[Zope] USE TRansaction : _begin()

[Michel]

	Hello,

I'm a young user of zope.
I use Zope with SYBASE (we created a Product SybaseDAv2 and it seems to
work perfectly).
Zope created only one connection to sybase and all my Zope users used this
connection to send SQL requests.

Now I would like to modify some tables from my database. I need to use
transaction. 
I unchecked "use transaction" into properties of my SybaseDAV2.
I created 3 DTML Methods (begin, commit and rollback) which call a ZSQL
Method (begintran, commitran,rollbacktran) but it doesn't work because the
first user doesn't avoid the second user to modify the same data.

By reading documentation, I found there are these methods implemeted with
my SybaseDAv2 product :
 _begin(self)
 _finish(self)
 _abort(self)

But how can I call them ? 
I tried :

<dtml-call SybDA._begin()>
<dtml-call expr="SybDA._begin()">
<dtml-call expr="TM._begin()">
and a lot of other possibilities .... but it doesn't work!!

SybDA is the name of SybaseDAv2 product in my example.

Maybe this will not work too. So How can I use transaction into Zope ?
Could you send me an example ?

	Thank you very much for your help

		OFFNER Michel
		IGBMC
		France