Multilevel Graph Clustering with Density-Based Quality Measures

3.5 Further Implementation Notesformat are used. Each file stores exactly one table. The columns are separated bytabs (\t) and rows by a single newline (\n )character. Strings may be delimitedby quotation marks. The value NA may be used for missing values. The first rowcontains the table header with column titles and the first column is always used asindex. To save storage space all files are transparently compressed using the gzipformat.Separate files are used for different data. For example graphs are stored in threefiles containing vertex data, edge data, and meta data. For each vertex its name ororiginal identifier is stored. The edge table contains the pairs of end-vertex indicesand the edge weights. Additional files are used to store clusterings and similar.In order to retrieve data easily a hierarchical naming convention is employed.The dot is universally used as separator in filenames. The first component namesthe graph and following components differentiate data sets. The naming schemeis best explained by example as in the table below. Meta data is organized in asimilar fashion. Here character strings are used as row indices and the dot is usedas hierarchical separator.57