Re: WIP - xmlvalidate implementation from TODO list

Hey Jim!

On 06.01.26, Jim Jones <jim(dot)jones(at)uni-muenster(dot)de> wrote:
> The result of <XML validate> is R.
That was an oversight on my behalf, I had a hard time understanding the
standard, but now the validation of DOCUMENT and CONTENT being accepted
makes more sense.

The current patch has some issues.

> xmloption is document_or_content. But xmlvalidate_text_schema() always
validates as a document.
As Andrey noticed, we should indeed support both a document and content.
Which entails into an iterative validation (for each node provided) on
content mode, so I should likely add the xmloption back. The fact it worked
with the example I created was actually luck.

Also, I am not sure if some variables used inside of the PG_TRY are memory
safe -- notice that none right now is set to volatile, despite being
accessed in different parts of the block; other functions in xml.c do
handle such correctly it seems (like xml_parse).

About the syntax proposal by Jim, I have no problems with complying to it.
It does increase considerably the scope from what I originally intended,
but that's the price to have something actually nice.

I can think of several useful extensions we could consider in a further
implementation:

Schema Dependencies/Imports
CREATE XMLSCHEMA base AS '...';
CREATE XMLSCHEMA extended
IMPORTS base
AS '...';

Schema Versioning
CREATE XMLSCHEMA patient VERSION '1.0' AS '...';
CREATE XMLSCHEMA patient VERSION '2.0' AS '...';
XMLVALIDATE(doc ACCORDING TO XMLSCHEMA patient VERSION '2.0')

Custom Error Messages
CREATE XMLSCHEMA patient
AS '...'
ERROR MESSAGE 'Patient record does not match schema v2.0';

Schema inference from samples (if the lib supports it, that is)
CREATE XMLSCHEMA patient
INFER FROM (SELECT data FROM patient_samples);

And much more, but perhaps that's already too ambitious for a first version.

I'll wait for the others to ring their bells.

Regards, Magueta.