Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stecf.org/conferences/adass/adassVII/reprints/mcglynnt.ps.gz Äàòà èçìåíåíèÿ: Mon Jun 12 18:51:47 2006 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 03:48:41 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï

Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
Astrobrowse: A Multi­site, Multi­wavelength Service for
Locating Astronomical Resources on the Web
T. McGlynn 1 and N. White
NASA/Goddard Space Flight Center, Greenbelt, MD 20771, Email:
tam@silk.gsfc.nasa.gov
Abstract.
We report on the development of a Web agent which allows users
to conveniently find information about specific objects or locations from
astronomical resources on the World Wide Web. The HEASARC Astro­
browse agent takes a user­specified location and queries up to hundreds
of resources on the Web to find information relevant to the given target
or position. The current prototype implementation is available through
the HEASARC and provides access to resources at the HEASARC, CDS,
CADC, STScI, IPAC, ESO and many other institutions. The types of re­
sources the user can get include images, name resolution services, catalog
queries or archive indices.
The Astrobrowse e#ort is rapidly evolving with collaborations on­
going with the CDS and STScI. Later versions of Astrobrowse will use
the GLU system developed at CDS to provide a distributable database
of astronomy resources. The Astrobrowse agent has been written to be
customizable and portable and is freely available to interested parties.
1. Introduction
The myriad astronomical resources now available electronically provide an un­
precedented opportunity for astronomers to discover information about sources
and regions they are interested in. However, many are intimidated by the very
number and diversity of the available sites. We have developed a Web service,
Astrobrowse 2 , which makes using the Web much easier. The Astrobrowse agent
can go and query many other Web sites and provide the user easy access to
the results. In the next section we discuss the history and underlying philos­
ophy of our Astrobrowse agent. The subsequent sections address the current
implementation, status and future plans.
1 Universities Space Research Association
2 http://legacy.gsfc.nasa.gov
481

482 McGlynn and White
2. Why Astrobrowse?
Astronomers wishing to use the Web in their research face three distinct prob­
lems:
Discovery Given the hundreds of Web sites available it is virtually impossible
users to know of all the sites which might have information relevant to a
given research project.
Utilization Even when users know the URLs of useful Web sites, each Web site
has di#erent formats and requirements for how to get at the underlying
resources.
Integration Finally, when users have gotten to the underlying resources, the
data are given in a variety of incompatible formats and displays.
As we began to design our Astrobrowse agent to address these problems
we factored in several realizations: First, as we looked at the usage of our
HEASARC catalogs we found that by about 20 to 1, users simply requested
information by asking for data near a specified object or position. The particular
ratio may be biased by the data and forms at our site, but clearly being able just
to do position based searches would address a major need in the community.
Second, we saw that the CGI protocols are quite restrictive so that regard­
less of the appearance of the site, essentially all Web sites are queried using a
simple keyword=value syntax. This commonality of interface presents a unique
opportunity. Earlier X­windows forms that many data providers had created,
and emerging technologies like Java do not share this.
Another consideration was that for a system to be successful, it should
require only minimal, and preferably no e#ort, on the part of the data providers.
We could not build a successful system if it mandated how other sites use their
scarce software development resources.
Finally, and perhaps most important, we recognized that problem of inte­
gration is by far the most di#cult to solve. Integrating results requires agreement
on formats and names to a very low level. This is also an area which can require
deep understanding of the resources provided so that it may appropriately be
left to the astronomer. We would provide very useful service to users even if we
only addressed the issues of discovery and utilization.
With these in mind, the outline of our Astrobrowse system was straightfor­
ward: Astrobrowse maintains a database which describes the general character­
istics of each resource and detailed CGI key=value syntax of the Web page. It
takes a given target position, and translates the query into the CGI syntax used
at the various sites and stores the results. In current parlance, Astrobrowse is a
Web agent which explodes a single position query to all the sites a user selects.
Since very many, if not most, astronomy data providers have pages which sup­
port positional queries, Astrobrowse can access a very wide range of astronomy
sites and services.

Astrobrowse: Locating Astronomical Resources on the Web 483
3. Implementation
The HEASARC Astrobrowse implementation has three sections: resource selec­
tion, where the user chooses the sites to be queried; query exploding where the
positional query is sent to all of the selected resources; and results management,
where Astrobrowse provides facilities for the user to browse the results from the
various sites.
3.1. Resource Selection
Once the total number of resources available to an Astrobrowse agent grows
beyond 10­20, it is clear that a user needs to preselect the resources to be queried.
The current Astrobrowse implementation provides nearly a thousand resources.
Querying all of them all of the time would strain the resources of some of the data
providers and would also confuse the user. We currently provide two mechanisms
for selecting resources. A tree of resources can be browsed and desired resources
selected. Alternatively a user can search for resources by performing Alta­Vista­
like queries against the descriptions of those resources. E.g., a user might ask
for all queries which have the words `Guide Star' in their descriptions. The user
can then select from among the matching queries.
3.2. Query Exploding
The heart of Astrobrowse is the mechanism by which it takes the position or
target specified by the user and then transforms this information into a query
against the selected resources. For each resource the Astrobrowse database
knows the syntax of the CGI text expected, and especially the format of the
positional information, including details like whether sexagesimal or decimal
format is used and the equinox expected for the coordinates. The current system
uses a simple Perl Web query agent and spawns a separate process for each query.
3.3. Results Management
Astrobrowse takes the text returned from each query and caches it locally. If
the query returns HTML text then all relative references in the HTML -- which
presumably refer to the originating site and thus would not be valid when the
file is retrieved from the cache -- are transformed into absolute references.
Our Astrobrowse interface uses frames to provide a simple mechanism where
the user can easily switch among the pages returned. A number of icons return
the status of each request, and allow the user to either delete a page which is
no longer of interest, or to display it in the entire browser window.
3.4. The Astrobrowse Database
A database describing Astronomy Web sites is central to the functioning of
Astrobrowse. For each resource, a small file describes the CGI parameters and
provides some descriptive information about the resource. The file is human­
readable and can be generated manually in a few minutes if one has access to
the HTML form being emulated. We also provide a page on our Astrobrowse
server to automatically build these files so that users can submit new resources
to be accessed by our agent.

484 McGlynn and White
Figure 1. An Astrobrowse Screen Shot.
4. Future Plans
We believe the current Astrobrowse provides a convincing proof­of­concept for
an astronomy Web agent and is already a very useful tool but we anticipate
many changes in the near term. Among these are:
. Access to virtually all astronomical Web pages supporting positional queries.
We expect to support about 3,000 to 10,000 resources compared to the cur­
rent approximately 1,000 resources.
. Providing a few uniform keys for resources so that users can select data
conveniently by waveband and data type.
. Conversion of the database to formats using the CDS's GLU format and
use of the GLU system to manage distributed access and updates to the
resource database.
. Substantial experimentation in the user interfaces to select resources and
display results.
In the longer term we hope that Astrobrowse can be expanded beyond the
limits of positional searches for astronomical resources and become the basis for
tools to help integrate astronomy, space science and planetary data.