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[ddlm-group] Suggested clarification to DDLm attribute_import_details.mode

  • To: ddlm-group <ddlm-group@iucr.org>
  • Subject: [ddlm-group] Suggested clarification to DDLm attribute_import_details.mode
  • From: James Hester <jamesrhester@gmail.com>
  • Date: Thu, 3 Sep 2015 13:53:42 +1000
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Dear DDLm group,
I propose that the text of the definition for the_import_details.mode attribute is changed from:
====     Code identifying how a definition save frame is to be imported.     "Full" imports the entire definition frame including the leading            and trailing save statements.     "Contents" imports only the lines within the save frame.====
to
====    Code identifying how the definition referenced by_import_details.frame_id is to be imported.   "Full" imports the entire definition together with any childdefinitions (in the case of categories) found in the targetdictionary. The importing definition becomes the parent of theimported definition. As a special case, a 'Head' category importing a'Head' category is equivalent to importing all children of theimported 'Head' category as children of the importing 'Head' category.   "Contents" imports only the attributes found in the imported definition.====
Reasoning:
(1) We have agreed not to use nested save frames in DDLm, so thesemantic parenting and child assignment behaviour of the importingprocess must be explicitly described.When using nested save frames, the hierarchy of save frames foundinside an imported definition is implicitly included in the importingdefinition.(2) We should strive to avoid syntax-specific terminology ('saveframes') in DDLm, as DDLm can then function as a universal languagefor describing meaning regardless of file format.(3) (Head category special case): If a dictionary wishes to import allcategories of some base dictionary, an import statement for eachtop-level (i.e. child of the Head category) imported category must beplaced inside the importing dictionary's Head category.  As adictionary must logically have only one 'Head' category at the top ofthe category tree, it is never meaningful or useful to have theimported Head category as a child of the importing Head category.  Wecan therefore special case this situation as a shorthand for importingall categories of the base dictionary.
Notes:
(1) The demonstration DDLm dictionaries use _import.get only in'Contents' mode to import definition fragments, and have leftunresolved the issue of how to specify base dictionaries.  The aboveproposal fixes this while not requiring any correction to existinguses of _import.get.(2) Importing in 'Full' mode is currently the only way that add-ondictionaries (e.g. the magnetic CIF dictionary adding new definitionsto modulated structures dictionary) can identify the base dictionary.While human readers will presumably have indicators in the text, dRELsystems will rely on explicit importing in order to interpret andexecute dREL methods involving items from the base dictionary (mostimportantly, to find category keys).(3) The _import.get directive in 'Full' mode need not be interpretedas a requirement for dictionary processors to find and process allimported definitions, but rather as a description of the semanticspace in which the dictionary is located.  While dREL applicationswill (most likely) need to process all such directives, morerestricted uses (e.g. type validation) may ignore such imports.(4) _import.get 'Full' mode was historically used to assemble the coredictionary from parts (structure, experiment, diffraction, model etc.)with the top-level core dictionary consisting of series of imports andnot much else.  Such usage is still possible.
I welcome comments, and I will take the absence of comments asapproval of the proposal.
James.-- T +61 (02) 9717 9907F +61 (02) 9717 3145M +61 (04) 0249 4148_______________________________________________ddlm-group mailing listddlm-group@iucr.orghttp://mailman.iucr.org/cgi-bin/mailman/listinfo/ddlm-group

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