ther structural classes and are denoted in the corresponding <code>classSchema</code> object by an <code>objectClassCategory</code> of 1.</p>
<p><em>Abstract</em> classes are classes which cannot be instantiated, i.e. it is not possible to create objects from them. They are commonly used as a stepping stone towards the construction of more sophisticated classes which need to share certain functionality. This is why abstract classes may only inherit from other abstract classes.</p>
<p>An abstract class is de