Model-Driven Web Feature Service

1. Model-Driven Web Feature Service A Way Towards Enhanced Semantic Interoperability Peter Staub, ETH Zurich FOSS4G 2007 – Victoria B.C., September 26, 2007

2. Overview • Data modeling and semantic interoperability: Fundamentals • Research project mdWFS • Why a model-driven WFS? Enhancements in semantic interoperability • Concepts, methods • Prototype implementation

3. I – Modeling and Interoperability Fundamentals What is Interoperability? Swiss plug does not fit American socket So, an appropriate adaptor plug (and a voltage transformer) is needed! Interoperability: Format Support + Data Model Transformation 230V ~50 110V ~60 

4. <<Metamodel>> Real World Real World MOF <<Metamodel>> <<Metamodel>> Conceptual Schema Mapping Metamodel CSL X Metamodel CSL Y Schema Translation :Instance Translation <<Model>> <<Model>> <<Model>> <<Model>> Conceptual Schema B (PIM) Conceptual Schema A (PIM) Logical/Physical Schema A (PSM) Database B, Transfer format B Logical/Physical Schema B (PSM) Database A, Transfer format A I – Modeling and Interoperability Fundamentals Data Modeling and Semantic Interoperability <<instantiate>> <<instantiate>> Application Domain „Model“ A Application Domain „Model“ B <<instantiate>> <<instantiate>>  Formal mapping <<derive>> <<derive>> <<derive>>  PIM>PSM Mapping GML App. Schema <<derive>> <<instantiate>> <<instantiate>>  Encoding GML Instance Document

5. II – Project mdWFS Project mdWFS Web-based cross-border GIS: a regional planning use case What are the shortcomings of existing approaches? Overcoming these shortcomings with a model-driven WFS „Model-Driven Approach for Accessing Distributed Spatial Information Using Web Services“

6. II – Project mdWFS Problem and Requirements Shortcomings of OGC Web Services [OWS]: • OWS allow for syntactic interoperability but not for semantic interoperability Preconditions for a web-based semantic transformation on the conceptual level • Machineable CSL for data models • Formal language for expressing schema mapping rules • Web service interface Web service requirements • Access to geospatial data based on conceptual source data schema and conceptual target data schemas • Interoperability with existing OWS: WFS

7. II – Project mdWFS mdWFS Interface Idea: model driven Web Feature Service mdWFS • Extension of OGC WFS specification • Ability to store and deliver conceptual models (UML/XMI) • New operationDoTransform() enables WFS carrying out semantic transformations • Each semantic transformation results in an according set of WFS feature types • WFS is configured by target schema at conceptual level!

8. III – mdWFS: Concept and Methods WFS Protocol Extensions for mdWFS Specification of communication protocol for mdWFS  new request parameter SERVICE=mdWFS (default: WFS) Specification of WFS protocol extensions GetCapabilities WFS: FeatureTypeList mdWFS: SchemaList DescribeFeatureType WFS: XMLSchema (transfer format schema) mdWFS: XMI (data model) GetFeature  new request DoTransform performs semantic transformation and configures a standard WFS

9. III – mdWFS: Concept and Methods What is needed? • Metamodel: UML 2 profile for geospatial applications (e.g. Interlis CSL) • Model Parser to convert models (textual notation) into XMI 2.1 • Language specification for semantic model mappings [UMLT]: Extension of UML, Activity diagram • Model editor to create conceptual model mappings using UMLT • Transformation operations to execute semantic transformations

10. IV – UMLT Specification Schema Mapping Language UMLT Requirements: • Comprehensible for non-computer scientists • Metamodel, HUTN (Human Useable Textual Notation) • Visual, textual AND XML (i.e. XMI) representation • Application of international standards Basic principle: • Independent extension of UML metamodel • Metamodel of UMLT as UML 2 model • EBNF (extended Backus-Naur form) for UMLT grammar specification

11. IV – UMLT Specification Schema Mapping Language UMLT: Superstructure

12. IV – UMLT Specification Schema Mapping Language UMLT: Elements

13. V – Prototype Implementation UMLT Example: Source and Target Data Model

14. V – Prototype Implementation UMLT Example: Transformation Model Centroids

15. V – Prototype Implementation UMLT Example: Trafo. Model in Model Editor

16. V – Prototype Implementation Prototype Implementation Server = Source System Client = Target System Model A: UML/XMI Model B: UML/XMI Request model catalogue Provide model catalogue 1 3 2 mdWFS Order required model Send ordered model A [XMI] 0 4 ili2ora 5 Establish Model Mapping AB ORACLE DoTransform-Request 6 8 Model B + Trafo. Model AB[XMI] 9 AB SQL/Java DoTransform-Response 11 10 Model B ili2ora WFS GetCapabilities DescribeFeatureType GetFeature 7 deegree

17. Conclusion, Lookout • Current evolution of GIS: use of CSL (precond. for semantic Trafo)But: metamodels/profiles and „modeling styles“ differ in detail • mdWFS: semantic transformation is established at conceptual level; independent from any format or (DB-)system • Concept based on GI standards allows for integration into existing (OWS based) infrastructures To do: • Finish implementation of transformation operations • Further development of UMLT • Prototype evaluation in the context of geodata infrastructures

18. Thank you very much! peterstaub@ethz.ch Acknowledgements German Federal Agency for Cartography & Geodesy Swiss Federal Office of Topography TU Munic project team Colleagues at ETH Zurich