384 A Context-Based and Policy-Driven Method to Design and Develop Composite Web Services step is to satisfy the needs of bodies that have interests and/or obligations in strengthening or restricting the execution of Web services on top of their resources. For instance, a Web service does not obtain the necessary authorizations to operate on a resource since this Web service does not comply with this resource’s requirements such as permitted execution-time. CP4WS manages the deployment of Web services on resources with policies. For standardization purposes with the policies associated with Web services’ behaviors, WSPL is also adopted to specify deployment policies. Deployment Policy for Permission. It is about a Web service that receives the neces- sary execution authorizations from a resource. These authorizations are based on the state of the resource, which manifests itself using its R- context. The following illustrates a deployment policy for permission in WSPL. It states that a resource accepts the execution request of a Web service subject to evaluating <Condition> to true. This condition refers to some arguments like number of active component Web services (line 07) that the resource supports their execution and next acceptance of the resource to additional component Web services (line 12). In the policy, <TrueConclusion> (line 17) shows the permission of execution, whereas <FalseConclusion> (line 20) shows the contrary. In case of positive permis- sion of execution, yes-permission-deployment procedure is executed (line 18), which results in updating the following arguments: resource&state per active participation of W-context of the Web service (Table 1) and number of active component Web services of R-context of the resource. 01: Policy (Aspect=”PermissionDeployment”) 02: <Rule xmlns=”urn:oasis:names:tc:xacml:3.0:per- mission:policy:schema:wd:01” 03: xmlns:proc=”permission-deployment” RuleId=”Pe rmissionDeploymentWS”> 04: <Condition> 05: <Apply FunctionId=”and”> 06: <Apply FunctionId=”integer-less-than” DataType=”boolean”> 07: <SubjectAttributeDesignator AttributeId=”Numbe rofActiveComponentWebServices” 08: DataType=”integer”> 09: <SubjectAttributeDesignator AttributeId=”Maximu mNumberofComponentWebServices” 10: DataType=”integer”> 11: </Apply> 12: <SubjectAttributeDesignator AttributeId=”NextAc ceptanceofComponentWebServices” 13: DataType=”boolean”> 14: </Apply> 15: </Condition> 16: <Conclusions> 17: <TrueConclusion> 18: <proc:do> yes-permission-deployment </proc: do> 19: </TrueConclusion> 20: <FalseConclusion> 21: <proc:do> no-permission-deployment </proc:do> 22: </FalseConclusion> 23: </Conclusions> 24: </Rule> Deployment Policy for Restriction. It consists of preventing a Web service form being executed over a resource. Besides the example of resource failure, restrictions could be geared towards the reinforcement of the execution clauses that are agreed upon between a Web service and a resource. For example a Web service binds a resource for execution before the scheduled time. The following illustrates a deployment policy for restriction in WSPL. It states that a Web service can be restricted from execution subject to evalu- ating <Condition> to true. This condition checks that a positive permission (line 04) of execution has been issued (line 06) and the agreed execu- tion time is valid. The execution time of a Web 385 A Context-Based and Policy-Driven Method to Design and Develop Composite Web Services VHUYLFHLVLGHQWL¿HGXVLQJQH[WFRPSRQHQW:HE services per active participation argument of R- context of the resource. 01: Policy (Aspect=”RestrictionDeployment”) 02: <Rule xmlns=”urn:oasis:names:tc:xacml:3.0:gen- eralization:policy:schema:wd:01” 03: RuleId=”RestrictionDeploymentWS”> 04: <Condition> 05: <Apply FunctionId=”and”> 06: <SubjectAttributeDesignator AttributeId=”YesPer missionDeployment” 07: DataType=”boolean”> 08: <Apply FunctionId=”equal” DataType=”boolean”> 09: <SubjectAttributeDesignator AttributeId=”Executi onTime” DataType=”String”> 10: </Apply> 11: </Apply> 12: </Condition> 13: <Conclusions> 14: <TrueConclusion RestrictionDeployment = “No”> 15: <FalseConclusion RestrictionDeployment = “Yes”> 16: </Conclusions> 17: </Rule> CP4WS TO IMPLEMENT AMIN SCENARIO We discuss the work we carried out following the use of CP4WS to design the