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<== Date ==> <== Thread ==>

Subject: RE: Querying PCAS
From: "Jeff Hill" <[email protected]>
To: "'Michele Joyce'" <[email protected]>, <[email protected]>
Date: Mon, 8 Nov 2004 10:44:21 -0700
> 
> Is there a way to querying portable channel access servers for the pv
> names that it contains? As well as information about that pv 
> (owner etc)

It is not currently possible to do this, although functionality of that
nature could be (probably should be) considered for a future release. I can
imagine a need to query a server for its PV names on demand and also can
imagine server initiated PV name update requests being sent to a directory
service when the server starts, or when new PVs are configured. 

It's probably also worth noting that a strong potential exists for the
permutated PV name space to be substantially inflated compared to the
configured name space. For example, in the EPICS process control database
users configure record names, but the permutated PV name space will of
course include all of the record names combined with all of the appropriate
field names. Additional name combinations occur when users find that a
relatively small number of PV alias names are efficient working shortcuts
for committee designed names, when transitioning in redesigned namespace
hierarchies, and even when working compromises are needed to resolve name
space design conflict stalemates (NAMF;). Therefore, there could be a
potentially large answer forthcoming to a "query for the PV names". The size
of the answer could of course be reduced if higher level applications become
dependent on the design of the name hierarchy. However, the name space
design could vary with the different types of data stores used in process
control, data acquisitions, etc. It might also vary between projects, within
project organizations, or within project upgrades. Therefore, the dependence
of high level applications on a particular design of the namespace
hierarchies would compromise their versatility, and should probably be
avoided. This probably implies that the high level application should either
rely only on a flat namespace, or else rely on a uniform interface to
externally provided services when traversing the name space hierarchy.

Jeff



References:
Querying PCAS Michele Joyce

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