Implementation of Webservices in AristaFlow

Research Paper (undergraduate), 2006

38 Pages



I Introduction
1 Standards & Technologies - Web Service
2 Standards & Technologies – Workflow Management System

II AristaFlow
1 About
2 AristaFlow Component Descriptor
2.1 AFD - Component
2.1.1 Component Types
2.1.2 Activities
2.1.3 Taxonomies
2.1.4 Workflow Elements
2.2 Defining the component
2.2.1 Example 1: Credit Card Service An empty component definition Adding an activity Completing the credit card component
2.2.2 Example 2: Activity Supplier
2.2.3 Example 3: Weather Forecasts

III Adventure Builder
1 About
2 Overview of Adventure Builder
2.1 Architecture and Design
2.1 Communication Architecture
3 Advanced Workflow with AristaFlow
4 Sample Scenarios
4.1 Scenario 1: Choose Products
4.2 Scenario 2:Make Order
4.3 Scenario 3:Customer Support
5 Conclusion & Outlook


Chapter I Introduction

Since its introduction, Web service is expanding rapidly due to the growing need for application-to-application communication and interoperability. It provides a means of integrated service combining software and services from different companies and locations. Early examples of Web services have allowed customers to find local restaurants or to check weather forecasts. Nowadays they are becoming much more complex, such as payment, traffic or tracking systems.

As the Web services are integrated in business processes more than ever, new challenges are arisen for workflow management systems due to a complicated environment and the unreliable nature of Web services. The workflow management systems do not only need to incorporate a set of fixed business processes for a specific domain or delegate a lot of people-related tasks, they also have to meet new requirements in fields like interoperability, reliability, scalability and exception handling. AristaFlow is such a next generation process management system which will face these challenges. It is based on a new conceptual framework for dynamic process changes and on advanced implementation concepts. And it enables the realization of adaptive, process-aware information systems. [Adept-APM]

In our sample scenario, a fictitious enterprise is selling adventure packages. The sample application incorporates the Web services functionality to integrate businesses of multiple partners. And with the help of Adept, the workflow engine of AristaFlow, all components are combined together. As a result, the adventure builder is now able to provide enhanced and more automated interaction experience for their customers: more efficiency and greater choices, along with more flexibility.

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Introduction 1 Standards & Technologies - Web Service

In March 1991 as Tim Berners Lee, Robert Cailliau and Nicola Pellow from CERN created the first web browser supporting HTML (HyperText Mark-up Language), HTTP (HyperText Transport Protocol) and URL (Universal Resource Location), web sites were only plain HTML pages. [WB-Wiki] For example, a phone directory site initially provided only static pages similar to traditional phone books.

About 3 years later Common Gateway Interface (CGI) has been introduced. Since then, web application has gained the capability to generate HTML pages dynamically. Web sites like search portals begin to flourish which offered customized pages and results to the requests from the client web browser. However, web applications were still restricted. They could only used through limited user interface bound to the HTML pages.

Web service goes beyond this limitation. A Web service is represented as XML and available via the Web. Thus, unlike browser-based applications concerning the representation of specific data themselves, a Web service can be accessed and interpreted by any kind of applications on any devices. Furthermore, applications are able to incorporate Web service functionality to combine different Web services for their own use. Yahoo!, eBay, Google, almost all big internet companies are providing Web services, such as maps, web search and traffic services. You can integrate these services in your application easily.

You might wonder at this point why Web service is got so successful and, much importantly, why it makes sense for an enterprise to use Web services as the underlying architecture for their applications. Let’s take a closer look at Web services:

Web service has emerged as an initiative of the industry to realize service oriented architecture (SOA), which is an architectural style that promotes software reusability by creating reusable services. [WS-Design] In order to enable a wide acceptance and to achieve interoperability, it is based on the existing and universally accepted standards. And it provides an open and flexible architecture. So Web services can be accessed by any client regardless of the platform on which the client is implemented. And a client is able to find and use any Web service regardless of the service’s implementation details.

According to the World Wide Consortium (W3C) Organization, which establishes the standards for Web services, a Web service is a software system designed to support interoperable machine-to-machine interaction over a network. [WSGloss] It is identified by a URI on the Web or intranet and has an interface that is described in a machine-processible format such as Web Services Definition Language (WSDL). Clients interact with the Web service in a manner prescribed by its interface using XML-based protocols, such as Simple Object Access Protocol (SOAP) sent over broadly accepted Internet protocols, such as HTTP.

