A workflow services middleware model on ShanghaiGrid 1

Transcription

1 A workflow services middleware model on ShanghaiGrid 1 1 Ying Li 1, 2, Minglu Li 1, Jadi Yu 1 and Lei Cao 1 Department of Computer Science and Engineering,Shanghai Jiao Tong University, Shanghai , China 2 Computer Science and Technology School,Soochow University,Suzhou ,China {liying, li-ml,jdyu,lcao }@cs.sjtu.edu.cn ingli@suda.edu.cn Abstract The ShanghaiGrid is an ongoing Grid Computing Environment (GCE) based on the Grid Service standards and the Open Grid Services Architecture. The ShanghaiGrid is a City Grid, which is to provide a general shared information Grid platform. Based on this point, a workflow management system is very import especially for user-defined workflow. By using the workflow, users in GCE would compose several Grid services as a new Service and provide it to others. This will enlarge the extensibility and business-originated usage in the GCE. This paper discusses the type of workflow, proposes a model of client-side workflow management system, and the design of several important workflow services. A service discovery process based on workflow is given in this paper too. 1 Introduction The Shanghai City Grid is an ongoing project supported by Shanghai government. The aim of the City Gird is to promote Shanghai become one of the most advanced information cities in the world [1]. Grid based computational infrastructure is an ideal computing platform to meet large-scale resources and heterogeneity system [2]. The grid technology would enable the municipal government to integrate its information resources dispersed in different organizations and strengthen collaboration and information sharing. This will be invaluable for improving the efficiency of government and its emergency response speed. The aim of Shanghai city gird is listed below [1]: 1. Solve isolated island of information 2. Shield the resource heterogeneity 3. Change from web browsing to resources sharing 4. Resolve the problems of dispersed resources and establish the uniform standards. In the City Grid there exist several kinds of Grid: Data Grid, Computing Grid, Information Grid, and Knowledge Grid. The Computing and Data Grid mainly aim at the scientific field. The Highperformance execution in distributed computing environments often requires careful selection and configuration not only of computers, networks, and other resources but also of the protocols and algorithms used by applications. Selection and configuration in turn require access to accurate, up-todate information on the structure and state of available resources [3]. According to this, the Data Grid and Computing Grid are just a base facility of the City Grid, provide City Grid some critical data and information, and are seldom used by public. So the City Grid is mainly regarded as information Grid to serve the public in the city. The main problem of City Grid is the information integration. In ShanghaiGrid, all resources are regarded as Grid 1 This paper is supported by 973 project (No.2002CB312002) of China, grand project (No.03dz15027) and key project(no ) of the Science and Technology Commission of Shanghai Municipality.

2 Services. Individuals, organizations and business companies can publish their information or services as a Grid Service, which can be accessed by public in the Grid Computing Environment (GCE). The GCE in this context is a set of tools and technologies which allow users easily access Grid services and applications [4]. In the research, the ShanghaiGrid is aimed as a shared platform for various Information Grids [4], some core services or middlewares will be provided to support the platform. A lot of work has been done on the ShanghaiGrid, some core middlewares have been designed [4], but they lack of suitable workflow services especially the user-defined workflow services. Here we propose such a model, which is base on the software architecture of the ShanghaiGrid, and based on the middleware of the Grid Services Delivery Toolkit (). The is located at the middleware layer in the software architecture of the ShanghaiGrid. It is an important tool to glue the distributed parts of a Grid-enabled application and Services together in the GCE. It is also designed to support the major existing Service Discovery facilities and mechanisms such as GIIS/GRIS [5], UDDI [6], as well as the Java Network Launching Protocol (JNLP) [4]. In general, we can regard the as a platform to easily publish and invoke Grid Services. We will first survey some of workflow technical using in web services and Grid services. Then point out the shortcomings of such technicals in the context of ShanghaiGrid. 2 Technical survey of workflow 2.1 WSFL The Web Services Flow Language [17] (WSFL) is an XML language for the description of Web Services compositions as part of a business process definition. It was designed by IBM to be part of the Web Services technology framework and relies and complements existing specifications like SOAP, WSDL, XMLP and UDDI. WSFL considers two types of Web Services compositions: FlowModel : an executable business process. WSFL defines a set of activities and models as specifications of the execution sequence of the composed Web Services. GlobalModel: provides a facility to model interactions between business partners. Although the WSFL1.0 was published by IBM in 2001, but so far there is no distinguished implementation of WSFL. 2.2 XLANG The Web Services for Business Process Design (XLANG) [18] designed by Microsoft Corp according to the conception of the automation of business processes based on web services requires a notation for the specification of message exchange behavior among participating web services. The goal of XLANG is to make it possible to formally specify business processes as stateful long-running interactions. The high-level features are listed below [18]: Sequential and parallel control flow constructs Long running transactions with compensation Custom correlation of messages Flexible handling of internal and external exceptions Modular Behavior Description Dynamic service referral Multi-role contracts 2.3 BPEL4WS The Business Process Execution Language for Web Services (BPEL4WS) [19] was proposed by IBM in BPEL4WS absorbs the advantage of WSFL and XLANG. It not only can be used as an implementation language but also can describe the interfaces of business processes. It allows programmers to create complex processes by creating and integrating different activities together. An initial implementation of BPEL4WS called BPWS4J was also released by IBM via alphaworks [8]. 2.4 GSFL The Workflow Framework for Grid Services (GSFL) was put forward in article [7]. The Grid Services Flow Language is an XML based language that allows the specification of workflow descriptions for Grid services in the OGSA framework. It has been defined using XML Schemas. It has following features: [7]

