Composition of semantically enabled geospatial web services

Abstract

Applications such as disaster and emergency management require near-instant access to data from different sources to make decisions and take actions rapidly. Although previous experiences have shown that the geospatial data availability in many scenarios is not a problem, this data is usually provided from multiple heterogeneous data sources distributed over the web, requiring the data to be discovered and integrated. Also, the data not necessarily is ready to be used, requiring preprocessing steps to turn it into actionable information. Although OGC standards have made significant progress towards syntactic interoperability of services and feature-level data access, they do not solve semantic heterogeneity problems. At the same time, Semantic Web Technology can provide semantic interoperability but has had a slow uptake, since it is complex and does not follow current trends for data formats and access, thereby heading in an opposite direction of what developers and users expect. Even for services that provide semantically enabled data, service discovery and manual composition in a distributed environment are still time-consuming and error-prone. Typically, one must select multiple data provision services, and apply the processes with the need to understand their functionality and input /output restrictions. As a consequence of these difficulties, there is a lack of tools and methods to facilitate the construction, verification and execution of composition of geospatial web services. This research project aims to address limitations on service composition verification, execution, and sharing. We develop a theoretically founded environment in which geospatial service composition can be verified. The theory formally defines what composability of semantically enabled geospatial web services is, providing a base for the development of an algorithm for verifying the composability of services, which grants compile-time protection against a class of errors. This protection allows not to run an invalid composition that could lead to unnecessary long running time as well high usage of the server processing capabilities. This thesis also provides guidelines for defining lightweight services for sharing, processing geospatial data and for cataloguing geospatial data and services based on OGC Standards, and on current trends in web technology, such as REST architecture, WebSockets, and JSON-LD. We expect that the proposed services will facilitate the implementation of OGC standards and lower the need for third-party software. We also extend the OGC services to be semantically enabled, providing service functionality descriptions by using the Hydra Core Vocabulary. These descriptions allow applications to discover and use web services without being specifically programmed for each service, lowering human interaction, and allowing the implementation of a generic client. Lastly, we develop JSON-W, a notation to describe and share compositions which allow a lossless roundtrip to RDF serialization. This makes the compositions interoperable and at the same time maintain the ease to use and transfer to the Web of the JSON format.