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<!! Copyright (C) 1999 Dietmar Kuehl, Claas Solutions GmbH >
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<TITLE>logical-inspectability.3</TITLE>
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<H1>Abstract View of Data Structures</H1>
<A NAME="Description"><H1>Description</H1></A>
For abstract data structures two things are important:
<OL>
<LI>
The operations working on the data structure.
<LI>
The current state of the data structure.
</OL>
It is quite common to provide a number of methods for data structures
which perform the essential operations on these data structures. Also,
some of the state, e.g. some sort of "size", is exposed to the user.
However, often it is necessary to find out more about the current
contents of the data structure. For example, the STL adaptor
<nobr><tt>stack</tt></nobr> does not provide non-destructive access to the elements
currently stored in the stack although this is clearly part of the
logical concept "stack": It is only possible to get all elements by
removing each of the elements in turn. However, in some applications
(e.g. during searching a path in a graph) it is useful to get the
contents of the stack.
<P>
The concept of <B>logical inspectability</B> refers to exposure of
all state information of a data structure which is part of it's logic
description. For example, the state of a stack is made up of all
elements of the stack including their order and the current size of
the stack. A stack has methods to push a new element on the stack,
to access the current top element, to test whether there are elements
stored in the stack and to remove the top element. To expose the
whole state of the stack means, that there are also access methods to
get all elements of the stack. However, it is not possible to change
these elements or to add or remove elements at a different position than
the stack's top. Correspondingly, the stack is not required to
expose any information about the underlying container used to implement
the stack: This can e.g. be a list or a vector but this does not matter
for the stack's state.
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Copyright © 1999 <A HREF=http://www.claas-solutions.de/kuehl>Dietmar Kühl</A> (<A HREF="mailto:dietmar.kuehl@claas-solutions.de">dietmar.kuehl@claas-solutions.de</A>)<BR>
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