Introduction to Linked Open Data

Transcription

1 Introduction to Linked Open Data Manolis Koubarakis National and Kapodistrian University of Athens (UoA) Dept. of Informatics and Telecommunications 1

2 Presentation Outline The UoA group in MELODIES Open data Linked open data and ontologies (what are they?) Linked Earth Observation Data and Linked Geospatial Data Project TELEIOS and its achievements in developing Virtual Earth Observatories (and Linked Open Earth Observation Data) The NOA Fire Monitoring application (as an example of a service like the ones presented earlier we could have developed it in MELODIES). 2

3 The UoA Group in MELODIES 1 Professor (Manolis Koubarakis) 9 Researchers (Ph.D. and M.Sc. Students) Konstantina Bereta Dimitris Bilidas Kalliroi Dogani George Garbis Stella Giannakopoulou Maria Karpathiotaki Babis Nikolaou Panayiotis Smeros Ioannis Vlachopoulos 3

4 Expertise Databases Artificial Intelligence Web Recently: Semantic Web and Linked Open Data Flagship project: TELEIOS ( 4

5 MaDgIK ( Larger UoA group to which we belong Led by Professors Alex Delis, Dimitris Gunopulos, Mike Hatzopoulos, Yannis Ioannidis and Manolis Koubarakis Other expertise: databases, digital libraries, open access, distributed systems, grid and cloud computing, data mining Flagship projects: OpenAire, Optique (Big Data), Human Brain 5

6 Why are we in MELODIES? Well, Ugo and Jon thought it was a good idea (Thanks to both of you!). TELEIOS ( the first project internationally that brought the linked data paradigm to Earth Observation. We would like to continue this pioneer work in MELODIES! 6

7 Role in MELODIES WP2: Development of Technical Platform Leaders of Task 2.3: Linked Data Management Framework 7

8 Presentation Outline The UoA group in MELODIES Open data Linked open data and ontologies (what are they?) Linked Earth Observation Data and Linked Geospatial Data Project TELEIOS and its achievements in developing Virtual Earth Observatories (and Linked Open Earth Observation Data) The NOA Fire Monitoring application (as an example of a service like the ones presented earlier we could have developed it in MELODIES). 8

9 Open Data The open data movement is about making data public so they can be used freely by everyone. Lots of such data becoming available today is government data. 9

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13 EU s Public Sector Information (PSI) Directive June 2013 Access=Re-use Accessiblity on an INSPIREd basis (machine readable, metadata, interoperable) Charging against marginal costs as a rule PSI re-use watchdog brought in Enhanced EC monitoring and guidance See 13

14 Open Earth Observation Data Paper on Landsat data use and charges by the US National Geospatial Advisory Committee Landsat Advisory Group: Landsat data must continue to be distributed at no cost. The Sentinel missions by ESA have already adopted a fully open and free data access policy. Autumn 2012 edition of the newsletter of the European Association of Remote Sensing Companies makes the case for a free and open data policy for GMES, arguing that this will fuel the development of the geo-information services industry, and as a result, bring maximum economic benefit to Europe. 14

15 Summary There is lots of open data out there. There is more to come! The exploitation opportunities are very big! 15

16 Presentation Outline The UoA group in MELODIES Open data Linked open data and ontologies (what are they?) Linked Earth Observation Data and Linked Geospatial Data Project TELEIOS and its achievements in developing Virtual Earth Observatories (and Linked Open Earth Observation Data) The NOA Fire Monitoring application (as an example of a service like the ones presented earlier we could have developed it in MELODIES). 16

17 Linked Open Data Started as a W3C community effort. Goal: to extend the Web with a data commons by publishing various open data sets as RDF on the Web and by setting RDF links between data items from different data sources. The LOD community is developing a set of best practices for achieving this. 17

