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<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Ira,<div><br></div><div>Semantically-speaking "unknown" and "no-value" do mean different things:</div><div><br></div><div> unknown: There is a value but we don't know what it is.</div><div> no-value: We know there is no value.</div><div><br></div><div>Clearly every printer has a geographic location (and thus a value exists), however the value of that location may not be known because nobody has entered one and/or the printer has no way to get its location automatically. While we certainly could use "no-value" for printer-geo-location and treat it as "no value set", I like using a more specific tag if one exists.</div><div><br></div><div>That said, I wonder - how does the Semantic Model map "unknown" to the XML schema?</div><div>(or does it?) If there isn't a mapping of unknown then I would suggest we formally deprecate the "unknown" value tag and use "no-value" for printer-geo-location as you suggest - it hasn't been used widely (or at all as far as I can see) and I don't want to depend on something that can't be mapped to another protocol binding.</div><div><br></div><div><br></div><div>On Sep 15, 2011, at 3:05 PM, Ira McDonald wrote:</div><div><div><blockquote type="cite">Hi Mike,<br><br>I like all of it, except that in printer-geo-location we should<br>get rid of that MIB-centric "unknown" and instead use the<br>semantically equivalent "no-value".<br><br>Cheers,<br>- Ira<br>
<br clear="all">Ira McDonald (Musician / Software Architect)<br>Chair - Linux Foundation Open Printing WG<br>Co-Chair - IEEE-ISTO PWG IPP WG<br>Chair - TCG Embedded Systems Hardcopy SWG<br>IETF Designated Expert - IPP & Printer MIB<br>
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<br><br><div class="gmail_quote">On Thu, Sep 15, 2011 at 5:56 PM, Michael Sweet <span dir="ltr"><<a href="mailto:msweet@apple.com">msweet@apple.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div style="word-wrap:break-word">All,<div><br></div><div>I've received a few queries about how the "unknown" and "no-value" attribute value tags are used in IPP recently. What I've been telling people is basically the following, but I'd like to document this somewhere, perhaps as an errata for one of the IPP RFCs (probably RFC 2911 and 3380) along with some updates to the IPP registry for the affected attributes.</div>
<div><br></div><div>Comments?</div><div><br></div><div><br></div><div>The "no-value" Attribute Value Tag</div><div><br></div><div>This value may be set or returned for any settable Job, Subscription, or Printer attribute. The typical usage is to specify an xxx-default Job Template attribute that has no default value, such as "orientation-requested-default" - in that case the Printer may apply a default based on the document such as automatically applying "orientation-requested" with a value of 4 (landscape) for a landscape document.</div>
<div><br></div><div>The "no-value" value may also be returned for read-only description attributes that are a mandatory part of an object. For example, the Job object's "time-at-completion" attribute can be returned as "no-value" when the Job has not yet entered a terminating state.</div>
<div><br></div><div><br></div><div>The "unknown" Attribute Value Tag</div><div><br></div><div>This value may only be set or returned for specific Printer attributes. Currently only the proposed "printer-geo-location" attribute has been defined to potentially have an "unknown" value.</div>
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