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Formalizing Web Service and Modeling Web Service-based System

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Formalizing Web Service and Modeling Web Service-based System Powered By Docstoc
					                         Formalizing Web Service
                and Modeling Web Service-based System
                  Based on Object Oriented Petri Net1

                               Xiaofeng Tao 1,2, Changjun Jiang 1,2
                 1 Dept. of Computer Engineering & Technology,Tongji University,
                                     200092, Shanghai, China
                 2 Tongji Branch, National Engineering & Technology Center of High

                          Performance Computer, 200092, Shanghai, China
                                    taoxiaofeng@163.com
                                   cjjiang@online.sh.cn



          Abstract. Recently Web Service has become a hot spot. Its main idea is to
          integrate a group of services to construct new value-added Web Service-based
          systems, which run on the World-Wide-Web. It’s necessary to get formalizing
          and modeling techniques and graphic tools for reliable Web Service and its
          application construction. In this paper, an approach to formalizing Web Service
          and modeling its application system based on Object Oriented Petri net (OOPN)
          is proposed. By means of this approach, a formal description of Web Service
          based on OOPN can be obtained, and control flow of Web Service-based
          system can be modeled. Furthermore, this approach is on the top of
          WSDL, so it’s of practicality for application.



1 Introduction

To quickly develop Web Service-based distributed application, there is a need for a
kind of technique to abstract, formalize, model, and analyze it at the design time.
Presently Business Process Execution Language for Web Services (BPEL4WS) [3] is a
complex procedural language for Web Service integration, which is based on the
stack of WSDL, SOAP, and UDDI. However, it only describes the business process
with a kind of XML-based document, and doesn’t provide a formal validation.
   In this paper, an approach based on OOPN is proposed for describing Web Service
and modeling control flow of Web Service-based application. There are some good
features in this approach. Firstly, this approach is on the stack of WSDL. Through the
relationship between WSDL and OOPN, it’s easy to describe Web Service based on
OOPN. So it’s valuable for engineering application. Secondly, because of the object-

1   This work is support partially by projects of National 863 Plan (2002AA1Z2102A), Excellent
     Ph.D. Paper Author Foundation of China (199934), Foundation for University Key Teacher
     by the Ministry of Education, Shanghai Science & Technology Research
     Plan(03DZ15029,03JC14071).
oriented conception, this approach can capture the necessary semantics of Web
Service. Thirdly, the reliable control flow can be graphically model based on OOPN.
Furthermore, the modeled system is based on formal description, so it can be easily
analyzed.
   The remainder of this paper is organized as follows. Some basic conceptions are
presented in Section 2. Section 3 is devoted to the mapping relationship between Web
Service and OOPN, as well as construction of a formal Web Service based on OOPN.
Section 4 gives steps for modeling control flow of Web Service-based system.
Section 5 discusses the analysis and verification of Web Service-based system.
Section 6 provides some concluding remarks.


2 Basic Conception



2.1 Web Service

Considered components for describing Web Service in WSDL, without regard to the
concrete protocol and property of Web Service, a formal definition of Web Service
can be expressed as follows. Notablely,this definition is just used to describe its
structure for modeling, not a complete definition.
Definition 1: a Web Service is a 6-tuple,WebService=(Message , Operation ,
Interface,Binding,Endpoint,Service) where Message is a finite set of messages,
Operation is a finite set of operations, Interface is a set of {Operations, Message,
F}where F is a relationship between Message and Operation, Binding is a function
mapping a concrete protocol to an Interface,Endpoint is a function mapping a
concrete endpoint to a bound Interface, Service is a set of endpoints.


2.2 OOPN

OOPN, a high level Petri net, is a kind of modeling language for engineering
application, strictly defined by object-oriented conception. OOPN is made up of
external object structure, internal object structure and control structure.
Definition 2[2]: an OOPN system is a 4-tuple,OOPNS=( O,G,P,F),where O is a
finite set of object place nodes, G is a finite set of message-passing transition nodes, P
is a finite set of message-synchronization place nodes, and F is a finite set of directed
arcs.
Definition 3[2]: OOPN object is a 6-tuple, O=(Method,Status,Property,OM,
IM,F),where Method is a finite set of method transition nodes that represent an
subnet of OOPN, Status is a finite set of dynamic state place nodes, Property is a
finite set of still state place nodes, IM is a finite set of input message place nodes, OM
is a finite set of output message place nodes, F is a finite set of directed arcs.
3   Mapping Relationship between Web Service and OOPN