18 The Linked Open Data Cloud 18

19 MELODIES related data in the LOD Cloud Geographical data e.g., Geonames or OpenStreetMap etc. Earth Observation data published by our group in TELEIOS e.g., CORINE, Urban Atlas. See (data of relevance to Greece) and (European data). More to come in MELODIES! 19

20 Key Linked Data Technologies URIs: a generic means to identify entities or concepts in the world HTTP: a simple, yet universal, mechanism for retrieving resources, or descriptions of resources RDF: a data model for structuring and linking data that describes things in the world SPARQL: a query language for querying linked data 20

21 Example (does not exist right now) Note the difference between the person Angelina Jolie and the various Web pages for her. It is common to use hash URIs to refer to the real person:

22 Example (cont d) dbpedia-owl:starring: dbpedia-owl:director :

23 Dereferenceable URIs Linked data design principles prescribe that URIs should be dereferencable. Dereferenceable URIs allow us to obtain a copy or representation of the resource they identify. In this way, we can navigate the Web using e.g., HTTP and obtain useful information.

24 Problem Data sets will typically talk about the same object using different URIs. For example:

25 Solution: Linking Use the special kind of link owl:sameas that identifies the resources:

26 The Greek Administrative Geography (GAG) According to the Kallikratis administrative reform of 2010, Greece consists of: 13 regions (e.g., Crete) Each region consists of perfectures (e.g., Heraklion) Each perfecture consists of municipalities (e.g., Dimos Chersonisou) You can find the dataset at 26

27 Other Links Beyond owl:sameas Natura 2000 Example of link to GAG: This protected area is contained in the perfecture of Macedonia. Public transport Examples of links: This bus stop is in the municipality of Athens. This bus stop is near a public building. Public buildings You can find these datasets as well at These datasets were prepared as a graduate course term project by teams of at most 3 students. 27

28 5-star Linked Open Data 28

29 RDF Basics The world consists of entities (resources in RDF jargon). Resources are identified by URIs and described by simple properties and property values. Example: Angelina Jolie stars in the film Changeling directed by Clint Eastwood. 29

30 RDF Statements RDF statements are triples of the form subject predicate object. Example: < < < < < < 30

31 RDF Graphs dbpedia:changeling_(film) dbpedia-owl:starring dbpedia-owl:director dbpedia:angelina_jolie dbpedia:clint_eastwood 32

32 RDF Schema The RDF Vocabulary Description Language 1.0 (or RDF Schema or RDFS) is a language that can be used to define the vocabulary (i.e., the terms) to be used in an RDF graph. The RDF Vocabulary Description Language 1.0 is used to indicate that we are describing specific kinds or classes of resources, and will use specific properties in describing those resources. The RDF Vocabulary Description Language 1.0 is an ontology definition language (a simple one, compared with other languages such as OWL; we can only define taxonomies and do some basic inference about them). The RDF Vocabulary Description Language is like a schema definition language in the relational or object-oriented data models (hence the alternative name RDF Schema we will use this name and its shorthand RDFS mostly!). 33

33 Example Class Hierarchy owl:thing rdfs:subclassof dbpedia-owl:person rdfs:subclassof rdfs:subclassof dbpedia-owl:actor dbpedia-owl:film_director rdf:type rdf:type rdf:type dbpedia:angelina_jolie dbpedia:clint_eastwood 34

34 Example Property Hierarchy dbpedia-owl:spouseof rdf:subpropertyof rdf:subpropertyof dbpedia-owl:husbandof dbpedia-owl:wifeof 35

35 Standard Vocabularies Linked data are written using standard vocabularies i.e., vocabularies that have been agreed by certain communities for describing certain kinds of resources. Examples: Dublin Core schema.org 36

36 Dublin Core Dublin Core is a community effort that has defined a set of metadata attributes (e.g., creator, creation date, title etc.) for describing a wide range of digital resources. See for more information. 37

37 Example 38

38 This is an initiative by Bing, Google, Yahoo! and Yandex to provide a collection of schemas that webmasters can use to markup their pages in ways recognized by major search providers. 39