system implement- ing Amin scenario. For compatibility purposes, Sun Microsystems’s tools are used: J2EE 1.4 to develop Web services and XACML Open Source to develop policies. Figure 5 illustrates the archi- tecture of this system that comprises four types of managers. It should be noted that the role RIHDFKPDQDJHULVDVVRFLDWHGZLWKDVSHFL¿F step in CP4WS. Figure 6 shows some snapshots related to the use of the system implementing Amin scenario. The VSHFL¿FDWLRQPDQDJHU supports design- HUVGXULQJWKHVSHFL¿FDWLRQRIFRPSRVLWH:HE services. This calls for identifying the appropri- DWHFRPSRQHQW:HEVHUYLFHV7KHVSHFL¿FDWLRQ work is carried out through a composition environment, which is a set of integrated tools that assist designers create and edit new and ex- LVWLQJVSHFL¿FDWLRQVRIFRPSRVLWH:HEVHUYLFHV respectively. We use a composition environment that was developed in one of our previous proj- ects (Maamar, 2006e). This environment, also, supports translating composite Web service VSHFL¿FDWLRQVOLNHWKHRQHVKRZQLQ)LJXUH LQWR%3(/VSHFL¿FDWLRQ The selection manager is responsible for identifying the component Web services that satisfy user needs. This manager is triggered upon XVHU¶VUHTXHVWDQGLGHQWL¿FDWLRQRIWKHDSSURSUL- DWHFRPSRVLWH:HEVHUYLFHVSHFL¿FDWLRQ,QWKH current system, the selection is not only driven by the resulting functionality of the composition the user needs (e.g., to reach a meeting place by taxi or by bus according to weather conditions). It also considers Web services QoS parameters that affect the selection process like response time, performance, and throughput. These con- straints are expressed with WSPL policies. The policy manager makes Web services bind to appropriate behaviors according to the progress of a composition. Finally, the context manager keeps track of the contexts of users, Web services, and resources. Contexts’ arguments are of different types and their values change over time. Figure 7 illus- WUDWHVWKHVSHFL¿FDWLRQRIW-context of Weather WS using the prototype. Therefore, the context manager is supported with a real-time triggering mechanism that feeds context parameters with fresh values. Details of contexts are structured DV;0/¿OHV%HIRUHVHQGLQJWKHVHOHFWHG:HE services’ addresses to the user for invocation, the policy manager ensures that these Web services comply with the policies reported previously. Upon approval of the policy manager, the selec- tion manager initiates the search of the resources on which the Web services will operate. Figure 8 386 A Context-Based and Policy-Driven Method to Design and Develop Composite Web Services User Specification manager 2. Submission Selection Manager 1. Request 3. Selection Policy Manager 4. Verification Repository of Web services Context Manager Binding Binding Repository of resources 5. Search 6. Services for invocation Composite level Component level Binding Approval(yes,no) Figure 5. Architecture of the system implementing Amin scenario Figure 6. Snapshots from the prototype 387 A Context-Based and Policy-Driven Method to Design and Develop Composite Web Services shows parts of the policy that restricts the execu- tion of Weather WS on a resource. RELATED WORK Web services are a very active area of Research and Development. However, to our knowledge, few projects have aimed at suggesting design and development methods for Web services based on context and driven by policies. We present in the following some projects that helped shape the steps and annotations of CP4WS. These projects mainly target design and development methods. In CP4WS, context is part of the exercise of modeling composite Web services. Other projects such as (Brenner, 2003) use Web services to man- aging context provisioning. Breener and Schiffers envision that context information will typically be provided by autonomous organizations (or context providers), which means heterogeneity and distribution challenges to deal with. Additional challenges are cited in (Brenner, 2003) including what is the optimal sequence for gathering and combining the required context information, how to secure the whole context provisioning process, and how is the cooperation between the providers of context achieved, and even enforced? In (Baresi, 2005), Baresi et al. propose a policy-based approach to monitor Web services’ functional (e.g., constraints