3 Service Providers, which are the list of services taking part in the workflow. Activity Model, which describes the list of important activities in the workflow. Composition Model, which describes the interactions between the individual services. Lifecycle Model, which describes the lifecycle for the various activities and the services which are parts of the workflow. 3 Workflow in ShanghaiGrid The Data Grid and Computing Grid are the basic infrastructure of the ShanghaiGrid, In Data Grid and Computing Grid, GSFL can be used to handle the workflow. Under such environments, the workflow is mainly static and consistent. Programmer will design and implement the workflow in the Grid environments. In ShanghaiGrid, we call that workflow a server-side workflow. A server-side workflow is transparent to Grid users. There exists another kind of workflow in ShanghaiGrid, the user-defined workflow or clientside workflow. In GCE, users can easily publish their Grid services and Grid applications, but in business environment, the trend to link these services together into a business process or a composition is more and more important. The ShanghaiGrid mentioned above is a typical Information Grid, it is a shared platform. So in ShanghaiGrid, the client workflow management system is more important. Users, organizations and other roles in the Grid need a facility to assemble the Grid Services to form business logic or a new Grid Services in a workflow. And the workflow is a dynamic process which may change frequently. The research is to design a client-side workflow management system based on the GCE. It should include such high level features: Grid Transaction support Grid based services discovery Rule-based workflow GUI-enabled workflow composing tools WSFL and XLANG lack implementation tools. BPWS4J is an implementation of the BPEL4WS specification that includes a run-time engine and an editor (which is an Eclipse plugin) for creating BPEL4WS processes. It s too complex for end-user to create such process and needs eclipse environment. Although GT3[9] includes GridAnt[10], a tool that provides a much needed functionality for developing and testing Grid applications with the GT 3, but it is not very suitable for the project and cannot be used by the ShanghaiGrid directly. One problem is that the GridAnt lacks of the GUI-based workflow composed tools. The other problem is that GridAnt cannot work together with the middleware, which is the core middleware in the project. A workflow middleware should be designed and implemented in ShanghaiGrid to support more flexible workflow management. 4 The design of the client-side workflow system based on GCE 4.1 The framework of the workflow management system on the Grid Fig.1 shows the framework of the workflow, each part is discussed blow: Workflow Client Tools (WCT). WCT gives a GUI based JNLP enabled interface to let uses or agents to assemble Grid Services in which information was retrieved from UDDI. In this project users can create temporary workflow or persistence workflow depends on the users rights. Workflow Repository Services (WRS) The user defined persistence workflow is also regarded resource and can be reused by others. The insets the information in UDDI and stores it permanently in the Workflow Repository Services. The WRS provides such as inserting, deleting, updating, or querying service to be invoked by the. Workflow Monitor Services (WMS) The WMS can query the instance currently running and return the status to the. Workflow admin Services (WAS) The WAS mainly includes role management, audit management and so on. Workflow Engine Services (WES) The WES is the core services in the workflow management system. The Workflow Engine is responsible for creating, assigning, controlling the tasks, and deciding in each moment the next action to be performed [11]. It invokes the Grid Services as the tasks.

