Data Stuctures whose size is manipulated at runtime. Like directory trees, or linked lists
Below is an exerpt from here:
http://www.zdnet.com/devhead/stories/articles/0,4413,2215844,00.html Quote:
Problems happen, though, when your programs become more dynamic. In these cases, you're going to need data structures that can easily grow and shrink on demand.
Suppose, for example, that instead of dealing with an employee data set, you're now creating a graphical computer-aided design (CAD or CAD/CAM) software package. Each time an engineer adds a new part to a drawing, whether it's a nut, bolt, or screw, you need to add that part to a data structure.
If you can guess the maximum number of parts that will eventually be added, you might be able to use an array to serve as a container for all these components. But then the engineer looks at the drawing and decides to change a part here, remove a part there, add 600 new bolts, remove 100 washers, etc. Now you're dealing with dynamic data storage. In a case like this, and in many others, you need a dynamic data structure, such as a linked list.
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Heres some links for you:
http://www.twente.research.ec.org/esp-syn/text/kit131.html http://www.fit.qut.edu.au/CompSci/PLAS/GPM/language/node67.html 