on exchanged data) and non-functional (e.g., security, reliability) re- quirements. In this approach Baresi et al. report on WKHGLIIHUHQWW\SHVRISROLFLHVWKDWFDQEHGH¿QHG along the life cycle of a Web service (Mukhi, 2004). These types are service policies, server policies, supported policies, and requested policies. In (UWA, 2002), the Ubiquitous Web Appli- cations (UWA) Consortium proposes a frame- work that comprises several methodologies, meta-models, and tools for designing ubiquitous Web applications. Organization and execution models permit designing the business processes that underlay such applications. The organiza- tion model expresses the hierarchical relations between activities of the same business process. These relations are described using an UML class diagram. In addition some properties (e.g., ACID properties) can be associated with each activity. The execution model describes the possible execu- WLRQÀRZVRIWKHGLIIHUHQWDFWLYLWLHVWKDWFRPSRVH WKHRUJDQL]DWLRQPRGHO7KHVHÀRZVFRQVWLWXWHWKH dynamic aspect of the business process and are expressed using an UML activity diagram. In (Brambilla, 2006), Brambilla et al. propose a Web engineering method for the high-level VSHFL¿FDWLRQRISURFHVVHVDQG:HEVHUYLFHVEDVHG applications. This method relies on extending the Web Modeling Notation (WebML (Ceri, 2000)) with standard process modeling concepts and Web services-based application distribution primitives. Process modeling concepts expressed in the Busi- ness Process Modeling Notation ( http://www.bpmn. org) are added to WebML so, process requirements in terms of interactions over the Web are expressed. Web services are used as a means to deal with the process distribution requirements. Interesting to note that this method has been implemented as a case tool through the use of WebRatio ( http://www. WebRatio.com). In (Detroyer, 2003), De Troyer and Casteleyn work on an adaptation of the existing Web Site Design Method (WSDM). The objective is to model complex business processes in the context of Web applications and to support some advanced features like transactions and persistence of pro- cesses. Task modeling and navigational design, which are the core steps in the conceptual design of WSDM, have been changed to accommodate the requirements of modeling complex processes. The ConcurTaskTrees (CTT) notation (Paterno, LVPRGL¿HGWRRQO\FRQVLGHUWKUHHFDWHJRULHV of tasks: application, interaction, and abstract. Abstract task refers to the task that needs to be decomposed. Application and interaction tasks refer to the tasks executed by applications and users respectively. The navigation structure that 388 A Context-Based and Policy-Driven Method to Design and Develop Composite Web Services Figure 7. W-context of Weather Web Service <rdf:RDF xmlns:WC=http://www.nitk.ac.in/ sattanathan/OWLC/Context/WC# xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns# <rdf:Description rdf:about=”http://defaultURI/WC#”> <WC:CorrectiveActionsPerFailureType>Nil</WC:CorrectiveActionsPerFailureType> <WC:ResourceAndStatePerActiveParticipation>Resource1/Suspended </WC:ResourceAndStatePerActiveParticipation> <WC:MaximumNumberOfParticipations>10</WC:MaximumNumberOfParticipations> <WC:ReasonsOfFailurePerActiveParticipation>Nil</WC:ReasonsOfFailurePerActiveParticipation> <WC:RegularActions>Book Taxi</WC:RegularActions> <WC:PrevisousWebServicesPerActiveParticipation>Nil </WC:PrevisousWebServicesPerActiveParticipation> <WC:NextWebServicePerActiveParticipation>TAxi or Bus Schedule </WC:NextWebServicePerActiveParticipation> <WC:Label>WEather</WC:Label> <WC:Date>Dec 25, 2005 6:28:39 PM</WC:Date> <WC:CurrentWebServicesPerActiveParticipation>Location <WC:NextPossibiliyOfParticipation>Possible</WC:NextPossibiliyOfParticipation> <WC:NumberOfActiveParticipations>7</WC:NumberOfActiveParticipations> </rdf:Description> </rdf:RDF> Figure 8 . Restriction Policy on Weather Web Service <Policy PolicyId=”Restriction” RuleCombiningAlgId=”urn:oasis:names:tc:xacml:1.0:rule-combining-algorithm:ordered-permit-over- rides”> <Description>Restriction policy on WEather Web Service</Description> <Target> <Subjects> <Subject> <SubjectMatch MatchId=”urn:oasis:names:tc:xacml:1.0:function:rfc822Name-match”> <AttributeValue DataType=”http://w3.org/ #string”>users.example.com</AttributeValue> <SubjectAttributeDesignator