Since WSDL has been a standard of Web Service description, it’s more significative
to map the components of WSDL into the ones of OOPN for engineering. That’s, the
approach in this paper is on the top of WSDL (A in Figure 1 illustrates the protocol
stack). In Definition 1 and Definition 3, five mapping relations can be obtained as
follows (all the proofs are omitted).
                          ∃Message→{IM,OM}                                      (E1)

                           ∃Operation→Method                                    (E2)

                               ∃Interface→O                                     (E3)

                                ∃FWS→FOOPN                                      (E4)

          ∃Service→{o} where o is an instance set of OOPN object                (E5)
  Based on the above five mapping relationship expressions, some conclusion can be
obtained as follows.
Definition 4: an OOPN-described Web Service is a 2-tuple, WS={O, o} where O is
an Interface object, and o is an instance of the Interface object.
Theorem 1: an Interface in a formalizing Web Service described by OOPN is a sub
object net of OOPN.
Theorem 2: a Service in a formalizing Web Service described by OOPN is a
concrete instance of a sun object net.


4   Modeling Web Service-based System

Once an OOPN description of Interface has been got from a WSDL document of
Web Service by means of mapping relationship, then a service is just a concrete
instance of this Interface. Thus, a group of services described by OOPN can be
integrated into the control flow model of Web Service-based system by OOPN rules.
B in Figure 1 illustrates the modeling step.


5   Web Service-based System Analysis

Analyzing the behavioral feature of the control flow model can be used to verify the
business logic of the Web Service-based system. For the convenience of analysis, it’s
necessary to reduce the complexity of the model into a behavior-equivalence modal
based on general Petri net. As a matter of fact, a “Port” and an operation of a Web
Service represent the same process in a system model, so a service subnet is
redundant for the behavioral feature of a model. Pruning the service subnet, the old
net can be changed into a general Petri net. With the help of reachable diagram, the
business logic of the system can be verified, and in the meanwhile, the deadlock of
the model can be checked. The detailed way to analyzing the model performance
based on Petri net can be found in [5].
                                                                               OOPN
                                                           OOPN-Based         Definition
                                2                          Web Service
                                                            Description       4
                                    Mapping Relationship                                   OOPN-based
                                         Between                                           Model of Web
        System                       WSDL and OOPN
        Model                                              3                               Service-Based
                      1      WSDL-                                                            System
       OOPN                                                 OOPN-Based
                             Based
     WSDL                                                   Web Service
                           Web Service
                                                             Description
                           Description
                            Document
 A. Protocol Stack                                         B. Modeling Step

Fig. 1. (A) Illustration of the protocol stack of this approach, (B) Illustration of the modeling
step of this approach



6    Conclusion

This paper has proposed an approach to formalizing Web Service and modeling
control flow of Web Service-based system based on OOPN. By means of this
approach, Web Service described by WSDL can be mapped into the one described by
OOPN. And then the control flow of Web Service-based application system can be
modeled by OOPN. Future work includes verifying the model and evaluating
dynamic performance of the system.


Reference

1.   Chinnici, R., Gudgin M., etc.: Web Services Description Language (WSDL) Version 1.2
     Part 1: Core Language, http://www.w3.org/TR/wsdl12/#Service (2003)
2.   Tao, X.F., Jiang,C.J., Duan J.T.: Construction of a Kind of Object-Oriented Petri Net and
     its Application, Mechanical Science and Technology, Vol. 22, No.5 (2003)
3.   Andrews, T., Curbera, F., Dholakia, H., etc.: Specification: Business Process Execution
     Language for Web Services Version 1.1. http://www-106.ibm.com/developerworks/libra-
     ry/ws-bpel (2003)
4.   Hamadi, R., Benatallah, B.: A Petri Net-based Model for Web Service Composition, In
     Proc. Fourteenth Australasian Database Conference (ADC2003) ,Vol. 17 (2003)
5.   Tadao, M.: Petri Nets: Properties,Analysis and Applications, Proceeding of IEEE, Vol 77,
     No. 4 (1989) 541-560

				
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