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3.1. Meta Meta Models
Element
Attribute
An element is a logical component either encapsulated by a corresponding start-tag
and end-tag or an empty-element-tag. Line 1 to 11 or 3 to 10 are elements in the
example but also line 2.
An attribute is also a markup construct that consists of a name-value pair in
a start-tag or an empty-element-tag. For example, language="C++" in line 2 or
name="SomeMethod" and visibility="public" in line 3 are attributes.
The simple example in Figure 3.10 demonstrates how XML could be used to model / describe
software classes or other kinds of models. As already mentioned, XML can be used as meta
model and XSD as its corresponding meta meta model. XSD can be simplified and interpreted
as a grammar definition for XML while XSD uses the same syntax as XML. Also, MOF and
UML (Subsection 3.1.1) share this advantage.
Figure 3.11 shows an example of an XML Schema Definition, which defines a software class
description formalism corresponding to the preceding XML example in Figure 3.10. Generally,
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Figure 3.11.: XSD class definition example
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