RWP04: Registry Replication

Tony Linde ael at star.le.ac.uk
Wed Apr 30 09:17:37 PDT 2003


<<Type of services: >>
<<Type of objects: >>

I don't think Keith is trying to represent himself as an expert on
astronomy: his example is generic. For AstroGrid, we're defining a narrow
set of parameters that can go into a registry query. 

<<Who's coming up with things like a standard list of object types ?>>

For IVOA, we need to define those parameters: that is the job of Rwp03:
  http://www.ivoa.net/twiki/bin/view/IVOA/IVOARegWp03

Cheers,
Tony. 


-----Original Message-----
From: amicol at eso.org [mailto:amicol at eso.org] On Behalf Of Alberto Micol
Sent: 30 April 2003 12:18
To: Keith Noddle
Cc: IVOA Registry mailing list; dm at ivoa.net
Subject: Re: RWP04: Registry Replication


SELECT * FROM REGISTRY WHERE 
   ( 
      TYPE="white dwarf star" AND 
      (WAVELENGTH="optical" OR WAVELENGTH="uv") AND 
      (KEYWORD="BPM 16274" OR 
         KEYWORD="GD 50" OR 
         KEYWORD="HST photometric standards" 
      ) 
   ) 
then one way of presenting this in XML is shown ... etc

Dear Keith, 
  
Type of services: 
   The first problem I have is that the query does not esplicitly 
   defines what type of services you want to identify in the registry. 
   I think a SERVICE_TYPE is required. It could take some values 
   like "catalogue browser", "data archive", "documentation", etc. 
   If someone is interested in ANY service type, then the query should 
   explicit that with a constraint like: 
       SERVICE_TYPE="ANY" 
Type of objects: 
   You use the constraint TYPE="white dwarf star" 
   This is not a service_type, but specifies what class of objects the user 
   is interested in. It should be probably called OBJECT_TYPE. 
   The main problem here is in the value: "white dwarf star" 
   How is that going to be used ? 
   Will only resources matching exactly "white dwarf star" be returned ? 
   What if the resource I maintain lists OBJECT_TYPE="white dwarf" ? 
   It will not match ... 
   We have to come up with a standard list, a thesaurus, 
   to homogenise those types! 
   Probably the best thing is to start with the IAU thesaurus 
   http://msowww.anu.edu.au/library/thesaurus/english/ 
   (but I remember other similar efforts like the IUE object class ...). 
Wavelength: 
   Wavelength is another item value you defined. 
   Here the Data Model should intervene with a proper definition both for
the 
   name of the item (I remember a joke by Jonathan McDowell that introduced 
   the FREWAVERGY!), and for the values (optical and uv are ok, but we need 
   to define many more). 
Keyword: 
   As you presented this, it looks like KEYWORD is a generic container, 
   which could take very different values spanning from object names (GD 50)

   to more or less free text (HST photometric standards). 
   Maybe this is too generic ... ? 
   One of the problem I have with the registry is that I do not know 
   in advance whether a service will list a certain characteristic 
   in its metadata, or within the data itself. 
   Example: 
   The "GD 50" white dwarf might be listed in a set of resource keywords, 
   in some other cases it will be a record in a resource (eg an entry 
   in a  catalogue of white dwarfs); 
   in this second case your query will fail, even though the object is to 
   be found in the resource. 
   I described the same problem in the Rwp02 astrovirtel use case for the 
   Distance attribute, where a catalogue might offer the distance as a field

   in its records, or there could be a metadata keyword saying that the
objects 
   in a catalog are all to be found within so many mega parsec. 
Summary: 
My main point here is that the registry must describe things using 
not only a well defined set of keywords, 
but also a well defined set of keyword values! 
Phometric aspects (the Wavelength values): it will be 
the Data Model WG to come up with a proper description and set of values; 
service_types and other service (or resource) specific metadata 
(I mean non-Bob's document for level 0, but other keywords for deeper
levels) 
will be defined by the Registry WG. 
What I do not know is: 
Who's coming up with things like a standard list of object types ? 
Do we need one ? (I think so ... the IAU thesaurus might show the way) 
Alberto 
-- 
Alberto.Micol at eso.org                         Tel: +49 89 32006365
HST Science Archive       ST-ECF              Fax: +49 89 32006480
ESA/RSSD/SN               c/o ESO             Karl Schwarzschild Str.2,
http://archive.eso.org/   No ads, thanks.     Garching bei Muenchen,
http://www.stecf.org/     HTML emails         D-85748 Germany
Keith Noddle wrote: 
Thanks for the feedback Ray - much appreciated! 
I think we're all converging on the model proposed by Tony which, to 
paraphrase Ray, is the full-(specialist/limited)-(source/private) model. 
I think this pretty much satisfies the points raise by Wil and Ray as 
well as meeting most of the useful requirements I originally proposed. 
I'll start work on the design and get something posted on the IVOA Wiki 
for comment - I'm conscious of the need to get a presentation together 
in short order for Cambridge! 
The other major aspect of the RWP04 work is the development of a 
registry query schema. Tony, Elizabeth and I have been working on 
something similar(!) for AstroGrid and whilst we don't yet have schema, 
we have a simple example XML query (below) upon which I would welcome 
everyone's comments. We are looking into XQuery/XPath, but that might 
not be appropriate for the current iteration of AstroGrid. Again, your 
comments would be welcome. 
Keith. 
-- 
Keith Noddle                    Phone:  +44 (0)116 223 1894 
AstroGrid Technical Lead        Fax:    +44 (0)116 252 3311 
Dept of Physics & Astronomy     Mobile: +44 (0)7721 926 461 
University of Leicester         Email:  ktn at star.le.ac.uk 
Leicester, UK   LE1 7RH         Web:    http://www.astrogrid.org 
-------------------------------------------- 
If the query we are trying to satisfy can be expressed in pseudo-SQL as: 
SELECT * FROM <registry> WHERE 
   ( 
      TYPE="white dwarf star" AND 
      (WAVELENGTH="optical" OR WAVELENGTH="uv") AND 
      (KEYWORD="BPM 16274" OR 
         KEYWORD="GD 50" OR 
         KEYWORD="HST photometric standards" 
      ) 
   ) 
then one way of presenting this in XML is shown below 
<query> 
   <selectionSequence> 
      <selection> 
         <item>type</item> 
         <value>white dwarf star</value> 
      </selection> 
      <operator>AND</operator> 
      <selectionSequence> 
         <selection> 
            <item>wavelength</item> 
            <value>optical</value> 
         </selection> 
         <operator>OR</operator> 
         <selection> 
            <item>wavelength</item> 
            <value>uv</value> 
         </selection> 
      </selectionSequence> 
      <operator>AND</operator> 
      <selectionSequence> 
         <selection> 
            <item>keyword</item> 
            <value>BPM 16274</value> 
         </selection> 
         <operator>OR</operforator> 
         <selection> 
            <item>keyword</item> 
            <value>GD 50</value> 
         </selection> 
         <operator>OR</operator> 
         <selection> 
            <item>keyword</item> 
            <value>HST photometric standards</value> 
         </selection> 
      </selectionSequence> 
   </selectionSequence> 
</query> 
This only requires 6 tags and is sufficiently flexible to cope with most 
queries I can think of - but I'm not an astronomer...!




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