Treelike data: adjacency list or nested sets?

Hello, I'm developing a system (with PHP-MySQL) in which I will have different articles published. Any given article can correspond to a category (or sub-category (or sub-sub-category)). Something like this: Cat 1 Sub 1.1 Sub-Sub 1.1.1 Sub-Sub 1.1.2 Sub 1.2 Sub 1.3 Cat 2 Sub 2.1 Sub 2.2 Sub-Sub 2.2.1 Sub-Sub 2.2.2 [etc] As per my research on this topic of publishing 'treelike information', there are two posibilities: a) Adjacency list id | parent | label 1 0 Cat 1 2 1 Sub 1.1 3 2 Sub 1.1.1 [so on...] b) Nested sets (as explained in the book JOE CELKO'S SQL FOR SMARTIES (Morgan-Kaufmann, 1999, second edition), that I don't have...) label | lft | rgt Cat 1 1 12 Sub 1.1 2 7 Sub 1.1.1 3 4 Sub 1.1.2 5 6 Sub 1.2 8 9 Sub 1.3 10 11 [so on...] Anybody is doing something like this that can share experience with us? I can not find a clue yet if one system is better than the other for what I need. I realized that the 'Nested Sets' system have a very good approach and is very easy to get all the sub (and sub-sub) categories on a given category (any record where lft is between lft and rgt: SELECT e1.* FROM example as e1, example as e2 WHERE e1.lft BETWEEN e2.lft AND e2.rgt AND e2.label = 'Cat 1'; ) But I'm having problems trying to find -as example- which are all the Categories (in the other system are all the records where parent = 0)... Any ideas? Regards, Tomas Garcia Ferrari Bigital http://bigital.com