<div dir="ltr">HI Mark<br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Apr 18, 2017 at 12:23 PM, 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:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><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></div></div></div></blockquote><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div> + 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></div></blockquote><div><br></div><div>Seems to me your are trying to model a more complex concept here, something that could (should?) be captured using a custom DataType with two attributes, a time0 (ivoa:datetime) and a time span (ivoa:RealQuantity).</div><div>According to STC, any observation of some property such as a datetime, or a position etc needs quite some information for interpretation. I.e. a position is not just a realquantity or group of such quantites, it needs a zero-point, a reference frame, whatnot. Same with time. <br></div><div>I am sure there are lots of models where a simple ivoa:datetime, serialized for example to '2017-05-01 13:00:00 cet' , would be ok. E.g. to "model" the start time of a telecon. This is I guess why a datetime-like type exists in databases, programming languages and XML schema for example.</div><div>For astronomical observations one may(?:) often need the more involved machinery of STC. But then probably one would use realquantity in most places and one would not want to add all of this to the basic set of primitive types or even quantities.</div><div><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div></div><br><div><div><div><div><div><div><div>So, I still think we need both.<br><br></div></div></div></div></div></div></div></div></blockquote><div>So I wonder whether we do.</div><div><br></div><div>Gerard</div><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div><div><div><div><div></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_5085437855901685582m_-1583310391526222104gmail-m_8131231324588115954gmail-m_5555787170495511556gmail-MsoPlainText">...</p><span class="m_5085437855901685582m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><span style="color:black"></span></div></div></blockquote><span>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><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_5085437855901685582m_-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_5085437855901685582m_-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_5085437855901685582m_-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_5085437855901685582m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><br>>> <span></span><span class="m_5085437855901685582m_-1583310391526222104gmail-m_8131231324588115954gmail-"></span><span style="color:black"> </span><span class="m_5085437855901685582m_-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_5085437855901685582m_-1583310391526222104gmail-HOEnZb"><font color="#888888"><br></font></span></div><span class="m_5085437855901685582m_-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_5085437855901685582m_-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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