Data and Software
In LEO, we aim to develop a software stack that is composed of tools that support the life cycle of linked open EO data. These tools are either developed in the context of LEO or they have been already developed in related projects (e.g. TELEIOS) and are used to meet the needs of LEO. At first, using the WP2 software GeoTriples, raw geospatial data of several formats are translated into the RDF data model. The data produced are stored then in Strabon SPARQL endpoints. Afterwards, Silk uses the endpoints that contain the RDF data as input, to generate and store spatial, temporal and similarity links from the data stored to enhance its quality and value. The data can be accessed, queried and/or visualized by the precision farming application (WP5) and the WP4 applications Sextant, LEO DSE and LEODroid, via the endpoints. Finally, a precision farming application is being developed that heavily utilizes the data.
GeoTriples is a tool developed in the context of Work Package 2 of LEO. It is designed and developed for transforming geospatial data sources into RDF. It covers the Transformation into RDF phase of the life cycle of linked open EO data. GeoTriples features two main functionalities; The mapping generation and the production of an RDF dump from the input data. The mapping generator employs and extends R2RML to create mappings that dictate the method of conversion of the raw data (e.g. ESRI shapefiles
and spatially enabled databases) into the RDF data model. The mappings are also enriched with subject and predicate object maps in order to properly deal with the specifics of geospatial data and then represent it using an appropriate vocabulary. The latter component is responsible for creating the RDF dump files in all popular RDF syntaxes (e.g. N3, TURTLE, RDF/XML etc) by taking the created mappings into account. A detailed analysis of GeoTriples is provided in deliverable D2.1 of WP2. GeoTriples is an open source tool that is distributed freely according to the Mozilla Public License v2.0. It is currently accessible (and source code) from the following URL: https://github.com/LinkedEOData
Strabon is a semantic geospatial and temporal DBMS for storing and querying geospatial data that changes over time. It is used in LEO to support the Storage/Querying phase of the life cycle of linked open EO data and query the data produced from the GeoTriples tool. The development of Strabon started during the EU FP7 Project Semsorgrid4Env and continued during the EU FP7 project TELEIOS. Strabon is an implementation of the data model stRDF, the query language stSPARQL and the respective part of the OGC standard GeoSPARQL. stRDF and stSPARQL extend RDF and SPARQL 1.1 respectively providing a function set and data types for making the querying of spatiotemporal information via stSPARQL or GeoSPARQL possible, such as finding spatial and temporal relations (e.g. intersection) between two resources. Its functionality is based on a spatially enabled database back end (currently PostgreSQL and MonetDB). Aside from this functionality, Strabon also allows the user to project results of her queries on a map. Strabon is an open source application that is distributed freely according to the Mozilla Public License v2.0. Along with a detailed tutorial on stRDF and stSPARQL, it is accessible from the following URL: http://strabon.di.uoa.gr
MonetDB is an open-source column-store DBMS which achieves very efficient storage and query processing by innovations at all layers of a DBMS, e.g. a storage model based on vertical fragmentation, modern CPU-tuned query execution architecture, automatic and self-tuning indexes, run-time query optimization and a modular software architecture. In LEO we use two distinctive characteristics of MonetDB that were developed in TELEIOS: the query language SciQL and the Data Vaults framework. SciQL is a new SQL-based query language for scientific applications that uses multidimensional arrays to represent EO data (e.g., time series of images) and query their content declaratively. The Data Vaults provides a true symbiosis between a DBMS and existing (remote) file-based repositories such as the ones used in EO applications. The data vault keeps the data in its original format and place, while at the same time it enables transparent data and metadata access and analysis using the SciQL query language. MonetDB is an open source application that is distributed freely according to the MonetDB Public License Version 1.13 . The mercurial repository hosting the source code of MonetDB is accessible from the following URL: http://dev.monetdb.org/hg/MonetDB/
The Silk Link Discovery Framework4 is a tool for discovering relationships between data items within different Linked Data sources. Data publishers can use Silk to set RDF links from their data sources to other data sources on the Web. Using the declarative Silk Link Specification Language (Silk-LSL) developers can specify which types of RDF links should be discovered between data sources as well as which conditions data items must fulfill in order to be interlinked. These linkage rules may combine various metrics and can take the graph around a data item into account, which is addressed using an RDF path language. Silk accesses the data sources that should be interlinked via the SPARQL protocol and can thus be used against local as well as remote SPARQL endpoints. In LEO, we extended Silk in order to be able to discover precise geospatial and temporal links among RDF data published with the tool GeoTriples described above. Silk, enhanced with the new extensions that we developed, will support the Interlinking phase of the life cycle of linked open EO data. Silk is an open source application, freely distributed according to the Apache License v2.0. The mercurial repository hosting the source code with the spatial and temporal extensions is accessible from the following URL: https://github.com/psmeros/stSilk.
