I can see depricating an item in an approved dictionary. DDLm has
not been approved and it is clear that the xref section cannot be
meaningfully used in its present form. Anyone using the posted draft
dictionary must understand that changes will be made and that any
development work done using this dictionary may be nonconforming.
The need to avoid dataname duplication is a red herring. We are
redefining items in the draft database, thus effectively using the same
name to refer to a value with different attributes from those in the
original draft.
But it is not worth getting too hung up on this. Deprecating an item
that has never been used does no harm, but it clutters up the
dictionary unnecessarily and unless we arrange for the item to self
destruct after five years, it will remain forever. So let's make sure
we get the concepts and code correct for the things that matter.
David
Herbert J. Bernstein wrote:
Dear Colleagues,
There are two very distinct sets of issues in David's
message:
1. The management of specification changes in the DDLm
dictionary; and
2. The issues of the particular change being considered
here.
Let me address only the first issue here: the management
of specification changes in the DDLm dictionary.
Both John B. and David seem uncomfortable with the idea of
deprecation rather than abrupt removal of a feature or
definition. I refer you to the wikipedia article on
deprecation at
http://en.wikipedia.org/wiki/Deprecation
and quote the first paragraph:
"In computer software or authoring programs standards and
documentation, the term deprecation is applied to software features
that are superseded and should be avoided. Although deprecated features
remain in the current version, their use may raise warning messages
recommending alternative practices, and deprecation may indicate that
the feature will be removed in the future. Features are
deprecatedrather than being removedin order to provide backward
compatibility and give programmers who have used the feature time to
bring their code into compliance with the new standard."
In standards work, the approach has changed over time. At the time
of Fortran 77, ANSI did not permit deprecation, only removal of
a feature. Now ANSI not only permits deprecation, must, at least for
software standards, it is the norm for the reasons stated in the
wikipedia.
Thus the real question is whether there is enough invested in
the items being removed to justify retaining them for a while
in deprecated form. We have no way of knowing. DDLm has been
posted on the IUCr web site since 2007. We have no way of
knowing who has seen it and started code development based on
it. The prudent thing to do, whether we deprecate or remove,
or add a feature is to call attention to the change. We can
and should do that in separate change documents, but it also
helps to put the warning directly in the DDLm dictionary itself.
If we simply remove a deprecated item, we lose a very convenient
place to put that notice.
There is also the issue of never duplicating tags. Especially
while DDLm is in this developmental state, there is the risk,
if we remove a tag completely, that we will reintroduce it
later with the same name, but a different meaning -- causing
unnecessry confusion.
So, what I suggest is that we follow the following discipline:
1. If we are removing an item, that we retain that item
in the dictionary for at least 5 years with one of the
following notations:
***DEPRECATED ITEM DO NOT USE
RETAINED FOR REFERENCE ONLY***
***DEPRECATED ITEM DO NOT USE
FOR NEW DEVELOPMENT WORK
RETAINED ONLY TO SUPPORT
EXISTING CODE AND DATA****
2. That all deprecated items be gathered
into a segregated section of any relevant
dictionary.
3. When a deprecated item is finally removed
from a dictionary, that a record be kept in
a separate deprecated items dictionary to
ensure against reuse of the deprecated
tag with a conflicting meaning.
Regards,
Herbert
=====================================================
Herbert J. Bernstein, Professor of Computer Science
Dowling College, Kramer Science Center, KSC 121
Idle Hour Blvd, Oakdale, NY, 11769
+1-631-244-3035
yaya@dowling.edu
=====================================================
On Mon, 31 Jan 2011, David Brown wrote:
Not having done any programming for many
years and not being familiar with
the current jargon, I find keeping up with the rapid-fire discussion on
_aliases requires some effort on my part and the discussion has usually
move on before I havc a chance to comment.
However, being incommunicado on weekends, I took Herbert's draft home
where
I could sit down without distraction and see what eactly what was
proposed. The errors and ambiguities in the draft did not help me get
my
heasd around the proposal, but I made some progress, and here are my
comments. First the general comments, then particular comments
interleaved
in the draft.
