Basic requirements:
1. in_data=prefuse.data.Graph, prefuse.data.Table
out_data=prefuse.data.Graph
2. user interaction descrptions:
without wrapper:
*selects two datasets from data manager window, one network graph, one cleaned table.
*clicks "Node merging", a pop-up window shows up and asks the user to load a file that specify the merging functions.
*click ok to generate a network, display which nodes and which nodes have been merged.
a wrapper algorithm:
load a network file, load a csv file, load a file that specify the merging functions and then merge nodes.