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Astronomical Data Analysis Software and Systems IV
ASP Conference Series, Vol. 77, 1995
R. A. Shaw, H. E. Payne, and J. J. E. Hayes, eds.
WDB---A Web Interface to Sybase
B. F. Rasmussen
Space Telescope­European Coordinating Facility,
Karl­Schwarzschild­Strasse 2, D­85748 Garching bei M¨unchen,
Germany
Abstract. WDB is a software toolset that tremendously simplifies the
integration of Sybase databases into the World Wide Web. WDB lets
you provide WWW access to the contents of Sybase databases without
writing a single line of code, yet provides the flexibility to easily add new
capabilities as needed. This article describes the technical implications of
implementing such an Interface. The tool itself, and full documentation
is available on the WWW at theWDB Home Page 1 .
1. Introduction
To run WDB, all that is needed is the WDB script (written in sybperl) and
a set of high­level form definition files, each describing a different view on the
database. WDB automatically creates HTML forms, on­the­fly, to allow users to
query the database, and given these query constraints, it will query the database
and present the result to the user. WDB even comes with a utility to automati­
cally extract information about a table from the database and create a working
template form definition file.
A number of conversions are possible on the data coming from the database
before they are shown to users: formatting of coordinates into hours, minutes,
and seconds; formatting dates; etc. The most noticeable feature is the possibil­
ity to convert data from the database into hypertext links---and as it is possible
through WDB to access any database element directly via a Web URL---the
entire database can then be turned into a huge hypertext system. These hyper­
text links can be links to other elements in the database, thereby providing a
simple way of jumping between related information. There could also be links to
other documents on the Web, providing easily integration between data in the
database and related documents on the Web. One could also have links to other
databases with a WDB or similar interface---providing a simple mechanism for
cross­database links.
1
http://arch­http.hq.eso.org/bfrasmus/wdb/wdb.html
1

2
WWW­Client
WWW­Client
WWW­Server DB­Server
WDB
pipe connection
short­lived
socket
Short­lived­
Figure 1. A WDB Connection.
2. Architecture
WDB is implemented as a CGI script which can generate forms and send them
to the user, retrieve the contents of the form, process it and return the results
to the user. The forms and description of how the individual fields in the form
links to fields in the database are defined using Form Definition Files (fdf 's)
located on the server.
Due to the nature of a WWW connection, the WDB system has to be
designed differently from a normal database application (see Figure 1). As there
are no long­lived connections, the server has no notion of what has been going
on earlier in a session. The WDB process is exited immediately after the results
are send back to the user. This means that all information needed to perform a
given action has to be sent from the client each time. Of course, the client will
have this information from the last result it received from the server.
The way this information is sent back and forth between the WWW client
and the server is by the URL. It is a standard for specifying a piece of information
on the Internet, and is composed of a protocol name (ftp, http, gopher), the name
of the server, and a path on that server pointing to the piece of information
needed. This can be a file or, on an http server, a CGI script such as WDB.
The trick is that if there is any extra information in the URL after the path,
then it is passed to the script as what is called PATHINFO.
(ex. http://arch­http.hq.eso.org/cgi­bin/wdb/PATHINFO)
2.1. Flow of Control in WDB.
The actual flow of control is better illustrated in Figure 2. What happens is the
following :
1. One ``clicks'' on a URL leading to the WDB script. The URL contains
extra information in the path (PATHINFO), specifying what information
in the database the user would like to query. This is typically obtained
from a normal hypertext page with a menu of available query forms.
2. The server receives the URL request, starts the WDB script and passes the
extra information in PATHINFO, actually the name of the Form Definition
File (fdf) to use, and the word ``form''.
3. WDB reads the fdf and generates an HTML form according to the speci­
fications in the fdf. The form is returned to the user and WDB exits.

3
WWW­Client WWW­Server WDB
URL fdf­name/"form"
HTML­Form
Submit fdf­name, field contents
"query"
SQL
DB. rows
HTML Page
URL with key fdf­name, keys, "query" SQL
HTML Page
DB­Server
DB. row
Figure 2. Flow of Control.
4. The user fills out the form with the query constraints and presses the
``Submit'' button. This sends the WDB URL (with PATHINFO) plus the
contents of the form (encoded) to the WWW Server.
5. The server receives the URL, starts the WDB script and passes the extra
information in PATHINFO, plus the form content.
6. WDB parses the PATHINFO which in this case is the name of the fdf
plus the word ``query''. This tells WDB to construct a SQL query from
the information in the fdf file and the user's constraints.
7. The SQL query is send to the database server.
8. The database server processes the query and returns a number of rows.
9. WDB retrieves the rows from the database server and after having con­
verted the data according to the specifications in the fdf, constructs an
HTML page with the result. If more than one row was returned, a tabular
output format is chosen, allowing the user to select a row, via a hypertext
link, to get all the details.
10. The HTML page is returned to the user, and WDB exits.
11. The user clicks on a hypertext link for a row. This link contains the WDB
URL with the fdf name, the word ``query'' and the key(s) for the current
row in the PATHINFO.
12. The WWW server receives the URL, starts the WDB script and passes it
the extra information in PATHINFO.
13. WDB constructs a new database query, this time using the key(s) instead
of the form contents.

4
14. The database processes the query and returns the result.
15. WDB retrieves the row from the database server, converts the data ac­
cording to the specifications in the fdf, and this time, as only one row is
returned, constructs a HTML page with all the details. The HTML page
is returned to the user and WDB exits.
3. Conclusions
WDB has proven very successful---mainly because of its simplicity and the ease
with which it can be extended. One of the goals of WDB was to provide an easy,
yet flexible, way to make database information available. In the simple case, no
coding should be necessary. However, if special behavior is needed, it should
be possible to add it without changing the core system. Also, if some special
behavior has been defined for one field in a form, it should be easy to reuse this
in other forms.
This has been achieved by allowing extensions to be added in the individ­
ual Form Definition Files using the powerful Perl language. This makes local
customization a lot easier than with most existing WWW/Database gateways.
WDB already has a large user base. At the time of writing, more than
30 sites world­wide have installed it. An e­mail mailing list is maintained for
announcements of new releases. To be added to this list, send e­mail to the
author (bfrasmus@eso.org).
References
McCool, Rob 1993, The Common Gateway Interface 2 , National Center for Su­
percomputing Applications (Champaign, University of Illinois)
McCool, Rob 1994, NCSA httpd Overview 3 , National Center for Supercomput­
ing Applications (Champaign, University of Illinois)
Brenner, Steven E. 1994, CGI Form Handling in Perl 4 (Cambridge, University
of Cambridge)
2 http://hoohoo.ncsa.uiuc.edu/cgi/overview.html
3 http://hoohoo.ncsa.uiuc.edu/docs/Overview.html
4 http://www.bio.cam.ac.uk/web/form.html