IMPLEMENTATION OF WEB SERVICES IN ARISTAFLOW

Seminar Paper / Studienarbeit

by

Zhang, Ke

presented at

Chair of Software Technology

Professor Colin Atkinson, Ph. D.
Department of Mathematics and Computer Science
University of Mannheim

May 2006

Abstract

The purpose of this paper is to describe ideas for combining Web Services and workflow engines (here AristaFlow¹), where they might fit and where they might provide the enterprise with advantages in terms of integration, dynamic processing and interoperability. This paper also showcases guidelines for designing component descriptors using WSDL and other XML Standards and guidelines for developing flexible application accessing methods in AristaFlow. More understanding of how to use these techniques are explained by our sample scenarios on the basis of the Java™ Adventure Builder Reference application².

Contents

I INTRODUCTION 1

1 Standards & Technologies - Web Service 2
2 Standards & Technologies – Workflow Management System 4

II ARISTAFLOW 7

1 About 7
2 AristaFlow Component Descriptor 9
2.1 AFD - Component 9
2.1.1 Component Types 9
2.1.2 Activities 10
2.1.3 Taxonomies 11
2.1.4 Workflow Elements 12
2.2 Defining the component 14
2.2.1 Example 1: Credit Card Service 12
2.2.1.1 An empty component definition 14
2.2.1.2 Adding an activity 15
2.2.1.3 Completing the credit card component 16
2.2.2 Example 2: Activity Supplier 17
2.2.3 Example 3: Weather Forecasts 20

III ADVENTURE BUILDER 23

1 About 23
2 Overview of Adventure Builder 24
2.1 Architecture and Design 25
2.1 Communication Architecture 26
3 Advanced Workflow with AristaFlow 27
4 Sample Scenarios 30
4.1 Scenario 1: Choose Products 30
4.2 Scenario 2:Make Order 30
4.3 Scenario 3:Customer Support 32
5 Conclusion & Outlook 33

REFERENCES 34

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.

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.

[...]

¹ AristaFlow: a next generation process management software based on a conceptual framework for dynamic process changes, on novel process support functions, and on advanced implementation concepts enabling realization of adaptive, process-aware information systems (PAIS). See
http://www.aristaflow.de [Adept-APM]

² A fictitious enterprise selling adventure packages using Web services to integrate with its numerous partners. (referred to as Java™ Adventure Builder [AB-Reference])