Well-formed vs. valid

Tim Bray tbray at textuality.com
Mon Feb 22 19:26:35 GMT 1999

At 10:58 AM 2/22/99 -0800, Jeffrey E. Sussna wrote:
>One thing disturbs me, however. Much talk seems to be made about documents 
>or document fragments being useful because they are well-formed. I don't 
>want something well-formed, I want something "valid". Whether validity is 
>determined by reference to a DTD or to a schema of some other kind, I need 
>more than just the lowest-level syntactic conformance to the XML spec. I 
>need to be able to determine that the XML in question conforms to the 
>syntactic and semantic constraints imposed by my application. 

I've never seen an application so simple that its syntactic/semantic
constraints could be expressed in a schema, DTD or any other flavor.
That's why every commercial DBMS-based app has zillions of lines of
data validation code that have to be run before you actually use
incoming data.

Having said that, I think that validation is a good thing and 
essential in lots of applications, and will become a better thing
once we have a more modern schema facility.

>Furthermore, I don't want to have to rely on implicit knowledge contained 
>within a proprietary parser in order to do so. 

In my experience, you *always* have to write some application-specific
validation code. -Tim

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