Developing Real World Web Services-based Applications
By Sandeep Chatterjee
This three-part series of articles will explore the world of Web Services, and the challenges in developing Web Services-based applications for the real world. In this first installment, I look at the requirements for building real world applications and their implications for application architecture. In the second installment next week, I will discuss Web Services-based applications for our increasingly “pervasive” world that can be written once and later automatically optimized for multiple platforms and devices. Finally, in the third installment I will take a detailed, code-level view of developing a Web Services-based taxi portal application. This series of articles will also offer a glimpse into the Web Services Mediator (WSM), which is a middleware layer that sits above standard Web Services technologies such as Simple Object Access Protocol (SOAP) Servers, and facilitates the development and maintenance of real world applications.
Introduction
Web Services are software components that are exposed to a network via a statically-defined interface, allowing other applications to be developed that leverage that exported functionality. Although any one Web Service implements and provides useful functionality, their true value comes in composing together multiple Web Services into compelling applications and other Web Services. The composed application or service connects with each remotely-hosted and -managed Web Service, and provides a single user touch point. The classical example of a Web Services-based composite application is an enterprise procurement system that connects to the inventory Web Services of a company’s suppliers and makes purchasing decisions to optimize cost and lead time.
Web Services are interesting and differ from other distributed computing technologies because they are based on SOAP messages, which are encoded XML transported over HTTP (among other common protocols). Essentially, Web Services provide a reasonably lightweight and open standards-based mechanism for computer-to-computer communications. While many believe that these unique characteristics will drive the adoption of Web Services, it is, in fact, a well thought out application architecture that will foster innovation, support short time-to-market, and keep the lid on operational overhead. There is no doubt that “killer apps” will be important, but an appropriate application architecture will guide early adopters, sway the minds of risk-averse development managers, and determine the impact and lifecycle of this burgeoning technology.
Real World Requirements
Applications in a real world production environment have unique requirements that disallow simply throwing components together in a haphazard manner. Real world applications must be easy to develop quickly and cost-effectively. They must be reliable and fault-tolerant, support simple porting to multiple platforms, and efficiently use limited and shared system resources, including memory, network bandwidth, and energy. Finally, and perhaps most importantly, real world applications must be easily maintainable to meet changing business needs and environments as well as customizable to meet preferences for performance, interactivity, and quality-of-service (QoS) metrics.
Consider, for example, a Web Services-based portal application that allows users to schedule a taxicab pickup. Each taxi company has its own Web Service with its own unique interface to which the portal application must bind to schedule the pickup. The portal must constantly be updated to use new Web Services as new taxi companies emerge, and to not use Web Services that become unavailable - either because the server is down or because the company has gone out of business. In a real world production environment, the time and costs associated with these constant updates and application re-writes would be prohibitively expensive.
Instead, what is needed is an architecture for developing Web Services-based applications that facilitates meeting real world requirements.
About the Author
Dr. Sandeep Chatterjee joined HP in 2001 as a
member of its Mobile Middleware Labs. He is responsible for architecting and
developing a next-generation Web Services platform for enterprise as well as
mobile environments. Web Services Mediator (WSM) introduces a "mediation"
layer between Web Services and the applications that consume them, brokers
communications, and bridges multiple standards, messaging formats, and
services.
More information on the WSM can be found at HP’s Mobile Middleware Labs site http://mml.hpl.hp.com.
Prior to his employment at HP, Dr. Chatterjee was Entrepreneur-in-Residence at FidelityCAPITAL, the venture capital arm of Fidelity Investments. He later founded and was President & CTO of Satora Networks, which developed tools and technologies for building appliances and services for the mobile and pervasive Internet.
Dr. Chatterjee holds a B.S. in Electrical Engineering and Computer Science from the University of California at Berkeley, and a M.S. and Ph.D. in Computer Science from the Massachusetts Institute of Technology (MIT). His doctoral thesis in networked client architectures was selected as one of the top thirty-five inventions in the thirty-five year history of MIT’s Laboratory for Computer Science, and his invention is preserved and showcased in a time capsule at the Museum of Science in Boston, Massachusetts.
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