1. _identifier_set: What does this set identify? The _id seems to
flag
arbitrary groups aliases. 'alias_set' would be a better name for this
category, or even just 'set'. What's in a name? It sets certain
switches
in the brain, and if these are misset by the dataname, it may take a
lot of
work to get them reset. Not conducive to instant communication.
2. Why do we need both _alias and _alias_identifier_set categories?
They
have indentical information (if the datanames (Syd's word) or tags
(Herbert's word) are any indication). I suppose (though this is no
where
spelled out) that _identifier_set would have its own save frame in the
dictionary and would not be an attfibute of a datanmae. If this is a
correct interpretation it would provide a place whare all the alias
datanames in the dictionary could be listed within a single loop).
This
seems redundant, but I cannot speak from programming experience. If
alias_identifier_set does not appesr in its own save_ frame, how does
it
differ from 'alias'?
3. If my supposition in 2. is correct, we would appear to have a
problem.
We will now have a variety of flavours of CIF dictionaries, each
expressing
a particular programmer's preferences for grouping the aliases. This
will
make no difference to the CIFs themselves as these groupings are
irrelevant
once a CIF has been written, but if, for example, I am given a program
written by Herbert and different program written by either of the
Johns, I
might need a different mmCIF dictionary for each of these two programs,
dictionaries that differ only in the way the aliases are gouped. When
I
load my CIF it cannot give instructions on which dictionary to call up
because is will have no knowledge of the idiosyncrasies of the program
I
have chosen to use. A possible solution would be to use the _import
feature to create a virtual dictioanry at run time. Thus the
_identifier_set information would be held in a local dictionary that
would
be imported into the authorised CIF dictioanry at run time. However,
there
are limitations on what can be imported. The _identifier_set category
could be imported but it would be impossible to import the
_identifier_set_id into the alias loop by this mechanism. Since I am
not
sure that I understand how Herbert intends to use this feature, I do
not
feel competent to suggest a way in which this problem could be
handled.
Having programs that used different dialects of CIF dictionaries does
not
seem to be in line with the traditional development of CIF,
particularly
for a feature that is unlikely to be much used, even if they do not
affect
the CIFs themselves. We should think carefully about the implications
of
this move.
4. My detailed comments follow the feature they comment on below:
save_definition.xref_code
_definition.id '_definition.xref_code'
_definition.update 2011-01-26
_definition.class Attribute
_description.text
;
Code identifying the equivalent definition in the dictionary
referenced by the DICTIONARY_XREF attributes.
Use of _definition.xref_code is deprecated in favor of
use of _alias.xref_code
;
_name.category_id definition
_name.object_id xref_code
_type.purpose Identify
_type.container Single
_type.contents Code
save_
This item is deprecated. It should be deleted. The alias and xref
iitems have never been tested and it is clear from the current DDLm
that
thay are placeholders that are awaiting development. If there are any
programs that make use of the items they can only have been written by
members of this group. The current xref defintiions inadequate and
unworkable. .The is no excuse for leaving this item in if we don't need
it.
save_ALIAS
_definition.id alias
_definition.scope Category
_definition.class List
_definition.update 2011-01-26
_description.text
;
The attributes used to specify the aliased names of
definitions.
Every tag has an implicit alias to itself with a null
_alias.xref_code to allow use of the primary tag in
the ALIAS_IDENTIFIER_SET category.
The use of _alias.identifier_set_id in the key of
this catgeory is provide a placeholder for the
to conform the key of the parent ALIAS category
to the key of the child ALIAS_IDENTIFIER_SET
for automatic joins. It is not intended that
_alias.identifier_set_id should be used in the
ALIAS category when no join is being done.
This last paragraph would be easier to undestand if all the words were
present and the sentences grammatical.. In any case it should appear
under
_alias,identifierr_set, not here. If I am right in thinking alias is
an
attribute and alias_identifier_set is not, how does one join a
non-attribute to an attribute?
