Re: [Gnu-arch-users] Re: File-tpye plug-in architecture for Arch?

[Andrew Suffield]

On Mon, Dec 22, 2003 at 04:13:33PM -0800, Tupshin Harper wrote:
> Charles Duffy wrote:
> 
> >On Mon, 2003-12-22 at 17:16, michael josenhans wrote:
> > 
> >
> >>Any good XML patch should take the DTD into account when merging.
> >>   
> >>
> >
> >Much of the argument here is that knowing that the new document
> >validates is insufficient to know that the new document is semantically
> >valid (ie. that when loaded into the app which created the two documents
> >from which it was created, said app will represent a document that is in
> >fact The Right Thing).
> >
> >Consider the case where an app loading a merged document presumes that
> >each style element will have a distinct "name" value, but where each
> >branch added a different style element with the same name; a DTD cannot
> >validate that this did not occur, and so may produce a document which
> >validates against the DTD but still crashes the app which created the
> >document.
> > 
> >
> DTDs can't handle this level of specifity, but XSDs can.

No they can't. They're more detailed than DTDs; they are not a
description of the semantics of the file (schemas are just more syntax
constraints).

You can go through the entire discussion and replace "DTD" with
"schema" and it's stlll all accurate. Unless you can guarantee that
validation against the schema means the file is acceptable to the
application, you can't even be sure it's safe. And the schema is no
help in doing something useful when merging.

(Random example: let the file contain some data and a gpg signature of
that data. You can't describe that with a schema.)

-- 
  .''`.  ** Debian GNU/Linux ** | Andrew Suffield
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