About UML:: questions

In learning to use UML to model the process, encountered a problem, that is, in the expression of the UML meta-class, "::" What does the colon mean. For example, Extend UML::D ependencies::abstraction, what does that mean. Is the use of namespaces. There is a lot of information, no definite answer.  However, there are specific instructions in the official document of UML2.0, which requires a look at the official statement. Currently, it is called namespace, so what are the meta classes of UML? This is another problem.
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By querying the official UML file, we can find the content of namespace and solve: this problem.
In the process of looking at the UML specification file, I saw "an instance of a stereotype was linked to an instance of a metaclass" this sentence, which prompted me, stereotype and metaclass is connected , so the Internet to find relevant content.
Stereotype in UML (http://blog.csdn.net/lsh6688/article/details/6240277) mentions: "We know that when we model UML, there is usually a problem with the application domain, We often use it in software development, in fact, other modeling areas can also be used. For example, if we want to model our home appliances, it is clear that we may need graphic symbols for television, or graphical symbols for set-top boxes, and these graphic symbols related to the application area are not fully defined in UML. How is UML done? The answer is stereotype, just use stereotype we can create any graphic symbols we need. ”

In "UML stereotype" (Mo Jian's blog http://blog.sina.com.cn/mylinking) This article, saw that there is such a sentence: " It is important to note that in the case of existing model elements or built-in stereotype to meet your modeling needs, try not to add a custom stereotype. Because it can cause other people who understand UML to read the meaning of what you want to say without any bias. ”

Through the above two articles, one is that stereotype is a great convenience for modeling, on the other hand, it also prompts developers to use UML's existing model elements for modeling when modeling.

So now the question is, what are the model elements of UML?

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In a word can describe the feeling of the present, suddenly look back at the person but in the dim place. Before looking at the UML specification file is the infrastructure (Infrastructure), but the meta-model is actually the upper structure (superstructure), all the answers can be found in the superstructure, took two days, finally solved.