Semantically-Assisted Geospatial Workflow Design

Gobe Hobona, David Fairbairn, Philip James

g.e.hobona@newcastle.ac.uk

ACM GIS – 8th November 2007 - Seattle

Overview

• Background

• OGC Web Services

• Workflow Enactment

• A Role for Semantics

• Prototype Implementation

• Conclusions

Background

• Open Geospatial Consortium (OGC)

• JISC Grid/OGC Collision Programme• Security : SEE-GEO

• Workflow : SAW-GEO

• OGC Interoperability Experiments (OWS-4 and beyond)

• Challenge: How to support the user in the construction of workflows to address a variety of problems?

OGC Web Services

• Web Map Services (WMS)• Generates geovisualisations/maps from any geo-data source

• Web Feature Services (WFS)• Disseminates vector geospatial data

• Web Coverage Services (WCS)• Disseminates raster geospatial data

• Web Processing Services (WPS)• Runs geocomputational models or geospatial operations on

user-supplied datasets

Workflow Enactment

• Recognised by ISO19119

• Several options for workflow enactment• SCUFL, BPEL, Keppler etc

• Selected BPEL because• OASIS Standard, i.e. WS-BPEL 2.0

• Multi-vendor support including IBM, Sun Microsystems, ActiveEndpoints, Oracle etc

• Availability of open source enactors

An Example Geospatial Workflow

Based on OGC OWS-4 GeoProcessing Workflow Scenario

client

WorkflowEnactor

WPS 1Generalise

WPS 2Clip

WFS

Possible Applications for Geo-Workflows

• Emergency Management• Where each activity depends on the result of a previous activity

• Geographic modelling• Where several steps are needed before a final model is produced e.g.

ESRI Model Builder

• Climate Change scenarios• Where a number of possible routes for workflows are possible

depending on the state of certain variables

A Role for Semantics in Orchestration

SOA

Problem Domain

Concept 1

Concept 2

Concept 3

Concept 4

Services ResourcesWorkflowenactor

Concept1

Concept3

Concept5

EXACT SUBSUMPTION

Calculating Workflow Similarity (1)

Thing

A

BC

DE

I

JK

LM

A path through several other concepts

X A concept

Key:

A path linking two concepts. The concept on the ‘arrow-head’ subsumes the other

Calculating Workflow Similarity (2)

Highsimilarity(request)

Lowsimilarity

Input A A A A A I

Activity B B B B J J

Activity C C C K K K

Activity D D L L L L

Output E M M M M M

Proposed Formula

•α is an application-specific weight applied to each activity in the workflow•n is the number of activities in the requested workflow•Pk is the number of edges between the concept representing the kth activity in the workflow and the concept tagging a candidate service

A Geospatially aware Ontology

• Earth and environmental problem domains present problems of space

• Requiring a geo-aware ontology

• SWEET*

•Earth Realm•Physical Process•Physical Property•Non-Living Substances•Living•Data

•Human Activity•Numerics•Natural Phenomena•Space•Time•Units

* Raskin, R. G. and Pan, M. J. Knowledge representation in the semantic web for Earth and environmental terminology (SWEET).Computer & Geosciences, 31, 9 (2005), 1119-1125.

SWEET

Profile of SWEET

0

50

100

150

200

250

300

sub-ontology

Num

ber

of D

efin

ed C

lass

es

Implementation

• SWEET ontology uploaded from OWL documents into PostgreSQL

• Metadata held in a conventional DBMS with a catalogue service interface

• For each query, semantically related concepts found using Jena

• Additional methods implemented to calculate the number of edges

Architecture

Catalogue Service

Metadata

Eclipse IDE

SAW-GEO Plug-In

BPEL Editor

Client-side Server-side

Ontology

Jena

Response from Search

<Result class="http://sweet.jpl.nasa.gov/ontology/space.owl#AdministrativeRegion">

<Resource id="tiger:poly_landmarks@http://geoserver.itc.nl:8080/geoserver" edges="0" type="wfs" owl="http://sweet.jpl.nasa.gov/ontology/space.owl#AdministrativeRegion"/>

<Resource id="topp:tasmania_state_boundaries@http://gist.fsv.cvut.cz:8080/geoserver" edges="1" type="wfs" owl="http://sweet.jpl.nasa.gov/ontology/space.owl#Region"/>

<Resource id="tiger:giant_polygon@http://geobrain.laits.gmu.edu:8099/geoserver" edges="2" type="wfs" owl="http://sweet.jpl.nasa.gov/ontology/space.owl#SpatialObject"/>

</Result>

Search Concept

Number of edges between Search Concept and tag

Ontology and Suggested Flow views ‘plugged into’ ActiveBPEL Designer

Evaluation

• 15 OGC web services with 180 resources compiled from a Google search for GetCapabilities documents

• Resources tagged with references to OWL Concepts• Tags assigned according to specialist words in resource titles

• Resource titles obtained from GetCapabilities methods

• Average response time for discovery and edge count• Greatest cost where several resources are tagged with

concepts ‘far away’ from the search concept

• Possibilities for parallelisation as each concept can be searched for on a separate machine

Conclusions and Future Work

• Proposed formula offers an algorithmic approach for comparing linear workflows

• Limitations to complete automation due to variations between properties of service inputs and outputs

• Future work should investigate non-linear workflows and the inclusion of conditional activities

• Need for a test corpus for evaluating catalogues of OGC web services

Thank You

g.e.hobona@newcastle.ac.uk