PrivaCV.com includes a simple tree of skills. Right now about 80 skills. Soon about 1000. Browse the tree. Look at a market. Add a skill. Maybe you coudl do this on a relational database, but certainly harder.
Other trees are needed. Skills will be followed by trees for geographic locations and citizenship. That will allow me to create a list of all the python developers in Krakow for example.
Zopache.com is my hierarchical blog. This page is on zopache.com It is quite a large tree. 60 nodes or so. See how fast it loads? We can browse this tree of objects using the Zopache development environment. That demonstrates the concepts of traversal, and object publishing. You access objects by traversal.
In this section I cover how I model people as trees in PrivaCV.