Re: PV Access

[Ben Franksen via Tech-talk <tech-talk at aps.anl.gov>]

Am 26.03.20 um 10:18 schrieb Ralph Lange via Tech-talk:
> The '{db:"record.VAL"}' definition appears in the *configuration* of the
> calc-Link.
>
> Every new link type (listed at the head of the referenced document) defines
> its own syntax for JSON configuration. The namespace for the keys in that
> configuration syntax is completely separate. The fact that the calc link
> understands a "db:" tag in its configuration does not mean that
> tag/functionality is available anywhere else, e.g. in the configuration of
> a different link type or at top level when configuring a field in a
> database record.

The documentation does not mention "db" as a valid JSON link type at
all. This keyword only appears in the example. At the same time, the
docs say:

args
A JSON list of up to 12 input arguments for the expression, which are
assigned to the inputs A, B, C, ... L. Each input argument may be either
a numeric literal or an embedded JSON link inside {} braces. [...]
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I guess the docs couldbe a bit clearer here. At least providing a
reference to where this "db" JSON link type is defined.

> All existing link types (DB/CA, numerical CONSTANT, hardware links from
> link.h) continue to work as before - otherwise introduction of the link
> support would have broken all existing applications and databases. (We're
> not *that* evil.)

A clean break would have been a possibility that I would hesitate to
call "evil", /if/ publicly anncounced and with a deprecation period. If
it had been deprecated in base-3.15, then I guess removing support for
such PV names in base-7.0 would be perfectly appropriate. The number of
affected users probably tends to zero anyway.

Just my 2 cents.

Cheers
Ben

________________________________

Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V.

Aufsichtsrat: Vorsitzender Dr. Volkmar Dietz, stv. Vorsitzende Dr. Jutta Koch-Unterseher
Geschäftsführung: Prof. Dr. Bernd Rech (Sprecher), Prof. Dr. Jan Lüning, Thomas Frederking

Sitz Berlin, AG Charlottenburg, 89 HRB 5583

Postadresse:
Hahn-Meitner-Platz 1
D-14109 Berlin

Attachment: pEpkey.asc
Description: application/pgp-keys