Beulens, A.J.M.

Kassahun, A.

Krause, A.

Scholten, H.

English

Wageningen Yield 

CSM’2009 - 46 - Aug-29-2009, 21:34
Chaining EnvironmentalWeb Services: Composing a Web Service Chain
HUUB SCHOLTEN
WageningenUniversity, The Netherlands
ADRIE J.M. BEULENS
WageningenUniversity, The Netherlands
AYALEW KASSAHUN
WageningenUniversity, The Netherlands
ARNO KRAUSE
Alterra, The Netherlands
Keywords: chaining ofWeb services, model-based decision support, environmental application domain,
semantic interoperability, ontology, defining chain functionality
Chaining environmentalWeb services
Decision making in the context of environmental problems is extremely complex, as the multifaceted
interdependencies between relevant physical and man-induced processes need to be considered simulta-
neously. Interactions between these processes make the problems an all encompassing threat, as realised
by the global climatic change, to which policymakers and scientists must join forces.
To support solving environmental problems and problems from other application domains with a
similar complexity, all kind of modules are used to build decision supporting systems. These loosely
or tightly coupled components can include one or more models, data and tools for pre-processing data,
visualisation, statistical analysis. Building monolithic or client-server architecture decision support-
ing systems for a specific problem (problem type, location and time frame) requires substantial efforts,
including collecting the modules, technical coupling, organising proprietary issues and arranging the
proper expertise to use them.
Nowadays, many organisations that are involved in solving complex environmental issues (or similar
other ones) consider to move from selling (modules for) such decision supporting systems to providing
their functionality as service instead. There are several reasons to do so. First the ease of maintenance,
as all services are unique and no copies are needed for specific decision support systems. Furthermore,
these organisations can use these services ubiquitous for their own purposes and sell services to others.
In this way the organisations can easily manage their proprietary tools and data. The final argument
to migrate to a Web service approach is to facilitate interoperability between components that run on
different platforms.
Several initiatives aim at better using and sharing information, data and tools. Achieving a Single
Information Space in Europe for the Environment (SISE) is supposed to be a major initiative to realise
such an information infrastructure. Other initiatives, e.g. the Shared Environmental Information System
(SEIS) and its backbone, the Infrastructure for Spatial Information in Europe (INSPIRE) are main con-
tributions to the infrastructure aimed by SISE, but these initiatives mainly focus on data collection and
Aug-29-2009, 21:34 - 47 - CSM’2009
data sharing and data on itself does not lead to solutions for the environmental problems or to adaptation
to climate change. Models, applications and services are also needed. Without data, these models and
applications are not more than an empty shell containing expert knowledge.
There are many initiatives on Web service chaining, but most are in the field of business applications
and only a few in the environmental domain. Moreover, as far as we know, no initiative supports (semi-
)automated Web service chaining. Therefore, a research initiative has been set up by a consortium
of organisations, excelling in Web service technology and/or in model-based decision support for the
environmental domain. This initiative aims at establishinga research project that will focus on combining
data services and application services (models and other tools) by web enabling them, making use of
existing standards and when necessary, extending the standards.
This initiative, called CHESS, i.e. chaining environmental Web services, aims at developing a
CHESS-system, consisting of the CHESS Integrated Framework (CHESS-IF) and (environmental) Web
services (data, models, tools, etc.); see Figure 9. The purpose of the CHESS-system is to enable and
support users from the environmental domain to find, bind/chain and execute environmental services
distributed over the World Wide Web to create a required application on demand. To realise this the
CHESS-IF has to carry out 3 tasks. The first task, performed by the analyser with the help of the meta
repository is to find Web services that are required to solve the problem at hand. The second task,
performed by the chain designer, is to bind these Web services to an executable chain of environmental
Web services and a workflow, prescribing the chain. In the third task end-users have to execute the chain
of Web services with the help of a simple user-interface.
Figure 9: Conceptual overview of the CHESS-system. The focus in this paper is on the definer, while
Kassahun et al. (2009) will discuss the semantic mapper, both part of the analyser.
Considerable effort has to be spent to convert a minimum set of Environmental data models, tools,
etc. to Web services. The CHESS-system has to be tested in case studies, ranging over a wide spectrum
of environmental problem types.
Three different roles of experts can be distinguished. The (human) composer interacts with the
definer-part of the analyser to define what functionality, data, etc., is needed to solve the environmental
problem at hand. Domain experts, i.e. end-users, have to use the resulting environmental application to
get advice on that problem. Web service builders convert existing, relevant data, models, tools, etc. into
Web services that are CHESS-compliant.
One of the key factors for the success of the CHESS-initiative will be semantic interoperability be-
CSM’2009 - 48 - Aug-29-2009, 21:34
tween the components of the CHESS-system and between chained environmental Web services. This
will be assured by using existing, international and open standards in the broker-part of the meta repos-
itory, e.g. UDDI (Universal Description Discovery and Integration, i.e. a platform-independent registry
for businesses worldwide to list themselves on the Internet), WSDL (Web Services Description Lan-
guage, i.e. an XML-based language that provides a model for describing Web services), OpenMI (Open
Modelling Interface and Environment, i.e. a standard for model linkage in the water domain). For the
information, missing in these standards, an ontology will be developed. Starting points for this ontology
