Re: _item.mandatory_code can be undefined!

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• Previous message: Peter Keller: "_item.mandatory_code can be undefined!"

On Aug 9,  6:41pm, Peter Keller wrote:
> Subject: _item.mandatory_code can be undefined!
> Dear all,
>
> In DDL 2.1, _item.mandatory_code for _item.mandatory_code itself is 'no'
> (if you see what I mean). This means that _item.mandatory_code does not
> have to be specified for a dictionary item. But, if it isn't, there is no
> default value in the DDL to apply to the dictionary item! This makes no
> sense, if you think about it, because it is either necessary or
> unnecessary for an item to be determinable (implicitly or otherwise).
> There is no third possibility.
>
> By analogy with _category.mandatory_code, I guess that
> _item.mandatory_code for _item.mandatory_code should be 'yes' . An
> alternative, which is less likely to break anything, would be to add
>
>     _item_default.value   no
>
> to save__item.mandatory_code in the DDL.
>
> Regards, and sorry about the recursion,
> Peter.

There is some history to this issue which is related to providing compliance
to earlier dictionaries and CIFs.   It was agreed that in order to provide
an easier integration with older dictionaries that there be a placeholder
definition for every item in the mmCIF dictionary.  This really results
in a large number of essentially redundant definitions for data items
that are children of other items. In these cases only the definition of
the data item and perhaps the item name have been specified in the mmcif
dictionary. Placing a default value on the mandatory code would result
in conflicting definitions for this attribute as in almost all cases these
items are part of the key for the category in which they reside.  Rather
that load up all of the definitions with an additional mandatory code
attribute we have chosen to make this specification optional.  However,
you will note in the mmCIF dictionary that it is provided all data
items except in the case of redundant children.  This is not a problem
for the specification of this attribute in categories as there is
no redundancy in these definitions.

Regards..

John


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