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Re: Permitting new physical units?

  • To: Multiple recipients of list <coredmg@iucr.org>
  • Subject: Re: Permitting new physical units?
  • From: John Westbrook <jwest@ndbdev.RUTGERS.EDU>
  • Date: Mon, 2 Mar 1998 14:49:06 GMT

I wonder if there may be a simpler way to achieve a solution
to the problem that keeps all of the information required 
to construct a data item name within the given definition.
In the example that Syd has presented, the new DDL attribute
_units_construct can be expanded into the set of allowed 
strings which define the permitted units for a the given
data item.  Although it is not stated in the new DDL definition,
I assume that any one of these strings can then be used as a suffix
to the root data item name producing a complete data item name
including the specification of units.    

The same result could be obtained by permitting the item units
DDL attribute to assume multiple values (be of type 'list') and
then extending the rule for forming data item names to include
the possible appending of one of units attributes to the data
item name.   The units_default attribute would indicate the
default case, and the units which are used in the event no
units suffix is added to the data item name. 

Since it has been a design goal of DDL1.x to localise, as much
as possible, the attributes of a definition within the definition
data block, I think that the above solution is more DDL1 friendly
if unit information is to be added only in the form of suffixes to 
data item names.

If on the other hand, you would want to be more creative in 
the construction of data item names, where unit information might
be embedded anywhere within the data item name, then you
would certainly have to move in the direction of the 
regex syntax that Syd has proposed.   If this is the 
case, then I think that the _units_construct DDL definition should
be modified to define the construction for entire data item
name, rather than the just the portion dealing with units.


  John Westbrook                                   
  Rutgers, The State University of New Jersey      
  Department of Chemistry                          
  610 Taylor Road                                  
  Piscataway, NJ 08854-8087      
  e-mail: jwest@ndb.rutgers.edu                    
  Ph:  (732) 445-4290  Fax: (732) 445-4320         

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