Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stecf.org/conferences/adass/adassVII/reprints/gamielk.ps.gz Äàòà èçìåíåíèÿ: Mon Jun 12 18:51:46 2006 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 03:27:16 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: reflection nebula

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.
Distributed Searching of Astronomical Databases with
Pizazz
K. Gamiel, R. McGrath and R. Plante
National Center for Supercomputing Applications, University of Illinois,
Urbana, IL 61801
Abstract. Robust, distributed searching of networked­based astro­
nomical databases requires an investment not only by individual data
providers, but also by the astronomical community as a whole. We de­
scribe both these investments and introduce a supporting software project
called Pizazz. It is our hope that the community will appreciate the so­
cial requirement placed on them to work together and to participate in
e#orts towards a globally integrated, distributed astronomical search and
retrieval system.
1. Background
Establishing the infrastructure required for robust, distributed searching of databases
is not a simple proposition. In our view, there are four major steps involved;
analysis of existing data sources, choosing a model, profiling, and implementa­
tion.
In this case, analysis means finding various astronomical database sources
around the net of interest to the community and analyzing the interactive capa­
bilities and content. For example, what is the protocol used, what is the query
format, what is the response format, etc.
Next, we must choose a model for interacting with the identified data
sources in parallel. We narrow these models to two. The first model is the
``hands­o#'' model, that is, we do not impose any changes on the original data
sources whatsoever. In such a model, one would build a distributed searching
gateway that would o#er a single user interface, but would map the user's query
to each and every original data source in its native protocol and interaction style.
While this is obviously an appealing option for the original data providers, we
find that the wide range of protocols and interactive paradigms that must be
supported severely limit the overall usage and value of response. We feel this ap­
proach is short­sighted and ultimately of little value. The second and preferred
model is to agree on a single protocol for information retrieval. By agreeing on
a single protocol, we ensure a consistent and highly extensible interface to each
and every original data provider. If we agree, for example, on a single protocol
and profile, one can easily imagine autonomous user agents interacting with the
system on behalf of users.
Profiling is a step that must be taken regardless of which model is cho­
sen. Profiling, in the current context, means agreeing on general features of a
375

376 Gamiel, McGrath, and Plante
distributed searching system. For example, a profile for such a system might
state that all original data providers must provide access to title, author, and
abstract fields. It may state that a response must include the same information
and maybe a URL. In other words, a profile is a document that ensures some
level of consistency when interacting across data sources.
The last step is implementation. This involves work depending on which
model is chosen. If the ``hands­o#'' model is chosen, one must implement the
distributed searching gateway and for each original data source, a driver must be
written in order to interoperate with that source, mapping to the user interface.
In this model, the programmer must be available at a moment's notice to alter
any of the possibly hundreds of drivers when the original data provider alters
their interface. Since no open standards are imposed, it is certain that frequent
changes will occur, particularl since most of these systems will probably be
HTML/CGI­based systems and will change for purely superficial reasons. If the
second model is chosen, a communications server must be written and installed
at the original data provider's site. A gateway application that need only speak
a single protocol in parallel is then written. In this model, the gateway need only
point to new data providers as they come online, not requiring any changing of
source code.
2. Pizazz
We chose a model based on a single information retrieval protocol, namely
ANSI/NISO Z39.50. Z39.50 is a well­defined international standard used in
academic, government, and commercial institutions. It defines a standard for
interactive search and retrieval of database records from a data source over the
Internet. We here announce a software distribution called Pizazz that includes
a Z39.50 server toolkit. More information on Pizazz and other project details
can be found at http://webstar.ncsa.uiuc.edu/Project30/.
The server toolkit included with the Pizazz distribution builds on an existing
application called pizazzd. The typical scenario is that a data provider who
wants to participate in the distributed searching system will download Pizazz
and build the default pizazzd server. The provider will then alter a single C
file that includes callbacks for the four major information retrieval functions,
namely initialize, search, present, and close. In those four functions, the provider
will make calls to his own native database system, building the response as
appropriate with pizazz library calls we provide. Once that interface is written,
the provider then notifies NCSA and a pointer to their server is added to the
distributed searching gateway.
It would be a disservice to say that creating this interface is simple. How­
ever, we are committed to making it as easy as possible with helper tools and,
more importantly, feedback from users (``user'' in this sense is the programmer
who builds the interface between pizazzd and the native database). By far the
most di#cult part of implementing the interface is in support of the nested
RPN query structure. The user has access to function calls for walking the
query tree structure and while doing so, must generate a query based on terms
and attributes suitable for his native system.

Searching Astronomical Databases with Pizazz 377
The information retrieval model used by pizazzd is as such. The server
receives a single initialize request from the client. The initialize callback is
invoked where any native database initialization is performed. Typically, the
server then receives a search request which includes the database name to search
and a potentially complex, but standard, RPN query, along with other search
parameters. The search callback is invoked where the query is translated and
passed to the native database system. The search results in the formation of
a logical result set. From that result set, the client may then request to have
records presented. In that case, the server receives a present request asking,
for example, records 1 through 5 from the Default result set in HTML format.
The present callback is invoked and the requested records are retrieved from
the native database and returned to the client. Finally, the client sends a close
request, whereas the close callback is invoked, releasing any resources used by
the native database.
More information on the Pizazz software distribution can be found at the
project home page, http://webstar.ncsa.uiuc.edu/Project30/. The project team
recognizes and appreciates the complexity of interfacing a communications server
with a native database system and, accordingly, are happy to help with the e#ort
in any way possible. Contact information may also be found on that Web page.
3. Conclusion
Designing a distributed, networked­based astronomical information system re­
quires a four­step approach including original data source analysis, modeling the
system, profiling the system, and implementation of the system. We described
each step and proposed our solution. We have a project underway to implement
such an information system and are committed to helping the astronomical com­
munity realize the dream of a robust, single interface to any and all relevant data
sources on the Internet.