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A Semantic Web, Linked Data application


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Topos is a web application that uses Linked Data and other sources of information from Web services to present a specialized view for a given geographic location. This view is composed from three user interface components: the location is shown on a map, news stories about this location are placed in a timeline and Linked Data collected for this location are presented in a concept graph. Topos demonstrates the ability to query and connect Linked Data from the Web, make inferences using the ontologies underlying the data and present the syndicated information through a specialized browser with a rich user interface. 


Technical Overview

Topos is a client / server application. At the client side is a web application consisting of a Adobe Flex – based user interface component for selecting the location and the query options, and for presenting the RDF / linked data results as a graph using the FlexViz visualization library. Additionally, the Google maps API is used to show a map for the selected location and the Simile Timeline component is used to present in a timeline the NYT stories for the selected location.


Topos client screenshot


Usage is very simple. The user can select a location either from a list of locations (top left in the screen) or from the pointers in the map (bottom left) then presses the ‘Get Linked Data’ button. The provided options are i) to load or not the linked data (dereference owl:sameAs IRIs), ii) to analyze or not NYT stories using the Open Calais service and iii) to present the resulting linked data as either an RDF/triples graph or as a Concept graph.


Client – Server communication

Communication between the client and the server is done via HTTP. The Web client is POSTing XML encoded requests and similarly receives XML encoded responses. No authorization is required for accessing the server and the XML data are not encrypted and no session information is used by either the client or the server.


Topos server

The HTTP server is implemented using SWI Prolog and Thea Prolog library for OWL. Thea library is used for parsing initially the Linked Data ontologies and subsequently for converting the collected RDF triples into OWL ontology axioms and perform reasoning on the triples based on the underlying Ontologies. The SWI’s HTTP package library is used to implement a simple but efficient HTTP server. Prolog DCG is used for parsing the NYT search API results. The body text of the stories is then fed to the Open Calais service using Thea Open Calais service wrapper.

Using the application, fairly straightforward, open select location and options, view the timeline and graphs.


Topos server functions



Topos web application can accessed from here



A short paper describing Topos has been submitted to the Linked Data triplification challenge 2010.


Contact - Support

Topos is open source and support is provided on a "best-effort" basis by its developer. For any questions, comments and suggestions please contact:

Vangelis Vassiliadis [github]