{smcl}
{* 21jun2004}{...}
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{center:{hi:What are Stata graphs}}
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{p 0 2 0}o Nested collections of class-system objects

{p 0 2 0}o Objects containing sub-objects including styles describing how 
           they are to look {c -} styles

{p 0 2 0}o Objects capable of drawing themselves

{p 0 2 0}o Objects containing scripts (or logs) for reproducing themselves

{hline}
{p 4 4 4}{it}
You will probably be surprised to hear that I do not think of the {cmd:graph}
command as Stata's graphics.  Rather, {cmd:graph} is a not-so-thin parsing and
object creation engine that creates objects in the class system.  Objects that
know how to draw themselves and replay themselves from files.  And, objects
that can contain other objects.

{p 4 4 4}{it}
It is the direct manipulation of these objects that lies at the heart of the
graphics system.

{p 4 4 4}{it}
There are a few computer science terms that we should mention about the
object-oriented programming paradigm on which the graphics system is built.
In themselves they are not that helpful for the topic at hand, but they
provide a context for how things are done in the graphics classes.{sf}
{p_end}
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{hi:What is special about objects?}

{p 0 2 0}o Encapsulation {c -} programs and data are bound meaning that 
	class member programs run only on objects for that class

{p 0 2 0}o Inheritance {c -} classes/objects can inherit their data 
	(perhaps sub-objects) and member programs from an already existing 
	class

{p 0 2 0}o Polymorphism {c -} member programs with the same names can work 
	differently for different classes of objects.

{hline}
{p 4 4 4}{it}
What all of this means for our purposes is that we can create a graph object
for ourselves by {it:inheriting} from another object and picking up all of
that object's characteristics {c -} both data (variables) and programs.  It
also means that programs, and we are talking about pretty-much standard ado
programs, are associated with a particular object (or really class of object)
and that program can only be run on objects of its own class.

{p 4 4 4}{it}
The object-oriented programming facilities in Stata, but not the graphics
classes themselves, are documented in {bf:[P] class} or in help {help class}.

{p 4 4 4}{it}
For those wanting to know little more about the structure of graphs, the
following ancillary slides introduce some material differently than the talk.

{p 7 9 0}
    {view what_cmd.smcl:>>What is the {cmd:graph} command} (ancillary)

{p 7 9 0}
    {view what_sav.smcl:>>What are saved graphs} (ancillary)

{p 7 9 0}
    {view class.smcl:>>A touch of class {c -} quick review} (ancillary)

{p 7 9 0}
    {view style.smcl:>>You gotta have style} (ancillary)


{sf}
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{center:{view twoways.smcl:<<}   {view tindex.smcl:index}   {view anatomy.smcl:>>}}