 | Level: Introductory Paul Harmon (pharmon@slip.net), Analyst, Distributed Architecture Service, Cutter Consortium
01 Jun 2001 With its recently announced Model Driven Architecture, the OMG hopes to greatly simplify the challenges of integrating complex, networked environments for the e-business era. Paul Harmon offers a first look at this new UML-based architecture, with particular attention to how it relates to existing architectures such as CORBA.
If you're a software developer, no one needs to tell you about the challenges of integration. Most software developers are struggling to integrate a rapidly expanding collection of old and new applications written in different languages. These applications are designed to run on different operating systems, using different databases, and supporting network and middleware protocols that range from CORBA and DCOM to Web services, XML, SOAP, UDDI and .NET. The 800 companies that make up the Object Management Group (OMG) have
been working together throughout the past decade to simplify the
problems of integration. When most of us think of the OMG, we think of
CORBA, the OMG's Common Object Request Broker Architecture, which was designed
to function as a platform- and language-neutral way for applications
to communicate. You may also think of the OMG's widely displayed architectural
diagram that shows CORBA as a bold, double-headed arrow providing a bus
between a variety of applications and services above and below the bus. In a move that may complicate this picture, the companies that comprise the
OMG have recently adopted a new architecture. This doesn't mean they've
abandoned CORBA; in fact, they've recently published a half-dozen new
CORBA-related specifications (see Resources).
They have, however, accepted the reality that CORBA is only one of the many
different network protocols that companies now have to integrate. The Model Driven Architecture
The OMG's new architecture is called the Model Driven Architecture (MDA). MDA is based on the Unified Modeling Language (UML), the OMG's popular software modeling language. In effect, the OMG's new architecture pops up to a higher level of abstraction in an effort to find a universal way to integrate applications. Using UML, developers can diagram the interfaces and relationships between any applications in a platform-, language-, and network-independent manner. Using software tools, developers can use UML diagrams to generate the middleware links in any code they choose. The core of the OMG's MDA is UML and a Meta-Object Facility (MOF) that
makes it possible to model not only UML but any other metamodel, including
CORBA and the OMG's new Common Warehouse Meta-model (CWM). At the same
time, the OMG has standardized on an XML language or tag set -- the XML Metadata
Interchange (XMI). XMI can be used to pass UML information between
tools, databases, and applications. Using XMI, one visual modeling tool
can pass UML diagrams to another design tool, to another application, or to a
database. The OMG's new architecture is represented by a series of concentric
circles (see Figure 1). In the center are UML and other MOF models. It is
assumed that a company will maintain its overall integration in the center
and generate languages, network linkages, services, and applications from a
core model. The new MDA approach shifts the OMG's focus from specific
technologies like CORBA to a broader, architectural approach. More
important, it focuses on integrating all software applications and systems
at user companies, not on simply providing an infrastructure. In other
words, MDA is an architecture for the e-business era.
Figure 1. The OMG's new Model Driven Architecture
Wells Fargo's model-driven approach
To make the model-driven approach more concrete, it's useful to
consider how Wells
Fargo bank handles its middleware problems. Wells Fargo has created a
Business Object Services (BOS) framework that is defined in UML
and supported by a set of components maintained on Rational Rose. The BOS
environment extends from the interfaces of Wells Fargo's latest Web
applications to interfaces, to legacy mainframe applications, and to databases.
In effect, when developers want to link a new application to legacy
applications, they define the linkage in the BOS UML framework and then
use Rational Rose to automatically generate the code they require. BOS
supports a wide variety of protocols, bridges, and proxies, and can
generate complex linkages that would require a long time to code by hand.
Wells Fargo's middleware approach was created before the OMG adopted its
new MDA architecture, and it is one of the success stories that convinced
the members of the OMG to formalize the Model Driven Architecture
approach. To some, generating code from UML diagrams may sound like CASE all over
again. It's important to note the difference, as illustrated by the Wells
Fargo example. MDA is not about generating complete applications from
diagrams; It's about generating all the linkages to integrate
applications from UML diagrams. It's also about having a common,
high-level UML model of integration that can generate whatever proxies,
bridges, and protocols are required to integrate a new application with
those already in existence.
