In an SQL database
So in the image that you linked 100% of things there can be displayed from SQL. (as well as from Text and NoSQL but they're less optimal.) I personally cannot imagine them using a different format. Certainly not plain text files. SQL works perfectly and it's just up to you which variant of SQL you want to go with, for example PostgreSQL; Oracle; MySQL and so on. I'd suggest MySQL as the most commonly used one followed by PostgreSQL as a more feature-rich SQL server. It sound like you're looking for a hierarchical structure within the database which can be done in two ways, here is a great article on the database setup you'll want to go with: http://explainextended.com/2009/09/24/adjacency-list-vs-nested-sets-postgresql Personally I would go with an adjacency list.
