[evla-sw-discuss] MIB Data Port Spec revisions

[Bill Sahr]

I have a list of 4 changes that have been proposed for the
MIB Data Port Spec (formerly known as the MIB Broadcast
Stream Spec).  I will list them below.  Recipients of this
message will have until COB on Wed, 10/29/2003 to comment.
If, at that time, no strong objections to the changes have
been received, the changes to the spec will be accepted.
I am allowing only a short response period because all of
these changes have already been thoroughly discussed.

1. A revision to the DDR format has been proposed.
    For the revised format:
    - the Attention and Length fields have been dropped
      (separate ports will be used instead of an Attention
       bit, and the Length field is seen as unnecessary)
    - the Antenna ID will be a STRING
    - the Device ID will be a STRING

2. An alert record type will be added to the MIB Data
    Port Spec.  The format of the alert message is simply
    a minor variant on the DDR format - the ARRAY of
    monitor points is replaced by a STRING containing
    the text of the alert.  All other DDR fields will
    be present.

3. A revision has been proposed to the MONITORPOINT
    record that consists of changing the monitor point
    ID from a SHORT (two byte integer) to a STRING.

4. It has been proposed that we encode DDRs in XML
    rather than the proprietary format that is now a
    part of the spec.

The last point deserves a bit of discussion.  Originally,
a proprietary, in-house encoding was proposed because we
planned to write DDRs directly to the archive, and we sought
to keep the records as small as possible.  Now, DDRs will
be unpacked and the contents of the fields will be used to
fill an Oracle database.  So, the original impetus for the
proprietary scheme has disappeared.  Rich argues that
use of XML makes the job much easier on the client side.
As a prototype/testbed, he has created an XML schema that
describes the structure of a DDR.  Castor was then run on that
schema to automatically produce the Java classes that serve
as the basis for filling the archive database.  If we adopt
XML as the encoding of the DDRs, then we can use the schema-
based generation of the Java classes as an integral part of
our approach, with changes in the DDR requiring only a change
in the schema and Castor-based regeneration of the Java
classes to adapt to the DDR changes.  Chunai has stated
that the change to XML encoding of DDRs is straightforward,
and she is quite willing to do the required work.

The use of XML in the DDR would also be consistent with the
use of XML to describe the monitor and control points in
a Device, and with the use of XML on the service port and
the session port.

The current version of the MIB Broadcast Stream Spec can be
found on the Computing Working Docs web page:

http://www.aoc.nrao.edu/evla/techdocs/computer/workdocs/index.shtml