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<p>Dear all,</p>
<p>my two cents below.</p>
<p>A model is a representation and abstraction of anything, be it a
real system, a proposed system, a futuristic system design, an
entity, a phenomenon, or an idea. Most of (astro)physical models
are mathematical models. Mathematical models may have many
different forms, including continuous-time and discrete-time
dynamical systems, statistical models, partial differential
equations, etc. Modeling is the act of constructing such a model
(DM make many non-mathematical models in IVOA :-) ).</p>
<p>To Simulate, according to Oxford English Dictionary, is:“To
assume falsely the appearance or signs of (anything); to feign,
pretend, counterfeit, imitate; to profess or suggest (anything)
falsely.” To Simulate implies to imitate or mimic. The ACM defines
Simulation as the act of executing, experimenting with or
exercising a model (generally, a mathematical model designed to
represent a physical or real-word system) for a specific
objective.</p>
<p>Consequently, on the one hand, a "modeled" observation could be
understood as refeering to the output of a (possibly static, but
certainly parametric) model designed to create such mock
observations. A "simulated" observation, on the other hand, might
be the result of a more complex (and sometimes lengthy) process as
it requires to run a simulation (as en experiment on a model with
one or more parameters varying throughout the simulation, such as
time). </p>
<p>I guess, this is a bit different from the proposal. But both are,
in fact, 'mock' observations. So, I don't see the need for both
definition, 'mock' being enough imho.</p>
<p>Btw, I agree that 'Theory' has been permanently misleading in
IVOA context :-)</p>
<p>All the best,</p>
<p>Herve</p>
<p><br>
</p>
<div class="moz-cite-prefix">Le 07/06/2026 à 12:06, Stéphane Erard
via semantics a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:D2FAEB0B-C520-4EE1-A8DA-44F1E094450F@obspm.fr">
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<p
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all</p>
<p
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</p>
<p
style="margin: 0px; font-style: normal; font-variant-caps: normal; font-stretch: normal; line-height: normal; font-family: "Bear Sans UI"; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal;">As
discussed this morning in the TCG, here is a suggestion about
Data Source vocabulary: </p>
<p
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</p>
<p
style="margin: 0px; font-style: normal; font-variant-caps: normal; font-stretch: normal; line-height: normal; font-family: "Bear Sans UI"; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal;">The
current proposal distinguishes: Artificial / Observation /
Theory</p>
<p
style="margin: 0px; font-style: normal; font-variant-caps: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Times; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal;"><span
style="font-style: normal; font-variant-caps: normal; font-stretch: normal; font-size: 13px; line-height: normal; font-family: "Bear Sans UI"; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal;">-
The distinction between "</span><span
style="font-kerning: none">modelling the world without
reference to specific individual world objects</span><span
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and "</span><span style="font-kerning: none">predicting
observations of specific individual world objects</span><span
style="font-style: normal; font-variant-caps: normal; font-stretch: normal; font-size: 13px; line-height: normal; font-family: "Bear Sans UI"; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal;">"
is probably not relevant in many cases.</span></p>
<p
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The need to distinguish observations from made-up data is common
to every field (associated to the opposition noise vs modeling
uncertainty)</p>
<p
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The need to distinguish data with physical content from
'artificial' data is also sensible, although the distinction may
depend on the discipline</p>
<p
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It is stressed that the word "Theory" is often misleading in the
VO (at least another similar comment this morning!) — in most
cases it refers to computations / modeling, which is different
and more specific</p>
<p
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</p>
<p
style="margin: 0px; font-style: normal; font-variant-caps: normal; font-stretch: normal; line-height: normal; font-family: "Bear Sans UI"; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal;">Proposal
(not yet formalized)</p>
<p
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"Observation" is reserved to actual measurements and derived
data. This includes made up samples in the lab, which implies
that another level is available to characterize the source
itself (lab measurements in general are often distinguished with
Experimental, as opposed to Observation)</p>
<p
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"Modeled" refers to computed data generalizing observations
— typically large models (universe, planetary / stellar
atmospheres or interiors…), which are explored to grab
scientific meaning. This includes the current case of no attempt
to simulate existing objects, but not only (also models with
parameters tuned to fit the real world).</p>
<p
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"Simulation" refers to mock-up data with mostly practical value,
typically much less computation-intensive (ie : simulation of an
instrument output, first level simulation of a source, etc).
According to this definition, this is where you would find
properties averaged over a class of objects (eg. stellar class
spectra, asteroid type spectra) — which is debatable (but those
are often difficult to characterize, as there is no associated
source)</p>
<p
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</p>
<p
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I stress that the need to have both Modeled and Simulation has
to be demonstrated, especially if the distinction ifs not always
clear and obvious.</p>
<p
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</p>
<p
style="margin: 0px; font-style: normal; font-variant-caps: normal; font-stretch: normal; line-height: normal; font-family: "Bear Sans UI"; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; min-height: 17px;">Best
wishes</p>
<p
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</blockquote>
<pre class="moz-signature" cols="72">--
Herve WOZNIAK
Astronome
LUPM
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