Astronomical Data Analysis Software and Systems XVII
ASP Conference Series, Vol. XXX, 2008
J. Lewis, R. Argyle, P. Bunclarck, D. Evans, and E. Gonzales-Solares, eds.
Web services at TERAPIX
Olivier Ricou1, Anthony Baillard2, Emmanuel Bertin2, Fr´ ed´ eric
Magnard2, Chiara Marmo2and Yannick Mellier2
1EPITA Research and Development Laboratory (LRDE), Le Kremlin
Bicˆ etre, France
2Institut d’Astrophysique, Paris, France
built around software tools developed at the TERAPIX centre. These services
allow to operate from a remote site several pipeline tasks dedicated to astronom-
ical data processing on the TERAPIX cluster, including the forthcoming EFIGI
morphological analysis tool.
We present an implementation of V.O.-compliant web services
The EFIGI1(Extraction de Formes Idealis´ ees de Galaxies en Imagerie) project
hosted at TERAPIX2proposes to address both the computational and algorith-
mic aspects of the extraction of useful morphological information from a large
number of galaxies. Measuring galaxy morphology is computationally intensive,
but requires only modest amounts of data to be analysed for each detection (the
necessary data bandwidth is typically 20kB/s); it is therefore particularly suited
to implementation as a web service.
Instead of developing a web service restricted to galaxy morphology mea-
surements, we investigated the possibility to offer a simple and generic mean to
access several services related to astronomical image analysis/processing. These
services have in common that they are all directly related to executables that
work on or generate FITS data files and XML-VOTable metadata files in batch
mode. The executables have been developed and are maintained in-house, which
means that they can easily be modified if needed. Since different users have dif-
ferent needs, we provide three ways to run our services:
• a web form for testing or occasional runs.
• a web service to pipe to other services or to include in programs.
• a Globus interface — the gate to Grid computing — for more intensive
Ricou et al.
2.Technology and conformance to standards
The astronomical community is currently involved in an international effort to
normalise the format of metadata and web service protocols: the Virtual Obser-
vatory (VO). It is therefore logical to design a system which conforms as much
as reasonably possible to the VO recommendations:
• The tools designed at TERAPIX provide support for VOTables in output
(Bertin & Tissier 2007), although it is not yet clear whether this standard
will remain popular in the future.
• Our web service prototype transfers files with MTOM according the new
VO recommendations. Unfortunately this new protocol is rarely included
in Web service libraries. Java and .NET can run MTOM but not Python
• The Grid service, based on Globus, offers Reliable File Transfer (RFT),
security, accounting and the ability to connect to other VO Grid like the
Japanese VO (Ohishi et al. 2004) or the German AstroGrid (Henke et al.
Our software architecture relies on Condor3to dispatch the jobs on the
TERAPIX cluster according to user authorisations, providing the same interface
for internal and external use. TERAPIX insiders can directly operate Condor
while external users must connect to one the three services which hand the job
to Condor (see Fig. 1). Of course, priority is given to internal users, however
regular external users can be registered to increase their privileges. A future
extension might be to connect to the registry of the VO for authentication.
The services, as displayed in Fig. 1, rely on Apache for the CGI, on Axis 24
for the SOAP web services using MTOM for the file transfer, and on Globus for
the grid access, including authentication with GSI and file transfer with RFT.
3.How to use it
The Web form http://efigix.iap.fr/ws/efigi wi.html. Fill the form,
press “Run EFIGI”. A mail is sent at the end of your run, containing a tempo-
rary link to the results.
The Web service http://efigix.iap.fr/ws/ws.html. Get the WSDL de-
scription of the EFIGI service to generate the stubs and data types in your
favorite language as long as it knows MTOM (essentially restricted to Java and
.net at this time), and write your own client to call the service. An example of a
client program, written in Java, is provided on the EFIGI web site. It uses the
Axis 2.1.3 version of WSDL2Java.
The Grid service http://efigix.iap.fr/ws/globus.html. Install the Globus
Toolkit5version 4. Get a one week certificate as a guest user or ask us for a
Figure 1.The software architecture of the different services
long-term certificate. Prepare your submission file and submit it. In principle
only the client part of Globus is required, but in practice it is advised to install
the full distribution to take advantage of all Globus features.
4.The current EFIGI prototype
The current EFIGI pipeline prototype is based on modified versions of several
TERAPIX tools6including nFIGI, PSFEx, SExtractor, and STIFF. It re-
quires two FITS images in input: the first image contains one or several galaxies
to be measured and the second image contains the Point Spread Function (it
may actually contain a mix of galaxies and point sources from which a proper
model will automatically be derived). The final product consists of an XML VO-
Table containing the morphological measurement vectors and diagnostic images.
An XSLT filter is provided to present the results in a user-friendly way (Fig.
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Ricou et al.
2). The current version of the EFIGI web service has limited functionalities and
is only meant for testing. We expect the final version and additional services
to be online in December 2007. Announcement will be made on the TERAPIX
Example of an XSL-transformed result from the current EFIGI
We intend to provide web services based on other CPU-bound TERAPIX tools
in the near future. Managing efficiently data-intensive tasks on a grid-computing
environment is more problematic, and will be investigated at later times.
This work is supported by grant 04-5500 (“ACI masse
de donn´ ees”) from the French Ministry of Research.
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