model-driven web feature service

Model-Driven Web Feature Service

A Way Towards Enhanced Semantic Interoperability

Peter Staub, ETH Zurich

FOSS4G 2007 – Victoria B.C., September 26, 2007

Peter Staub, ETH Zurich 2

Overview

• Data modeling and semantic interoperability: Fundamentals

• Research project mdWFS

• Why a model-driven WFS? Enhancements in semantic interoperability

• Concepts, methods

• Prototype implementation


What is Interoperability?

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Swiss plug does not fit American socket

So, an appropriate adaptor plug (and a voltage transformer) is needed!

I – Modeling and Interoperability Fundamentals

Interoperability: Format Support + Data Model TransformationInteroperability: Format Support + Data Model Transformation

230V ~50 110V ~60


Data Modeling and Semantic Interoperability

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PIM>PSM Mapping

GML App.Schema Logical/Physical

Schema A (PSM)

<<Model>>

<<derive>> <<derive>>

Logical/PhysicalSchema B (PSM)

<<Model>>

Encoding

GMLInstanceDocument

Database A, Transfer format A

<<instantiate>>

Database B, Transfer format B

<<instantiate>>

MOF

<<Metamodel>>

<<instantiate>> <<instantiate>>

MetamodelCSL X

<<Metamodel>>Metamodel

CSL Y

<<Metamodel>>

Schema Translation

<<derive>>

Conceptual Schema Mapping

<<derive>>

:Instance Translation

<<instantiate>> <<instantiate>>

ConceptualSchema A (PIM)

<<Model>>

ConceptualSchema B (PIM)

<<Model>> Formal mapping

Real World Real World

Application Domain„Model“ B

Application Domain„Model“ A

I – Modeling and Interoperability Fundamentals


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

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„Model-Driven Approach for AccessingDistributed Spatial Information Using Web Services“

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

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mdWFS Interface

Idea: model driven Web Feature Service mdWFS

• Extension of OGC WFS specification

• Ability to store and deliver conceptual models (UML/XMI)

• New operation DoTransform() 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!

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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 DoTransformperforms semantic transformation and configures a standard WFS

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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

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III – mdWFS: Concept and Methods


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

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IV – UMLT Specification


Schema Mapping Language UMLT: Superstructure

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Schema Mapping Language UMLT: Elements

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UMLT Example: Source and Target Data Model

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V – Prototype Implementation


UMLT Example: Transformation Model

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Centroids



UMLT Example: Trafo. Model in Model Editor

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7ili2ora

Prototype Implementation

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Client = Target System

Model B: UML/XMI

ORACLEORACLE

Server = Source System

Model A: UML/XMI

0

mdWFS

WFSWFS

1Request model catalogue

2Provide model catalogue

3Order required model

4Send ordered model A [XMI]

5 Establish Model Mapping ABili2ora

SQL/Java

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AB

6DoTransform-Request

Model B + Trafo. Model AB [XMI]

deegree

9Model B

DoTransform-Response10

GetCapabilitiesDescribeFeatureType

GetFeature11



Conclusion, Lookout

1. Current evolution of GIS: use of CSL (precond. for semantic Trafo)But: metamodels/profiles and „modeling styles“ differ in detail

2. mdWFS: semantic transformation is established at conceptual level; independent from any format or (DB-)system

3. 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

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Thank you very much!

[email protected]

Acknowledgements

German Federal Agency for Cartography & Geodesy

Swiss Federal Office of TopographyTU Munic project teamColleagues at ETH Zurich

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model-driven web feature service

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