UML Models e-business

Software Magazine, April, 2001 by Paul Harmon

EVERY DAY, IN HUNDREDS OF THE LARGEST companies worldwide, software developers use tools like Rational Software's Rose, Computer Associates' Paradigm Plus, and Microsoft's Visual Modeler to plan and design software applications. In all these cases, the developers use the Unified Modeling Language (UML) to create virtual models for the software systems they plan to build.

Companies model complex software applications for the same reason they hire architects to design buildings before actually having them built. In the long run, a detailed blueprint saves time and money. It allows developers to consider alternatives, select the best option, work out details, and achieve agreement before anyone starts building the application. It's much less costly to use a model than it is to modify a building or an e-commerce application after it has been assembled. More importantly, a good model documents the application's structure and simplifies modifying it later. This is critical when you consider that 90% of the costs involved in large applications occur as they are changed, extended, and otherwise maintained.

UML is an open standards success story of the late '90s. In three years, a dozen object-oriented modeling methodologies were replaced by UML, which is currently supported by all major software modeling tools. The Object Management Group (OMG) drove the rapid transition to UML and continues to maintain it as the world's premier open, object-oriented analysis and design standard.

As companies work to develop Internet portals, e-commerce, and business-to-business applications, they use UML models to drive their designs and maintain consistency. UML turns out to be a key ingredient in the new model-driven development approach to software development proving so popular with e-business developers.

At the same time, UML has served as the basis for another software breakthrough--a universal approach to metamodel integration. Companies will soon use metamodels derived from OMG's work with UML to automatically integrate information about many types of applications that use XML.

Standardizing a Solution

In 1996 OMG announced it was interested in creating an open, standard object-oriented notation and called for proposals. Rational Software, Cupertino, Calif., submitted UML Version 1.0, which had been developed by Booch, Rumbaugh, and Jacobson. Ultimately, 21 other companies sent proposals to OMG. In 1997, the submitting companies blended their work into a seamless specification that covered most user and vendor needs. OMG's version of UML represented the best efforts of the teams from such companies as Hewlett Packard Co., Palo Alto, Calif.; IBM Corp., Armonk, N.Y; Microsoft Corp., Redmond, Wash.; Oracle Corp., Redwood Shores, Calif.; Ptech Inc., Boston; Reich Technologies, Brest, France; Softeam, Baltimore; and Taskon, Trondheim, Norway. The OMG board approved the resulting UML Version 1.1 specification in November 1997. Since then, OMG has managed UML as an open standard. An OMG task force gathers information about problems and improvements, and also schedules revisions.

OMG's specification defines UML as "a graphical language for visualizing, specifying, constructing, and documenting the artifacts of a softwareintensive system."

Because UML is an open standard, anyone can download the complete specification from 0MG's Web site free of charge. Similarly, 0MG controls the process of maintaining and extending UML, and any company can join the standards organization.

Unlike the earlier methods that combined a graphical notation system and a procedural methodology, UML doesn't include a software development methodology. When 0MG issued its call for proposals, it indicated it thought it was too early to try to standardize an object-oriented methodology; the steps involved in developing object-oriented systems vary too greatly. Developers creating a transaction processing system follow very different steps from those developing a real-time embedded system, for example. 0MG suggested it would standardize on a notation first and put off an effort to standardize a procedural methodology.

OMG's UML is based on a common UML metamodel. The UML metamodel is, in effect, a class diagram and a set of semantic and s yn tactic rules that defines the core ele ments and relationships used in UMLI As such, the metamodel derives all other terms from that core set of elel ments and relationships. Varying application development efforts call for differing diagrams.

The UML metamodel ensures that UML is more systematic and internally consistent than any earlier software modeling technology. At the same time, it means that tool vendors know exactly how to transform an element5 in a class diagram into its equivale element in a sequence diagram or state diagram, and so forth.

In addition to core symbols, the metamodel contains supplementary symbols, called extensions. Extensions are usually represented by graphical; adornments added to existing core symbols. For example, an arrowhead added to a line indicates the relationship's direction. Also featured are stereotypes, which are created by those interested in customizing UML. The name of a stereotyped symbol is always put between guillemets (e.g., [much less than]stereotype[much greater than]). Using stereotypes, an industry group can extend UML to incorporate some special-purpose notational system. If the group follows the rules, and stereotypes are derived from core UML elements, they can be incorporated into UML diagrams and used by UML tools. An extensive package of stereotypes is referred to as a UML profile. Any introductory book on UML will introduce all the core symbols and most extensions.