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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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