Global Drought Monitoring Service through the GEOSS Architecture ...
Global Drought Monitoring Service through the GEOSS Architecture ...
Global Drought Monitoring Service through the GEOSS Architecture ...
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Architectural Implementation Pilot, Phase 3 Version: 2.0<br />
<strong>Global</strong> <strong>Drought</strong> <strong>Monitoring</strong> and European <strong>Drought</strong><br />
Observatory-Water SBA Engineering Report<br />
Date: 11/Feb/2011<br />
documents, a W3C standard) syntax for queries. However, <strong>the</strong> DAC was conceived to be flexible<br />
and federate also semantic services that use different interfaces.<br />
The DAC shall also provide an interface (towards <strong>the</strong> presentation layer) for being<br />
queried with any combination of semantic, geospatial and free text constraints. At <strong>the</strong> time being<br />
<strong>the</strong>re is no well-recognized standard interface or syntax allowing such combined queries. Hence,<br />
<strong>the</strong> choice was to use <strong>the</strong> lightweight OpenSearch 44 interface. The OpenSearch is a basic<br />
interface, allowing querying a catalogue with a simple free text search. There exist several<br />
extensions of <strong>the</strong> basic OpenSearch syntax; two widely used extensions to submit geospatial<br />
queries are:<br />
• Geo extension: allows to specify a spatial extent/location as constraint in a query;<br />
• Time extension: allows building queries based on time and time spans constraints.<br />
In addition to <strong>the</strong> above extensions, we defined a “Concept-driven” extension to allow <strong>the</strong><br />
discovery of well-defined concepts and relations between concepts form semantic services.<br />
These three extensions form <strong>the</strong> DAC query interface.<br />
A detailed documentation describing <strong>the</strong> “Concept-driven” extension will soon be<br />
published on <strong>the</strong> OpenSearch Web Site. The AIP-3 Engineering Report Best Practices Wiki 45<br />
will be updated as soon as <strong>the</strong> detailed documentation will be available.<br />
5.6 Operation of <strong>the</strong> Water Ontology within <strong>the</strong> Euro<strong>GEOSS</strong> Discovery<br />
Augmentation Component<br />
5.6.1 Searching for Concepts/Terms<br />
Euro<strong>GEOSS</strong> DAC communicates with <strong>the</strong> GENESIS Vocabulary <strong>Service</strong> using SPARQL<br />
interface. According to user’s request <strong>the</strong> Euro<strong>GEOSS</strong> DAC performs different actions:<br />
1. When <strong>the</strong> user has searched for concepts/terms related to a keyword of interest (e.g.<br />
“drought”), <strong>the</strong> Euro<strong>GEOSS</strong> DAC performs a “GetConcepts” request; that is,<br />
Euro<strong>GEOSS</strong> DAC builds a SPARQL query to retrieve from <strong>the</strong> GENESIS<br />
Vocabulary <strong>Service</strong> all concepts/terms containing <strong>the</strong> searched keyword in <strong>the</strong> label<br />
and/or in <strong>the</strong> description. The matching concepts/terms are returned to <strong>the</strong><br />
Euro<strong>GEOSS</strong>/GENESIS Client Application.<br />
2. When <strong>the</strong> user is extending a set of concepts/terms, <strong>the</strong> Euro<strong>GEOSS</strong> DAC<br />
transforms <strong>the</strong> selected relation type (e.g. “more specific concepts”) into formal<br />
SKOS relations (e.g. skos: narrower and skos: narrowMatch). Using <strong>the</strong>se relations<br />
a set of SPARQL queries is executed, and matching concepts/terms are returned to<br />
<strong>the</strong> Euro<strong>GEOSS</strong>/GENESIS Client Application.<br />
5.6.2 Multilingual Concepts/Terms<br />
Each of <strong>the</strong> selected concepts/terms is identified by a URI. The Euro<strong>GEOSS</strong> DAC submits<br />
a SPARQL query to <strong>the</strong> GENESIS Vocabulary <strong>Service</strong> in order to retrieve all available<br />
44 http://www.opensearch.org/Home<br />
45 http://wiki.ieee-earth.org/Best_Practices/<strong>GEOSS</strong>_Transverse_Areas/Data_and_<strong>Architecture</strong><br />
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