GML (Unified Modeling Language) data model of the original dataset. A custommade on-the-fly transformation process from GML to RDF is implemented to provide the spatial objects from the individual URIs. Existing OGC Web Feature Service (WFS) is used as a source. The purpose of the study is to find out if such an on-the-fly transformation can be implemented and to find working solution for creating an OWL ontology from the UML/GML data model. The ways to link the objects to the dataset and to divide the dataset into the subsets in order to make the whole dataset browsable with those links are sought
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