<html aria-label="message body"><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On 16 Feb 2026, at 16:59, Gerard Lemson <glemson1@jhu.edu> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-line: none; text-decoration-thickness: auto; text-decoration-style: solid;"><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">Hi Paul<o:p></o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">From the abstract of the vo-dml spec: “VO-DML is a conceptual modeling language that is agnostic of serializations, or physical representations”.<o:p></o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">We do discuss possible serializations to XML/RDB in appendix B of the spec.<o:p></o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">Even such “direct” serializations need to make decisions how to map VO-DML constructs to the serialization format as generally there is some impedance mismatch.<o:p></o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">For example in XML how references are represented, in RDB how inheritance is dealt with, anywhere how datetime-s are mapped (which I assume should really use some STC-like stuff).</div></div></div></blockquote><div><br></div>I suggest dateTimes have their definition restricted somewhat so that they are UTC timescale and CoordsDM used for more complex cases <a href="https://github.com/ivoa/vo-dml/issues/37">https://github.com/ivoa/vo-dml/issues/37</a></div><div><br></div><div>I do think that dateTime is a good example of where VO-DML cannot be completely thought of as a conceptual modelling language entirely agnostic of serialisation or physical representations, as relativity does make the concept of “time instant” rather complex, and dateTime as a primitive is probably saying more about the serialisation of the value than the concept. It might be that a good way to think of primitives is that they do have a specific textual serialization.</div><div><br><blockquote type="cite"><div><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-line: none; text-decoration-thickness: auto; text-decoration-style: solid;"><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;"><o:p></o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">Laurent Bourges and I did a lot of work for the Simulation data model in VO-URP to make those things work. I think<span class="Apple-converted-space"> </span><s>we</s><span class="Apple-converted-space"> </span>one could create standard mappings from VO-DML to some serialization languages and should then deal with these issues there. Of course there is such a mapping for VOTable and it already had/s already ways to indicate something about serialization (XTYPE??).<span class="Apple-converted-space"> </span><o:p></o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;"><o:p> </o:p></div></div></div></blockquote><div>The current VO-DML tools also create some self contained “direct” mappings to XML, JSON and RDB that built on your earlier work <a href="https://github.com/ivoa/vo-dml/issues/43">https://github.com/ivoa/vo-dml/issues/43</a> - I think that this form of “direct" serialisation is worth “standardising” just as much as MIVOT was, but probably in a separate document.</div><div><br></div><br><blockquote type="cite"><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-line: none; text-decoration-thickness: auto; text-decoration-style: solid;"><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">Another reason why UCDs<span class="Apple-converted-space"> </span><i>conceptually</i><span class="Apple-converted-space"> </span>should not be primitive types is given on page 31:<br><br><i><o:p></o:p></i></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;"><i>The extent of a value type, i.e. its set of valid instances/values, is self-evident from its definition. That is, from the definition one can infer exactly which values exist in the set defined by the value type. Hence one can identify the instance by its value.</i><o:p></o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;"><o:p> </o:p></div><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;">According to this, as UCDs and other vocabularies have been, are and will keep on changing, UCDs should not be considered data types on their own.</div></div></blockquote><div><br></div>the request for UCDs to be a primitive type actually came from MANGO - but I am fairly convinced by this argument that they should not be - It is, however, useful to know what the UCD should be for serialization and some thoughts are gathered in <a href="https://github.com/ivoa/vo-dml/issues/19">https://github.com/ivoa/vo-dml/issues/19</a> - I now think that the best place for the doing this is in the binding.<br><blockquote type="cite"><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-line: none; text-decoration-thickness: auto; text-decoration-style: solid;"><div style="margin: 0in; font-size: 12pt; font-family: Aptos, sans-serif;"><o:p> </o:p></div></div></blockquote></div><br></body></html>