4 Workflow Client tools Admin Services Grid Services Repository services Engine Services Grid Services GCE Monitor Services Grid Services Fig.1 The framework of the workflow management system WRS instance and WES gets the workflow information from the WRS. The WES picks up the first task in the tasks-list and gets its URL, using this URL the WES discovers the GSR of a Grid service instance. If the Grid Service instance has been created and in valid status, the WSE looks up the Registry and gets GSR according to the GSH by using querying HandleMapper. If GSR does not exist, the WSE finds the GSH of Factory in Registry, creates a Grid service using the factory interface, which gets the GSH and GSR and then registers them in the Registry. When WES gets the GSR, it has enough information to bind it then receives its result. And then using that result as input to do the same steps mentioned above until the entire task in task list have been done. We can see from the framework that the Grid based workflow management system is similar to tradition ones [12,13,14], but all functions should be wrapped with Services. 4.2 transactions in the workflow The workflow in this model is divided into two catalogs: transaction-enabled and none-transaction enabled. The Grid traction model applied in ShanghaiGrid is base on the article [15,16]. 4.3 Service Discovery under the workflow As mentioned before, the user-defined workflow can be regarded as grid services in the GCE, and can be regarded as a sequence of Grid Services run under one transaction (if it is transaction-enabled workflow). In GCE we assume that each Factory and Grid service instance must register its GSH with Registry. Mapping relationship between GSH to GSR is registered in HandleMapper. The workflow based service discovery is described in Fig. 2: User (Client) looks up grid services through the UDDI according to the services descriptions, the UDDI returns the Grid Services URLs. We promote fuzzy search arithmetic of the schema that if there does not exist entire match, the UDDI will return a list of Grid Services to the user and let user choose one. The user uses the selected URL to contact, and judges if the URL is a workflow-based Grid services. If it is, the creates the WES and Start Look up desired services in UDDI User-defined workflow? Create instance of WES and WRS using factory Get Services information from task list Look up GSH in Registry Exist? Create and Register using Factory Success? Invoke Grid Services and get results End of task list? End Fig.2 The runtime procedure of workflow User (Client) looks up grid services through the UDDI according to the services descriptions, the UDDI returns the Grid Services URLs. We promote fuzzy search arithmetic of the schema that if there does not exist entire match, the UDDI will return a list of Grid Services to the user and let user choose one. Look up Handle-Mapper to get GSR

5 The user uses the selected URL to contact, and judges if the URL is a workflow-based Grid services. If it is, the creates the WES and WRS instance and WES gets the workflow information from the WRS. The WES picks up the first task in the tasks-list and gets its URL, using this URL the WES discovers the GSR of a Grid service instance. If the Grid Service instance has been created and in valid status, the WSE looks up the Registry and gets GSR according to the GSH by using querying HandleMapper. If GSR does not exist, the WSE finds the GSH of Factory in Registry, creates a Grid service using the factory interface, which gets the GSH and GSR and then registers them in the Registry. When WES gets the GSR, it has enough information to bind it then receives its result. And then using that result as input to do the same steps mentioned above until the entire task in task list have been done. 5 Case study Here we give an example of how the workflow works in a tour company on the Shanghai City Grid. The weather forecast company provides a weather service in the GCE and already using the registers the WeatherService in UDDI and GIIS/GRIS. There also exists hotel book service in the GCE called BookService. The tour company uses these two services to compose a tour booking services. Client can use web Brower or PDA visit the Web page of the company and book a two-day tour in the city. Client can chose what weather (some people like tour in the rain), price, date and other information of the hotel in booking. The tour company first uses the workflow client tools to create a workflow. In the workflow Design, the Company should add the weatherserivce node and bookservice node from all the services from the UDDI, then add two router to judge if the weather, price fit the needs of users. If either of the routers failed, the booking fails. Then the company registers the service using. knows this is a workflow service and stores the booking workflow (booking.xml) in the WRS. The generates the extend WSDL, applies an account in UDDI, gets a pair of ID and password, and publishes them in UDDI. The booking process is shown in the Fig.3 1. Using a browser a user looks for a tour booking services in UDDI. 2. The user gets some URLs corresponding to the desired tour booking services. 3. The user fills some demands and sends the requests to the, and the creates a workflow services, and generates a Timestamp T. 4. WES invokes the first action A a weather service. Users Agent (1) (2) UDDI (3) (14) (6) (13) s A B e (4) (5) (7) (12) Weather (8) Hotel booking (11) (9) (10) Credit Reserve Fig.3 An example of tour booking Services based on workflow 5. The Weather service returns the weather status of a certain period. 6. The workflow router judges the result and if it dose not fit the needs of user, it fails and returns the information to. 7. The WES invokes the action B hotel booking service.

