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

Subject: Re: Macro names
From: "Peregrine M. McGehee" <[email protected]>
To: Benjamin Franksen <[email protected]>
Cc: [email protected]
Date: Fri, 16 Aug 2002 16:22:42 -0600
Ben,

A fundamental issue we deal with is that even in the presence
of consistent and documented process variable naming conventions
the customers generally still insist on a higher-level device
access to the live and archived control system data.

There have been efforts in the past including the old
device library and layers such as CDEV although as far
as I know there is no device abstraction presently built
into the EPICS toolkit.

At Los Alamos we (in the context of the Spallation Neutron
Source project) are working on a Java-based device applications
layer [XAL] where the device structure is defined in a XML file.
Collaborative development is under way with the COSYLab folks
(Mark Plesko et al.) whose ABEANS framework is used on several
non-EPICS based facilities such as the Altacama Large Millimeter
Array (ALMA) project. 

We plan to use a XAL based layer to create device level 
applications for both live (Channel Access) and archived
(Channel Archiver - LibIO) data access at the Sloan 
Digital Sky Survey (an optical telescope) during the upcoming
(US) fiscal year.


Benjamin Franksen wrote:

> IMHO, the whole macro substitution mechanism is a conceptual mistake. It
> is a low-level approach (plain text substitution) on top of a structured
> and statically typed one (record instances and record types). All the
> widely known problems with database templates and macro substitution
> result from this. Generating higher levels of abstraction (typically
> device oriented) should build on top of the field, record and recordtype
> concepts, and therefore use high-level methods which preserve and extend
> the low-level (signal oriented) record database structure.
> 
> One important step to get there is the new link support which breaks up
> the monolithic one-string approach to device addressing and database
> links.
> 
> We need to replace the concept of database template file by some sort of
> meta-recordtype; and macro substitution by some sort of instantiation of
> these meta-recordtypes to meta-records. With structured (and
> compile-time checkable) renaming and aliasing of low-level features
> (fields) to meta-features.
> 
> Just my two pence.
> 
> Ben

- Peregrine
-- 
Peregrine M. McGehee    [email protected]      (505) 667-3273
Sloan Digital Sky Survey / Spallation Neutron Source
MS H820, Los Alamos National Laboratory, Los Alamos, NM 87545

References:
Macro names Andrew Johnson
Re: Macro names Benjamin Franksen

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