Cascading Geospatial Services for Integration of Authoritative National Datasets – CASE: European Location Framework
ISBN 978-85-88783-11-9
Authors
1Lehto, L.; 2Latvala, P.; 3Kähkönen, J.
1FINNISH GEODETIC INSTITUTE Email: lassi.lehto@fgi.fi
2FINNISH GEODETIC INSTITUTE Email: pekka.latvala@fgi.fi
3FINNISH GEODETIC INSTITUTE Email: jaakko.kahkonen@fgi.fi
Abstract
Providing European-wide access to geospatial data resources held on national level is the ambitious goal of the Infrastructure for Spatial Information in the European Community (INSPIRE) process and other similar integration initiatives. Service cascade is presented in this paper as a solution for facilitating access to national content to support Pan-European applications. The paper presents the process of providing centralized access point to geospatial data requested from several national INSPIRE-compliant Download Services. The research described in this paper has been conducted in the context of a major EU project, called European Location Framework (ELF), initiated by EuroGeographics (EG), the co-operation organization of the European National Mapping and Cadastral Agencies (NMCAs). The ELF project aims at developing European-wide INSPIRE-compliant services based on geodata resources maintained by the EG’s membership. The ELF project started in March 2013 and will run for three years. The project has 30 participant organizations, 13 of them representing EU/EFTA member states as official NMCAs. Thus, the data resources accessible by the project have quite extensive spatial coverage across Europe. The ELF project includes a work package specifically dedicated for data provision and service development. In this work package there is a subtask responsible for investigating the issues related to service cascade. The approach presented in this paper covers this development and focuses specifically on the provision of European level download services based on data services delivering content on national level. The concept of service cascade is evaluated in this paper as the solution for the data aggregation requirement. According to the service architecture model of the Open Geospatial Consortium (OGC), the basic idea in service cascade is that a service end point can be configured as a content source for another service, actually making this latter service a client of the source service. Service cascade can be regarded as an implementation of the basic INSPIRE principle, according to which European level Spatial Data Infrastructures (ESDIs) can be built on top of national level SDIs. This can be seen as the most cost-effective way for building services on multiple levels of local administration as well. In the past, service cascade has been studied for instance in the context of metadata services integration. The goal is to support the end user in accessing geospatial data content both as pre-aggregated on European level, and directly from national services. Thus, the cascading approach aims at supporting real-time aggregation of content from a set of distributed national data sources. One of the new challenges encountered when accessing national services from European-level applications is the need to introduce spatial integration capabilities to the traditional service cascade approach. At the moment only thematic integration is supported in the existing cascade mechanisms of the OGC service implementations. In this setup every single feature class is served by one and only one back-end service. When implementing cascaded integration over a set of national services, one has to resolve the problem of spatial query distribution and cross-border fusion of geospatial content. Another useful functionality for a cascading service in the context of data download is to convert the INSPIRE-compatible Geography Markup Language (GML) -encoded content coming from the back-end download services into a more Web-friendly format, like JavaScript Object Notation (JSON). This reformatted content could then be made available via modern Web interfaces as interactive end user applications. The solutions developed in the project for these challenges are discussed in detail in the final paper.
Keywords
service cascade; data aggregation; European SDI