Datasheet

Part I ✦ An Introduction to UML

UML plays an integral role in the development and use of the MDA approach. UML

is the language used to describe the key standards of MDA, namely UML itself, the

Meta-Object Facility (MOF), and the Common Warehouse Model (CWM). UML is

also used to create the work products of the MDA process, specifically the business

and implementation models.

Model-Driven Architecture (MDA)

Developers usually find that there is a division in most applications between the

business logic and the implementation mechanisms to support that logic. For exam-

ple, selling tickets to a performance is a business practice that could be imple-

mented using any of dozens of technologies and techniques. But no matter how it is

implemented, there are fundamental rules that must hold true. If the rules for con-

ducting the business transaction are bound to specific implementation technolo-

gies, then changes in those technologies require changes to the rules of the

transaction. Such changes incur the risk either of corrupting the transaction or of

causing delays while you untangle the business from the technology. This makes

even changing the application to take advantage of technological advancements a

risk to the business.

Model-Driven Architecture (MDA) separates the two fundamental elements of an

application into two distinct models. The platform-independent model (PIM)

defines business functionality and behavior, the essence of the system apart from

implementation technologies. The platform-specific model (PSM) maps the PIM to a

specific technology without altering the PIM. That last phrase is critical. Defining a

PIM is like defining the job description “bookkeeper”. We can define the purpose,

responsibilities, qualifications, and skills for the job, that is, the PIM, without know-

ing who will actually do the job. The PSM corresponds to hiring someone to do the

job defined by the bookkeeper job description.

This example highlights the power of the MDA approach. I can hire different people

over time. I can even hire multiple people at the same time to perform the book-

keeping duties. I can even take the job description to another company and use it

there. In the same manner, I should be able to take the same PIM and deploy it in

many technologies or even in different businesses.

The division of the two models also supports interoperability. A business function

does not need to know the implementation of another business function in order

to access it. The interface is defined in PIM fashion. The PSM takes care of the

mapping to the implementation. So the calling function is unaffected by changes

to the implementation of the called function. In the bookkeeper example, the

bookkeeper PIM/job description can define an interface to the general ledger.

Where or how the general ledger is implemented is irrelevant. The interface is

always the same. Whether I implement the bookkeeping system at a department

store, software consulting firm, or insurance company, and whether the system

03 526049 Ch01.qxd 8/20/03 11:47 PM Page 16