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Inside UML

This lecture delves into the complexities of UML (Unified Modeling Language) in the context of the CS6961 course. It addresses common concerns surrounding UML, including its perceived complications, incompleteness, and ambiguity. Key topics include the relationship between diagrams and models, the challenges posed by modeling languages, and potential future directions for UML. Students are encouraged to grasp the nuances of modeling while acknowledging the inherent difficulties in using UML effectively. The lecture aims to simplify and clarify key concepts for better understanding.

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Inside UML

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  1. Inside UML CS6961 – Lecture 15 Nathan Dykman CS 6961 - Lecture 15

  2. Administration • Grading Started • Please get in HW4, if you haven’t already. • Okay, topics of discussion coming up: • QA, Testing and Release Engineering • Metrics • Reverse Engineering of Complex Systems • Real World Examples • MDA and SOA • Refactoring • Did I miss anything? CS 6961 - Lecture 15

  3. Today’s Lecture • Today: I’m going to give you a peek behind the UML curtain • Give you an idea of how UML is put together CS 6961 - Lecture 15

  4. UML Worries • The main question people ask after dealing with UML after a while is: “Why it is so complicated?” • I’m sure you have some of these kinds of questions • Examples? • This lecture hopes to explain some of the complexity CS 6961 - Lecture 15

  5. UML: Incompleteness • The major part that throws people is that UML allows incomplete models • But, in some cases, complete information must be provided. (Example?) • Some view this as a major shortcoming • It is a shortcoming, but not as big as it seems. • But is incompleteness really bad? • Think about regular code files here. CS 6961 - Lecture 15

  6. UML: Incompleteness • The hard part about UML is that you can’t just save a model in “any old state” • There is work on this, actually. • But, most tools disallow some kinds of invalid models to be created • But, not all. A model can be semantically incorrect, but still created in a tool. • Why? CS 6961 - Lecture 15

  7. UML: Ambiguity • One constant annoyance in UML is that if something isn’t there, doesn’t mean it isn’t somewhere. • What’s worse, in some cases, missing information “assumes” default values, in others, it is merely “unspecified” • The rule is to assume the least possible • This works in most cases, but not all. CS 6961 - Lecture 15

  8. Class Example CS 6961 - Lecture 15

  9. UML: Ambiguity • This problem comes from a subtle part of UML. Diagrams aren’t models. • A diagram is merely just a view on a model. A model is complete. • Why is a diagram just a view on a model? • Programming languages don’t do this, right? • So, we can view the previous example as three different views on a single class. • In the model, there is one class CS 6961 - Lecture 15

  10. UML: Ambiguity • The problem is made a more difficult in that there is diagrams are the only UML syntax that tools provide • This made worse by the standard XML format of UML (XMI) • To my mind: XMI is pretty broken • The latest versions may help address this • But there are too many versions to deal with in the first place. CS 6961 - Lecture 15

  11. Modeling Future • In the future, it is likely UML and other modeling languages will require better textual formats as well as visual syntax • There is already a standard “human-usable” format that looks more like code • Sadly, very little support for it. • Some tools provide a data-grid like editors. • But, we need things like XML, Relational Schemas, etc. CS 6961 - Lecture 15

  12. UML: Complexity • Another major complaint about UML, is well, there is sure a lot of it • I agree with this. UML could lose some bulk • Main problem is nobody can really agree on what to cut, and everybody has something they want to add • UML in the middle of the “second-system” effect • Hopefully, feature set will shake out with more use CS 6961 - Lecture 15

  13. UML: Complexity • Of course, just because it’s there, doesn’t mean you have to use it • In many cases, a large part of UML is for specialized audiences • Some talk of making a xUML language for these advanced bits • Strive to use the smallest subset that does the job • But don’t reinvent the wheel either. CS 6961 - Lecture 15

  14. UML: Complexity • As model-driven development moves forward, hopefully the complexity will start to pay off • More complex code generation • Direct model execution or interpretation • Better integration with languages • For now, certain domains benefit the most • Telecommunications, embedded real-time are the best examples. CS 6961 - Lecture 15

  15. Behind The Curtain • One common benchmark on computer languages is “can it describe itself” • Some languages make this dead easy (Scheme) • Others, more complex (Perl Compiler in Perl) • This “benchmark” has major drawbacks • “Little languages” (Domain specific programming languages) suffer in this area. CS 6961 - Lecture 15

  16. The UML Metamodel • UML is used to describe UML. • Well, in reality, it’s more complex than that • Only a small subset of UML is used currently • Restricted class diagrams • Object Constraint Language (which has a metamodel as well) • Metamodeling still an area of research and development • My PhD work lives in this space, for example • EMF from IBM, Corona from Microsoft CS 6961 - Lecture 15

  17. Metamodel Example CS 6961 - Lecture 15

  18. Metamodel Example • As you can see, the metamodel really isn’t fit for normal consumption • Certain parts of the metamodel are much more complex than this • You have to learn how to “read the runes” • However, the UML metamodel is the core what is legal and illegal UML • What can relate to what, what contains what, the data, etc. CS 6961 - Lecture 15

  19. Metamodel Example 2 CS 6961 - Lecture 15

  20. Metamodeling • After seeing these models, I hope you feel a bit better about your class models • I mean, I could make you do this kind of thing. • Really. I did it, so you can too… Right? • Of course, these models aren’t example of “real-world models” • They have a very specific purpose. • “Real world” models much closer to code. CS 6961 - Lecture 15

  21. UML: Extensibility • UML was built to be extended. • For most people, it is enough to know that there is a thing called a “stereotype” • An a collection of stereotypes is a “profile” • This should work for you as well • But UML can be extended in much more powerful ways (tool support missing) CS 6961 - Lecture 15

  22. UML, DSMLs, Extensiblity • Microsoft’s new initiative focuses on “Domain Specific Modeling Languages” • Part of Visual Studio 2005 modeling tools is a toolkit for building new modeling languages • Codenamed Corona, now just part of VS 2005 • Keep a eye on this (It’s really cool) • UML, Eclipse/Java community will get shaken up by this, I think CS 6961 - Lecture 15

  23. UML Deconstructed • Trust me when I say we can have a class just on the future of modeling, DSMLs, advanced model development… • Well, I hope so, because… • It’s a planned seminar next semester (CS 7940-00x, TBA) • Prof. Kessler likely to be the official instructor • I’ll be lucky to TA a 1000 level class after this… CS 6961 - Lecture 15

  24. UML Seminar • Open to all that took this class • This includes seniors as well • If you’ve never taken a seminar, I encourage it highly! • Much different than this class • One credit hour: You must present a paper to the class (Suggested papers will be available) • Three credit hours: Independent project subject to my approval (limited to 2 students) CS 6961 - Lecture 15

  25. Coming Up • An assortment of topics of interest to you • Or, pick your instructors brain. • Again, if you have any other suggestions, let me know. • Also, look for HW5 this week! CS 6961 - Lecture 15

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