AttributeId=”urn:oasis:names:tc:xacml:1.0:subject:subject-id” DataType=”urn:oasis:names:tc:xacml:1.0:data-type:rfc822Name”/> </SubjectMatch> </Subject> </Subjects> <Resources> <Resource> <ResourceMatch MatchId=”urn:oasis:names:tc:xacml:1.0:function:anyURI-equal”> <AttributeValue DataType=”http://w3.org/ #anyURI”>http://webservice.weather.com/</Attribute- Value> <ResourceAttributeDesignator AttributeId=”urn:oasis:names:tc:xacml:1.0:resource:resource-id” DataType=”http://www.w3.org/2001/XMLSchema#anyURI”/> </ResourceMatch> </Resource> </Resources> <Actions> <AnyAction/> </Actions> </Target> <Rule RuleId=”RestrictionWS” Effect=”No”> <Target> 389 A Context-Based and Policy-Driven Method to Design and Develop Composite Web Services describes how a user should perform tasks, is then automatically generated for different users from the CTT augmented with temporal relationships between the different tasks. In (Cappiello, 2006), Cappiello and Pernici suggest a method to solve run-time data quality problems in self-healing Web services environments. Failures due to run-time data quality problems are detected and the proposed method produces a list of recovery actions for quality improvements. The main step in the method concerns working on the warning message generator, which is in charge of monitoring the system, detecting all the anomalies that occur in data management, and identifying the sources of data quality problems. A framework for analyzing and comparing Web application design methodologies is pre- sented in (Distante, 2007). Distante et al. present the business/user/system requirements for de- signing business process. Business requirements FRUUHVSRQGWRWKHLGHQWL¿FDWLRQRIWKHGLIIHUHQW activities included in a given Web transaction and their semantic associations, and the logical/ temporal order in which such activities must be executed by the user. User requirements include WKHVSHFL¿FDWLRQRIWKHVHWRIDFWLYLWLHVZKLFKFDQ be suspended and resumed in case of long-lived transactions, and the description of how an activity can be customized depending on the state of the ongoing transaction. The system requirements UHIHUWRWKHGH¿QLWLRQRIWKHLQIRUPDWLRQREMHFWV affected by the execution of an activity, and the GH¿QLWLRQDQGWKHPDQDJHPHQWRIWKHVWDWHVRID Web transaction. These design requirements are then used to evaluate and compare two Web ap- plication design methodologies, namely OOHDM (Schmid, 2004) and UWA (UWA, 2002). To wrap up this related work section, we highlight again the features of CP4WS per step. Five steps were developed. The first step uses UML use-cases to identify and specify users' needs. The second step uses service chart diagrams and state chart diagrams to specify the orchestration of the component Web services that constitute a composite Web service. The third step defines the arguments that form the context of the component Web services and of other participants like users and resources that interact with these component Web services. The fourth step uses WSPL to specify the policies that manage the behavior that the component Web services expose to the external environment. Finally, the last step uses WSPL again to manage the performance of the component Web services on top of the computing resources. CONCLUSION In this chapter, we presented our CP4WS method that targets those who are responsible for the design and development of information systems based on Web Services. We discussed how com- position of Web services permits addressing the VLWXDWLRQRIDXVHU¶VUHTXHVWWKDWFDQQRWEHVDWLV¿HG by any single, available Web service, whereas a composite Web service obtained by combining a set of available Web services might be used. The core concepts of CP4WS are context, policy, service chart diagram, state chart diagram, and UHVRXUFH&3:6FRQVLVWVRI¿YHVWHSVXVHUQHHGV LGHQWL¿FDWLRQ DQG VSHFL¿FDWLRQ :HE VHUYLFHV orchestration, Web services contextualization, :HE VHUYLFHV EHKDYLRU VSHFL¿FDWLRQ DQG :HE services deployment. As part of our future work, we aim at adding WZRPRUHVWHSVWR&3:67KH¿UVWVWHSZRXOG be dedicated to managing the exceptions that the multiple participants in Web services composition arise. First, there is no guarantee that a particular Web service is still available at time of request. A provider could withdraw its Web service without prior notice. 