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Modeling Web Application Architectures with UML
By: Jim Conallen, Rational Software
June 1999 A version of this material appears in the October 1999 (volume 42, number 10) issue of Communications of the ACM.

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Table of Contents

Abstract....................................................................................................................................................................................1 Overview...................................................................................................................................................................................1 Modeling...................................................................................................................................................................................2 Web Application Architecture ................................................................................................................................................3 Modeling Web Pages ...............................................................................................................................................................4 Forms........................................................................................................................................................................................7 Frames.......................................................................................................................................................................................8 Conclusion................................................................................................................................................................................9

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Modeling Web Application Architectures with UML

Abstract
Web applications are becoming increasingly complex and mission critical. To help manage this complexity, they need to be modeled. Unified Modeling Language (UML)is the standard language for modeling software intensive systems. When attempting to model web applications with UML, it becomes apparent that some of its components don’t fit nicely into standard UML modeling elements. In order to stick with one modeling notation for the entire system (web components and traditional middle tier components), UML must be extended. This paper presents an extension tothe UML, using its formal extension mechanism. The extension is designed so that web-specific components can be integrated with the rest of the system’s model, and to exhibit the proper level of abstraction and detail suitable for designers, implementers, and architects of web applications.

Overview
A new term has entered the IT vocabulary in the past few years: Web Application. It seems likeeveryone involved with business software systems has plans for building web applications, with many non-business related software efforts interested as well. For many early adopters of this architecture the term web application, like the systems themselves, have evolved from small successful web sites add-ons to robust n-tiered applications. It’s not uncommon for a web application to service tensof thousands of simultaneous users, distributed all over the entire world. Architecting web applications is serious business. When put to the test, the term web application has slightly different meanings to different people. Some believe a web application is anything that uses Java; others consider web applications anything that uses a web server. The general consensus is somewhere in between.For our purposes in this paper, we’ll loosely define a web application to be a web system (web server, network, HTTP, browser) where user input (navigation and data input) affects the state of the business. This definition attempts to establish that a web application is a software system with business state, and that its "front end" is in large part delivered via a web system. The general...