<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On 2017-06 -13, at 20:50, Markus Demleitner <<a href="mailto:msdemlei@ari.uni-heidelberg.de" class="">msdemlei@ari.uni-heidelberg.de</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Hi DM,<br class=""><br class="">On Tue, Jun 13, 2017 at 07:03:10AM -0400, Gerard Lemson wrote:<br class=""><blockquote type="cite" class="">On Tue, Jun 13, 2017 at 3:59 AM, Paul Harrison <<br class=""><a href="mailto:paul.harrison@manchester.ac.uk" class="">paul.harrison@manchester.ac.uk</a>> wrote:<br class=""><blockquote type="cite" class="">I notice that a recent change to the VO-DML schema introduces a <uri><br class="">element which is supposed to define a URI at which the data model can be<br class="">found - in my opinion this is not a good idea. I understand the desire to<br class=""></blockquote></blockquote>[...]<br class=""><blockquote type="cite" class=""><blockquote type="cite" class="">Each data model already has a "namespace" which is the <name> element and<br class="">just having a rule such as the models being available at<br class=""><br class=""><a href="http://www.ivoa.net/dm/name" class="">http://www.ivoa.net/dm/name</a><br class=""><br class="">would suffice for all "standard" models - though there could be a more<br class="">arbitrary mapping mechanism set up between namespace and model URL such as<br class="">is done with XML.<br class=""><br class=""><br class=""></blockquote>Indeed this mechanism is what we're trying to follow. If the description in<br class="">the document (still on volute, soon to be moved to IVOA doc library) is not<br class="">clear enough though we need to improve the text.<br class=""><br class="">The URI attribute is *not* intended to be location of the document, but to<br class="">be dereferenced to the latest minor version. Different minor versions will<br class="">have same URI, but different "version" attribute. So together , uri+version<br class="">are a unique identifier of the actual version, uri only of the major<br class="">version.<br class=""><br class="">But I expect Markus can explain this better.<br class=""></blockquote><br class="">Not really, as what I've suggested so far just tried making proposed<br class="">practices work. These, in turn, were inspired by XML Schema, where<br class="">the actual identifier of a schema is its URI. In XML instances, this<br class="">URI is mapped to a (conceptually, if not in VO practice) arbitrary,<br class="">short prefix. This sort of prefix mapping was even explicitly done<br class="">in early applications of utypes (you'll find it in early SSA, and<br class="">even in the current 1.1 you'll see remnants in the examples in the<br class="">appencides) -- which of course was an abomination.<br class=""><br class="">Now, for VO-DML we claim that the prefix is unique per major version<br class="">of a data model (which I think is an excellent idea). This means we<br class="">don't really need an XSD-style DM URI as an identifier any more, the<br class="">prefix is enough.<br class=""></div></div></blockquote><div><br class=""></div>I think that within the VO-DML identifiers domain the name acts as a unique namespace identifier, and having something else as another identifier might confuse things.<br class=""><blockquote type="cite" class=""><div class=""><div class=""><br class="">The only reason I wanted the DM URI in the VO-DML header is that in a<br class="">model declaration in an instance document it was still required, and<br class="">thus VO-DML writers would have had to maintain a prefix -> DM uri<br class="">mapping. That's a pain.<br class=""></div></div></blockquote><div><br class=""></div>I agree that there needs to be a conventional mechanism for locating the data model instance files for a particular name - which was why I was suggesting something like the</div><div><br class=""></div><div><a href="http://www.ivoa.net/dm/name" class="">http://www.ivoa.net/dm/name</a></div><div><br class=""></div><div>URL for a datamodel with namespace “name"</div><div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><br class="">Now, if nobody actually wants this identifying DM URI, I'd be totally<br class="">in favour of removing it (and saying the prefix identifies the DM,<br class="">and if you absolutely must know the minor version (for which you<br class="">should have no reason), look at @version), but it would have to go<br class="">from the mapping's model declaration, too.<br class=""><br class=""><br class="">But even if we decide there's no need for a DM URI to identify the<br class="">DM, I have to say there's something to be said for allowing the<br class="">declaration of URIs from where a writer would like a reader to pull<br class="">the model file (in VO XSD practice, the two URIs typically conincide,<br class="">but that's just a convention, and when there's not identifying URI,<br class="">this whole question goes away -- I don't think anyone will miss<br class="">@schemaLocation in VO-DML…).</div></div></blockquote><blockquote type="cite" class=""><div class=""><div class=""><br class="">At least for IVOA standard models, this dereferencable source URI<br class="">would be advisory, of course. Hence, if the mapping document said<br class="">"Dump some URI into the model's URI child [or, if you ask me,<br class="">attribute] that people can derference to pull the VO-DML file from;<br class="">what exactly you use is up to you, but expect clients to use the<br class="">official IVOA files for validation for official IVOA DM names,"<br class="">that'd I think help quite a few applications, in particular with<br class="">non-IVOA models.<br class=""><br class=""></div></div></blockquote><br class=""></div><div><div>It could be useful in such a circumstance to indicate where to find the “official release”, but as I said in my original post, only probably useful if you have a copy lying around on your hard drive and have forgotten where it came from - I noticed it because it was mandatory in the VO-DML schema and suddenly existing models were no-longer XML valid - I feel that it should probably be optional - In the short term the de facto official location of these models is the VO-DML project in volute - so clearly this information will have to be changed as each model is officially published as a standard.</div><div><br class=""></div><div>Anyway in conclusion it is not a big deal to me whether the URI information exists or not for locating the model instance file - what I was really concerned about was that there was not going to be some other way of indicating the VO-DML identifier namespaces - and it is clear that is unchanged.</div><div><br class=""></div><div>Paul.</div><div><br class=""></div><div><br class=""></div><div class=""><br class=""></div></div><br class=""></body></html>