ZEOS or PGDAC - How to lock a resource?

Hi!

We will porting an application to PGSQL from some table based app (BDE
like).

The older application used a special technic of the driver: if a record
edited, some exclusive (over transaction), "forever living" lock put on it.
On exit, cancel, or post this lock removed.

We used this to lock the main resource from concurrent edits.

For example:
A product (a Car) have many properties and sublists (details), like
color, transport date, elements (what we need to build into car: wheel,
etc), bill informations, subtransport times, etc.
Because ALL of them is the product, we must protect it with "Edit lock"
on open.
The subinformations are easily editable, and postable (there is autocommit).

Now I search for some technics in PGSQL.
As I read, the locks are transaction depended, because they are vanishes
on rollback/commit.

But we want to save the subelements on editing (one by one), not on
saving the main.
This meaning that we break the transaction with commit - ergo the lock
vanish.

For example:
Car Edit:
- Lock This car
- Edit color
- Open product elements tab
- Add two new elements
- Save them (ApplyUpdates, Commit)
- Add a bill date
- Save it (Apply, Commit)
- Post car record (Apply, Commit)
- Release resource
- Close Form

I read the help, but I saw only transaction-dependent locks.

Zeos or PGDAC is not like IBX/IBO (Firebird), so they don't have
Transaction Component, I can use only one transaction by connection.

How can I do a lock mechanism that:
- Session based
- No limit on how many I used
- Linked to a Row, or a Resource Name
- I can test to is it exists or not

Like Mutex in Windows, but in PGSQL...

Thanks for your help:
dd