What is linked open data?

Linked data is a collection of interrelated datasets published on the Web using the W3C Semantic Web Standards (RDF, OWL, SPARQL, etc.) According to W3C, "Linked data lies at the heart of what Semantic Web is all about: large scale integration of, and reasoning on, data on the Web". Linked data is very often open and freely available to everyone. Some datasets that form the current linked open data cloud can be found in the DataHub.

Linked open data is especially relevant today because lots of goverments are publishing their data on-line in an effort to increase transparency and accountability of goverment, and allow the developmentof new applications for their citizens. For some pioneer examples, you could visit the open data sites of the US and the UK goverments. Notice that in both cases there is an associated linked data effort.

More information about linked data can be found in the following sources:
1. Tim Berners-Lee's note, which describes the Linked Data principles.
2. Tom Heath's and Christian Bizer's book Linked Data - Evolving the Web into a Global Data Space.
3. The article Linked Data - The Story So Far by Christian Bizer, Tom Heath and Tim Berners-Lee.
4. Many relevant articles in the top semantic web conferences and journals.


One of the most well-known linked datasets is DBpedia, which consists of datasets that have been extracted from Wikipedia and enables declarative queries against the contents of Wikipedia.

Another typical example in the Linked Data community is GeoNames, which collects both spatial and thematic information for various placenames around the world. The placenames in GeoNames are interlinked with each other defining regions that are inside other placenames. GeoNames data is linked to the DBpedia data and other linked data sources.

Finally, in the context of the open data effort of the UK Government, Ordnance Survey has been making various UK geospatial datasets publicy available.

Linked open data on this portal

Linked open data on this portal are being published by the University of Athens group participating in the TELEIOS project. TELEIOS is a recent European project that addresses the need for scalable access to petabytes of Earth Observation data and the discovery of knowledge that is hidden in them. TELEIOS builds on scientific database, semantic web and linked data technologies. In TELEIOS, the knowledge extracted from satellite images (e.g., that an image pixel corresponds to a fire hotspot or that a tile of an image is part of a forest) is encoded in RDF using appropriate Earth Observation ontologies and is combined with other publicly available linked data sources (e.g., DBpedia, GeoNames, OpenStreetMap data) to allow for the expression of rich user queries.

Currently, this site makes public some of the linked datasets that have been created in TELEIOS. All these datasets are geospatial in nature and cover various aspects of Greece. They have been developed for using in the two use cases of project: "Real-time fire monitoring based on continuous acquisitions of EO images and geospatial data" (by the National Observatory of Athens) and "A Virtual Observatory for TerraSAR-X data" (by the German Aerospace Center - DLR).

In the future, our plan is to make available in this site as many linked open datasets as possible that are of interest to Greece.


The data on this site have been published with the collaboration of the following people:


The development of this portal is financially supported by project TELEIOS and a small grant from the Dept. of Informatics and Telecommunications, University of Athens.

We also gratefully acknowledge the contribution of the following students:

  • Meni Vaitsi
  • Marios Koskinas
that developed some of the datasets available on this site as part of their undegraduate dissertations.