<div dir="ltr"><div><div><div><div><div>Gerard,<br><br></div>I was thinking about this more on the way home yesterday.. I don't think datetime can handle all three cases.<br></div><div> + it certainly handles DATE-OBS, as an instant in time (date+time)<br></div> + it may handle MJDREF, as it could be considered different representation of a date+time as 'MJD' date.<br></div><br> + TSTART (TIMEOFFSET) requires additional information (the time0 of the frame) to determine, and can have a variety of units [ms, s, d, m, y, ... ] which the others don't.<br></div> while the first two represent an instant in time, this is really a span of time, which can be converted to an instant if you know the start point.<br></div><div> Yes.. that is the same as MJDREF, but MJD has a fixed, known start point while this one is arbitrary and cannot be internalized to the type.<br></div><br><div><div><div><div><div><div><div>So, I still think we need both.<br><br></div><div>Mark<br><br></div><div><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Apr 18, 2017 at 11:07 AM, Gerard Lemson <span dir="ltr"><<a href="mailto:gerard.lemson@gmail.com" target="_blank">gerard.lemson@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi Mark<br><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Apr 17, 2017 at 11:51 AM, CresitelloDittmar, Mark <span dir="ltr"><<a href="mailto:mdittmar@cfa.harvard.edu" target="_blank">mdittmar@cfa.harvard.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote"><blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex" class="gmail_quote"><div dir="ltr"><div class="gmail_extra"><p class="m_-1583310391526222104gmail-m_8131231324588115954gmail-m_5555787170495511556gmail-MsoPlainText">...</p><span class="m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><span style="color:black"></span></div></div></blockquote><span class="">I don't think this needs to be complicated, so let's put these on the back burner.<br></span></div><div class="gmail_quote"><div><br></div></div></div></div></blockquote><div>Thanks! </div><span class=""><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div></div><br>>> * Quantity and datetime would not have a
common ancestor, so we could<span></span><span class="m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span> not define
a TimeStamp<span></span><br>>> which would allow time represented as a
RealQuantity OR datetime.<span></span><span class="m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><div class="gmail_extra">>> <a href="https://volute.g-vo.org/svn/trunk/projects/dm/STC-2.0/doc/diagrams/alt/temporal%20domain%20diagram.png" target="_blank"><span style="color:windowtext;text-decoration-line:none">https://volute.g-vo.org/<wbr>svn/trunk/projects/dm/STC-<span></span></span></a><span class="m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><a href="https://volute.g-vo.org/svn/trunk/projects/dm/STC-2.0/doc/diagrams/alt/temporal%20domain%20diagram.png" target="_blank"><span style="color:windowtext;text-decoration-line:none"> 2.0/doc/diagrams/alt/temporal%<wbr>20domain%20diagram.png</span></a><span></span><span class="m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><br>>> <span></span><span class="m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><span style="color:black"> </span><span class="m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><br><br>>So are you saying you'd like a DatetimeQuantity? With only a "datetime unit" being sufficient?<br>>I had hoped 'ivoa:datetime' would be sufficient and the precise representation would be left to the mapping.<br><br></div>This sounds like you are suggesting that 'ivoa:datetime' should suffice for all uses.<br></div> MJDREF = 50814.02 / [d] zero point for times - MJD<br><div class="gmail_quote"> TSTART = 84244214.<a href="tel:(754)%20697-9934" value="+17546979934" target="_blank">7546979934</a> / [s] Observation start time<br> DATE-OBS= "2000-09-02T01:10:14" / Date and time of observation start<br><br></div></div></div></blockquote><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">I want all of these to be a TimeStamp type (abstract).<br></div><div class="gmail_extra"> * datetime = has vodml/html description: "Represents a moment in time using a date+timestamp."<br>which covers 'DATE-OBS', the other 2 are satisfied by RealQuantity.<br><br></div><div class="gmail_extra">But.. since RealQuantity and datetime do not have a common ancestor, I cannot define TimeStamp without either an anyType or a DateQuantity.<span class="m_-1583310391526222104gmail-HOEnZb"><font color="#888888"><br></font></span></div><span class="m_-1583310391526222104gmail-HOEnZb"><font color="#888888"><div class="gmail_quote"><br></div></font></span></div></div></blockquote><div><br></div></span><div>Yes, that is correct, but I see now (I think) what might cause confusion, namely the description of ivoa:datetime in the model as</div><div>"Represents a moment in time using a date+timestamp". What was meant there is that it is not just a day/date (2017-04-18), and not just a time ("13:00:01.3"), but the fully specified moment in time. <br></div><div>In the current description it does indeed sound as if date and time must be represented, i.e. too much like a prescription for valid serializations. This was NOT intended.</div><div>ivoa:datetime is supposed to represent the concept of a Timestamp as you mention it, and it should be up to serialization prescriptions to take care of valid representations.</div><div> </div><div>So if that interpretation is given to ivoa:datetime, would that type be sufficient for your requirements?</div><div><br></div><div>Cheers</div><div>Gerard</div><div><br></div><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><span class="m_-1583310391526222104gmail-HOEnZb"><font color="#888888"><div class="gmail_quote"></div><div class="gmail_quote">Mark<br><br></div><div class="gmail_quote"><div class="gmail_extra"><br></div></div></font></span></div></div>
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