Multiple 'Recorded' data items have evaluation methods

[vaitkus]

According to the DDLm/dREL specifications, data items that have the Recorded source cannot have Evaluation methods. This rule is not respected by the following data items:

• _diffrn_refln.index_m_1, ..., _diffrn_refln.index_m_8.
• _diffrn_reflns.limit_index_m_1_max, ..., _diffrn_reflns.limit_index_m_1_max.
• _diffrn_reflns.limit_index_m_1_min, ..., _diffrn_reflns.limit_index_m_1_min.
• _diffrn_standard_refln.index_m_1, ..., _diffrn_standard_refln.index_m_8.
• _exptl_crystal_face.index_m_1, ..., _exptl_crystal_face.index_m_8.
• _refln.index_m_1, ..., _refln.index_m_8.
• _reflns.limit_index_m_1_max, ..., _reflns.limit_index_m_8_max.
• _reflns.limit_index_m_1_min, ..., _reflns.limit_index_m_8_min.

The definition methods, however, do not actually do any complex calculations, but rather simply take a specific element from an equivalent list item, e.g. the method of _diffrn_refln.index_m_5 is:

       With  r  as  diffrn_refln

                   diffrn_refln.index_m_5  =  r.index_m_list [ 4 ]

Where _diffrn_refln.index_m_list data item is defined as a list of Recorded values.

Similar constructs can also be seen in the CIF_CORE dictionary, but in those cases, the scalar data items are defined as Recorded and have no Evaluation methods, while the List/Matrix/etc. data items are defined as Derived and with Evaluation methods that define them. For example, the _cell_measurement_refln.hkl data item is defined as Derived and has the following Evaluation method:

    With c  as  cell_measurement_refln

    _cell_measurement_refln.hkl = [c.index_h, c.index_k, c.index_l]

Should the CIF_CORE approach be adopted in this dictionary as well?

[vaitkus]

This issue was further discussed in PR COMCIFS/cif_core#561 and it was agreed that Evaluation methods should be allowed in cases where these methods simply transform the value into a different data structure or representation.

However, it would be good to agree if a similar approach should be adopted in other dictionaries as well. Codifying it in the dictionary design guidelines or somewhere similar might also be useful.