Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stecf.org/conferences/adass/adassVII/reprints/ortizp.ps.gz Äàòà èçìåíåíèÿ: Mon Jun 12 18:51:48 2006 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 03:09:11 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï

Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
Accessing Astronomical Data over the WWW using datOZ
Patricio F. Ortiz
Department of Astronomy, University of Chile, Casilla 36­D, Santiago,
Chile, Email: ortiz@das.uchile.cl
Abstract.
The Department of Astronomy of the University of Chile hosts a
number of astronomical databases created with datOZ (Ortiz, 1997).
This is a site in which databases are accessed interactively by the use of
an HTML interface and CGI database engines. Data can be retrieved by
the users in a highly flexible way, from lists of user­selected quantities, to
customized plots, including any additional multimedia information avail­
able for the database elements. The latest additions to the system point
in two directions: a) to allow access to combinations of database variables
for di#erent purposes, and b)to allow the retrieval and further correlation
of information stored in di#erent datOZ's databases, by means of a sec­
ond tool named CatMERGER. Another tool lets users search for objects
in all catalogs created with datOZ at the same time.
The most recent development is the creation of a new version of
datOZ capable of handling catalogs such as USNO's A1.0 with 488 million
objects. Specially designed indexing and data storage techniques allow
the catalog size to be reduced by half.
1. Introduction
Electronic sharing of scientific data is a concept which has been around for at
least the last fifteen years. The first e#orts pointed in the direction of creating
sites accessible via ftp. Pioneer work at the Strasbourg CDS (SIMBAD), and
by NASA (IPAC's NED, GSFC's ADC ftp site) amongst others, have set the
ground to share data in a more e#cient way amongst astronomers than the
traditional printed, journals.
The WEB gives scientists a much richer way of sharing information. We
can now have quite a number of things done by transferring just a few bytes
between our computers and host computers running httpd (the HTTP daemon)
by invoking CGI (common gateway interface) ``scripts''. The applications are
almost unlimited, and we see more and more of them at astronomical sites
around the world.
Scientists are usually interested in just a minor percentage of the data kept
in a catalog to pursue their research. We might need a few ``columns'' of a
catalog, and maybe just a small subset of the catalog's elements. There are
currently a few e#orts in the world pointing in that direction, VizieR at CDS,
Wizard at NASA, Pizazz at NCSA Skycat at STScI, Starlink at the UK, datOZ,
371

372 Ortiz
at the University of Chile, and possibly others. All of them should point to create
a uniform method of data retrieval.
In the following sections an overview of the features of databases created
with datOZ will be presented. Detailed information can be found in the ``user's
manual'' for the system, where static and dynamic databases are discussed.
2. What is datOZ and what does datOZ o#er?
datOZ is a computer tool which creates the interface and the source code capable
of handling a specific catalog (Ortiz 1997). The source code is written in C,
with some specific routines written in Perl. The data is stored in machine
format, with some degree of indexation for fast access, a key for large catalogs.
The modified version of datOZ for large catalogues fully indexes the data­file,
introduces compressed variables and reduces the number of significant figures
for RA and Dec without degradation of the positions.
Each database element can have associated several ``multimedia'' files (.gif,
.jpg, .ps, spectra­like data files, and a note­pad for extra annotations), and sup­
ports a kind of variable which allows hyper­links to other sources of information.
The system was built with the capability of accessing interfaces in more than
one language; something particularly useful if this system is to be accessed by
people in countries where English is not the o#cial language.
datOZ o#ers the user a database with fast and flexible data retrieval and
visualization capabilities; it also o#ers uniformity, as all databases look alike
and behave in the same way. These databases can receive requests from related
tools developed with the purpose of combining information amongst databases
created with datOZ. Links to these tools are found in the homepage.
datOZ's home page is: http://146.83.9.18/datoz t.html
3. datOZ Retrieval Modes
datOZ' databases have a flexible retrieval access mode also known as Advanced
Access Mode (AAM), which lets the user define the quantities he/she wants
to retrieve amongst the ``natural'' database variables or by using mathematical
expressions formed with these variables. The opposite of the AAM is the Basic
Access Mode (BAM) which restricts operations to the values of the database
variables.
The reason for implementing the flexible access mode has to do with the
fact that catalogs are usually created with one purpose in mind, and only certain
quantities become the catalog's variables. A typical case is when the catalog
contains ``variables'' for V, (B­V), (V­R), and (V­I), but if the user needs the
magnitude of an object in the I band he/she would normally have to retrieve V
and V­I and then perform the di#erence by him/herself. The AAM lets the
user specify the quantity to get as V ­ (V­I), i.e., I. The way to express this
quantity is using Reverse Polish Notation (RPN) (complete details are found on
the manual and HTML help pages).
Another advantage of the AAM is that the user can impose constraints on
math expressions formed with ``numerical'' variables. Let's assume that, from

