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WSOL – A Language for the Formal Specification of Various
Constraints and Classes of Service for Web Services
Vladimir Tosic, Bernard Pagurek, Kruti Patel
Research Report OCIECE-02-06
November 2002

WSOL – A Language for the Formal Specification of
Various Constraints and Classes of Service for Web
Services
Vladimir Tosic, Bernard Pagurek, Kruti Patel
Department of Systems and Computer Engineering, Carleton University 1125 Colonel By Drive
Ottawa, ON, K1V 6L8, CANADA
+1 (613) 520-2600, x3548

{vladimir, bernie, kpatel}@sce.carleton.ca
ABSTRACT
We are developing a language, Web Service Offerings Language (WSOL), for the formal specification of various constraints, management statements, and classes of service for Web Services. WSOL is an XML (Extensible Markup Language) notation

compatible with WSDL (Web Services Description Language).
A service offering in WSOL is a formal description of one class of service of a Web Service. It contains formal representation of various constraints: functional (pre-, post-, and futureconditions), Quality of Service (QoS, a.k.a. non-functional, extrafunctional), and access rights. It also contains management statements, such as statements about prices, monetary penalties, and management responsibilities. One Web Service can be

associated with multiple service offerings. For easier
specification of similar service offerings, WSOL enables
specification of constraint groups (CGs) and constraint group templates (CGTs). We have also developed a format for
representation of dynamic relationships between service
offerings.
WSOL service offerings are simple contracts and SLAs (Service Level Agreements) between Web Services. Describing a Web
Service in WSOL, in addition to WSDL, enables monitoring,
metering, and management of Web Services. The Web Service,
its consumer, or one or more designated third parties (usually SOAP message intermediaries) can meter QoS metrics and
evaluate constraints in WSOL service offerings. Further,
manipulation of service offerings can be used for dynamic
adaptation and management of Web Service compositions. In
addition, WSOL supports selection of a more appropriate Web
Service and service offering for particular circumstances.
The main distinctive characteristics of WSOL, compared to
recent related works, are its expressive power, features that reduce run-time overhead, and orientation towards management applications.

Categories and Subject Descriptors
K.6 [Management of Computer and Information Systems],
D.m [Miscellaneous], H.m [Miscellaneous].

General Terms
Management, Measurement, Languages.

Keywords
Web Service, constraint, class of service, service offering, SLA, WSDL, WSOL, management of Web Services.

1. INTRODUCTION
In the last couple of years, there has been a lot of work on Web Service technologies. The W3C (World Wide Web Consortium)
defines a Web Service as “a software application identified by a URI, whose interfaces and binding are capable of being defined, described and discovered by XML artifacts and supports direct interactions with other software applications using XML based messages via Internet-based protocols” [12]. URI means


Uniform Resource Identifier’ and XML means ‘
Extensible
Markup Language’ The three main Web Service technologies
.
are the SOAP protocol for XML messaging, the WSDL (Web
Service Description Language) description language, and the
UDDI (Universal Description, Discovery, and Integration)
directory. The ultimate goal of the standardization efforts related to Web Services is a standard platform, based on already widely used technologies like XML, for distributed application-toapplication (A2A) and business-to-business (B2B) integration [3].

While Web Services can be used for providing services to human end users, their true power is leveraged through compositions (a.k.a. orchestrations, choreographies, flows, networks) of Web Services. Hereafter, by a consumer...
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