Semantics for Spatial Data Infrastructures

1. Semantics for Spatial Data Infrastructures Werner Kuhn SDI Concepción

2. The Economist, May 3, 2003

3. The Economist, May 17, 2003

4. Topological Operators for areas, lines, points

5. Overlap in a GIS dialog window SDI Concepción

6. “Where can I cross the Havel?” Road data (e.g., GDF)

8. Composite Service plant ID 457 plant location R: 3405138 H: 5760997 Input Leakage Information Get Plant Location Get Nearest Airport airport code FMO emission rate 29 mg/s Get Wind Calculate Gas Dispersion Plume dispersion map Create Gas Dispersion Map wind report XML... plume GML... SDI Concepción

9. Application „wind is blowing from“ „wind is blowing to“ Level points_to_compulsion true points_to_compulsion false à à Name: Name: „ prevailing_direction “ Name: „ wind “ Name: „ wind “ „ prevailing_direction “ Data Type: Data Type: „string“ Data Type: „string“ Data Type: „string“ XML-ComplexType 2. same name, different data 1. different name, same data 3. same name, same data type, type, same domain concept type, same domain concept different or differently restricted domain concept(s) Semantic Heterogeneities SDI Concepción

10. Generalized Problem • Buffers, topology, navigation, and gas plume examples show problems with the semantics of geographic information describing • entities (e.g., road, ferry) • processes (e.g., driving, wind) • relations (e.g., distance, overlap) • Context is essential for semantics • Today‘s SDI separate data from operations (GML) • context contained in operations is lost • systems or users misinterpret data • Ontologies are supposed to provide that context • Today, they don‘t • They could do better • How? SDI Concepción

11. What do we mean by Semantics ? Concept refers to activates Symbol Referent stands for Jaguar SDI Concepción

12. Semantics of what ? • We are not trying to capture the meaning of natural language expressions! • We formalize the semantics of technicalsymbols used in GIS, databases, web services of information communities • But: information is from and for humans • it derives from data through human interpretation • it emerges at the user interfaces of GI technologies • Thus, we need to capture meaning (cognitive semantics) SDI Concepción

13. Medium-term research program(3-5 years) solve 3 semantic interoperability problems: data discovery service discovery service composition e.g., wind direction for gas plume e.g., road data for directions e.g., weather services

14. Semantic Interoperability • ...is the only real interoperability interoperating components share an understanding of their interfaces • today: „syntactic interoperability“ interoperating components share an interface, defined by a type signatureGM_Object :: distance (geometry : GM_Object) : Distance SDI Concepción

15. Today: annotation ISO 19107, Spatial Schema „The operation "distance" shall return the distance between this GM_Object and another GM_Object. This distanceis defined to be the greatest lower bound of the set of distances between all pairs of points that include one eachfrom each of the two GM_Objects. A "distance" value shall be a non-negative number associated to a distance unitsuch as meter or standard foot. If necessary, the second geometric object shall be transformed into the samecoordinate reference system as the first before the distance is calculated. If the geometric objects overlap, or touch, then their distance apart shall be zero. Some current implementationsuse a "negative" distance for such cases, but the approach is neither consistent between implementations, northeoretically viable. "Distance" is one of the units of measure data types defined in ISO TS 19103. NOTE The role of the reference system in distance calculations is important. Generally, there are at least three types ofdistances that may be defined between points (and therefore between geometric objects): map distance, geodesic distance, andterrain distance.“ SDI Concepción

16. Goal: axiomatization Service interfaces, requests, and responsescontainsymbols with undefined semantics GM_Object::distance(geometry :GM_Object) :Distance Alexandria ::distanceStades(Syene) = 5040 • type symbols (standing for classes of objects and literals) • values (standing for individual objects and literals) • operators (standing for methods) SDI Concepción

17. Ontology in Philosophy a philosophical discipline—a branch of philosophy that deals with the nature and the organisation of reality Science of Being (Aristotle, Metaphysics, IV, 1), asks the questions: • What exists? • What characterizes being? • Eventually, what is being? SDI Concepción

18. Ontology in Computer Science • An ontology is an engineering artifact. It is constituted by • a specific vocabulary used to describe a domain • assertions on the intended meaning of the vocabulary. • Thus, an ontology describes a formal specification of a certain domain: • shared understanding of a domain of interest • formal and machine manipulable model of a domain “An explicit specification of a conceptualization” [Gruber93] SDI Concepción

19. Ontologies SDI Concepción

20. clc: CORINE Land Cover categories SDI Concepción

21. Are ontologies enough? • They contain relationships between terms • superclass and subclass, is_a, part_of, has_property, synonym • Their axioms are • absent or • in obscure and untested logical axioms • They fail to capture context • activities determine semantics (e.g., driving across a river) • They are not grounded • what does „artifact“ or „entity“ or „process“ mean? SDI Concepción

