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Arviset, C., Dowson, J., Hernández, J., Osuna, P., & Venet, A. 2003, in ASP Conf. Ser., Vol. 295 Astronomical Data Analysis Software and Systems XII, eds. H. E. Payne, R. I. Jedrzejewski, & R. N.
Hook (San Francisco: ASP), 47
Interoperability of ESA Science Archives
Christophe Arviset, John Dowson, José Hernández, Pedro
Osuna and Aurèle Venet
ESA, Research and Scientific
Support Department, Science Operations and Data Systems Division,
Villafranca del Castillo, P.O. Box 50727, 28080 Madrid, Spain
Abstract:
The ISO Data Archive (IDA) and the XMM-Newton Science Archive
(XSA) have been developed by the Science Operations and Data
Systems Division of ESA in Villafranca, Spain. They are both built
using the same flexible and modular 3-tier architecture: Data
Products and Database, Business Logic, User Interface. This open
architecture, together with Java and XML technology have helped in
making the IDA and XSA inter-operable with other archives and
applications. The various accesses from the IDA and the XSA to
remote archives are described as well as the mechanism to directly
access these ESA archives from remote archives
The IDA and the XSA were both built--by a common team--using the
open 3-tier architecture described in
Figure 1. The main goal of this architecture
is to separate the data from the presentation, which allows a more
modular and flexible development.
As the data volume is not that big, data are saved on magnetic
disks for fast access as a normal UNIX file system. From the data
products, metadata is extracted and put in a Relational Data Base,
SYBASE. Note that the data ingestion from the data producer and
the metadata extraction are separate processes to allow new
metadata data extraction when user requirements evolve.
The middle tier, also called the Business Logic, provides
transparent access to the data products and to the metadata. This
key layer has been developed in Java and XML and resides on the
archive server.
On the client side, several types of applications can be found.
The standard IDA and XSA User Interface is a Java applet
downloaded by the end user to access the archive content.
Remote applications and other archives can also have access to the
data and the metadata, bypassing the standard User Interface, by
speaking to the Business Logic that will provide them with the
required services via Java Server Pages.
This architecture is especially powerful in the context of the
worldwide Virtual Observatory initiatives where archives will all
have to interoperate in a manner transparent to the end
user.
Figure 1:
Open
3-tierArchitecture
 |
On the IDA or XSA Query Panel, one can query against a target name
(see Figure 2). By entering a target name and
choosing the name resolver (NED or SIMBAD), the IDA or XSA will
make contact with the IPAC or CDS server to resolve the target
name into coordinates and then search the ISO observations catalog
against these coordinates. This is done completely transparently
to the user.
For SIMBAD and NED, the target name is resolved into coordinates,
calling the CDS server at Strasbourg, France or the NED one at
IPAC, USA respectively via a specific TCP/IP socket.
From the IDA or XSA Latest Results Panel, the button ``Articles"
indicates if there are known publications linked to the
observation (see Figure 2). By clicking on
the button, one gets an extra window showing the Title, Authors,
Journal, etc. By clicking the ``Abstract" button, the applet will
launch a browser window with the ADS WWW mirror at Strasbourg,
France with the abstract of the article associated with the
selected observation. The call is made through a standard URL/cgi-bin
script as defined by the ADS interface.
From the IDA Latest Results Panel, one can see the small icons
giving a quick overview of what the observations are about. By
clicking on one of them, a bigger window is launched with the
postcard giving more information on the ISO observation (see
Figure 2). By clicking the button ``Access
to IRAS", a browser window will open, from the InfraRed Science
Archive (IRSA) webpage located at IPAC, USA. The window will
contain the data covering the region of the sky of the selected
ISO observation. The call is made through a standard URL/cgi-bin
script as defined by the IRSA interface.
Figure 2:
Access from IDA to
External Archives.
 |
ISO and XMM-Newton products can also be obtained directly from
external archives or applications, bypassing the standard user
interface. That allows such data to be available from other well
established archives where multi-missions data can be found.
Such access can be achieved in 3 steps:
- delivery of the archive observation/exposure log to the
remote archive;
- integration of this log into the remote archive;
- linking from the remote archive to the Postcard
Server and/or to the Product Server.
The Observation log consists of a file (generally ASCII)
containing the list of ISO or XMM-Newton observations with
associated parameters (observation id, PI name, coordinates, time,
quality flag, release date...). In the case of XMM-Newton, each
observation contains several instrument exposures with
relevant specific parameters.
According to the requirements of the remote archive, the log can
contain more or fewer parameters depending on the intended use.
The standard format is ASCII (fixed width, tab or character
separated). This log is just a view of the content of the IDA or
XSA database and can be easily exported into other formats such as
XML, HTML, VOTable, etc... that will make it easier to ingest in
remote archive databases.
The delivery can be via FTP, http or electronic mail.
Through calling a URL/Java Server Page (JSP) containing the ISO
or XMM-Newton observation identifier, the Postcard Server (see
Figure 3) returns the ISO or XMM-Newton
postcard (GIF or PNG image) of this observation and ancillary
quality information embedded into an HTML page. Within this HTML
page, links to relevant documentation as well as the data quality
flag can be found.
This service is available for ISO in CDS, IRSA, ADS and
HEASARC and should soon be available for XMM-Newton from in CDS,
ADS and HEASARC.
Figure 3:
ISO and XMM-Newton
Postcard Servers.
 |
The Product Server uses similar concepts to the Postcard Server.
The URL/JSP returns an HTML page which automatically initiates
an FTP session for downloading the data products.
Both ISO and XMM-Newton Product Servers are now available and can
be accessed directly or from the corresponding Postcard Server.
The ESA science archives, in particular the ISO Data Archive and
the XMM-Newton Science Archive are based on an open 3-tier
architecture which allows easy interoperability with other
archives or applications. This will ensure their easy and fast
integration in the VO architecture.
The inter-operable mechanisms already in place are flexible, fast,
direct and secure both from the ESA archives to external archives
and in the other direction.
Currently, dedicated interfaces have been defined with the remote
archives inter-operating with the IDA and the XSA. But having
common standards, such as XML and VOTables, would help integration of
services in the context of the VO.
References
Hernandez, J. 2003, this volume, 275
© Copyright 2003 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
Next: Federating Catalogs and Interfacing Them with Archives: A VO Prototype
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