The Web service-based architecture contains three functions: Service provider, Service requester and Service registry. (See figure 1.1 below)

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Figure 1.1: Web Service Architecture [WS-Wiki]

A Service requester is a software system that makes use of Web services.

A Service provider exposes the capability as a Web service. It creates the service description, publishes that service description to one or more means of discovery and has the Web service ready to receive messages from Service requesters.

And at last, a Service broker’s responsibility is to advertise service descriptions and to help Service requesters search through its registry to find a service description of interest.

Currently, most of the contribution in Web services standardization is driven by a few large vendors: Microsoft (.NET), IBM (WebSphere), BEA (Weblogic), Sun (J2EE), SAP, HP (multiple, mainly management), Verisign (security), plus a multitude of other companies such as CA and webMethods.

Introduction 2 Standards & Technologies - Workflow Management System

A Workflow management system (WFMS) is defined as a system that helps organizations to specify, execute, monitor, and coordinate the flow of work cases within a distributed environment.

A WFMS maintains state information for each process execution. For this, it needs to be informed of state-changes. At the process execution time, it receives information and descriptions about the current state of process passed from its participants. On a specified event or after a state has finished the workflow engine checks the result with the pre-defined conditions. Depending on the process definition and context information it delegates activities amongst applications, people and machines respectively, e.g. sending an email when an activity is assigned to an employee.

At the operational level the WFMS manages the process flow and defines how tasks are structured, who performs them, what their relative order is, how they are synchronized, how information flows to support the tasks and how tasks are being tracked.

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Figure 1.2: Separation of process layer and application layer [AF-Overview]

As depicted in figure 1.2, the process logic and the application functionalities are separated from each other. Each software component in the application layer has its input/output descriptions and transformation rules in the application layer. I.e., a component would not execute, unless its mandatory input requirements are fulfilled.

Generally, the process logic is implemented by the developers and analysts at the workflow modeling time. They have to simulate and specify possible process workflows and assign activities to actors and install the optimized one in the WFMS. They describe workflow structure usually with standardized graphical notations, e.g. the Business Process Modeling Notation. In the following chapters we will use our own graphical notations to describe some workflows. (You can find legends of used symbols in “WorkflowSymbole.vss”.)

At run-time WFMS provides interfaces for interaction with external systems and end-users. Internally, the workflow engine controls the workflow and assists the coordination of processes and activities.

And optionally, if a monitoring interface is provided, administrators can observe the statistics, diagrams and control flow analysis of the running system (cf. figure 1.3). Otherwise statistics can be extracted or generated from the execution logs of the processes. This is also called process mining. A new variant is the adaptive process management. It can use automatically collected data more effectively. Case-bases, execution and change logs are enriched with semantic and syntactical information, so the process models can be adapted to changing needs. (See “Towards a Framework for the Agile Mining of Business Processes”)

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Figure 1.3: WFMS as UML diagram

In the example on the next page (Figure 1.4), a company has a business process for handling employees’ request for holidays.

People and software systems are involved

in this process. The workflow system manages the process automatically. After an employee has filled the request form via a web-interface, it checks if he has enough unused holidays, sends notifications to the manager and modifies the employee’s calendar if the request has been approved. Status of the request can be tracked by the employee at any time.

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Figure 1.4: Holiday request process

The holiday request example highlights the benefits of a WFMS:

Activities, participants, and data flows can be easily recognized and used for better process control. The workflow can be optimized through the standardizing and streamlining of working methods.

Unnecessary steps are eliminated in the process definition time to improve the efficiency of the business process.

Predictable and routine steps are replaced by software systems. On this way, the request response time is shortened and typical human failures like forgetfulness and inattention can be avoided.

And the greater flexibility of software control over processes enables redesign when business process needs change. For example, if a process for extra vacation payment is needed or the manager wants the system to approve requests automatically.


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Implementation of Webservices in AristaFlow
University of Mannheim
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Implementation, Webservices, AristaFlow
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Ke Zhang (Author), 2006, Implementation of Webservices in AristaFlow, Munich, GRIN Verlag,


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