To generate the graphviz documentation you will need the gdcdatamodel installed in your environment and you will need Graphviz installed (brew install graphviz should do it on OSX).

To build the visualization run

make

You should get an output like

python bin/schemata_to_graphviz.py
Building schema documentation...
experiment_metadata
pathology_report
sample
tag
...
graphviz output to ~/gdcdatamodel/docs/viz/gdc_data_model.gv

And there should be a graphviz output file and a PDF document rendered from it in viz/.