Experimental Physics and
Industrial Control System

[email protected] · Tue, 01 Nov 2005 12:48:13 -0600

Kay-Uwe Kasemir wrote:

> The 'include' issue that I mentioned might have been solved.
> I don't know how well this feature is supported today,
> but http://www.xml.com/pub/a/2002/07/31/xinclude.html
> gives examples of an 'Xinclude' mechanism for including
> XML docs from within XML docs.

This would be fine for DBD files, which only need simple file inclusion,
but it's insufficient to implement the more advanced template
instantiation features that are needed for databases.

For quite a long time now VCDT has supported a syntax for its '.vdb'
files which we were planning to add to the IOC as well, before the V4 DB
file syntax redesign occurred.  The intention is to replace MSI and the
.substitutions template syntax currently used in V3.  There are two
separate substitution mechanisms needed to do this properly - Macros
which pass substitution data from the parent into a template, and Ports
which pass information the other way (so a parent diagram can link to
records inside without having to know their names).

It would obviously be possible to create suitable XML tags to do this if
we do adopt an XML format, but I don't see how we'd be able to use the
standard XInclude mechanism that Kay discovered; we'd probably have to
implement it ourself in our own schema/DTD and parser.

If there is overwhelming pressure from the community to use XML
*instead* of our native formats I would want someone else with XML
experience to help design the schema/DTD and be responsible for
producing an editor for DBD files, and for at least a part of the
replacements for the command-line tools we currently call from the EPICS
build system (dbExpand, dbToRecordTypeH, dbToMenuH).  These tools should
not be written in Java because they get run frequently during the
application build process, which at some sites is already rather slow. 
I guess xslt might be usable for these, but I don't know how to use it.

- Andrew

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System