are the work resulting from three EC-sponsored projects OpenMI (in the project Harmon-IT, Gregersen
et al., 2005), Seamless (van Ittersum et al., 2008), AquaStress (Kassahun et al., 2008) and the framework
discussed by Scholten (2008).
An ontological approach to define the problem and process
Developing the CHESS-system is a challenging exercise. One of the bottlenecks in this ambitious en-
deavour consists of translating the mental model of some expert in the field (in Chess terms called the
composer) into requirements that can be used by the CHESS-IF to find and bind the proper environmental
Web services in the right order, generate a workflow depicting this and generate an end-user application
(the bound environmental Web services and a web based user interface. The composer’s mental model
will probably include facts on some specific location and time frame, a suitable mathematical model
type, problem domain and many more.
model/artifact
model representation power
model representation demand
model structure
meta-data
process knowledge
other requirements eisen
problem
problem description
probleem owner
goals
OS denition
domain knowledge
existing models
requirments to models
proces s es
project organisation
data management
model development
model analysis
model use
etc.
meta-knowledge
(basic terminology)
terminology
terminology
terminology
uses
uses
uses
Figure 10: Summary of a structured ontology for multidisciplinary problem-solving, consisting of 4
interrelated ontologies. At a highly abstract level, the ontologies are concepts (presented as rectangles)
and (highly abstract) relations between the ontologies (Scholten, 2008).
Scholten (2008) proposed a 4-leaf-clover-like structured ontology for multidisciplinary problem-
solving, consisting of a meta-ontology (with generic terminology), a process ontology, a problem and
object system ontology and a model ontology (or in more generic terms an ontology to describe problem-
solving artefacts (see Figure 10). This ontological framework distinguishes layers of increasing speci-
ficity (from generic to very detailed). In the context of the project AquaStress (Kassahun et al. 2008)
the 4-leaf-clover framework of Scholten (2008) has been extended and implemented for water stress
mitigation. This resulted in knowledge bases for the water stress mitigation process (analogous to the
process ontology), for the test-sites (analogous to the problem and object system ontology), for options
(analogous to the model ontology) and for indicators (linking the optionswith their effect on the problem
and measurable quantities in the object system). In the Seamless project, an ontology has been devel-
oped that facilitates communication between models or between model-components, including the units
of quantities to be coupled between model modules. To some extent the Seamless results (enabling dif-
ferent models, components and data to let them collaborate as a single (mainly agricultural) simulation
Aug-29-2009, 21:34 - 49 - CSM’2009
model, but unlike what CHESS aims, composite models in Seamless have to run on a single computer
and are not a chain of Web services that are only invoked from a single (end-user) computer.
The definer part of the CHESS-analyser has to handle the rough/vague ideas of the mental model of
the composer on the problem at hand and provide ways to arrive at a solution or an advice on how to
achieve such a solution. The definer has to translate this mental model into terms that can be used by
the semantic mapper. Here we will not present or discuss the design of this definer component, but we
will merely present some examples of items on which information has to be collected by this interactive
input of the CHESS-IF for a specific problem to be solved.
The composer has to provide following information and the definer will use the terminology from
the standards (OpenMI, WSDL, UDDI, etc.) and/or concepts from the additional ontology (part of the
meta repository in Figure 1):
• Questions related to problem and object system:
⋆ On problem: problem subject, wanted solution(s), problem complexity, problem description, problem
context, problem solving methodology, problem domain(s), etc.
⋆ On object system (OS): OS structure (entities, relations/processes between entities), time frame,
location, temporal resolution, spatial resolution, etc.
• On artefact(s): models, data, tools, dynamic, static, proprietary aspects, access issues, etc.
• On problem solving process: what to do (by the chain of environmental Web services), order of things
to do, quality of service, etc.
The result is a set of requirements with the views and perceptions of the composer on the problem
and its solution at hand in a semi-structured format that can be used by the semantic mapper.
Final remarks
If financed, a CHESS-project can realise a substantial part of an infrastructure to deal with environmen-
tal problems, whether induced by climate change or other man-induced environmental impacts. The
CHESS-IF can also be used to asses other problems, but in that case the CHESS-system should be ex-
tended with adequate Web services required to solve the new kind of problems.
A CHESS-project will set an ad hoc standard to environmentalWeb services. Following this standard
will make a Web service CHESS-compliant.
Major risks to deal with include: not enough Web services (first for the test case studies, later to deal
with a wide range of environmental problems. A next risk is to end up with an application that does not
help the end-user sufficiently. Further risks are related to problems with (semi-)automated chaining, due
to technical interoperability or semantic interoperability.
Two topics in CHESS will be innovative: semi-automated chaining ofWeb services and full semantic
interoperability.
Acknowledgements
The ideas in this publication are based on extensive discussions in the context of a FP7-ICT project
proposal. The main contributors in these discussions include Klaus Turowski and Sven Overhage (Uni-
versita¨t Augsburg, D), Marek Makowski (IIASA, A), Onno Roosenschoon (Alterra, NL), Anker Hojberg
(GEUS, DK), Maria-Helena Ramos (Cemagref, F), Lars Chresten Ekebjaerg (DHI, DK), Irina Ribarova
and Galina Dimova (UACEG, BG), George Arampatzis (NTUA, GR).
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Chaining environmental Web services: composing a Web service chain

Chaining environmental Web services: composing a Web service chain

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