=Paper=
{{Paper
|id=Vol-547/paper-58
|storemode=property
|title=Towards WSMO Ontology Specification From Existing Web Services
|pdfUrl=https://ceur-ws.org/Vol-547/100.pdf
|volume=Vol-547
|dblpUrl=https://dblp.org/rec/conf/ciia/BouhissiMB09
}}
==Towards WSMO Ontology Specification From Existing Web Services==
https://ceur-ws.org/Vol-547/100.pdf
Towards WSMO Ontology Specification From Existing
Web Services
Houda EL BOUHISSI1,2, Mimoun Malki1,3, Djelloul Bouchiha1,4,
1
EEDIS Laboratory, Departement of computer sciences, Sidi-Bel-Abbes University, Algeria
2
Houda.elbouhissi@gmail.com, 3 Malki@univ-sba.dz, 4 Bouchiha.dj@gmail.com,
Abstract. Semantic Web Services (SWSs) aim to improve the possibilities for
automated discovery, composition and invocation of Web Services by
providing ontology-based service descriptions expressed in a formal language.
Several approaches have been driving the development of Semantic Web
Service frameworks such as OWL-S (Ontology Web Language for Services),
WSMO (Web Service Modeling Ontology) and WSDL-S (Semantic Annotation
of Web Service Description Language descriptions). This paper focuses on
WSMO; it aims to give a service ontology specification according to WSMO
and using the reverse engineering techniques.
Keywords: Web Service, Semantic Web Services, WSDL, Ontology, Reverse
engineering.
1 Introduction
Semantic Web Services aim to reduce the human effort required to build Service
Oriented Architectures by enabling machines to understand the function and
interfaces of Web services through the addition of semantics; However to enable the
adoption of Semantic Web Service technologies by business it is crucial that adequate
tool support exists which supports the engineer of Semantic Web Services and
Semantically enabled Service Oriented Architectures through the full life cycle.
This paper describes a reverse engineering process [1], a software engineering
technique that consists of extracting useful information from a WSDL file of an
existing Web Service in order to build web service ontology according to the WSMO
conceptual model.
A prototype is implemented which assists the process in the stages. The produced
ontology is stored in WSML file, which provides a mean for the tasks such as
discovery, composition and execution of Web Services.
The remainder of this paper is structured as follows. Section 2 gives a general
overview of Web services; in section 3 we provide an overview of the Semantic Web
and ontology, in section 4, we describe Semantic Web Services and section 5,
discusses related works according to SWS. In section 6, we describe our approach and
present how our tool has been used to map the WSDL file of Google Search Web
Service into WSMO ontology. Finally section 7 concludes the paper and gives future
directives of the project.
2 Web Services
The W3C Web Services Architecture Working Group defines a Web service as: "A
software application identified by an URI, whose interfaces and bindings are capable
of being defined, described and discovered as XML artifacts. Web Service supports
direct interactions with other software agents using XML-based messages exchanged
via Internet-based protocols [2]. To define the infrastructure of the Service Web, a
stack of interrelated standards, such as SOAP, UDDI and, WSDL are presented:
The Simple Object Access Protocol (SOAP ) is a specification for interactions
1
among Web Services across the Internet. SOAP uses XML to exchange structured
and typed information.
WSDL (Web Service Description Language) is an XML-based language for
2
describing Web services and how to access them. WSDL is also used to locate Web
services.
As services become available, they may be registered with a UDDI registry 3
(Universal Description, Discovery and Integration) which can subsequently be
browsed and queried by other users, services and applications.
3 Semantic Web
The goal of the Semantic Web is to solve the current limitations of the Web by
augmenting Web information with a formal (i.e., machine processable) representation
of its meaning [3]. A direct benefit of this machine processable semantics would be
the enhancement and automation of several information management tasks, such as
search or data integration. The Semantic Web s success and proliferation depends on
quickly and cheaply constructing domain specific ontologies.
Ontologies [4] serve as metadata schemas, providing a controlled vocabulary of
concepts, each with explicitly defined and machine processable semantics. By
defining shared and common domain theories, ontologies help people and machines
to communicate concisely supporting semantics exchange, not just syntax.
4 Semantic Web Services
A key problem with the use of standards for Web Service description (e.g. WSDL)
and publishing (e.g. UDDI) is that the syntactic definitions used in these descriptions
do not completely describe the capability of a service and cannot be understood by
software programs. It requires a human to interpret the meaning of inputs, outputs and
applicable constraints as well as the context in which services can be used. To make
1 http://www.w3.org/TR/soap12
2 http://www/w3.org/TR/wsdl
3 http://www.uddi.org
proper use of the Web services advertised by WSDL documents, programmers have
to know in advance the intended meaning of the custom tags that specify the input
and output schemes as well as the names of services that a Web service provides.
