What's new in 4.2.0
The most recent release of DDLm was version 4.1.0 on Jan 13th, 2023. Below is a summary of significant additions since then. A full list of changes is available here.
Improving default values
In previous versions of DDLm, attributes in ENUMERATION_DEFAULT were used to provide a table of default values. The particular row of this table to use is chosen using the value of the data name given in _enumeration.def_index_id to find the matching row in the default value table. For example, a missing value for the atomic type of an atom is obtained by using the value of _atom_site.symbol to index into the enumeration_default table provided in the definition of _atom_type.atomic_number.
However, this scheme allows only a single data file value to be used to index. This causes problems for looking up neutron scattering lengths, which depend on both atomic number and atomic weight. Therefore, a new category ENUMERATION_DEFAULTS has been added to DDLm, working in exactly the same way as the previous category, except
that _enumeration.def_index_ids is a list of data names whose values should match one of those in _enumeration_defaults.index. The previous category is deprecated.
Note that the current CIF core dictionary has been updated to use the new scheme and the old values removed. Software which uses the old indexing method to obtain missing values will not function correctly.
The ENUMERATION_SOURCE category has also been added to document the source of default value tables.
Authorship
Attributes in new category DICTIONARY_AUTHOR have been provided to record contributions to dictionaries, and have been designated Recommended in the DICTIONARY_VALID loop. In keeping with this, a list of authors has been added to the dictionary.
Units
Units may be unspecified where they are not available in the standard list of units.
URIs and IRIs
IRIs are essentially URIs that can include unicode characters. This release adds the IRI type, and now URI and IRI types can be used to distinguish between "reference" and "absolute" types to aid in validation. URI or IRI references have type Uri-ref/Iri-ref, whereas URI and IRI are absolute.
DOI
The dictionary's DOI may now be given in _dictionary.doi, and is a Recommended attribute.
Licensing
A dictionary's licence in SPDX format can be provided using the _dictionary.licence attribute. The licence for the DDL dictionary
has been set to CC-BY-4.0.
Many clarifications
See the detailed changelog above for the many definition clarifications added since 4.1.0.