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Re: Re: Fw: PLEASE 'splain a DTD's purpose
Thanks for the words of experience and the chuckle!
Leah
----- Original Message -----
From: "Andrew BK" <
To: <
Sent: Friday, November 01, 2002 10:08 PM
Subject: [EDI-L] Re: Fw: PLEASE 'splain a DTD's purpose
> > Out of the mouths of babes....
>
> Out of the mouth of babes and sucklings hast thou ordained strength
> because of thine enemies, that thou mightest still the enemy and the
> avenger. Psalm 8:2, KJV
>
> The lowly DTD is useful only for describing the skeletal structure of
> the XML data. It is simply a catalogue of Elements available to use.
> It shows the attributes they may contain. It also shows the
> hierarchical arrangement of the element tree. Most of us know this.
>
> It can say which elements/attributes are required and which ones are
> optional. It can to some extent even describe the combinational rules
> based solely on structure (not data).
>
> It can say that an element is able to repeat, but cannot define an
> upper limit on the number of occurrences.
>
> It cannot say anything at all about the data content. It has no way
> to put bounds on the min/max length of a string. It does have the
> notion of a token list to allow only certain values in a field, but
> in practice I have found that this tends to regress to amere #PCDATA
> with allowable values described in comments.
>
> Even if an element is mandatory, DTD validation only verifies that
> the element is present, and doesn't give a hoot whether it contains
> any data. Thus, if Name in BillTo is required, this
>
> <BillTo>
> <Name></Name>
> </BillTo>
>
> will satisify the DTD validation. For us, this
>
> N1*BT~
>
> will not.
>
> Yes, I work for a company where it is my full-time job to translate
> XML to and from EDI, for both X.12 and EDIFACT.
>
> In practice, I have found that XML data is terribly unruly. I see
> empty mandatory elements all the time. I see City names with only one
> letter in test data.
>
> I've see comment blocks where the entire purchase order, formatted
> and structured has been pasted. Why, I could paste that block into a
> text editor and print it, complete with field layout, headings,
> underlines, and columns for the line items.
>
> I've seen entire paragraphs for item descriptions that must go into
> X.12's 80-char field, or worse, EDIFACT's pair of 35-char fields.
>
> If the XML data supports named references, then you get into another
> can of worms. Consider this:
>
> <Reference name="Payment Terms">10 days, 5%, 30 day max</Reference>
>
> And they want this turned into an ITD? or a PAT/PCD? Yeah, right.
> How did you even know to anticipate the string "Payment Terms"? The
> next customer sends "Pmt-Terms". And another "Terms of Payment". And
> no two format the #PCDATA content the same way.
>
> I had someone send this in a line item:
>
> <Reference name="Buyer's part number">ABCDEFG</Reference>
>
> They cried when I gave them this:
>
> N9*ZZ*Buyer's part number~
> MSG*ABCDEFG~
>
> No, no, no. That's a comment. I can't map from that. Why can't you
> just map it to the PO1 with product/service id BP? I wanted to see
> this, PO1*...*BP*ABCDEFG~ That is the only way we can process it.
> Some (or make that "most") people just don't get it.
>
> All this rubbish satisfies the DTD validation honky-dory. And as long
> as you're only doing rip 'n read, who cares? Let's just revert to
> taking orders over the phone or fax, eh? That's electronic.
>
> XML can be done right. Schemas do make a difference. But it still has
> quite a way to go before its practice catches up with EDI.
>
> Andrew
>
> > ----- Original Message -----
> > From: "xmEllen" <noemail@n...>
> > Newsgroups: microsoft.public.xml
> > Sent: Friday, November 01, 2002 2:03 PM
> > Subject: PLEASE 'splain a DTD's purpose
> >
> >
> > > Hi,
> > >
> > > I've been taking a class in XML where we have written DTD's and
> > > Schemas as part of our coursework.
> > >
> > > The class material says that DTDs and Schemas are recommended to
> > > ensure document conformity especially in Business-To-Business
> > > transactions where XML documents are being exchanged.
> > >
> > > OK, so I work for Company A. I write an XML document and also
> write a
> > > DTD to go with it. I send my XML document and DTD to company B.
> My
> > > DTD says that my XML document must have element X which must have
> > > exactly 3 specified child elements, and 2 specified attributes
> and
> > > so forth.
> > >
> > > While I am writing my XML document, I can use the DTD to validate
> the
> > > XML document to make sure that I've followed my own rules.
> > >
> > > But what's the point beyond insuring that I have followed my own
> > > rules? When company B gets my XML file, what does it matter to
> them
> > > that I followed my own rules for how the XML document should be?
> And
> > > what if the DTD referenced in my xml doc somehow gets changed by
> > > someone at Company B? Then what?
> > >
> > > IE has it's own DTD built inside which allows us to write and
> look at
> > > other people's html docs. But we cannot change this DTD - it is
> built
> > > into IE. We do have the ability to change and use any DTD we
> want?
> > > Wouldn't this spell confusion?
> > >
> > > I guess my question is what is the point of a DTD and Schema
> beyond
> > > insuring that xml writers follow their own rules.
> > >
> > > Thanks,
> > > xmEllen
>
>
>
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