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Re: SDD again

  • From: alex@v...
  • To: tbray@t...
  • Date: Fri, 8 May 1998 22:55:42 -0700 (PDT)

does validity constraint reliability
> At 06:52 PM 5/8/98 -0700, alex@v... wrote:
> >No, it is not false.  I hightlighted the word 'safe'.  If you absolutely
> >*must* know that everything was read and interpreted correctly, you *must*
> >use a validating parser.  There are many applications where this is not
> >an absolute requirement and, thus, you may use a well-formed parser.
> No.  This claim is without technical merit and I cannot let it pass 
> unchallenged.  It is trivially possible to achieve correctness and 100% 
> unquestioned reliability without the use of a validating processor.  If you 
> either (a) construct your DTD so that standalone='true' or (b) don't have 
> external markup declarations, then you can have NO DOUBT WHATSOEVER that the 
> document is being parsed correctly, for any sane denotation or connotation of 
> "correctly".  So please stop making this demonstrably false assertion.

Hmmm... nothing I am saying is asserting that you can't do (a) or (b).  

I think the issue is one of verification.  If I create an XML
document using an arbitrary DTD not authored by me, how do I know how to
create a standalone document without using a validating parser?  It is the
only thing I have that allows me to check that I did everything correctly.

(Now, I could do this manually.... but please, what user of XML is going to
 do that?)

Once I have used a validating parser and it passes the standalone=yes validity
constraint, I can then send it everywhere I please.... and it should work
just fine.

> Not only is your premise false in theory, it is vacuous in practice.  If you
> think, for any real-world application, that its validation against some DTD
> guarantees "correctness" in any nontrivial sense, then I don't want to 
> go anywhere near your software.  Validity is a highly specific claim, one
> which is of great utility in many applications, but it does not equate to
> having "safety" or "correctness".  Equally, lack of validity does not 
> equate to lacking "safety" or "correctness".

I did not say this in any way.  Validity as defined in XML and all the
"safety" or "correctness" that that allows you was only what I was implying.  
Validity only raises the "comfort level" in which one operates.  I can
*always* mis-use anyone's DTD at any point in time.  

> >In addition, there are some applications that need some level of guarantee
> >about whether external declaration subsets will be read and honored.  It is
> >this class of applications that we cannot address today with the current
> >definition of well-formed.
> This statement is correct, except for the unnecessary temporizing about 
> "some level of guarantee".  "Guarantee" is a binary condition; if you need 
> a guarantee that the organization to which you are sending information
> will have external declarations read, then you need to specify the use of 
> a validating processor at that end.  If not, then not.

Yes.  Which is something I have to do external to my document.... which is
quite fine with me.
> But please don't equate this particular guarantee with general concepts 
> of "safety" or "correctness" - doing so gives the impression that the use of 
> documents which are merely well-formed is in some way sloppy or irresponsible; 
> such a claim is fatuous and very, very, very unhelpful.

Ah, now the issue.  I am not implying this, and if I did, I certainly did not
mean to in any way.  This, to me, is an issue of application of the concept
of well-formed documents.  You must choose at what level you author and
processor your content at every step of the way.

For example, if you are working within a standardize industry or some 
partnership-constrainted data transport, you had better use validating
processors on the creation and receiving ends.  Once a *document* has
been identified to be valid, then you may use a well-formed processor.

If you are creating an ad hoc document, it seems to me to be
perfectly reasonable to only use a well-formed processor.  No problem

XML validity provides you some self-checks.  It does not guarantee semantic
correctness--which is something I would *never* claim.

R. Alexander Milowski      alex@v...     (612) 825-4132       v|e|o
                          MOS | sed s/SG/X/g > DYX

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