Experimental Physics and
Industrial Control System

[email protected] (Bill Lavender) · Thu, 14 Nov 1996 12:27:51 -0600 (CST)

> 
> Pete Jemian wrote:
> > 
> > Is there a field of a process variable that identifies what
> > type of record (maybe RTYP) the variable is?
> > 
> 
> sorry, no.
> 
[stuff deleted]
>
> While we feel that in general it is undesirable for high
> level general purpose tools to know what record they are 
> attached to, we also see that in many application specific
> situations it would be quite useful to have access to this 
> information. Perhaps we should add a new "record
> type name" data type to the database access level  (which
> I assume could only be fetched as a string). Client
> requests fetching this type against an old CA server 
> that does not support it would be refused.
> 
> Is there general interest in this change?
> 
> Jeff

You can put me down as one person who would definitely be interested
in such a change.  I am responsible for the software development on
three X-ray beamlines at the APS.  Of these, two of them are likely to
have a relatively unchanging set of equipment, but on the third beamline,
there is likely to be a constantly changing set of devices in the
experimental hutch as different experiments move in and out every few days.
In such an environment, having a way of double checking in the software 
that the device you are talking to is of the type you think it is would be
very desirable.  This is to try to help avoid situations where the
software thinks it is talking to a motor record (for example), but is
actually talking to some other kind of record.  On a system with a 
relatively unchanging set of equipment, this problem is relatively 
easy to avoid.  But if the equipment is changing several times a week,
this kind of mistake becomes almost inevitable.

Now we do have the DTYP field, but the information it gives is at too
low a level.  If I want to know the type of a record, generally I don't
want to know that it is an Oregon Microsystems VME58 stepping motor
controller, or some such.  Rather, I want to know whether the record
is just some kind of motor.  As it is, if I want to do any checking
of this sort with DTYP, I would have to keep my own private list of DTYPs
that correspond to motors, my own list of DTYPs corresponding to scalers,
and so forth.  I would rather be able to just query something like
an RTYP field and have it tell me that "yes, indeed, this is a motor".

Anyway, you can put this down as a big yes.

Bill Lavender
Illinois Institute of Technology
[email protected]
Phone: +1-312-567-5880,  Fax: +1-312-567-3576

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System