Unique identifier of the Voucher Component

[Ko Fujimura <fujimura@isl.ntt.co.jp>]

Hello Donald and all,

Donald Eastlake 3rd wrote:
> 
> Hi,
> 
> I suggest that in the next version of this an ID attribute should be
> added to voucher. To assure uniqueness, we might also recommend that the
> ID value be the based64 of a hash of the Exclusive Canonicalization
> <http://www.w3.org/TR/xml-exc-c14n> of the voucher element with the ID
> attribute dropped out. That is, something like
> 
> Base64 ( SHA1 ( ExclusiveCanonicalization (
>            XPath ( voucher,
>                    ( //. |
>                      //namespace::* |
>                      /@[ localname() != Id ] |
>                      /descendant::node()/@
>                    ) )
> )))

Thank you for inputting a good idea. Actually, I received a comment 
below about 3 month ago regarding this issue:

> > > We are currently working on a project where tickets are
> > > stored in a central system and
> > > can be sold by retailers using a POS terminal in a shop. The
> > > terminal communicates
> > > via GSM (SMS/internet/direct) to the central system.
... (snip)
> > > So here they are:
> > >
> > > 1. We need some unique number for every type of ticket to
> > >    identify the ticket.
> > >    If the terminal ask for a certain type of ticket we want
> > >    to search for this ticket-type in the central database.
> > >    I was looking for adding this number in the 'issuer'
> > >    part, but I think there needs
> > >    to be some global authorization organization for ticket
> > >    identifiers. What are you're thoughts about this?

I have been reluctant to add ID attribute to <Voucher> because
I think an implementation may use the hash value of the whole
Voucher Component as the unique identifier of the <Voucher>.
In this case, I thought it impossible to define the hash value 
as the value of ID attribute within the <Voucher>, which is the 
subject to calculate the hash value. But, Donald's idea enables 
us not to include the hash in itself. So, I agree to add ID
attribute to the <Voucher>. Any opinions?

Best regards,

Ko