<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal">Hi Mark<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Just to be precise: I was *<b>not</b>* trying to propose changes in the Transform model as is, though I admit that may not have been clear enough from my email.<o:p></o:p></p>
<p class="MsoNormal">I was sketching a *<b>domain model</b>* (<a href="https://en.wikipedia.org/wiki/Domain_model">https://en.wikipedia.org/wiki/Domain_model</a>), with goal to provide a more formal expression of the world the Transform model is trying to represent.
This with the hope it would help (maybe at least me) to understand some of the technical issues that arose in the discussions.<o:p></o:p></p>
<p class="MsoNormal">Maybe the Transform model can be seen as a *<b>logical model</b>* derived from such a domain model.<o:p></o:p></p>
<p class="MsoNormal">Such a logical model is generally aimed to support a certain problem domain, generally provides “denormalized” representations of concepts in the domain model, may rely more on implicit assumptions, and will be easier to implement in a
certain context. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A possible problem with leaving concepts out of a data model is that any usage of the model must rely on implicit understanding of their existence.<o:p></o:p></p>
<p class="MsoNormal">For example Mark states that “In the coords model, the visibility of individual axes is severely limited…”.<o:p></o:p></p>
<p class="MsoNormal">That does not mean there are no axes, though in the coords model axes are defined on CoordSpace, not on CoordFrame.<o:p></o:p></p>
<p class="MsoNormal">It is assumed that “For the most part, our data reside in standard coordinate spaces".<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Looking forward to seeing an updated version of the model.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Cheers<o:p></o:p></p>
<p class="MsoNormal">Gerard<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt">
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> dm-bounces@ivoa.net <dm-bounces@ivoa.net> <b>On Behalf Of
</b>CresitelloDittmar, Mark<br>
<b>Sent:</b> Tuesday, March 10, 2020 16:06<br>
<b>To:</b> Data Models mailing list <dm@ivoa.net><br>
<b>Subject:</b> Re: [trans] - Model comments<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">Gerard/All,<br>
<br>
Just attempting to separate Transform model discussion separate from the vo-dml Composition rule<br>
Gerard's last mail with suggested model changes:<br>
<a href="http://mail.ivoa.net/pipermail/dm/2020-March/005994.html" target="_blank">
http://mail.ivoa.net/pipermail/dm/2020-March/005994.html</a><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">1) What AST implements as Frame is modeled in the coords model..
<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> The version coming out next (post RFC comments), uses CoordSys to combine the "Frame" and "CoordSpace" information which == ast:Frame<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">2) The Transform model has also been updated to include a "SystemMap" which references source and target coords:CoordSys with a trans:TMapping<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt"> This has not been released on Volute, because David is working through the implementation thereof with AST to look for issues in compatibility with ast:FrameSet.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">In the coords model, the visibility of individual axes is severely limited. For the most part, our data reside in standard coordinate spaces, and the specific axes (other than Pixel), are rarely explicitly
defined. So the AxisMap design doesn't, I think, play well with the typical data product.
<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">I also don't see that supporting the compound mapping, though it may be modifiable to do so.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">The scenario for the compound mapping is something like<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Courier New""> Frame A (x,y) ==> [ shift ] => [scale] => [Permute] => | Poly2D | => (X',Y') Frame B</span><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Courier New""> | Poly2D |</span><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">With a similar set of operations for the 'inverse' path. There is no "Frame" spec between each individual operation.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">Mark<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
</div>
</body>
</html>