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Ranking Mechanisms in Metadata Information Systems for Geospatial Data

: Göbel, S.; Klein, P.

Fulltext urn:nbn:de:0011-n-157499 (114 KByte PDF)
MD5 Fingerprint: d0da7d1ed762be67cddb3c944691d36f
Created on: 09.11.2007

European Commission, Joint Research Centre -JRC-:
EOGEO 2002. Proceedings
Online im WWW, 2002
13 pp.
Earth Observation & Geo-Spatial Web and Internet Workshop (EOGEO) <2002, Ispra, Italy>
Conference Paper, Electronic Publication
Fraunhofer IGD ()
geodata archive; metadata; information retrieval; spatial ranking

The more information and data are produced in the actual information society, the more important become mechanisms and systems which organize data and provide information where to find which data. Most popular peculiarities of such information systems are digital archives, metadata information systems (MIS) or catalogue systems (CS). Recent initiatives offer access to a wealth of distributed data covered by the widespread information spectrum of different geodata disciplines, but offer only basic levels of interactivity and user assistance to access appropriate geodata and to interact with geospatial data archives. The most important issues to improve usability include semantic aspects (ontologies, formats and terminologies used in the different application areas), information retrieval aspects (interfaces between web portals and metadata servers respectively geospatial data archives as well as ranking aspects) and information visualization aspects (visual support in all phases of the information retrieval process: query formulation, search result presentation and query modification). From the technical point of view, the actual standardization work by technical comitees and working groups such as ISO/TC 211 or OGC provide a great benefit to establish well-defined infrastructures for geodata using common metadata formats (ISO 19115 geographic information - metadata), interface and data exchange mechanisms (SOAP, XML, GML) or other services such as the OGC catalog service. A lot of current initiatives on regional, national or international basis use these standards taking into account usability aspects and offer metadata-based information brokers or web portals to access data archives. Concerning semantic aspects and theme-overlapping approaches a comprehensive state-of-the-art analysis undertaken by the Fraunhofer IGD has shown that especially casual users are not supported by adequate mechanisms and concepts to intuitively dive into the geodata world and its wide range of geodata disciplines and covered information spectra. Often users are not familiar with theme-specific terminology and subsequently are not able to formulate promising queries using well-defined terms for keyword searches. Apart from keyword and fulltext searches most existing MIS for geodata offer geographical access variants using Web-GIS components (e.g. MapXtreme/Java or ACGM plug-in for GeoMedia WebMap) and additional alphanumerical search forms based on metadata formats, elements and attributes (e.g. domain values). Another traditional issue concerning usability of search engines and MIS for geodata targets the interpretation of search results and corresponding search result presentations. Most existing approaches do not offer any ranking mechanisms - at least they are not tranparent to users. In the context of InGeoForum (Information and Cooperation Forum for Geodata in Germany, see [3]) and the InGeo Information Center (see [4]) providing a themeoverlapping web-portal to metadata servers (e.g. cadastral data of surveys or offices) and metadata information systems (e.g. the virtual environmental data catalogue or Terra Map Server as MIS for orthophotos) this paper gives an overview of MIS for geodata and current scientific work referring to the usage of information visualization techniques within the different information retrieval phases to access geodata archives. Based on this state-of-the-art analysis new concepts and mechanisms are presented to improve usability of existing approaches: A theme-overlapping semantic network for geodata builds the basis for an information retrieval and a visualization component to access geodata archives. Here, this paper focuses on information retrieval and ranking aspects. Primarily, spatial ranking mechanisms are discussed taking into account hierarchical structures of gazetteers as well as topological relationships between geographic entities (specified search targets and candidates). Based on these spatial ranking concepts a global (multidimensional) ranking algorithm has been developed including further temporal and thematic ranking aspects/parameters. Practical issues of this multidimensional ranking algorithm are discussed in the context of the ISO 19115 metadata standard (DIS level) for geodata.