;
_category.parent_id ddl_attr
_category_key.primitive ['_alias.definition_id',
'_alias.xref_code',
'_alias.identifier_set_id']
save_
save_alias.definition_id
_definition.id '_alias.definition_id'
_definition.class Attribute
_definition.update 2006-11-16
_description.text
;
Identifier tag of an aliased definition.
;
_name.category_id alias
_name.object_id definition_id
_type.purpose Key
_type.container Single
_type.contents Tag
save_
save_alias.deprecated
_definition.id '_alias.deprecated'
_definition.class Attribute
_definition.update 2006-11-16
_description.text
;
Specifies whether use of the alias is deprecated
;
_name.category_id alias
_name.object_id definition_id
.object_id should be the second part of the _definition.id, i.e.,
'deprecated'. This needs correcting in many places.
_type.purpose STATE
_type.container Single
_type.contents YesorNo
_enumeration.default No
save_
save_alias.dictionary_uri
_definition.id '_alias.dictionary_uri'
_definition.update 2011-01-26
_definition.class Attribute
_description.text
;
Dictionary URI in which the aliased definition belongs.
_alias.dictionary_uri is deprecated in favor if
_alias.xref_code
;
_name.category_id alias
_name.object_id dictionary_uri
_type.purpose Identify
_type.container Single
_type.contents Uri
save_
This item should be moved to the _dictionary_xref category. The
xref.id
is sufficient link. Again, the fact that it may appear in the draft
dictionaries should not prevent it being deleted in DDLm since the
draft
dictionaries are just drafts and will be chaniged once we have sorted
out
how to do the aliases.
save_alias.identifier_set_id
_definition.id '_alias.identifier_set.id'
_definition.class Attribute
_definition.update 2011-01-26
_description.text
;
A code identifying an identifier_set of related tags.
This linked item is provided in the ALIAS category to
ensure that the key of the ALIAS category is
conformed to the key of the ALIAS_IDENTIFIER_SET
category. The alias has not been joined with
ALIAS_IDENTIFIER_SET, _alias.identifier_set_id
it is not intended that _alias.identifier_set_id
in the ALIAS category.
I cannot make much sense of the last sentence. Perhaps there are
missing
words?
This is a pointer to _identifier_set.id
;
_name.category_id alias
_name.object_id code
See above. 'code' is not the proper .object_id
_name.linked_item_id '_identifier_set.id'
_type.purpose Key
_type.container Single
_type.contents Code
_enumeration.default .
save_
save_alias.xref_code
_definition.id '_alias.xref_code'
_definition.update 2011-01-26
_definition.class Attribute
_description.text
;
Code identifying the dictionary containing the primary
definition of the dictionary as given in the
DICTIONARY_XREF category.
;
_name.category_id definition
_name.object_id xref_code
_name.linked_item_id '_dictionary_xref.code'
_type.purpose Key
_type.container Single
_type.contents Code
save_
save_IDENTIFIER_SET
_definition.id identifier_set
_definition.scope Category
_definition.class List
_definition.update 2011-01-27
;
Data items used to describe the identifier_set identifiers
used in this dictionary. Data items in this category
are NOT used directly as attributes of individual data items.
See linked item _alias_identifier_set.identifier_set_id
for such uses.
;
_category.parent_id ddl_attr
_category_key.generic '_identifier_set.id'
save_
save_identifier_set.id
_definition.id '_identifier_set.id'
_definition.class Attribute
_definition.update 2011-01-27
_description.text
;
A code identifying an identifier_set of related tags.
The coverage of an identfier_set may conform precisely
to the set of tags in a particular dictionary,
or to tags drawn from multiple dictionaries or
to a subset of tags from a single dictionary.
The same tag may belong to multiple identifier
sets, and a given tag may not belong to any
identifier set, in which case the only associated
identifier set is a null value.