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41 Ontologies An ontology is a formal, explicit, shared specification of a conceptualization of a domain (Gruber, 1993). Conceptualization: the objects, concepts, and other entities that are assumed to exist in some area of interest and the relationships that hold among them. A conceptualization is an abstract, simplified view of the world that we wish to represent for some purpose. The term ontology is borrowed from Philosophy, where ontology is a systematic account of existence (what things exist, how they can be differentiated from each other etc.). Today the word ontology is a synonym for a shared knowledge base. 42

42 Formal Languages for Ontologies Ontologies are typically expressed in some formal logic-based language. Web ontologies are written in RDFS or OWL. 43

43 Example: the GAG RDFS Ontology 44

44 SPARQL SPARQL stands for SPARQL Protocol and RDF Query Language. It is the standard query language for RDF data proposed by the W3C. It is based on matching graph patterns against RDF graphs. The simplest kind of graph pattern is a triple pattern. A triple pattern is like an RDF triple, but with the option of a variable in the subject, predicate or object positions.

45 Example rdf: foaf: rdfs: < < rdf:type foaf:person ; foaf:name Angelina Jolie" ; foaf:mbox <mailto:ajolie@gmail.com> ; foaf:homepage < ; foaf:interest < ; foaf:knows [ rdf:type foaf:person ; foaf:name Michael Douglas" ]. 46

46 Example SPARQL Query SELECT?name WHERE {?x foaf:name?name.?x rdf:type foaf:person.?x foaf:knows?y.?y foaf:name Michael Douglas. } Result:?name Angelina Jolie"

47 Presentation Outline The UoA group in MELODIES Open data Linked open data and ontologies (what are they?) Linked Earth Observation Data and Linked Geospatial Data Project TELEIOS and its achievements in developing Virtual Earth Observatories (and Linked Open Earth Observation Data) The NOA Fire Monitoring application (as an example of a service like the ones presented earlier we could have developed it in MELODIES). 48

48 Geospatial data on the Web 49

49 Open Government Data - Geospatial 50

50 Linked geospatial data Ordnance Survey 51

51 Linked geospatial data Open Street Map 52

52 The Greek Administrative Geography According to the Kallikratis administrative reform of 2010, Greece consists of: 13 regions (e.g., Crete) Each region consists of perfectures (e.g., Heraklion) Each perfecture consists of municipalities (e.g., Dimos Chersonisou) 53

53 Open EO Data Lots of open Earth Observation data have been made available in the last few years (e.g., by ESA), but this data still exists in different data silos (archives). 54

54 Challenge in MELODIES (also in LEO) Follow the lead of TELEIOS: open up existing EO silos by moving them over to the linked data paradigm. 55

55 EO Data Centers Before TELEIOS Users PDGS Catalogue Raw Data Processing Chains Archive 56

56 Scientific Database and Semantic Web Technologies TELEIOS Virtual Earth Observatories Web Portals Rapid Mapping Linked Geospatial Data Semantic Annotations Ontologies Knowledge Discovery and Data Mining KNOWL- EDGE GIS Data Derived Products Metadata Features Raw Data Ingestion Processing Content Cataloguing Extraction Archiving DATA

57 Applications Developed in TELEIOS The NOA fire monitoring and burnt scar mapping application New generation catalogues for the TerraSAR-X archive of DLR Rapid mapping applications in disaster scenarios See 58

58 The NOA Fire monitoring application 9.5⁰ East Back End: MonetDB / Strabon Front End: GUI Map Element Corine Landcover Admin Boundaries POIs External Sources Geospatial Ontology Data Vault Cataloguing Service & Metadata Creation HotSpots Linked Geospatial Data Semantic technologies Raw Data Processing Chain (SciQL based)

