ESA/IUE under the Web
A. de la Fuente,
ESA/Villafranca, Madrid, Spain.
The first implementation of a WWW browser at Villafranca took place
during summer 1993, within the context of the exploratory studies to define
a distribution mechanism for the IUE Final Archive.
After comparing the services provided by different architectures
(ref. 1), it was evident that hypermedia information systems - even at
the implementation level two years ago - were the adequate solution.
A pilot project started at that time with the following purposes:
The implementation of this pilot project was tested during the unique
opportunity of the Jupiter/Shoemaker-Levy 9 event in July 1994.
At that time, we had in place a
together with a well defined
mechanism to provide an updated flow of information, consisting of
images from different telescopes together with the latest news of the IUE
observations of the comet impact.
- to understand this new technology,
- to explore its usage for distributing IUE data to the users community, and
- to define an internal information service for project coordination.
Based on this experience, proper requirements for a
general information service (ref. 2) were defined,
fulfilling the needs of the IUE project (ref. 3).
In addition, IUE Final Archive data were internally distributed,
for quality control purposes, using this technology (ref. 4).
2. Design aspects
The main design issues considered in the definition of the service are:
- Selection of the information,
- balance between text and images,
- uniform presentation of the information,
- coordination with other information services, and
- optimized maintenance.
2.1 Selection of the information:
The main problem associated with the usage of WWW is the overwhelming
amount of information available;
one has to learn how to select the useful information, discarding irrelevant
Information providers can help in this task by keeping a strict quality
control on the services, to include relevant information with a concrete
users community as target.
In order to insure a high quality of the information at Villafranca,
the overall services are divided into external, publically available, and
internal, restricted to local staff, that will test and assess on the
maintenance requirements and usefulness of the information for the general
user. After a testing period, relevant information in the internal
service is moved to the external server.
2.2 Text and images:
One of the key aspects of hypermedia systems is to provide images embedded
this contributes to clarify the information, according with the old
principle one image is worth thousand words, ...
but the cost in terms of network load and time invested in the transfer
of files is actually larger.
In addition, many users access the WWW via text-based browsers,
due either to limitations in the client node, or to the users expertise:
text browsers are normally faster and provide additional facilities,
not available yet in other popular browsers.
It was therefore decided to limit the usage of graphics and images
to the cases were it was really necessary.
This concept will change in the future when network bandwidths
will increase and better servers will be available, with the possibility of
handling large amounts of intermediate buffers.
2.3 Uniform presentation of the information:
In order to improve the usability of the server, it is important to
define a consistent look and feel.
Information is presented in a uniform way, based on minimal set of rules:
- Uniform page header, with informative titles,
- limit the number of intermediate steps to get to the actual information,
using itemized lists in the intermediate (navigation) pages,
- consistent page bottom, with navigation aids, direct access to
information items, feedback facility to give comments about the
service and a consistent help, that refers to on-line manuals, and
- identification of the author and date of (page) creation/modification.
2.4 Coordination with other servers:
A key point in the WWW architecture is the distributed nature of the
information repositories. In order to provide a coherent information
service and to minimize traffic and maintenance effort, some coordination
with other centers is required.
In concrete, the information in the server is coordinated with
The coordination is based on a synchronized transfer of mirror
copies of selected items and a consistent definition of pointers.
The coordination is evolving rapidly, as more information servers are being
added to Internet and clear needs are identified for providing the
2.5 Optimized maintenance:
Critical points in the management of a professional on-line information
service are (1) the effective update of the information items,
and (2) continuous effort to maintain the service available and to
assure the integrity of the data.
In order to achieve this with our server, the different areas of information
are managed by the most appropriate persons, who are responsible for the
content. Her/his e-mail address is located at the page bottom, so that
comments, general feedback and even complains are properly handled.
Before including new pages, its format has to be validated with a local
tool that will check the conformance of the document to the (HTML 2.0)
On the other hand, to assure information integrity and to check
availability of the referenced documents, the whole system is
periodically transversed by programs which alert of broken, re-directed and
recently updated links.
In addition, all accesses are logged and routinely analyzed.
In this way, we can find out if the server is not running smoothly and
it is possible to measure the usefulness of the information.
Currently, the following information is available in the
IUE home page:
The general server contains
information on the station and about projects supported at Villafranca.
- Description of the project, staff and spacecraft status,
- Newsletters from December 1993 onwards,
- Access to the IUE Merged Catalog,
- Description of the ULDA project,
- Data archive request facility,
- Observing schedule,
- Distribution of IUE final archive spectra,
currently restricted to internal users at Villafranca,
- IUE images, in coordination with IUEDAC (Data Analysis Center at GSFC).
4. What did we learn?
The experience has been very positive:
the service requires a limited amount of software and maintenance,
and the tasks to keep the information updated are well identified.
During the Jupiter/Shoemaker-Levy 9 observing campaign, statistics
for the period July-December 1994 show that the server was
accessed from 41 different countries (Internet domains, to be precise)
by 1,170 different nodes (Internet subdomains) all over the world,
even though the service was announced to very few places.
The server is currently supporting 15,000 external accesses per month
from nearly 50 different Internet domains, and the statistics indicate
a growing trend.
This technology is clearly the way to make information available to the
community, and the plans for the near future are based on it:
First, to implement a ``New Technology'' ULDA, to distribute Final Archive
Second, this service will be used to distribute information
required by the projects supported at Villafranca.
- J.A. de la Fuente, F. Marcelo, 1993.
``Internet information services at Villafranca'',
- J.D. Ponz, O. Holm, M. Barylak, 1994.
``Information services using WWW at Villafranca.
- M. Barylak, 1994.
``ESA IUE under VILSPA's WWW information service'',
- I. Yurrita, O. Holm, 1994.
``IUEFA output product retrieval. Users guide'',
- H.-M. Adorf, D. Egret, A. Heck, R. Jackson, A. Koekemoer, F. Murtagh,
D. Wells: 1994,
``The AstroWeb Database of Internet Resources''
The Messenger 78, 44.