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\paperID{P2-3} % bogus id since we need one


\title{Adapting ISO and XMM-Newton Archives to Inter-Operability VO Standards}
\titlemark{Adapting ISO and XMM-Newton VO Standards}


\author{Pedro Osuna, Christophe Arviset, Jesus Salgado}
\affil{RSSD Archive Development Team, ESA VILSPA, PO BOX 50727,
28080 Madrid, Spain}


\contact{Pedro Osuna} \email{Pedro.Osuna@esa.int}


\paindex{Osuna, P.} 
\aindex{Arviset, C.} 
\aindex{Salgado, J.}

\authormark{Osuna, Arviset, Salgado}

\keywords{Infrared Space Observatory (ISO), XMM: Newton, archives, Virtual Observatory, SIAP, interoperability}

\begin{abstract}
The ISO Data Archive (IDA) and XMM-Newton Science Archive (XSA)
were already providing some support for inter-operability from
external archives and applications to the IDA and XSA. These
services allow to directly access IDA and XSA metadata and data
products without going through the archives usual user interfaces.
These services have been adapted to existing VO standard, in
particular the SIAP (Simple Image Access Protocol). This paper
describes the way ESA, as a data (ISO and XMM-Newton) provider has
adapted his system to the VO without modifying the internal
metadata and data repository structure.
\end{abstract}


\setcounter{footnote}{1}

\section{Introduction}
Within the ESA's Science Operations and Data Systems Division, the
Archive Development Group in Villafranca, Spain is responsible of
developing and maintaining ESA Scientific Archives. In particular,
the ISO Data Archive (IDA) and the XMM-Newton Science Archive
(XSA) have been developed using the same flexible and modular
3-tier architecture which have allowed them to be inter-operable
with other astronomical archives and applications.

The standard way of accessing these ESA archives is normally
through a powerful and similar Java interfaces (
\htmladdnormallinkfoot{IDA}{http://www.iso.vilspa.esa.es/ida}
\htmladdnormallinkfoot{XSA}{http://xmm.vilspa.esa.es/xsa}) where
users can interactively query, visualize and retrieve the
observations and sources' catalogues of these missions.

In the recent months, IDA and XSA existing inter-operability
services have been adapted to comply to the new VO standards, in
particular the SIAP (Simple Image Access Protocol). The archive
modular architecture has made this adaptation relatively easy,
without requiring to modify the way the archives are internally
organized.


\section{Inter-Operability System Before the VO}
For several years already, the IDA and XSA have offered some
inter-operability services which allowed external archives or
applications to bypass their standard user interfaces and access
the archives catalogue and products without requiring human
intervention. Furthermore, the IDA and XSA user interfaces are
also accessing remote archives (ADS, SIMBAD, NED, IRAS, $\ldots$) to
provide links to relevant information for the end user. An example
of such service is described in Figure~\ref{P2-3:ISOPostcardServer}
describing how the ISO Postcard Server is accessed from various
archives.

\begin{figure}
\epsscale{0.6} \plotone{P2-3_1.eps} \caption{ISO Postcard Server}
\label{P2-3:ISOPostcardServer}
\end{figure}

\noindent %%FO
Nonetheless, this access mechanism has some drawbacks:
\begin{itemize}
\item there is no real access to the metadata, but only to the
data products (quick look data or scientific data products) \item
the interface has to be defined on a case by case basis, by giving
the required metadata to the external archive
\end{itemize}

\noindent %%FO
Therefore, it has been decided to develop a system that could give
access to both archives metadata and data products. This was
initially provided by the new system Archive Inter-Operability
which was developed for ISO and XMM-Newton.