6HFRQGWKHUHLVQRJXDUDQWHHWKDWWKHVSHFL¿FDWLRQ RIDFRPSRVLWH:HEVHU YLFHLVHU URUI UHH&RQ ÀLFWLQJ  actions like concurrent acceptance and rejection, and GHDGORFNVPD\RFFXUGXULQJWKLVVSHFL¿FDWLRQH[HFX- tion. Finally, there is no guarantee that a particular 390 A Context-Based and Policy-Driven Method to Design and Develop Composite Web Services resource is up at time of execution of a Web service. A resource could be down due to power failure. The various examples back the importance of an addi- tional step on exception handling in CP4WS. The second step would be concerned with guidelines for backing the correct execution of a transactional Web service during the design phase. For this purpose we suggest mapping these guidelines onto transactional properties (compensatable, retriable, and pivot) that will be associated with Web services. The role of DWUDQVDFWLRQDOSURSHUW\LVWRGH¿QHWKHDFFHSWDEOH behavior of a Web service. For example the failure of a Web service could be tolerated in one scenario but not in another one. 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Proceedings of The 2nd International Semantic Web Conference (ISWC). De Troyer, O., & Casteleyn, S. (2003). Model- ing Complex process for Web application with WSDM. Proceedings of the International Work- shop on Web Oriented Software Technology (IWWOST). This work was previously published in International Journal of E-Business Research, Vol. 4, Issue 3, edited by I. Lee, pp. 77-95, copyright 2008 by IGI Publishing (an imprint of IGI Global). 393 Copyright © 2009, IGI Global, distributing in print or electronic forms without written permission of IGI Global is prohibited. Chapter 2.5 Dynamic Pricing for E-Commerce Prithviraj Dasgupta University of Nebraska, Omaha, USA Louise E. Moser University of California, Santa Barbara, USA P. Michael Melliar-Smith University of California, Santa Barbara, USA INTRODUCTION Over the last decade, H  FR P P HU FH KD VV LJ Q L ¿F D Q WO\  changed the traditional forms of interaction among humans in conducting business by automating business processes over the Internet. Early seller Web sites consisted of passive text-based catalogs of products that could be manually browsed by potential customers. Online passive catalogs were soon replaced by dynamically updated catalogs containing detailed product descriptions using combinations of text and images that could be searched in various formats and according to different search criteria. E-commerce techniques used by sellers for operations such as price set- ting, negotiation, and payment have matured from manual off-line processing of sales data to automated algorithms that dynamically determine SULFHVDQGSUR¿WVIRUVHOOHUV0RGHUQHFRPPHUFH processes for trading goods between buyers and VHOOHUV FDQ EH GLYLGHG LQWR ¿YH VWDJHV VHDUFK valuation, negotiation, payment, and delivery. Depending on the type of market in which the goods are traded, some of the above stages are more important than others. There are three principal market models that are used for online trading. The most common market model used by online sellers for trading goods over the Internet is the posted-price market model. The other two market models, the auction model (Sandholm, Suri, Gilpin, & Levine, 2002) and the marketplace model (Chavez & Maes, 1996), are used for markets in which niche or specialty items with sporadic or uncertain demand are traded. In the posted-price market model, a seller announces the price of a product on its Web site. Buyers visiting the seller’s Web site request a quote from the seller. The seller responds with a quote in response to the buyers’ requests, and the buyers examine the seller’s quote to make a purchase decision. Unlike auctions and market- . personalized services. Software and System Modeling Journal Special Section on “Service-Based Software and Systems Engineer- ing, 5(2). Maamar, Z. and Benslimane, D. and Anderson, A. (2006b). Using. acceptance and rejection, and GHDGORFNVPDRFFXUGXULQJWKLVVSHFL¿FDWLRQH[HFX- tion. Finally, there is no guarantee that a particular 390 A Context-Based and Policy-Driven Method to Design and. application, interaction, and abstract. Abstract task refers to the task that needs to be decomposed. Application and interaction tasks refer to the tasks executed by applications and users respectively.