[Jmri-developers] Making JMRI XML visible from the web

[Bob J. <Bob...@lb...>]

I've been working on a small project to make it possible to see JMRI 
XML files in a web browser.  This will reduce confusion when somebody 
says "I've put this file here....", and also can make it easier to 
figure out what's in a panel file.

To do this, the browser needs two things.  First, it needs formatting 
instructions, which it gets from a line at the top of the file that 
looks something like this:

<?xml-stylesheet 
href="http://jmri.sourceforge.net/xml/XSLT/panelfile.xsl" 
type="text/xsl"?>

(There are different formatting XSLT files for different types of 
JMRI files right now, just to make it easier to create them; 
panelfile.xsl is for panel files, etc)

Where should that stylesheet be located? Putting it on the web (i.e. 
using an HTTP reference to the file instead of getting it from the 
local file system) means that users will get the most recent one when 
they use it; since these stylesheets are probably going to 
continually evolve for a while, this is a good thing. On the other 
hand, this will only work if the browser has an active web 
connection.  That'll be unfortunate for some people, who don't have 
their railroad computers hooked to the Internet, but they're not 
losing something they ever had.  The advantage to doing this is that 
it will work where-ever the file is, without having to have a local 
copy of the XSLT file in a specific location on that computer.

The browser also needs to be able to find the file's content 
definition, the DTD.  This is a little more problematic.  Currently 
(1.9.1 and before), JMRI loads that DTD from a local file, even when 
it's not going to use it to check the format of the file.  (There are 
good technical reasons for this to be the default, which I can 
explain if anybody needs to know them).  That's because the files 
have this type of definition on them:

<!DOCTYPE decoder-config SYSTEM "../DTD/decoder-config.dtd">

The "../DTD/decoder-config.dtd" is a path-relative location of the 
DTD file for e.g. a decoder file.

You can probably see the problem:  If we leave it like this, browsers 
won't be able to display the page in lots of cases, because they 
can't find the DTD, because it has to be in a magic relative place. 
On the other hand, if we change it to e.g.

<!DOCTYPE decoder-config SYSTEM 
"http://jmri.sourceforge.net/xml/DTD/decoder-config.dtd">

browsers with Internet connections will be able to find it, but JMRI 
itself won't be able to find it without an Internet connection!!!

The problem with JMRI not finding it can be fixed in the JMRI code 
using a fall-back method, and I just committed that fix.  If the 
given DTD location doesn't work, JMRI will now look in it's own set 
of DTDs.

So, for new files, we have a nice solution to finding the most 
up-to-date DTDs, displaying XML files as web pages, and still having 
JMRI able to work without a web connection.

But, and here's the problem, that means that files written by JMRI 
1.9.2 won't be directly readable (unless somebody replaces the lines 
at the top with the old ones).

Is this a big deal?

If you want to see this in action, take a look at this link:
<http://jmri.sourceforge.net/xml/samples/LogixStateMachine.xml>

You can also copy the first lines from that file onto your own panel 
files to see what they look like.

Bob
-- 
Bob Jacobsen, UC Berkeley
jac...@be... +1-510-486-7355 fax +1-510-643-8497 AIM, Skype JacobsenRG