Tree Structures In SQL

Hi,

i'm writing a app in c# and have to store Trees in a Database.

I'm working with Datasets for the exchange between the DB and the App.

The trees have the same options like the windows folders. If u delete a node, all subnodes should be deleted too.

But something a Foreign Key from ParentID references (Id) with the delete-Rule on cascade seems not to be possible, because of multiple cascade Paths or cycles. Do i have to add some xtra constarins:

Not Possible:

create Table tree (
Id varchar Not null,
ParentId varchar Not null,
Constraint pk1 Primary Key (Id),
Constraint fk1 Foreign Key (ParentId) references tree(Id)
On Update Cascade
On delete CAscade
)


Do i have to write triggers, which delete The subnodes too and set the Update-/deleterulr on NO Action

Greetz