Semantic Web Services (SWSs) are the result of the evolution of the syntactic
definition of Web Services and the semantic Web. Semantic Web Services will allow
the semi-automatic and automatic annotation, advertisement; discovery, selection,
composition, and execution of inter-organization business logic, making the Internet a
global common platform.
5 SWSs Approaches
The Major initiatives in the area of SWSs are documented by recent W3C member
submissions: OWL-S [5], WSMO [6] and WSDL-S [7]. The proposals differ in scope,
modeling approach and the concrete logical languages used.
The first approach uses OWL-S, a description language that semantically describes
Web Services using OWL ontologies. OWL-S services are mapped to WSDL
operations, and inputs and outputs of OWL-S are mapped to WSDL messages.
The second approach, the Web Services Modeling Ontology, WSMO, provides
ontological specifications for the description of semantic Web services. One of the
main objectives of WSMO is to give a solution to application integration problems for
Web services by providing a conceptual framework and a formal language for
semantically describing all relevant aspects of Web Services.
WSDL-S is a third approach of creating semantic Web services is by mapping
concepts in a Web service description (WSDL specification) to ontological concepts.
The WSDL elements that can be marked up with metadata are operations, messages,
preconditions and effects, since all the elements are explicitly declared in a WSDL
description.
These approaches are complementary in many ways. Each initiative can be
characterized in terms of (1) a conceptual model describing the underlying principles
and assumptions; and (2) a language or a set of languages that provide the means to
realize the model.
The WSDL-S takes a bottom-up approach by annotating existing standards with
metadata using domain ontologies, the other approaches takes a top down approach
according to a conceptual model and a specific language.
In this paper, we focus on the WSMO approach; we aim to generate the WSMO
ontology semi-automatically using an implemented tool.
6 Reverse Engineering Process
The research contribution of this paper is the description of a reverse engineering
process, a software engineering technique that consists of extracting useful
information from a WSDL file of an existing Web Service in order to build web
service ontology according to the WSMO conceptual model.
It mainly aims at moving from web service application where service s
descriptions are described in a syntactic manner to semantic web service in order to
automate discovery, composition and invocation of Web Services.
The reverse engineering also reduces the efforts and the cost to build new web
service applications by reengineering.
We give first a short overview of WSMO and in the next sections; we describe our
approach in details.
6.1 WSMO Overview
The WSMO initiative aims at providing an overarching framework for handling
Semantic Web services (SWSs).
WSMO identifies four main top-level elements:
1. Ontologies that provide the terminology used by other elements;
2. Goals that state the intentions that should be solved by Web Services;
3. Web Services descriptions which describe various aspects of a service;
4. Mediators: to resolve interoperability problems.
Each of these WSMO Top Level Elements can be described with non-functional
properties like creator, creation date, format, language, owner, rights, source, type;
etc. WSMO comprises the WSMO conceptual model, as an upper level ontology for
SWS, the WSML [8] language and the WSMX [9] execution environment.
The Web Service Modeling Language (WSML) is a formalization of the WSMO
ontology, providing a language within which the properties of Semantic Web Services
can be described.
WSMX provides an architecture including discovery, mediation, selection, and
invocation and has been designed including all required supporting components
enabling an exchange of messages between requesters and the providers of services.
6.2 WSMO Ontology Approach
The planned research can be split into the following sequence of high-level steps
as presented in figure 1:
1. Extraction phase: extraction of information from the XML schema of the
WSDL file.
2. Analyze Phase: definition of a mapping from the XML Schema Conceptual
Model to the WSMO Ontology.
3. Translation phase: Translation of useful information into WSML specification.
Fig. 1. Phases for WSMO Ontology Generation.
6.1.1 Extraction phase
We use the content of the WSDL file to derive WSMO ontology. However, we focus
on the main part that provides us with information about the structure of valid XML
document which is the XML schema definition.
Useful information is: Simple definition types, complex definition types and
attributes.
6.1.2 Analysis phase
In this phase, we use the information extracted from the XML schema part of the
WSDL file to define a mapping from XML elements to terms used in a WSMO
Ontology. Figure 2 shows the definition of this mapping on the design level. This
mapping is done automatically by the analyzer module and the results at least are
stored in a simple XML file.
We propose simple mappings for each of the components extracted at the previews
phase. The mapping produced is roughly based on the following rules:
Fig. 2. Analysis Phase.
