The UML specifi cation is freely available. You
can fi nd it on the Internet pages of OMG [48].
The class is a central element of UML. The SysML language uses a different
term for it: block. I use the UML vocabulary in this chapter. If you want to read
this chapter through SysML spectacles, simply replace the word class by block .
All content items described in this chapter apply to SysML too. If there are differences
I ??™ ll say so in the appropriate places. I ??™ ve used the SysML vocabulary in all
the other chapters of this book. Over and above, SysML is fully described in this
chapter and the specifi c SysML extensions are discussed in Chapter 4.
3.1 History
UML has its roots in the software development domain. The language is a logical
consequence of the fast pace progress that has been made since Konrad Zuse took
his first computer into operation. As the performance of hardware has increased
software has become increasingly better performing too. This led to requirements
for increasingly complex systems. Ensuring that developers can meet this challenge
has meant that progress was also necessary in the area of their tools??”the
programming languages.
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