Pierre Didelon wrote:
>
> UCD must define preferentially concept I suppose, isn't it?
"Frederic V. \"Rick\" Hessman" wrote:
>
> The reason for separating "astronomical non-object concepts" and
> "sematics for astronomical objects" escapes me entirely, even if it
> were possible to do so (which it isn't). At least someone agrees that
> a natural but major extension to UCD "may be appropriate"..... :-)
Hi,
Reading the last messages, I realize that we must be *very* careful
with the vocabulary we use (especially as members of a board aiming at
describing semantic contents!).
I have already experienced how words like "objects", "concepts" and
"types" can be (mis)understood when discussing across (and even
within) different domains (mainly astronomy and computer science).
Let me explain a few points that don't seem clear:
Concept / properties :
Following the ontology vocabulary, a *concept* is something abstract
(can be seen as a class in object-oriented programming).
This concept can have *properties*.
When you define an *instance* of a concept, you associate values to
the
various properties.
example: "telescope" can be seen as a concept (something abstract).
Several
properties can be associated to the concept of a telescope (its name,
size,
mass, location, ...). A particular telescope (one that you can see, or
observe
with) will be an instance of the concept "telescope".
In the UCD vocabulary, most of the words correspond to *properties*.
Because
some properties are common to different concepts, we also created some
UCD-words
corresponding to *concepts*, and we can build complete UCDs by writing:
"property;concept". This was done to reduce the number of words: for M
properties
and N concepts, this leads to N+M words instead of N*M.
For the example above, we have the concept of telescope: "instr.tel".
It can have a name: ucd="meta.id;instr.tel", a size:
ucd="phys.size.diameter;instr.tel",
a location, eg: ucd="pos.earth.lon;instr.tel" and
ucd="pos.earth.lat;instr.tel", ...
Basically, concepts were only introduced in the vocabulary for
allowing
re-usability of words. But the most important UCD-words are those
describing properties: they are used to say what a quantity (can be a
number
or a string) is.
Objects / non-objects :
I'm confused with the "astronomical non-object concepts" and
"sematics for astronomical objects" expressions.
Astronomical objects (I understand sources detected in the sky, here)
are
named individually according to a controlled Nomenclature. The UCD have
no role to
play in this nomenclature. But there is one UCD word to say that a
quantity is an
object's name: meta.id : Identifier, name or designation
Or maybe we can write: "meta.id;src"
e.g. <PARAM ucd="meta.id;src" value="NGC 234">
Currently, most of the existing UCD words are used to identify the *properties* of the astronomical objects (detected sources).
Sebastien.
--
_______
/ ~ /, Sebastien Derriere mailto:derriere-at-astro.u-strasbg.fr
/ ~~~~ // Observatoire de Strasbourg Phone +33 (0) 390 242 444
/______// 11, rue de l'universite Telefax +33 (0) 390 242 417
(______(/ F-67000 Strasbourg France
Received on 2005-06-01Z16:50:45