Sextant is a visualization tool that was developed in the context of project TELEIOS and allows us to view geospatial information as layers over a map. It is used in LEO for browsing and visualization of linked EO data. With this tool we can visualize standard file formats for representing geospatial information (e.g. KML) as layers over a map and create thematic maps by combining several layers. The user can also search through Sextant the data of a SPARQL Endpoint by posing stSPARQL/GeoSPARQL queries and view the results as a new layer on the map. In the context of LEO, Sextant was altered to use OpenLayers 2.0, so that we could use it locally due to the sensitivity of the data. Furthermore a mobile version is being developed that will have all the functionalities of the desktop one, except for the query posing, for usability issues and will be distributed as an APK file for Android OS. Sextant is an open source application, freely distributed according to the Mozilla Public License v2.0. Along with demos and more detailed information, it is accessible from the following URL: http://sextant.di.uoa.gr
LEO Data Search Engine and LEODroid
The LEO Data Search Engine (DSE), combined with the LEODroid client application, covers the Search/Browse/Explore/Visualize phase of the life cycle of linked open EO data. The LEO DSE is a software system based on the RARE system developed and extended in the context of past and ongoing ESA projects. In its current state, the system disambiguates free text search queries, transforms the disambiguated queries into SPARQL requests, submits the SPARQL requests to an RDF data store, and combines responses in search result lists. It also acts as an adapter for navigating in the linked data. The sense disambiguation service resolves search terms by searching in ontologies registered in an RDF data store (such as a Strabon endpoint) and location names (toponyms) registered in gazetteers. In addition, it is able to recognize time constraints expressed in natural language. The LEO DSE is made of a number of interdependent services that may be deployed in the same or in different servers. LEODroid is a mobile application for Android devices. It provides an intuitive user interface to the LEO DSE, and takes advantages of the novel capabilities of modern smartphones and tablet PCs. LEODroid allows users to enter textual search strings, visualize search result lists, and navigate in the linked data starting from an entry in the result list. The first version of LEODroid supports the following features:
• Identification of the user geographical location. This is used if the user does not explicitly specify a place name in his search query.
• Visualization of the search result list, adapting the content to the type of each topic in the list.
• Visualization of geolocalized topics on an interactive map (e.g. satellite image footprint and POI marker).
• Visualization of topics information, adapting the content to the type of each topic.
• User bookmarks allow users register the current subject and come back to it later on.
The LEO DSE and the LEODroid mobile application are proprietary software, distributed in binary form free of charge for non commercial use. Commercial use of the software shall require a license agreement with Space Applications Services.
In the agricultural market, mature precision farming techniques are already available where agricultural machinery like fertilizer spreader can adjust the product quantity to be applied on part fields. These solutions, however, are too expensive for SMEs (small and medium enterprises). For this reason, LEOPatra is being developed, which draws back on linked open data sources and runs on cheap smartphone hardware. The application shall support the farmer to apply nitrogen fertilizers site-specific on his fields.