Data Source vocabulary

[Hervé WOZNIAK]

Dear all,

my two cents below.

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 
:-) ).

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.

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).

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.

Btw, I agree that 'Theory' has been permanently misleading in IVOA 
context :-)

All the best,

Herve


Le 07/06/2026 à 12:06, Stéphane Erard via semantics a écrit :
>
> Dear all
>
>
> As discussed this morning in the TCG, here is a suggestion about Data 
> Source vocabulary:
>
>
> The current proposal distinguishes: Artificial / Observation / Theory
>
> - The distinction between "modelling the world without reference to 
> specific individual world objects" and "predicting observations of 
> specific individual world objects" is probably not relevant in many cases.
>
> - The need to distinguish observations from made-up data is common to 
> every field (associated to the opposition noise vs modeling uncertainty)
>
> - The need to distinguish data with physical content from 'artificial' 
> data is also sensible, although the distinction may depend on the 
> discipline
>
> - 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
>
>
> Proposal (not yet formalized)
>
> - "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)
>
> - "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).
>
> - "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)
>
>
> But 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.
>
>
> Best wishes
>
> Stéphane
>
-- 
Herve WOZNIAK
Astronome

LUPM
Université de Montpellier - CNRS
Place Eugène Bataillon - CC 72
F-34095 Montpellier Cédex 05

Tel/Phone : +33 4 6714 3902   Fax : +33 4 6714 4190
http://herve.wozniak.fr/

"Essentially everything of astronomical interest is either part of a galaxy, or from a galaxy, or otherwise relevant to the origin or evolution of galaxies." (B. Tinsley, 1980)
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