knowledge tree..

Anon

I am trying to code a small knowledge base for myself and some friends. I want it to be
a tree structure, so that one can browse from the more general to the specific, like so:

My problem is, how do i store a structure like this in a DB that requires me just one read and that is easy to add/remove nodes?

Also, i want certain branches of this tree to be accesed by just certain people. Any ideas on how I can implement permissions on a tree like this ?

Maybe a tree is not the way to go, so any ideas/comments are appreciated.

thanks!

Anon

funnily enough, i've just helped put together a heiarchical mysql database.

without going into too much of the details, each element has a unique id, and a parent value. so, in your example, php has a parent of languages, and languages has a parent of root. toplevel elements have a NULL parent. an element can of course have multiple children.

you may also want some way to order the children of a given element amongst themselves, but alphabetically may be sufficient for your needs.

a couple of points to note; when you move a node all its children will be moved with it. if you delete one, you must either delete all descendants, or move the children of the delete element up one level.

as to permissions.. i defined an is_descendant() function with which i could check if the branch being accessed was one which the user had access to.

one final note: hiearchical dbs, while nice, can cause a lot of server load; select queries inside loops and suchlike.

Anon

rad, thanks for answering..

i still have some questions, if you have the time 🙂

first, i think i can cut processing of the hierarchical dbs. Since the tree will not change that much, i though of adding one column to the table that has a "level" value. Everytime I add a node or change one, this value gets calculated. This is an extensive calculation, but only gets done every time the tree gets modified, which is not that often. With this "level" value i can read all the table just once and draw it.

On permissions. How did you implement them ? Do you explicitly say which node a user can access? or you just say which node they dont have access to ?

Thanks again!

Anon

edmz,

you can add a field in your table for access level..

Ex. treeID | parentID | name | access_level

Then you can assign each user an access level into a session variable..

this would allow you to have a check_access_level() function to hide or display each items in your tree.

Just an idea..

Anon

On permissions. How did you implement them ? Do you explicitly say which
node a user can access? or you just say which node they dont have access to
?

erm. i'd give each user a list of nodes/branches they can access, and then check whether the current node is a descendent of on of those.