account_fiscal_position should have a foreing rules to cancel removal

Dear all,

This is OpenERP 6.03 with French accounting rules.

While working on a new fiscal rule, I was able to delete an important rule,
which is for applying taxes in the European Union.

I had nearly a heart attack!

Fortunately, I had a PostgreSQL backup and could access the table structure using pgAdmin3.
This is table account_fiscal_position. I used vim to import the missing line.

Then I discovered that the taxes registered in the fiscal rule had been removed also.

At PostgreSQL level, there should be a foreign rule to cancel removing a fiscal rule when it contains taxes.

The table definition is:

CREATE TABLE account_fiscal_position_account
(
  id serial NOT NULL,
  create_uid integer,
  create_date timestamp without time zone,
  write_date timestamp without time zone,
  write_uid integer,
  position_id integer NOT NULL, -- Fiscal Position
  account_dest_id integer NOT NULL, -- Account Destination
  account_src_id integer NOT NULL, -- Account Source
  CONSTRAINT account_fiscal_position_account_pkey PRIMARY KEY (id ),
  CONSTRAINT account_fiscal_position_account_account_dest_id_fkey FOREIGN KEY (account_dest_id)
      REFERENCES account_account (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE SET NULL,
  CONSTRAINT account_fiscal_position_account_account_src_id_fkey FOREIGN KEY (account_src_id)
      REFERENCES account_account (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE SET NULL,
  CONSTRAINT account_fiscal_position_account_create_uid_fkey FOREIGN KEY (create_uid)
      REFERENCES res_users (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE SET NULL,
  CONSTRAINT account_fiscal_position_account_position_id_fkey FOREIGN KEY (position_id)
      REFERENCES account_fiscal_position (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE CASCADE,
  CONSTRAINT account_fiscal_position_account_write_uid_fkey FOREIGN KEY (write_uid)
      REFERENCES res_users (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE SET NULL
)
WITH (
  OIDS=FALSE
);

I don't know OpenERP very well, but I guess it there should be an additional check to cancel any accidental removal.
A fiscal rule with taxes ... should never be removed. A user should remove taxes one by one and then remove the fiscal rule.
This way, there is little chance for accidental removal.

Also, just for information, I had used this rule in 100s of entries.
So maybe removing a fiscal rule being used ... should not be allowed in any cases, as it breaks the information system.