Global Drought Monitoring Service through the GEOSS Architecture ...

Architectural Implementation Pilot, Phase 3 Version: 2.0
Global Drought Monitoring and European Drought
Observatory-Water SBA Engineering Report
Date: 11/Feb/2011
network registry. Such a specialized drought vocabulary or a water ontology would link to
drought indicators and drought and water datasets used in common with the European Drought
Observatory. The Simple Knowledge Organizing System (SKOS) had been used to express this
GEMET data structure, so the water ontology, developed in AIP-3, would also be translated into
SKOS data structures and linked to relevant terms in the reference thesauri as an AIP-4 activity.
5.4.1 Water Ontology-enablement within the DAC Semantics
One possible candidate as a foundation water ontology was the USA Consortium of
Universities for the Advancement of Hydrologic Sciences (CUAHSI) water ontology, version 1.
The CUAHSI water ontology does list water stores of surface and subsurface (soil) water,
thereby meeting some of the requirements needed in a hydrologic drought indicator. Fugazza
has converted the CUAHSI Ontology Web Language (OWL) into SKOS, as an AIP-3
contribution (See AIP-3 Semantics Engineering Report).
5.5 How the EuroGEOSS Discover Augmentation Component supports semantic
searches
To conclude, the Discovery Augmentation Component enables semantics-aware
discovery by matching the search patterns entered by the end user against a collection of
multilingual, SDI-related thesauri: these are controlled vocabularies providing multiple textual
representations for terms and organizing them according to specificity and relatedness. As a
consequence the user’s query is first related to a set of language-neutral identifiers (URIs) (like
the URIs used for geographic spatial entities, noted above in section 5.2.1.2). These URIs
represent entities in a concept graph that the user may navigate for identifying related terms that
are relevant to her search. These data structures are hosted by the GENESIS Vocabulary Service.
These thesauri are provided in the Simple Knowledge Organizing System (SKOS)
format, a lightweight ontology for expressing knowledge organization systems (such as
taxonomies, classification schemes etc.), and have been harmonized in the context of the
EuroGEOSS project by relating terms from distinct thesauri, thus allowing the user to move from
one categorization to the other, i.e., one scientific discipline to another within a GEO SBA or
from one SBA (water) to another SBA (agriculture). Once the user has identified an exhaustive
set of terms that are relevant to her query, the broker translates the corresponding URIs back to a
customizable set of languages and executes multiple queries against the catalogs it is federating
(recalling the desired datasets).
The EuroGEOSS Discovery Augmentation Component (DAC) implements a query
expansion strategy deriving multiple traditional geospatial queries from a single semantic query.
The DAC is able to accept a semantic query and, accessing a configurable set of external
semantic services (e.g. controlled vocabularies, gazetteers, etc.), split it into several geospatial
queries directed to a set of federated traditional/standard services for geospatial resources
discovery. Results are finally combined in a meaningful way and sent back to the client.
This framework realizes the Separation-of-Concerns pattern assigning specific tasks to
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