re: PSVI

[David Megginson <david@megginson.com>]

Simon St.Laurent writes:

 > a) rely on PUBLIC identifiers mapped to a local cache.  Treat the
 > system identifier as merely a convenience for the sender, but
 > require PUBLIC identifiers which match to a list of DTDs maintained
 > by the program.  See http://xmlhack.com/read.php?item=392 for
 > information and Arbortext's implementation.

This works only if you control both ends of the transaction.
Normally, if you're *providing* information in XML, you won't control
the receiver's environment -- the receiver will be using an
off-the-shelf XML parser that automatically resolves the DOCTYPE using
the system identifier, and when their system stops working, they'll
come screaming to you (and at you).

I've received a few private e-mails from companies in the news
industry who learned this the hard way (usually by pissing off an
important customer).

 > b) modify the DOCTYPE declaration of incoming documents to reflect a type 
 > your program expects, and point it at a local resource.  I've written a 
 > DOCTYPEChanger filter in Java which does this - 
 > http://simonstl.com/projects/doctypes/.  It's not that difficult.

Again, this doesn't help the provider, who is the one who has to
decide whether to include the DOCTYPE declaration in the outgoing
XML.  If I'm publishing XML that may be used by hundreds or thousands
of customers, many of whom have existing XML installations, can I
really trust that every one of them (or even most) will get something
like this right?


All the best,


David

-- 
David Megginson                 david@megginson.com
           http://www.megginson.com/