Presumably the second line should read 'need not belong to any'. The
wording above is ambiguous.
The last line should read 'identifier set id' and its default value
should
be given explicitly. What is nul?
Possible nul values are 'nul', '0', ' ', '?', '.', etc.
To help ensure that dictionaries can be merged,
each code should either begin with an IUCr-registered
prefix or, if not prefixed, have been approved
by COMCIFS. The special prefix 'local_' may be
use for purely internal purposes of an organization.
I assume these are not datanames that appear in the dictionaries but a
list
of COMCIFS enumerations, some of which might appear in a non-exclusive
enumeration list. What happens if someone chooses 'joeblow' as an id?
;
_name.category_id identifier_set
_name.object_id code
_type.purpose Key
_type.container Single
_type.contents Code
save_
save_identifier_set.description
_definition.id '_identifier_set.description'
_definition.class Attribute
_definition.update 2011-01-27
_description.text
;
A description of the identifier_set
;
_name.category_id identifier_set
_name.object_id code
_type.purpose Describe
_type.container Single
_type.contents Text
save_
save_ALIAS_IDENTIFIER_SET
_definition.id alias_identifier_set
_definition.scope Category
_definition.class List
_definition.update 2011-01-27
;
The attributes used to specify the identifier_set of
tags to which a given tag belong.
A given tag may belong to multiple identifier_sets
and may be cited against multiple dictionaries.
Note that _alias_identifier_set.identifier_set_id is a
component of the key of ALIAS_IDENTIFIER_SET. If the
denormalized join presentation is used to bring the object
ids of this child category up into the parent
ALIAS category, then _alias.identifier_set_id will
we used as an implicit addition to the key of
the denormalized ALIAS category.
Until DDLm can be formally revised to automatically
handle the necessary promotion of child catgeory keys
in denormalized joins, a place-holder
_alias.identifier_set_id has been defined in the
ALIAS catgeory.
;
_category.parent_id alias
_category.parent_join Yes
_category_key.primitive
['_alias_identifier_set.identifier_set_id',
'_alias_identifier_set.definition_id',
'_alias_identifier_set.xref_code']
save_
save_alias_identifier_set.definition_id
_definition.id '_alias_identifier_set.definition_id'
_definition.class Attribute
_definition.update 2011-01-27
_description.text
;
Together with _alias_identifier_set.xref_code, identifies
an alias belonging to an identifier_set. An alias may
belong to any number of identifier_sets, including zero.
;
_name.category_id alias_identifier_set
_name.object_id definition_id
_name.linked_item_id '_alias.definition_id'
_type.purpose Key
_type.container Single
_type.contents Tag
save_
save_alias_identifier_set.identifier_set_id
_definition.id '_alias_identifier_set.identifier_set_id'
_definition.class Attribute
_definition.update 2011-01-27
_description.text
;
Identifies an identifier_set to which the alias
identified by _alias_identifier_set.definition_id
and _alias_identifier_set.xref_code ) belongs.
A pointer to _identifier_set.id
;
_name.category_id alias_identifier_set
_name.object_id code
_name.linked_item_id '_identifier_set.id'
_type.purpose Key
_type.container Single
_type.contents Code
save_
save_alias_identifier_set.xref_code
_definition.id '_alias_identifier_set.xref_code'
_definition.class Attribute
_definition.update 2011-01-21
_description.text
;
A code identifying the actual dictionary,
virtual dictionary or other logical grouping
to which the identifier tag belongs.
What is this identifier tag - '.definiton_id' or '.definiton_set_id'?
;
_name.category_id alias_identifier_set
_name.object_id code
_name.linked_item_id '_dictionary_xref.code'
_type.purpose Key
_type.container Single
_type.contents Code
save_
We also need to refined the _dictionary_xref category. '.uri; should
be
added, '.format' should be better derfined or deleted. Perhaps
'.version'
should also be added. Definining the dictionaries is just as important
as
definiting the definition_sets
David
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