DOCBOOK: Newbie - How to include entities?

A newbie asks:

So far, my book looks like this:


	<!DOCTYPE book PUBLIC "-//Davenport//DTD DocBook V3.0//EN" [

	<!ENTITY john		"John Lennon">
	<!ENTITY paul		"Paul McCartney">
	<!ENTITY george	"George Harrison">
	<!ENTITY ringo		"Ringo Starr">

	<!ENTITY chap1		SYSTEM "chap1.sgml">
	<!ENTITY chap2		SYSTEM "chap2.sgml">
	<!ENTITY chap3		SYSTEM "chap3.sgml">
	]>

	<book>
		<bookinfo>
		<!--	bookinfo entries go here...	-->
		</bookinfo>
		<toc></toc>
		&chap1;
		&chap2;
		&chap3;
	</book>

1. The john, paul, george, and ringo entities are used throughout
the chap1, chap2, and chap3 files.  I would like to keep the john,
paul, george, and ringo entities (plus many others) in a separate
file and include them.  Can I do this?  How?

2. I am writing a users manual that will be showing error messages
like "An error occurred in module ? - please contact the help desk."
I currently do something like this:

	<!ENTITY part1	"An error occurred in module ">
	<!ENTITY part2	"please contact the help desk.">

	&part1; moduleX &part2;
	&part1; moduleY &part2;
	&part1; moduleZ &part2;

Is it possible to create an entity or macro where I can substitute
the % (or some other symbol) with a parameter?  Maybe something
like

	&errmsg(moduleX);
	&errmsg(moduleY);
	&errmsg(moduleZ);

to produce the same results?  Is it possible to pass multiple arguments?

Thanks -
Jim Ide