59 Data Sources in the Fire Monitoring Application SEVIRI images (shapefiles from NOA) CORINE land cover (shapefiles from EEA) Greek Administrative Geography (the pdf of the relevant Greek law and a shapefile) Greek Coastline (shapefile from NOA) Geonames (RDF from ) Road network, POI etc. (from OpenStreetMap translated into linked data by the LinkedGeoData project Notice that only two data sources were linked data 60

60 Foundational Technologies The data model strdf and the query language stsparql The system Strabon 61

61 The Data Model strdf strdf stands for spatiotemporal RDF. It is an extension of the W3C standard RDF for the representation of geospatial data that may change over time. strdf extends RDF with: Spatial literals encoded in OGC standards Well- Known Text or GML New datatypes for spatial literals (strdf:wkt, strdf:gml and strdf:geometry) Valid time of triples with new data type strdf:period

62 strdf: An example

63 strdf: An example (WKT) ex:burntarea1 rdf:type noa:burntarea. ex:burntarea1 noa:hasid "1"^^xsd:decimal. ex:burntarea1 noa:hasarea " "^^xsd:double. Spatial Literal (OpenGIS Simple Features) ex:burntarea1 strdf:hasgeometry "POLYGON(( , , , , )); < Spatial Data Type Well-Known Text

64 strdf: An example (GML) ex:burntarea1 rdf:type noa:burntarea. ex:burntarea1 noa:hasid "1"^^xsd:decimal. ex:burntarea1 noa:hasarea " "^^xsd:double. ex:burntarea1 strdf:hasgeometry "<gml:polygon Spatial Literal (GML Simple Features Profile) srsname=' <gml:outerboundaryis> <gml:linearring> <gml:coordinates>38.16, , , </gml:coordinates> </gml:linearring> </gml:outerboundaryis> </gml:polygon>"^^strdf:gml ,23.80, Spatial Data Type GML

65 stsparql: An example Find all burnt forests close to a city SELECT?BA?BAGEO WHERE {?R rdf:type noa:region.?r strdf:hasgeometry?rgeo.?r noa:hascorinelandcoveruse?f.?f rdfs:subclassof clc:forests.?city rdf:type dbpedia:city.?city strdf:hasgeometry?cgeo.?ba rdf:type noa:burntarea.?ba strdf:hasgeometry?bageo. Spatial Functions (OGC Simple Feature Access) FILTER(strdf:anyInteract(?RGEO,?BAGEO) && strdf:distance(?bageo,?cgeo, ogc:meter) < 2000) }

66 stsparql vs. GeoSPARQL GeoSPARQL is a recent effort by OGC to develop an extension of SPARQL for querying geospatial data expressed in RDF. stsparql and GeoSPARQL have been developed independently. stsparql geospatial query functionality is very close to a subset of the recent OGC standard GeoSPARQL: Core Geometry extension Geometry topology extension Strabon supports both stsparql and GeoSPARQL

67 Strabon: The World s Fastest and More Functional Spatiotemporal RDF Store ( strdf graphs stsparql/ GeoSPARQL queries Query Engine stsparql to SPARQL Translator Parser Optimizer Evaluator Transaction Manager Strabon Storage Manager Named Graph Translator Repository SAIL RDBMS GeneralDB PostgreSQL PostGIS PostgreSQL Temporal MonetDB

68 So what? TELEIOS lesson: If we know what your data sources are, and together we transform them into linked data and store them in Strabon then application development is just a few stsparql queries away. Can we replay this in MELODIES? 69

69 Rapid Mapping in the NOA Fire Monitoring Service

70 Creating a map Get all hotspots detected in the Peloponnese on 24/08/2007. SELECT?h?hGeo?hAcqTime?hConfidence?hConfirmation?hProvider?hSensor?hSatellite WHERE {?h rdf:type noa:hotspot ; noa:hasgeometry?hgeo ; noa:hasacquisitiontime?hacqtime ; noa:hasconfidence?hconfidence ; noa:isproducedby?hprovider ; noa:hasconfirmation?hconfirmation ; noa:isderivedfromsensor?hsensor ; noa:isderivedfromsatellite?hsatellite. FILTER(" T00:00:00"^^xsd:dateTime <=?hacqtime &&?hacqtime <= " T23:59:59"^^xsd:dateTime). FILTER(strdf:contains("POLYGON(( , , , , ))" ^^strdf:wkt,?hgeo) ). }

