The Form Definition Files.

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.
As examples of such special behavior can be mentioned :

• Conversion of LaTeX special characters in a text field to the equivalent HTML representation.
• Conversion of coordinates stored in the database as milliarc seconds to hours minutes seconds format.
• Conversion and formatting of dates.
• Computed fields with a value expressed as a function of the values of the other fields in the form.
• Upper-/lower-case conversion of text fields.
• Inclusion of in-lined images.
• Adding hypertext links to fields. Possibly pointing to other WDB objects.

( Some of these conversions can be implemented using database views, however this usually makes it either impossible or very inefficient to search on the corresponding field. )
The way this is obtained in WDB is by using Form Definition Files (fdfs). When a new query form has to be added to the system all that is needed is to create a new fdf file specifying what fields should be in the form and how they should be presented to the user.
ßForm attributes

An fdf is composed of a set of form attributes, and a set of field attributes for each field in the form. Examples of form attributes include :

{ }DATABASEx
NAME
Name of the form.

TABLE
List of tables to query.

DATABASE
Name of the database to use

TITLE
Text for the <TITLE> tag in the query form and the result page.

JOIN
Join conditions if more than one table is specified.

ßField attributes

Field attributes describe how to find the field in the database and how to present it to the user. Examples of field attributes include :

{ }columnx
FIELD
Field identifier. Used internally to uniquely identify a field.
label
Label/title in forms etc.
column
Database column definition. Defaults to the value of FIELD. values can include Sybase computed fields, and table-names.
type
Database type of field [ int | char | datetime | ...].
length
Length of field including formatting etc.

A whole lot of other attributes can be added to the fdf if needed. For example a 'url' attribute can be added if the field should have a hypertext link. - Or converters could be added to specify how data from the database should be converted to what is to be presented to the user (the 'from_db' attribute), - or how the text entered by the user should be converted to what actually should be searched for in the database (the 'to_db' attribute).
The conversions are expressed using the very powerful Perl language. In fact WDB was coded entirely in Perl, with a few extensions to enable access to Sybase.

ßExample of a Form Definition Files.

The following fdf file demonstrates several of the features of WDB.

NAME       = preprints
TITLE      = ESO Preprints Database
DATABASE   = library
TABLE      = preprint
ORDER      = authors
DOCURL     = /eso/preprint.html
RECTOP     = $val{'title'}
COMMENTS_TO= malbrech@eso.org
PERL       = require "eso_util.pl";	# Include extra perl functions 
#------------------------------------
FIELD      = date
label      = Received
type       = int
length     = 10
from_db    = &cvdatein( $val{'date'}, "DD MMM YY" );
to_db      = &cvdateout( $val );
default    = '>01-Jan-'.`date +%y` 
no_tab

FIELD      = authors
label      = Authors
type       = char
length     = 255
tablen     = 20
from_db    = &textohtml($val{'authors'})

FIELD      = title
label      = Title
type       = char
length     = 255
from_db    = "<em>".&textohtml($val{'title'})."</em>"
url        = "$WDB/eso/$form{'NAME'}/query/".&cgi_encode($val{'title'})
no_full
key

FIELD      = reference
label      = Reference
from_db    = "$val{'institute'}, <em>$val{'numb'}</em>"
computed
no_tab
no_query

FIELD      = institute
column     = inst
label      = Institute
type       = char
length     = 255
no_tab
no_full

FIELD      = numb
type       = char
hidden

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Next: About this document Up: WDB Poster (ADASS'94) Previous: Flow of Control

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Bo Frese Rasmussen
Fri Nov 25 16:28:57 MET 1994