<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <HTML> <HEAD> <TITLE>Programming in XPCE/Prolog: Section C.1</TITLE><LINK REL=home HREF="index.html"> <LINK REL=contents HREF="Contents.html"> <LINK REL=index HREF="DocIndex.html"> <LINK REL=summary HREF="summary.html"> <LINK REL=previous HREF="globalarch.html"> <LINK REL=next HREF="sec-C.2.html"> <STYLE type="text/css"> /* Style sheet for SWI-Prolog latex2html */ dd.defbody { margin-bottom: 1em; } dt.pubdef { background-color: #c5e1ff; } pre.code { margin-left: 1.5em; margin-right: 1.5em; border: 1px dotted; padding-top: 5px; padding-left: 5px; padding-bottom: 5px; background-color: #f8f8f8; } div.navigate { text-align: center; background-color: #f0f0f0; border: 1px dotted; padding: 5px; } div.title { text-align: center; padding-bottom: 1em; font-size: 200%; font-weight: bold; } div.author { text-align: center; font-style: italic; } div.abstract { margin-top: 2em; background-color: #f0f0f0; border: 1px dotted; padding: 5px; margin-left: 10%; margin-right:10%; } div.abstract-title { text-align: center; padding: 5px; font-size: 120%; font-weight: bold; } div.toc-h1 { font-size: 200%; font-weight: bold; } div.toc-h2 { font-size: 120%; font-weight: bold; margin-left: 2em; } div.toc-h3 { font-size: 100%; font-weight: bold; margin-left: 4em; } div.toc-h4 { font-size: 100%; margin-left: 6em; } span.sec-nr { } span.sec-title { } span.pred-ext { font-weight: bold; } /* Footnotes */ sup.fn { color: blue; text-decoration: underline; } span.fn-text: { display: none; } sup.fn span {display: none;} sup:hover span { display: block !important; position: absolute; top: auto; left: auto; width: 80%; color: #000; background: white; border: 2px solid; padding: 5px; margin: 10px; z-index: 100; font-size: smaller; } </STYLE> </HEAD> <BODY BGCOLOR="white"> <DIV class="navigate"><A class="nav" href="index.html"><IMG SRC="home.gif" BORDER=0 ALT="Home"></A> <A class="nav" href="Contents.html"><IMG SRC="index.gif" BORDER=0 ALT="Contents"></A> <A class="nav" href="DocIndex.html"><IMG SRC="yellow_pages.gif" BORDER=0 ALT="Index"></A> <A class="nav" href="summary.html"><IMG SRC="info.gif" BORDER=0 ALT="Summary"></A> <A class="nav" href="globalarch.html"><IMG SRC="prev.gif" BORDER=0 ALT="Previous"></A> <A class="nav" href="sec-C.2.html"><IMG SRC="next.gif" BORDER=0 ALT="Next"></A> </DIV> <H2><A NAME="sec:C.1"><SPAN class="sec-nr">C.1</SPAN> <SPAN class="sec-title">What is ``Object-Oriented''?</SPAN></A></H2> <P><font size=-1>XPCE</font> is an object-oriented system. This implies that the basic entity in <font size=-1>XPCE</font>'s world is an object, an entity with state capable of performing actions. Such an action is activated by sending the object a <EM>message</EM>. <P>So far, most object oriented systems agree. Starting from these notions however one can find object oriented environments that take widely different approaches for representing objects, actions on objects and sending messages. <P>Rather than specifying operations on each individual object most OO environments define some way of sharing the operation definitions (called <EM>methods</EM>). There are two ways to share methods. One is to create objects as a copy of other objects and then modify them (by attaching and deleting slots and methods) to fit the particular need. If a series of similar objects is needed, one first creates an object that satisfies the common functionality and then creates multiple copies of this object. This approach is followed by SELF <CITE><A class="cite" href="Bibliography.html#chambers:89">Chambers <EM>et al.</EM>, 1989</A></CITE>. The other ---more traditional--- approach is to define a <EM>class</EM>. A class is an entity in the object oriented environment that defines the constituents of the persistent state and the methods for each of its <EM>instantiations</EM>. <P><font size=-1>XPCE</font> takes the latter approach, but adds some notions of the object-copying approach because GUI's often contain unique objects and because object modification is more dynamic and therefore more suitable for rapid prototyping. <P></BODY></HTML>