Tools for MDA
The OMG is a standards body. Its Model Driven Architecture is a
standard -- an abstract description of an architecture -- just as its
CORBA standard is a simple description of how middleware could be developed. CORBA
implementations can be developed from scratch by developers following the
CORBA specification. In most cases, however, CORBA developers use CORBA
tools sold by tool vendors like IONA, BEA, and PeerLogic. With the introduction of the OMG's new MDA standard, a new market for
tools has been created. As with CORBA, some companies, like Wells Fargo,
will implement the MDA standard by themselves. They will select an
existing UML tool, like Rational Rose, then build extensions and
specific components to enable the MDA tool or framework to generate the
middleware integration linkages their developers need. In order for MDA to become widely used, however, vendors need to develop software tools that will make implementation easier and faster for companies that don't want to create their own MDA tools. We asked Dr. Richard Soley, CEO of the OMG, about this new market and
he suggested that:
"traditional development tool vendors like IBM,
Microsoft, Rational, and Computer Associates will probably release MDA
tools in the near future. At the same time, it's likely that smaller
vendors of process-management tools and rapid-application development
tools will lead the charge to the model-driven approach. All application
development has been moving to modeling in order to capture the rigorous
specifications required for multiplatform distributed development. The
OMG has simply provided an open, neutral, standardized architecture that
will assure that everyone can do this in a compatible manner using the
widely-accepted UML language."
In keeping with Dr. Soley's prediction, Adaptive, io-software, Kabira
Technology, and Secant Technologies have all announced that they have released, or
will be releasing, MDA-compliant products (see Resources). The first MDA tools will be released before the end of this year. With
any luck they'll began to have an impact in 2002, easing some of the burden
of integrating enterprise applications in the corporate environment.
Conclusion
Summing up the new OMG initiative, Dr. Soley explained that it's:
"about integration and interoperability. For 12 years the OMG has
focused on making sure you can integrate what you've built with what you
are building and what you will build in the future. As the pace of
technology continues to quicken, and the demands for integrating your
existing legacy systems increase, your new Internet systems and your upcoming
e-business systems all fall on your shoulders, you need an architecture
that makes integration and interoperability central to your
infrastructure. The bad news is that there will never be a single
operating system, a single programming language, or a single network
architecture that replaces all that has gone before. The good news is
that by popping up a level and using UML models, you can still create
systems that economically integrate all the operating systems, programming
languages, networks, and legacy applications that you will have to live
with. That's what MDA is all about."
Resources - There are no books out on MDA yet, but I understand a couple are in the works. The best general article I've seen on MDA is Impact of Model-Driven Architecture by David Flater of the National Institute of Standards and Technology.
- If technical detail is what you crave, download the OMG Architecture Board's Model Driven Architecture: a Technical Perspective.
- The official, latest version of the UML specification
is always available on the OMG's Web site.
- Of course, there are also lots of books on UML. I usually recommend Martin Fowler and
Kendall Scott's
UML Distilled: A Brief Guide to the Standard Object Modeling Language
(Addison Wesley, ISBN 0-201-65783-X)..
- Another great UML resource (the one that launched them all) is Booch, Rumbaugh, and Jacobson's
Unified Modeling Language User Guide, also from Addison Wesley (ISBN 0-201-57168-4).
- IBM was one of the original sponsors of XML Metadata Interchange, the new standard that combines the benefits of XML and UML.
- If you're in the least bit worried that CORBA's all washed up, allay your fears with the IBM
WebSphere Application Server Guide.
- You may also want to read up on the new
CORBA specifications released under the umbrella known as CORBA 3.
- Companies mentioned in this article:
About the author | | | Paul Harmon edited the Component Development Strategies newsletter throughout the '90s and is an analyst with Cutter Consortium's Distributed Architecture Service. He recently coauthored Developing E-Business Systems and Architectures: A Manager's Guide, with Michael Rosen and Michael Guttman (Morgan Kaufmann, ISBN 1-55860-665-3). To contact Mr. Harmon, please send e-mail to
pharmon@slip.net. |
Rate this page
| |