71 Improve product accuracy Correlate fire products with auxiliary data to increase their thematic accuracy e.g., delete the parts of the polygons that fall into the sea. DELETE {?h noa:hasgeometry?hgeo} INSERT {?h noa:hasgeometry?dif} WHERE { SELECT DISTINCT?h?hGeo (strdf:intersection(?hgeo, strdf:union(?cgeo)) AS?dif) WHERE {?h rdf:type noa:hotspot.?h strdf:hasgeometry?hgeo.?c rdf:type coast:coastline.?c strdf:hasgeometry?cgeo. FILTER( strdf:anyinteract(?hgeo,?cgeo)} GROUP BY?h?hGeo HAVING strdf:overlap(?hgeo, strdf:union(?cgeo))}

72 Creating a map (cont d) Get all coniferous forests in Peloponnese SELECT?a?aGeo WHERE{?a rdf:type clc:area; clc:haslanduse?alanduse; noa:hasgeometry?ageo.?alanduse rdf:type?alandusetype. FILTER(?aLandUseType = clc:coniferousforest). FILTER(strdf:contains("POLYGON(( , , , , )) ^^strdf:wkt,?ageo)). }

73 Creating a map (cont d) Get all capitals of prefectures of the Peloponnese. SELECT?feature?fName?fGeo WHERE{?feature rdf:type gn:feature; noa:hasgeography?fgeo; gn:name?fname; gn:featurecode?fcode. FILTER(?fCode = gn:p.ppla?fcode = gn:p.ppla2 ). FILTER(strdf:contains("POLYGON(( , , , , )) ^^strdf:wkt,?fgeo)). }

74 Final map

75 Sextant (

76 Readings Linked Data and Semantic Web The book Linked Data: Evolving the Web into a Global Data Space by Tom Heath and Christian Bizer available from The book The Semantic Web Primer by Grigoris Antoniou and Frank van Harmelen available from The (more theoretical) book Foundations of Semantic Web Technologies by Pascal Hitzler, Markus Krötzsch and Sebastian Rudolph. See The slides of my graduate course Knowledge Technologies. Get them up from (the site is in Greek; just download the slides using the links ). The work of project LOD2 ( The linked data life cycle that I mentioned is discussed in a paper and a tutorial found at Tutorial.html. 77

77 Readings Linked Data and Semantic Web The W3C Semantic Web Activity web site ( Browse! There are many interesting introductory tutorials. You should definitely see one of the introductory tutorials by Ivan Herman e.g., IH/Tutorial.pdf which gives a very good introduction to the current state of the art in this area. The ESWC invited talk by Jim Hendler available at which looks at what the Semantic Web has achieved so far and deals with various criticisms of the area. 78

78 Readings Linked Earth Observation Data TELEIOS Web site (start with the short video on the top page). Strabon Web site Sextant Web site Linked open data for the fire monitoring application The NOA fire monitoring application is described in detail in the following publication: The version of the fire monitoring application developed by NOA in the Greek project SWeFS is available at 79

79 Readings Linked Geospatial Data The book Linked Data: A Geographic Perspective by Glen Hart and Catherine Dolbear, CRC Press, See the slides of our tutorials available at: and the accompanying paper you will find there. 80

80 Plan for Tomorrow Come to our session on linked data. Bring a data source. Let us try to turn it into linked data together! Do you have a service? Let us try to build it together Tell us what we can do for you! 81

81 Thank you for your attention! Questions? Remember us when you are planning Horizon 2020 projects! 82