Global Drought Monitoring Service through the GEOSS Architecture ...

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Architectural Implementation Pilot, Phase 3 Version: 2.0 Global Drought Monitoring and European Drought Observatory-Water SBA Engineering Report Date: 11/Feb/2011 documents, a W3C standard) syntax for queries. However, the DAC was conceived to be flexible and federate also semantic services that use different interfaces. The DAC shall also provide an interface (towards the presentation layer) for being queried with any combination of semantic, geospatial and free text constraints. At the time being there is no well-recognized standard interface or syntax allowing such combined queries. Hence, the choice was to use the lightweight OpenSearch 44 interface. The OpenSearch is a basic interface, allowing querying a catalogue with a simple free text search. There exist several extensions of the basic OpenSearch syntax; two widely used extensions to submit geospatial queries are: • Geo extension: allows to specify a spatial extent/location as constraint in a query; • Time extension: allows building queries based on time and time spans constraints. In addition to the above extensions, we defined a “Concept-driven” extension to allow the discovery of well-defined concepts and relations between concepts form semantic services. These three extensions form the DAC query interface. A detailed documentation describing the “Concept-driven” extension will soon be published on the OpenSearch Web Site. The AIP-3 Engineering Report Best Practices Wiki 45 will be updated as soon as the detailed documentation will be available. 5.6 Operation of the Water Ontology within the EuroGEOSS Discovery Augmentation Component 5.6.1 Searching for Concepts/Terms EuroGEOSS DAC communicates with the GENESIS Vocabulary Service using SPARQL interface. According to user’s request the EuroGEOSS DAC performs different actions: 1. When the user has searched for concepts/terms related to a keyword of interest (e.g. “drought”), the EuroGEOSS DAC performs a “GetConcepts” request; that is, EuroGEOSS DAC builds a SPARQL query to retrieve from the GENESIS Vocabulary Service all concepts/terms containing the searched keyword in the label and/or in the description. The matching concepts/terms are returned to the EuroGEOSS/GENESIS Client Application. 2. When the user is extending a set of concepts/terms, the EuroGEOSS DAC transforms the selected relation type (e.g. “more specific concepts”) into formal SKOS relations (e.g. skos: narrower and skos: narrowMatch). Using these relations a set of SPARQL queries is executed, and matching concepts/terms are returned to the EuroGEOSS/GENESIS Client Application. 5.6.2 Multilingual Concepts/Terms Each of the selected concepts/terms is identified by a URI. The EuroGEOSS DAC submits a SPARQL query to the GENESIS Vocabulary Service in order to retrieve all available 44 http://www.opensearch.org/Home 45 http://wiki.ieee-earth.org/Best_Practices/GEOSS_Transverse_Areas/Data_and_Architecture Page 58
Architectural Implementation Pilot, Phase 3 Version: 2.0 Global Drought Monitoring and European Drought Observatory-Water SBA Engineering Report Date: 11/Feb/2011 translations for each of the selected concepts/terms. 5.6.3 European Drought Observatory (Client) Query EuroGEOSS DAC communicates with the EuroGEOSS Discovery Broker through the OGC CSW ISO AP 2.0.2 interface. For each of the selected concepts/terms, EuroGEOSS DAC creates a query that contains geographic (i.e. the envelope characterizing the specific AOI), and multilingual Keywords constraints (i.e. the concepts/terms selected through the EuroGEOSS/GENESIS Client Application). This set of queries is submitted to the EuroGEOSS Discovery Broker. As shown in the “Drought—Europe” video, the user has identified a geographic area on the map interface, while at the same time, highlighted and clicked on a concept. Before sending back the results to the client, the EuroGEOSS DAC groups them according to the matched concept/term. 5.6.4 WPS Request The European Drought Observatory (EDO) WPS Client sends an Execute request to the WPS Server, including references to the input thematic layers selected by the user (WCS endpoint and coverage name). 5.7 Use of EuroGEOSS Semantic Discovery within the European Drought Observatory (Returning back to the Scenario) The User Interface to DAC includes two tabs: 1) “Search” and 2) “configuration.” The process begins with a “Simple Search” text box, in which a user types in the overall query item of interest “drought.” The “Advanced Search” panel becomes active, containing a text string box in which the user types the keyword, underneath of which are buttons “Get concepts,” “relation,” “extend node,” “clean selection,” and “search.” The “Get concepts” button obviously retrieves the concepts, which are then displayed in graph form as nodes on a tree or graph. The “relation” button, when pressed, offers the selection of “more general terms,” “more specific terms,” “corresponding terms,” and “related terms.” The color coding used in the graphs are: 1) “orange” for more specific, 2) “yellow” for more general, and 3) “green” for corresponding. For example, “drought indicator” is a “more specific” example of “drought.” As shown in the demonstration video, a user can draw a box around an area of interest on a map, while simultaneously having entered the concept of interest to the user. Then the search results will be retrieved. The returning data matches the requested concepts. Then the selected datasets can be displayed upon a map server (Scenario Step 04) (see section 6.4) 5.8 Interoperability Arrangements with GEOSS We use the following service interface: Page 59
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