• Subject: Re: XML Attributes
  • From: "Phil Hall" <hallp@xxxxxxxx>
  • Date: Sat, 18 Nov 2000 22:19:04 -0600

> See, the different "standards" and understandings of XML are
> clashing as we speak.  :)
>
> XML is self describing data.  Yes, makes sense.
> XML isn't valid without a DTD.  Wait, that's a contradiction to the above.

You don't need a DTD to have 'valid' XML. There are two types of XML.

1. Well formed XML - where the 'syntax' of the XML is valid and no DTD is
needed, for example;

<account>
    <name>Joe</name>
</account>

is a valid well formed XML snippet, but;

<account>
    <name>Joe
</account>

Is not well formed or valid, because there is no closing </name> tag.
A checking parser will flag the XML as in error.

Again no DTD is needed for this basic level of XML, and hence it's more
free form, and with that you need to do extra work when dealing with
the element data to validate the data yourself. But the XML stream
*is* 'valid' XML.

2. Valid XML - where there is a DTD that describes the content of the XML
stream. The DTD describes what the elements are, what type they are, if they
can be omitted or if they are required etc. If the XML stream is well formed
(as in point 1) but doesn't validate against the DTD, then the XML is
flagged as invalid. I wish the W3 would have chosen a different word instead
of 'valid' such as 'self-validating' which is more in line with what using a
DTD is about.

But as someone who has used XML, you already knew all of this.



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