22. interpretation interpretation Spatial Reference Systems The underlying problem geoinformation = < x, z > ??? SDI Concepción

23. Vision Users of geographic information should be able to refer thematic data to semantic reference systems, just as they refer geometric data to spatial reference systems. Software should support the • referencing and grounding process • projections to simpler semantic spaces • semantic translation among different reference systems. SDI Concepción

24. Semantic Reference Systems Spatial Reference System [ISO 19112] „system for identifying positions in the real world“ • e.g., geodetic reference systems Temporal Reference System [ISO 19108] „basis against which time is measured“ • e.g., calendars Semantic Reference System [t.b.d.] basis on which thematic data are interpreted:‚forest‘, ‚wetland‘‚ ‚road width‘ etc. • e.g., ontologies SDI Concepción

25. Long-term research program(5-7 years) • create methods and tools to design and use semantic reference systems for • grounding (e.g. “move”) • projecting (e.g. roads and ferries to edges) • translating (e.g. cadastre to navigation) • based on real-world case studies • transportation, emergency management, planning SDI Concepción

26. Ferry example: Grounding

27. Grounding in Image Schemas • Sensory-motor patterns of cognition (Johnson) container, surface, path, link, center-periphery, force... • developed through bodily experience • have internal structure • enable the perception of meaningful information from the environment (Gärdenfors) SDI Concepción

28. projection Ferry example: Semantic Projection SDI Concepción

29. Application „wind is blowing from“ „wind is blowing to“ Level points_to_compulsion true points_to_compulsion false à à Name: Name: „ prevailing_direction “ Name: „ wind “ Name: „ wind “ „ prevailing_direction “ Data Type: Data Type: „string“ Data Type: „string“ Data Type: „string“ XML-ComplexType 2. same name, different data 1. different name, same data 3. same name, same data type, type, same domain concept type, same domain concept different or differently restricted domain concept(s) Gas plume example: Translation SDI Concepción

30. provides meaning restricts meaning Domain Concept + property A (range)+ property B (range) provides meaning restricts meaning Application Concept + property A+ property B (range restriction)(range restriction) + property C Semantic Reference System SDI Concepción

31. Protégé Implementation SDI Concepción

32. Problem: Semantic Heterogeneity 1 Which terms can I use for an efficient keyword-based search of water level information? Discovery • Synonyms: one concept – different terms • water level, tide scale • measuring gauge, control point • Homonyms: one term – different concepts • „water level“ – river vs. groundwater  The returned results are incomplete!  Not all returned results are relevant! SDI Concepción

33. Problem: Semantic Heterogeneity 2 How do I interpret the terms of a schema and formulate a query? Retrieval  Meaning of terms used in the database schema is often ambiguous SDI Concepción

34. Ontological description of the query concept “water level” Query Concept based on equivalent concepts based on Shared Vocabulary Approach: Ontological Descriptions What is the water level at point X at time Y in the Elbe River? Application Ontology Concept Ontological description of the application concept “höhe” SDI Concepción

35. define query concept request with query concept request for shared vocabulary request for matching concepts Request with terms of matching concepts Architecture: Ontology-Based Discovery SDI Concepción

36. Architecture: Ontology-Based Retrieval GetFeature request Request for feature type Request for concept definitions SDI Concepción

37. Why Spatial is Special (for Semantics) • Space and time are primarily understood through processes • Semantics of symbols is not always a matter of convention • physical grounding • needs measurement ontologies • But human perception and social reality play an important role • simplest case: geographic names and location descriptions • Need spatial reasoning at the type level • Granularity, vagueness, uncertainty and are central aspects of spatial information • ... SDI Concepción

38. Conclusions • Spatial reference systems motivate semantic reference systems • from static ontologies to computational reference systems • providing referencing, projection, and translation • Semantics of spatial information poses both, general and special challenges. • Our success measures are in solving interoperability problems SDI Concepción

39. Some Big Challenges Grounding of ontologies („semantic datum“) • what is meant by wind direction? • what is transportation? Reasoning about processes • what does distance mean? • what does touch or overlap mean? • what is driving? • how is a gas plume determined? Improved similarity models ad hoc categories Karten bilden bei logistischen Entscheidungen der Helfer eine wichtige Grundlage: "Muss ich einen Helikopter einsetzen oder kann ich fahren?" Auch bei der Einrichtung von Hilfsstationen seien Karten und Bilder wichtig: "Wo habe ich eine ebene Fläche, die einigermaßen weit weg vom Wasser ist, die groß genug ist, um ein Zelt-Lazarett aufzubauen?“ [dpa Gespräch mit Robert Meisner, DLR, 7. Januar 2005] Formal Definition of Interoperability Automated generation of semantic annotations SDI Concepción

40. For more information... • MUSIL web site (Muenster Semantic Interoperability Lab): http://musil.uni-muenster.de • email to kuhn@uni-muenster.de SDI Concepción