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

Subject: RE: dataAccess
From: Jeff Hill <johill@lanl.gov>
To: 'Marty Kraimer' <mrk@aps.anl.gov>
Cc: 'Benjamin Franksen' <benjamin.franksen@bessy.de>, 'Andrew Johnson' <anj@aps.anl.gov>, 'Bob Dalesio' <ldalesio@lanl.gov>, 'Ralph Lange' <Ralph.Lange@mail.bessy.de>, 'Eric Norum' <norume@aps.anl.gov>, 'Ken Evans' <evans@aps.anl.gov>, 'Ned Arnold' <nda@aps.anl.gov>, 'Matej Sekoranja' <matej.sekoranja@ijs.si>
Date: Fri, 25 Feb 2005 14:26:21 -0700
> 
> In the tutorial "dataViewer" is used in several places. I think
> you mean propertyViewer.

That pure virtual base is currently called "dataViewer", but I
agree that "propertyViewer" is probably a better name matching
well with what the intended use is. Ditto for dataManipulator =>
propertyManipulator. 

I suppose one could go further with this approach to naming. One
could change the name of the library to "property access". I will
need to think about that. The name dataAccess was originally
Ralph's so it will be necessary to hear his thoughts.

> 
> I can see how almost everything in the da*.h files could be
> described in Java (unsigned is one exception). 

This will be a problem only when properties cross over a Java
versus C/C++ boundary. In that situation the support libraries
will need to return an error when conversion is out of range for
the primitive types on either side of the fence. 

> Everyplace where dataAccess uses multiple inheritance, 
> the classes are equivalent to Java interfaces. 

Multiple inheritance occur in only one of the interface classes -
in pure virtual base class (PVB) daString. The daString interface
publicly inherits from PVB classes streamPosition, streamWrite,
and streamRead.

I did this because I wanted users to pass only one argument when
passing a string. I am definately open to alternatives. Perhaps a
very simple handle class that maintains internally private
references to daString, streamPosition, streamWrite, and
streamRead. To avoid overhead, there could be a complete set of
inline functions in this handle class for the member functions in
each of the interfaces.

Your alternative suggestions are enthusiastically solicited.

> If we go with the V4 DBD idea of struct and array, 
> utilities like dbToStructH,etc, could generate a
> header file AND code that uses dataAccess to get/put the struct
> fields.

This occurred to me also, and this might work, but many details
still need to be considered.

Jeff



> In fact it looks easy to create an equivalent set of Java
classes
> and
> interfaces for what appears in da*.h. Of course, this is not
> the
> implementation but only the user interface.
> 
> I can also see how  record/device support could be written in C
> instead
> of C++ and dataAccess could still be used by iocCore supplied
> libraries
> to transport data into and out of records. If we go with the V4
> DBD idea
> of struct and array, utilities like dbToStructH,etc, could
> generate a
> header file AND code that uses dataAccess to get/put the struct
> fields.
> 
> We still have lots to think about in order to implement the
> Functional
> Requirements for V4. If we decide to use dataAccess it is only
> part of
> what is required.
> 
> Marty




References:
dataAccess Marty Kraimer

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