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Namespace persistence etc

From: Phil Archer <phila@w3.org>
Date: Wed, 13 Jul 2016 06:12:46 +0100
To: SDW WG Public List <public-sdw-wg@w3.org>, Scott Simmons <ssimmons@opengeospatial.org>
Message-ID: <e3f74ffa-37f6-2f2d-447a-943387de39c0@w3.org>
@Scott - please chime in with any variance to this from an OGC perspective.

Dear all,

I must begin by apologising for not being on the SSN call today/last 
night. I could make up some convoluted reason but the truth is that I 
forgot.

I know one of the topics discussed was the issue around vocabulary term 
persistence so I should set out a few things about that.

The principle is, I think, straightforward: any change made to a 
vocabulary shouldn't break existing implementations. Since we don't know 
who has an implementation, we can't write to everyone and ask "if we 
change this will your thing break?" Therefore we have to be cautious.

That's what leads to W3C saying that vocabulary terms may not be deleted 
or their semantics changed radically. But it only applies at the 
namespace level. If you have a new namespace, you can do what you like 
since nothing will break. *However* it's going to be really confusing if 
some terms in the old and new namespaces are the same but with radically 
different semantics. So my interpretation is:

Same namespace:
===============
No deletions.
No changing or tightening or semantics (i.e. don't add a new domain or 
range - make a sub class|property and put the new restrictions on that)
Deprecation is OK.
Loosening semantics is OK (so you *can* remove a domain or range 
restriction since it is extremely unlikely that doing so will break 
anyone's existing implementation).
Adding new terms is fine.
Clarifying existing definitions is OK.
Adding new translations of labels is expressly encouraged.

Different namespace
===================
We can be a little more relaxed here. Recall that documents on w3.org 
are persistent so the original documentation will always be there (at 
the original URI or redirected from it).

No need to replicate the whole of the old vocabulary, so no need to 
include deprecated terms - they are deprecated by not being included in 
the new namespace.

Assuming the vocabulary has the same name then terms that appear in both 
old and new should broadly be the same although semantics can change a 
little. It's a matter of judgement.

The case I keep in mind is Dublin Core/DC Terms. dc:creator took either 
text or a URI as a value - which was confusing. dcterms:creator should 
take a URI.

Hope this helps clarify things.

Phil.

-- 


Phil Archer
W3C Data Activity Lead
http://www.w3.org/2013/data/

http://philarcher.org
+44 (0)7887 767755
@philarcher1
Received on Wednesday, 13 July 2016 05:11:38 UTC

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