Later on, VO inter-operability working groups defined the SIAP
(Simple Image Access Protocol) which provides the following major
functions:
\begin{itemize}
\item Image Query (access to metadata) \item Image Retrieval
(access to data products)
\end{itemize}


\section{New AIO Architecture for the VO}
With the existence of our AIO system to provide inter-operability
to our archives and the advent of the SIAP, it appeared natural to
us that the AIO system should be adapted to be able to support
SIAP standard. We did not want to build a completely new SIAP
system beside our existing AIO, but rather building an extra layer
on top or our AIO to support SIAP requests. The resulting
architecture is described in Figure~\ref{P2-3:VOAIOArchitecture}.

\begin{figure}
\epsscale{0.6} \plotone{P2-3_2.eps} \caption{VO AIO Architecture}
\label{P2-3:VOAIOArchitecture}
\end{figure}

Normal project clients (such as the IDA and XSA Java user
interfaces) are interfacing with the Project Business Logic. This
Business Logic, also called middle tier allow transparent access
to the metadata and the data products. If the organization of the
data is modified, the clients do not have to be modified as this
is dealt with by the Business Logic.

The AIO provided an extra layer of abstraction for other clients
to access metadata and data products, bypassing the standard user
interfaces. As a new client, the AIO interfaces with the Project
Business Logic.

Furthermore, an extra layer has been added to allow clients to
make SIAP requests through the AIO system.

Finally, all clients (normal user interfaces, AIO system, other VO
clients) can access the metadata and data products through the
same final interface which is the Project Business Logic.

To provide ISO and XMM-Newton metadata and data products to the
VO, the internal existing systems (user interfaces, Project
Business Logic, database, data products repository) did not have
to change at all.

\section{Translation Layers}
To allow the existing systems to be re-used to support VO
standards (SIAP, VOTable), translation layers have been built to
translate VO SIAP specific request into known requests to our
existing systems.

A SIAP Image Request is translated into an AIO metadata request,
which then is transformed into a Database Request (standard SQL
query). The Data\-base Request is then returned as the result of the
SQL query, but is then translated into a VOTable as per the SIAP
standard. For the results to be also viewable, we have added two
more formats of the results (ASCII and HTML).

Similarly, a SIAP Product Request is translated into an AIO
product request, which then is transformed into a product request
to the existing data repository. The products are then returned in
a URL stream for the SIAP client to make use of it. If wanted, the
products can also be returned on a FTP server.

The translations are made through the translation layers using XML
files. Metadata query can be made based on UCDs as per SIAP
format, but it will finally be translated into an SQL query based
on our existing database structure (table and column fields) which
are of course not in UCDs.

All is illustrated in Figure~\ref{P2-3:TranslationLayers}.

\begin{figure}
\epsscale{0.6} \plotone{P2-3_3.eps} \caption{Translation Layers}
\label{P2-3:TranslationLayers}
\end{figure}



\section{Conclusion}
Thanks to an already modular and flexible 3-tier architecture
design of the ISO Data Archive and XMM-Newton Science Archive, it
has been quite easy to adapt our existing inter-operability system
for them to support VO standards (SIAP, VOTable).

The use of translation layers between the various parts of the
systems has proven to be very appropriate as it allows to support
VO standards without necessity of modifying your existing database
and data products repository. You can then allow searches on UCDs
without having to modify anything in your existing database.

All this development has been performed with JAVA JSP and Servlets
coupled with XML which have proven to be a good suite for
developing this type of application.

This system is very flexible and although originally designed to
provide Simple Image Access, has also been improved to provide
access to ISO and XMM-Newton spectra using exactly the same
mechanisms.

Full documentation about how to use these services can be found
at:
\begin{itemize}
\item ISO : http://pma.iso.vilspa.esa.es:8080/aio/doc \item
XMM-Newton : http://xsa.vilspa.esa.es:8080/aio/doc
\end{itemize}



\acknowledgements

The authors would like to acknowledge the rest of the ESA RSSD
VILSPA Archive Development Team who have participated in the IDA
and XSA development : John Dowson, Jose Hernandez, Inaki Ortiz,
Guillermo San Miguel and Vrata Venet as well as the ISO and
XMM-Newton Archive Scientists, Alberto Salama and Matteo
Guainazzi.

\begin{references}
\reference Arviset, C.\, 2003, \adassxii, \adassref{xii:O10-6}{47}
\reference Arviset, C.\, 2004, \adassxiii, \paperref{D3}
\end{references}

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