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<H2><A NAME="sec:1.6"><SPAN class="sec-nr">1.6</SPAN> <SPAN class="sec-title">A
brief history of (X)PCE</SPAN></A></H2>
<P>The ``PCE Project'' was started in 1985 by Anjo Anjewierden. His aim
was to develop a high-level UI environment for (C-)Prolog. The
requirements for this environment came from the ``Thermodynamics Coach''
project in which Paul Kamsteeg used PCE/Prolog to implement the UI for a
courseware system for thermodynamics. This system included a
`scratch-pad' that allowed the student to create structured drawings of
component configurations. The application had to be able to analyse the
drawing made by the student.
<P>PCE has been redesigned and largely re-implemented on a SUN
workstation using Quintus Prolog and later SWI-Prolog <CITE><A class="cite" href="Bibliography.html#SWI-Prolog:manual">Wielemaker,
1996</A></CITE> in the Esprit project P1098 (KADS). This project used
PCE to implement a knowledge engineering workbench called Shelley
<CITE><A class="cite" href="Bibliography.html#Anjewierden:90b">Anjewierden <EM>et
al.</EM>, 1990</A></CITE>. During this period PCE/Prolog has been used
by various research groups to implement graphical interfaces for
applications implemented in Prolog. Most of these interfaces stressed
the use of <A NAME="idx:directmanipulation:14">direct-manipulation</A>
graphical interfaces. Feedback from these projects has made PCE
generally useful and mature.
<P>During the versions 4.0 to 4.5, <font size=-1>XPCE</font> was moved
from SunView to X-windows and since 4.7 compatibility to the Win32
platform is maintained. In addition, the virtual machine has been made
available to the application programmer, allowing for the definition of
new
<font size=-1>XPCE</font> classes. These versions have been used mainly
for small internal case-studies to validate the new approach.
Larger-scale external usage started from version 4.6 and introduced the
vital requirement to reduce incompatible changes to the absolute
minimum.
<P>In version 5, the XPCE/Prolog interface was revisited, improving
performance and making it possible to pass native Prolog data to XPCE
classes defined in Prolog as well as associate native Prolog data with
XPCE objects. Various new graphical primitives, among which HTML-4 like
tables and graphical primitives for rendering markup containing a
mixture of graphics and text.
<P>As of XPCE 5.1, the license terms have been changed from a
proprietary license schema to the open source GPL-2 licence.
<P>As of XPCE 6.0, the licence terms have been changed from GPL to the
more permissive LGPL for the XPCE kernel (compiled C-part) and GPL with
an exception allowing for generating non-free applications with XPCE for
the Prolog libraries. Please visit the SWI-Prolog home page at <A class="url" href="http://www.swi-prolog.org">http://www.swi-prolog.org</A>
for details.
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