6 8. The hotel booking service starts a workflow, and then judges the client s credit rank. 9. Returns the rank of the client. 10. If user s credit is good, the hotel reserve service reserves the room and returns the booking information to the Hotel booking Service. 11. Returns the booking information 12. Ends the workflow and returns information to the WES 13. Stops the workflow 14. WES returns the results. The Timestamp is standing for the expiration of the transaction. If in a certain period the WES fails to return the results to the, the will send fail information to the user. 6. Conclusions and future work In this model, we regard the workflow as two parts: user-defined workflow (client side workflow) and Server side workflow. We apply the GSFL as the server side workflow management system, and design & implement a client side workflow management system, which is composed with several Grid Services and a JNLP-enabled GUI workflow design tools. Using this client side workflow system, users can easily extend and compose their own workflows. The Client side workflow Engine Service we proposed is a lightweight Engine. It does not contain performance evaluation, Dynamic Scheduling, fault torrent and so on.. And the workflow management system is a centralized system heavily depending on the middleware which is the core of this model. Such matters will be taking into account to improve the workflow management system. International Workshop on Grid and Cooperative Computing, Shanghai. December, [5] Almond, J., Snelling, D, UNICORE: uniform access to supercomputing as an element of electronic commerce, Future Generation Computer Systems 15 (1999) [6] [7] S. Krishnan, P. Wagstrom, and G. V. Laszewski, GSFL: A Workflow Framework for Grid Services Argonne National Laboratory. Aug [8] [9] [10] The Java CoG Kit User Manual, [11] J. A. Espinosa, A. S. Pulido IB (Integrated Business), A Workflow based Integration Approach, Proceedings of the 35th Hawaii International Conference on System Sciences 2002 [12] Khalid Belhajjame, etc, A flexible workflow model for process-oriented applications,proceedings of the Second International Conference on Web Information Systems Engineering (WISE 02) [13] A.Goh, et.al, ECA Rule-based Support for Workflows, Artificial Intelligence in Engineering,15(2001), pp37-46 [14] Jian Cao Minglu Li Shensheng Zhang Qianni Den, Composing Web Services based on Agent and Workflow, Proceeding of the Second International Workshop on Grid and Cooperative Computing [15] Feilong Tang, Minglu Li, and Jian Cao, A Transaction Model for Grid Computing, Proceeding of the Second International Workshop on Grid and Cooperative Computing, September, [16] Minglu Li, Feilong Tang, and Jian Cao, An Integration Architecture for Grid Resources,Proceeding of the Second International Workshop on Grid and Cooperative Computing, Shanghai. December, [17] pdf/wsfl.pdf [18] [19] References [1] Yadong Gui, City and Super Compute, Internatioanl Forum on Digital City and City Grid ---IBM Grid Technology workshop, November5, 2003 [2] I. Foster, C. Kesselman, J. M. Nick and S. Tuecke, The Physiology of the Grid-An Open Grid Services Architecture for Distributed Systems Integration,Global Grid Forum June, [3] [4] Ruonan Rao, Baiyan Li, Minglu Li, and Jinyuan You, The Delivery and Accounting Middleware in the ShanghaiGrid, Proceeding of the Second