Re: Control System Data Access API

[Claude Saunders <saunders@aps.anl.gov>]

I'm of the opinion that a device layer needs to be a separate namespace 
entirely, not just aliasing within the same (CA) namespace (for the same 
reasons Ralph raised). That's not to say it still can't be a part of CA 
server, or a separate gateway. Aliasing within the same namespace is 
mainly useful for protecting applications from changing underlying 
implementations (as in the set of linked records to provide a single 
value).  We have such aliasing now with the gateway.

Secondly, I think one of the big benefits of a "device layer" is the 
ability to bring to bear other resources such as a relational database. 
So an atomic write to a [particular device].setpoint would actually wind 
up kicking off a write to data access and a relational database (for 
whatever reason).

Of course, what I'm suggesting is more complicated .... :)

   - Claude

Ralph Lange wrote:

> Hmm...
>
> You're mixing granularity levels: Nowadays every PV name that doesn't 
> contain a dot is regarded as a record name.
>
> So, when you're aliasing [particular_device].Setpoint to 
> [particular_record].VAL any generic or display tool will soon start 
> asking for things like [particular_device].Setpoint.EGU .RTYP .DRVH 
> .DRVL .STAT .SEVR and so on and so on.
>
> Do you want to create explicit alias definitions for all (pseudo) 
> fields of that (pseudo) device record? You will end up with zillions 
> of alias definitions on a single IOC.
>
> If you try to escape by aliasing only on the same (record) level, you 
> don't gain as much. Simply having other names for records just creates 
> ambiguity - which of the many names for the same record do you use for 
> archiving? For snapshots? For the alarms? How do you compare snapshots 
> that contain the same record under different names?
>
> Guess this needs more thought - maybe too simple?!
>
> Ralph
>
>
> Marty Kraimer wrote:
>
> > If I read this correctly it is just asking for the CA server to 
> > support aliases.
> >
> > Marty
> >
> > nda@aps.anl.gov wrote:
> >
> > > Hmmm, a clever and simple idea.
> > >
> > >   Ned