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Re: [ddlm-group] LOOP versus LIST

A list with lists nested to arbitrary depth can be a single data 
value either in a loop or just for a single tag.

DDL2 make no distinction between a one-element loop and the same unlooped
tag with the same value.  DDL1 (see _list) and DDLm (see 
_definition.class) try to make a distinctions among things that are 
and are not permitted to be looped.

I do not understand why it is desirable to make such a distinction for
a single row table, following the DDL2 approach of allowing it
to be handled as either

   _xxx.aaa data1
   _xxx.bbb data2
   _xxx.ccc data3

or

loop_
   _xxx.aaa
   _xxx.bbb
   _xxx.ccc

   data1  data2  data3

seem harmless to me, but DDL1 and DDLm make the distinction and a proper
parser should note violations of what was specified for the category.

An index key is not a name, but a string, so I think it reasonable to
accept the empty string as a table index value.

Case sensitivity is an interesting question.  I would prefer case sensitive
table indices, but I suppose that matter should be discussed.



At 12:41 PM -0500 1/5/10, Joe Krahn wrote:
>I assume that a list of items defined via a loop is distinct from a list
>of items defined by a list. Is that correct?
>
>Likewise, is a list of one item distinct from a scalar value?
>
>Currently, CIF files don't differentiate between a one-element loop and
>a scalar. For example, RCSB components.cif does not use loops for atom
>data when there is only one atom. Is this stated anywhere?
>
>Also, is an empty string a valid TABLE index? Other CIF names require at
>least one character, but my understanding is that a TABLE index is any
>valid string, which includes an empty string. Strings are also
>case-sensitive, so I assume that TABLE indices are also case-sensitive.
>
>Thanks,
>Joe Krahn
>_______________________________________________
>ddlm-group mailing list
>ddlm-group@iucr.org
>http://scripts.iucr.org/mailman/listinfo/ddlm-group


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