[xml] where is the format of PUBLIC defined?

[Rick Jones <rick jones2 hp com>]

I'm swimming in circles trying to get on board with catalogs, to deal with a 
problem I have with netperf4 (http://www.netperf.org/svn/netperf4/trunk).

I'm guessing it is some variation on "To understand recursion, first you must 
understand recursion."

Specifically, to allow the netperf DTD (src/netperf_doc.dtd) to exist in 
different places between the system running netperf and the systems running 
netserver and still be able to validate the XML-encoded messages that netperf 
and netserver exchange.

To that end I am presently of the belief I need to switch from something akin to:

<?xml version="1.0" standalone="no" ?>
<!DOCTYPE netperf SYSTEM "./netperf_docs.dtd" >
<netperf xmlns="http://www.netperf.org/ns/netperf";>

to something that replaces SYSTEM with PUBLIC.  Thus far I've been able to learn 
that after PUBLIC one has a string and a URL (URL?), what has me confused is the 
format of the first string.  Every example I've seen in my web searches so far 
looks more or less like:

PUBLIC "-//OASIS//DTD DocBook XML//EN"

from which I gather there is some sort of "structure" to the string - with 
sections separated by "//" but I'm utterly unable to find anything (so far) that 
describes that structure - or I've seen it and simply not recognized it :(

Without fully understanding it all, I'm presently guessing I want something 
along the lines of:

<?xml version="1.0" standalone="no" ?>
<!DOCTYPE netperf PUBLIC "-//netperf//Netperf XML//EN"
  "http://www.netperf.org/netperf_docs.dtd/1.0";>
<netperf xmlns="http://www.netperf.org/ns/netperf";>

but without understanding the format of that first string with PUBLIC I've no 
idea if I'm going down the right path.  It appears that the very last part is 
some sort of language specification, next going right to left is a description, 
and then some sort of organization?  Not at all sure what the "-" signifies.

And then after that I have to create some catalog XML and stash it away 
somewhere on each system that lets libxml2 map from the string(s) in PUBLIC to a 
file in the filesystem on each system yes?

Gentle taps with a nerf clue bat would be most appreciated,

rick jones