Next: The Submillimeter Array Data-Handling System
Up: Sky Surveys
Previous: INES: The Next Generation Astronomical Data Distribution System
Table of Contents -
Subject Index -
Author Index -
Search -
PS reprint -
PDF reprint
Benfante, L., Volpato, A., Baruffolo, A., & Benacchio, L. 2001, in ASP Conf. Ser., Vol. 238, Astronomical Data Analysis Software and Systems X, eds. F. R. Harnden, Jr., F. A. Primini, & H. E. Payne (San Francisco: ASP), 160
The OaPd System for Web Access to Large Astronomical Catalogues
Lucio Benfante, Alessandra Volpato, Andrea Baruffolo, Leopoldo Benacchio
Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio, 5 - 35122 Padova, Italy
Abstract:
At the Padova Astronomical Observatory (OaPd), we are developing
a system for managing large sets of astronomical data, such as the
GSCII catalog that will be released in the near future.
In this paper we describe the different parts of the retrieval system:
the Database Management System (DBMS) containing the data and the
meta-data of the catalogs, the CORBA services, the Java Servlets and
finally the Java Applet Client. A brief description of the hardware
and of the support software is also presented.
The result is a system that allows one to access a set of astronomical
catalogs using heterogeneous clients (i.e., Astrobrowse, StarCat). The
first public release is expected in January 2001.
At the Padova Astronomical Observatory (OaPd), we are developing
a system for managing large sets of astronomical data, such as the
soon-to-be-released GSCII catalog.
The main purpose of the system is to allow a powerful and efficient
querying activity on large astronomical catalogues through the
Internet by using a simple Web interface. The only requirement for the user
is to have a java-enabled Web browser.
Figure 1 shows the overall architecture of the system
as described in Baruffolo, Benacchio & Benfante (1999). In the
following sections we briefly describe both the hardware
and software components of the system.
Figure 1:
Overall architecture of the system
 |
The catalogue data and meta-data are managed by the Informix Dynamic
Server (IDS), an object-relational Database Management System. The IDS
is enhanced by the PosAstro DataBlade. This OaPd-developed module
provides functionality that is required to handle spatial information
for astronomical objects.
Functionalities and features available in the current version of the
PosAstro DataBlade allow one to create tables containing astronomical
coordinates objects that can be queried by content. The DataBlade
supports the creation of R-Tree based indices on coordinates objects
(Guttman 1984, Baruffolo 1999) that are used by the database query
engine to optimize execution of queries.
The system is mainly based on Java code and platform-independent
protocols. Nevertheless the use of some legacy C code was
necessary. To allow the access to that code in a language-neutral,
platform-independent and distributed manner, we embedded it into
CORBA
objects.
The C code that is now available as CORBA services
is:
- the C version of the SLALIB for string decoding, sexagesimal
conversion, coordinates and astrometry functions (Wallace 1999),
- the library for querying the
NED
name
resolver,
- the library for querying the
Simbad
name
resolver.
The server services are provided to the clients by a set of HTTP Java
Servlets (Davidson & Coward 1999). The main servlets are the ASU
Servlet, the Catalogue Metadata Servlet and the Name Resolver
Servlet.
The ASU Servlet provides the main query service for the system. It
receives a standard ASU query (Albrecht et al. 1996) and, after
retrieving data from the Database Server, it returns the requested
catalogues data to the client in the selected format. Any client
following the ASU specification (e.g., ESO's
Skycat) will be able to submit queries
and retrieve results.
The current allowed output formats are HTML with tables, Tabbed
Separated Values (TSV) and Starbase format (Roll 1996).
Support for FITS and XML output will be provided at a later date, if
necessary .
The servlet uses the CORBA services for name resolving and for
astronomical coordinates manipulation (via Slalib).
The Catalogue Metadata Servlet provides the client with the meta-data
of the catalogues available in the database. Examples of these
meta-data are the list of catalogues, the list of fields of each
catalogue, the units of a field, etc.
The servlet communicates with its clients by exchanging serialized
Java objects through an HTTP connection. To make this communication
easier, the applet utilises a servlet-specific Java library providing
a simple interface for the Metadata Servlet services.
The Name Resolver Servlet is an HTTP wrapper to the CORBA name
resolving services.
Its textual communication protocol is very simple. It receives as
input the name of the name resolver to query (NED or Simbad) and a
name of an astronomical object to resolve. The output will be the
resolved coordinates of the object or an error code.
The user interface is implemented with a Java applet to allow
portability and service via the Web. The applet is a thin client for
the OaPd catalogue server. It is structured as a ``wizard'' that
guides the user in forming the queries and checks its input. The query
execution is done on the server side.
For requesting server-side services, the applet contacts the servlets
through the HTTP protocol. Figure 2 shows the
interaction among the applet and the servlets.
Figure 2:
Java Applet Client communications
 |
The server-side part of system runs on a COMPAQ AlphaServer DS10
466 MHz, equipped with 640MB of RAM. The operating system is Compaq
Tru64 UNIX (ex Digital UNIX). The data, meta-data and indexes of
the catalogs are managed by the Informix Dynamix Server 2000. The
final projected disk space is 250GB.
The server-side Java objects are executed by a
Compaq Java 2 Virtual Machine
(VM). For the client-side Java
Applet a Java 1.1 VM has been ordered. The servlet engine is
Tomcat,
mounted on an Apache Web Server.
The CORBA objects are handled by the
ORBacus
Object Request
Broker for C++ and for Java.
References
Guttman, A. 1984, ACM SIGMOD Conference, 47
Albrecht, M, et al. 1996, ``Astronomical Server URL'',
http://vizier.u-strasbg.fr/doc/asu.html
Roll, J. 1996, in ASP Conf. Ser., Vol. 101, Astronomical Data Analysis
Software and Systems V, ed. G. H. Jacoby & J. Barnes
(San Francisco: ASP), 536
Baruffolo, A. & Benacchio, L. 1998a, in ASP Conf. Ser., Vol. 145, Astronomical Data Analysis
Software and Systems VII, ed. R. Albrecht, R. N. Hook, &
H. A. Bushouse
(San Francisco: ASP), 382
Baruffolo, A. & Benacchio, L. 1998b, SPIE Proc., 3349, 274
Baruffolo, A., Benacchio, L. & Benfante, L. 1999, in ASP Conf. Ser., Vol. 172, Astronomical Data Analysis
Software and Systems VIII, ed. David M. Mehringer, Raymond L. Plante, &
Douglas A. Roberts (San Francisco: ASP), 237
Baruffolo, A. 1999, in ASP Conf. Ser., Vol. 172, Astronomical Data Analysis
Software and Systems VIII, ed. David M. Mehringer, Raymond L. Plante, &
Douglas A. Roberts (San Francisco: ASP), 375
Davidson, J. D. & Coward, D. 1999, ``Java Servlet Specification, v2.2'', Sun Microsystems, http://java.sun.com/products/servlet/
Wallace, P. T. 1999, Starlink Project, Starlink User Note 67.45
© Copyright 2001 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
Next: The Submillimeter Array Data-Handling System
Up: Sky Surveys
Previous: INES: The Next Generation Astronomical Data Distribution System
Table of Contents -
Subject Index -
Author Index -
Search -
PS reprint -
PDF reprint
adass-editors@head-cfa.harvard.edu