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Re: Seattle Discussions

	Yves is right in saying that cif items may be given in any order. 
Even if an order is defined in CBF, there is no guarantee that the order
will be maintained once the header is written as a cif.  Equally, if the
header is prepared using cif software, there is no guarantee that the
order in which the information is entered will be preserved by the time
the cif is written into the cbf. 

	There are two strategies for dealiing with this.  Syd has a
program which extracts from a cif only those items that appear on a 
request list.  Syd's program fills in the data values (where
these exist in the file being read).  The output is a cif in which the
data items are included in the order requested by the user. 

	A second approach is to recognise that every data item has a
unique value which may or may not be given in the cif.  Each such item
which is relevant to a particular application will have a unique memory
location in the program.  Thus if _*_offset is included in the header, the
corresponding value will be written into its proper place in the memory,
similarly with _*_scaling.  The instruction _*_linearity will also be
stored as the header is read.  Thus by the time the program is ready to
process the image, the instruction will direct the program to look for the
two numeric values already stored.  There is no need for the program to
have read the _*_linearity instruction before storing the parameters.  The
program must have a memory location identified for any parameter it will
ever need. 

	Thus there does not seem to be any particularly difficult problem 
in the reading of the file, even when the data items are all scrambled

				David Brown


*****************************************************
Dr.I.D.Brown
Brockhouse Institute for Materials Research, 
McMaster University, Hamilton, Ontario, Canada
1-(905)-525-9140 ext 24710
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