Accessing Astronomical Data over the WWW using datOZ 373
lII
bII
Figure 1. Distribution of O stars in the galaxy.
the same catalog, we need sources brighter than 17 in the I band, but as we
saw, I is not one of the catalog variables. We can define the expression to use
as a constraint as: V V­I ­ and impose it to be < 17 .
One of the most important pluses of the AAM is that it lets the user
submit a file with a list of the names of the objects which he/she needs to get
information for, and get whatever data is stored in the database for those objects
only. This is particularly useful when we deal with catalogs with a large number
of objects, such as Hipparcos, or ROSAT for example. The files are transfered
from the computer where the user is running Netscape to the database's host
computer and then analyzed locally.
4. datOZ Visualization Tools
Visualization is the key to getting most of the science out of the data stored
in a catalog. It allows quick checking of determined properties, and it is also a
valuable teaching tool. datOZ provides its databases with the capability to use
any numerical variable to generate fully customized PostScript plots.
There are several types of plots that can be obtained: histograms, scatter
plots, scatter plots with variable symbol size, scatter plots with error
bars, annotated scatter plots (where the user prints the value of a variable
instead of a symbol), All­sky, equal area projection plots, and line plots.
Plots can be viewed on the spot with ghostview, ghostscript, or any
other PostScript previewer, and/or saved to disk using any of the ways Netscape
provides.
5. Searching for Neighbors with datOZ
The word ``neighbor'' must be understood in a broad sense here. It could mean,
of course, objects ``close'' in the sky, or it could apply to closeness in any nu­
merical variable or expression.

374 Ortiz
The neighbor search operation is extremely valuable to explore the content
of a catalog for diverse purposes. Besides using elements in the catalog as
reference points, it is possible to provide a list of coordinates and ask which
objects in the catalog are located near these reference points. The submission
of files with lists of reference positions is an extremely valuable task to quickly
search for matches. This feature is one of the most used in the catalogs installed
in our system.
6. Conclusions
datOZ has proved to be a very powerful tool to handle astronomical information,
at the present time, the following catalogs are implemented in our Department
(Cerro Cal’an): Galactic Globular Clusters, Harris W.E. Astron. J. 112, 1487
(1996). QSO's and AGNs Veron­Cetty M.P., et al. (1996). ROSAT Bright
Sources Catalog Max­Planck­Institut fuer extraterrestrische Physik, Garching
(1996). Catalog of Principal Galaxies, Paturel et al. 1989 Third Revised
Catalog (RC3), de Vaucouleurs G. et. al. (1991). AAT Equatorial photo­
metric calibrators, Boyle et al.'s (1995). A Catalogue of Rich Clusters of
Galaxies, Abell G.O., Corwin Jr. H.G., Olowin R.P. (1989) IRAS Catalog
of Point Sources, V2.0 Joint IRAS Science W.G. IPAC (1986). Hippar­
cos Main Catalog ESA, (1997). Spectrophotometric Standards used at
CTIO MK Spectral Classifications ­ Twelfth General Catalog Buscombe
W., and Foster B. E. (1995). Northern Proper Motions, Positions and
Proper Motions, SOUTH, Bastian U., and Roeser S. (1993). Catalog of
558 Pulsars, Taylor J.H. et al. (1983). Line Spectra of the Elements,
Reader J., and Corliss Ch.H. (1981). USNO's A1.0 -- 488 million stars,
Monet, D. (1996).
The near future will bring big survey works (Sloan, 2DF, 2MASS, AXAF,
and EROS, to name a few). Making the data available to the community will be
crucial to increase these projects' science impact. The current trend of having
data available on CD's or ftp sites may discourage an important number of
scientists to explore or analyze the data, tools like datOZ will make the data
readily available to anyone.
7. Acknowledgments
I thank the support of project FONDECYT 1950573 lead by Dr. Jos’e Maza. To
the organizers of ADASS 97 my most sincere thanks for allowing me to assist
to the conference. I am also very thankful of Professors Luis Campusano and
Claudio Anguita for valuable comments and support to mount some databases
on their machines; and to Sandra Scott for installing a demonstration database
at the University of Toronto during the ADASS 97 conference.
References
Ortiz, P. F. 1997, in Proceedings of the Fifth workshop on Astronomical Data
Analysis, Erice, 1996.