1. Rule 1 : Simple type definition:
If a simple type is used to create a new type based on restricting a built-in type, we
create a new concept with the same built-in type and an axiom to define the
restriction. For example the following simple type definition:
The type age is mapped to the WSMO ontology concept with its build-type
positiveinteger.
We deduce also a new axiom which is the restriction of the type: age>=35.
2. Rule 2 : Complex Type Definition
Complex type definitions can obtain sub-components that are a mixture of simple
elements, attributes and other complex type definitions.
We propose to map each complex type to a concept in WSMO Ontology. Sub-
components with simple type built-in are mapped to attributes with the same built-in
type and attributes are mapped to attributes with the same built-in type.
If sub-component itself is a complex type, here we proceed in a recursive manner,
we create first the corresponding concept , then the sub-component are mapped to
attributes with the build-in type.
For example, a complex type definition:
The type employe is mapped to a concept with the corresponding attributes name and
age and their built-in types.
Finally, the complex type embedded in another complex type is mapped at one
hand to sub-concept of the complex type and at the other hand to a concept.
3. Rule 3 : Attributes
An attribute may be associated directly to the root or embedded in a simple or
complex type.
If an attribute depends to the root, we propose to create a new concept with the
built-in type.
If the attribute is embedded in a simple or a complex type, it is mapped to an
attribute of the concept of the complex or the simple type.
For example the following declaration:
The type job is mapped to a concept embedding an attribute jobid with the build-in
type string.
Furthermore, later than this phase, the list of the terms used for the ontology is stored
in an XML file.
6.1.3 Translation phase
The goal of this phase is to translate the list of terms stored previous to in WSML
specification.
This translation generates an ontology expressed in WSML language according to
the WSMO conceptual model.
This phase proceeds with the help of a WSML template file stored in the local
folder. The WSML template has several constants that are replaced with specific
information extracted from the XML file produced in the analyze phase. Once the
specific data is replaced, the new created WSML file is stored to be used next.
6.2. Implementation
In order to validate our approach, we create a prototype with eclipse platform and java
language.
WSDL2WSMO (Web Service Modeling Language to Web Service Modeling
Ontology), a semi automatic tool for the translation of the WSDL file to an
incomplete WSMO ontology.
The Translator engine takes as input a WSDL specification and it returns as output
a partial WSMO ontology description of the Web Service expressed in the WSML
language.
Upon loading a WSDL file (Figure 3), WSDL2WSMO parses the WSDL file and
extracts the XSD definitions defined between the WSDL type tags.
The extracted WSD definitions are mapped to terms used by the ontology
following a set of mapping rules. The mapping rules produce a list of terms which is
stored in an XML file.
Finally, WSDL2WSMO translates the terms into WSML specification and
generates a WSML file.
Fig. 3. Using the tool.
6.3. Case study: Google search
Google.com has exposed a Web service [10] that allows to put Google Search area in
web pages.
The user can embed a simple, dynamic search box to display search results in his
web pages or use the results in innovative, programmatic ways.
The WSDL description of Google search contains 20 types. Using the
WSDL2WSMO tool, we were able to compile the WSDL specification into the
corresponding WSMO ontology specification.
After this translation, the programmer is left with a WSML ontology file and three
tasks to complete the WSMO specification (Web Services, Goals and Mediators).
7 Conclusion & Future Work
Summarizing, Semantic Web Services are an emerging area of research and currently
all the supporting technologies are still far from the final product.
We have described the current main approaches of Semantic Web Services and we
have proposed a new approach, reverse engineering process based to specify WSMO
Ontology from WSDL. Nevertheless, there are still a number of issues concerning
Semantic Web Services being investigated in a number of initiatives.
These issues will have the attention of industry and academia for the next few
years.
Finally the present research has attempted to give a partial specification of the
WSMO ontology with the information extracted from the XML schema part of the
WSDL file.
The work described in this paper may be generalized to include UDDI registry in
order to obtain complete specification of WSMO ontology and make the process
completely automatic.
8 References
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Available online at: http://www.w3.org/TR/2002/ WD-wsa-reqs-20021114.
[3] Berners-Lee, T., Hendler, J., and Lassila, O. (2001). The Semantic Web. Scientific
American, 284(5):34 - 43.
[4] Gruber,T.(1993). A Translation Approach to Portable Ontology Specifications. Knowledge
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[5] OWL Services Coalition, OWL-S: Semantic Markup for Web Services, Dec 2003,
http://www.daml.org/services/owls/1.0/owl-s.html.
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