Example with a context (The Object-Oriented Thought Process by Matt Weisfeld, 3rd Edition):
Visual modeling tools provide a mechanism to create and manipulate class diagrams using the Unified Modeling Language (UML). UML is discussed throughout this book, and you can find a description of this notation in Chapter 10, “Creating Object Models with UML.”
As you can see, Unified Modeling Language has the definite article the in front of it, which, I believe, is absolutely correct. That's exactly how it's used in the Wikipedia article for UML as well as it just makes perfect grammatical sense to use one in this situation. However, a few pages further down, for no rhyme or reason the author all of a sudden completely does away with the article:
Over the years, many tools and modeling methodologies have been developed to assist in designing software systems. One of the most popular tools in use today is Unified Modeling Language (UML). Although it is beyond the scope of this book to describe UML in fine detail,we will use UML class diagrams to illustrate the classes that we build.
Can you think of an explanation as to what he might have done that for?