As a newborn paradigm for integrating Web services with semantic Web
technology, semantic Web services (SWS) have been followed with vast
interest from research community. Particularly, semantic Web services
composition and contracting have been identified as among the most
prominent issues in SWS arena, but a number of obstacles remain pending
and unsolved nonetheless, such as the semantic gap among partner services,
process compliance verification, and business rules analysis, etc.
The heterogeneity nature of Web services also bring in challenges for
their interoperability and manageability. Different partner services can adopt
syntactically different terms and vocabulary to express the same semantics,
and vice versa. Even worse, Web services may exacerbate this gap since
many of them are QoS-oriented, and those QoS parameters can be defined by
different equations and matrix in practice. This semantic gap is imposing
great impact on various issues of semantic Web services composition and
contracting.
A semantic Web services composition or contracting process usually
involves both Web services orchestration and choreography. Moreover, many
complicated constraints, such as inter-task constraints, need to be
incorporated into the control flow of the overall contracting process.
Accordingly, they also need a general verification methodology to check their
compliance so as to ensure each partner to cooperate correctly.
Meanwhile, business rules are very important for guiding various Web
services’ cooperation. However, the current de-facto standards barely provide
any abstract and high level guidance to design and implement business rules,
making it a particularly time-consuming and error-prone task. Moreover, due
to that service contracting usually involves multiple parties whose interests
and concerns may vary from each other, there is no guarantee that the
designed business rules can work together in a compatible, efficient and
logically correct way. For instance, there may be potential conflicts among those rules, which may put the overall process into the jeopardy of
inconsistency. In this regard, rule analysis and verification for services
contracting are urgently required to augment the reliability and usability.
In this thesis, we address our work on four aspects: process modeling,
semantic verification, rule analysis, and exception handling.
First of all, we choose a formal variant of Description Logics, namely,
ALCQO(Q*), which is capable of extending the conceptual modeling ability
of classical DLs with process modeling and numerical constraint
representation ability, while still retains decidability for major reasoning
problems.
Secondly, we propose a general modeling and verification mechanism
for Web services composition. To provide a general guidance for users, we
articulate a suite of transformation rules to automatically rewriting a
workflow-based Web services contracting process into our ALCQO(Q*)
framework, while can be regarded as harmless w.r.t. the overall reasoning
complexity. Moreover, the verification process can be built on the
transformation result and benefit from its soundness and completeness.
Thirdly, we propose a semantic analysis mechanism for business rules.
We choose ALCQO(Q*) as the underlying logic, and provide a formal
mapping to transform ECA rules, so that the semantics in the original ECA
rules can be captured and are computationally traceable. To this end, we
further investigate some important properties for business rules, namely,
redundancy, termination and conflict, and propose several sound and
complete algorithms to resolve them.
Lastly, we propose to capture exception contexts to facilitate exception
handling in a composite service. Particularly, we present a mechanism to
capture external exception contexts from partners’ applications through
Contexts enhanced Web Services Conversation (CeWSC), which introduces
just a minimal overhead by an effective use of SOAP header and
acknowledgement. Moreover, we also provide an enhanced event-driven
mechanism to incorporate exception contexts into exception handling for a
composite service to facilitate its flexible and reliable execution.
| Date of Award | 15 Jul 2010 |
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| Original language | English |
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| Awarding Institution | - City University of Hong Kong
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| Supervisor | Qing LI (Supervisor) |
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