Cluster Visualization

some wikipedia pointers for later reading:
* http://en.wikipedia.org/wiki/Data_clustering
* http://en.wikipedia.org/wiki/Self-organizing_map
* http://en.wikipedia.org/wiki/Artificial_neural_network
* http://en.wikipedia.org/wiki/Formal_concept_analysis
resp. their (differing) german equivalents:
* http://de.wikipedia.org/wiki/Clusteranalyse
* http://de.wikipedia.org/wiki/Self-Organizing_Maps (!)
* http://de.wikipedia.org/wiki/Neuronales_Netz