ESA/IUE under the Web

J.D. Ponz, M. Barylak, A. de la Fuente, O. Holm
ESA/Villafranca, Madrid, Spain.

1. Introduction

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 dedicated server, 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.

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:

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 items. 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 with text, 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:
  1. Uniform page header, with informative titles,
  2. limit the number of intermediate steps to get to the actual information, using itemized lists in the intermediate (navigation) pages,
  3. 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
  4. 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 information.

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) standard.

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.

3. Services

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.

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 data. Second, this service will be used to distribute information required by the projects supported at Villafranca.


  1. J.A. de la Fuente, F. Marcelo, 1993. ``Internet information services at Villafranca'', TN/7051-00/AF-FM/930929.
  2. J.D. Ponz, O. Holm, M. Barylak, 1994. ``Information services using WWW at Villafranca. Users requirements'', SD/WIS001-03/JDP-OH-MB/941004.
  3. M. Barylak, 1994. ``ESA IUE under VILSPA's WWW information service'', SD/WIS002-02/MB/941024.
  4. I. Yurrita, O. Holm, 1994. ``IUEFA output product retrieval. Users guide'', TN/8034-02/IY-OH/940830.
  5. 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.