Starting model coordinates should link out to standard mmCIF files.

[tomgoddard]

Currently IHM starting model coordinates are in the ihm_starting_model_coord table. This is a redundant representation of atomic model coordinates usually represented by the mmCIF atom_site table. Important information such as secondary structure is not available when representing coordinates with this special redundant table. Also software capable of reading the atom_site table can't easily be reused on this table because of the different name and all the missing associated mmCIF tables (such as secondary structure).

It seems more sensible to have the IHM file contain a starting model table that links out to mmCIF atomic model files, rather than trying to duplicate that information in the IHM file.

[jdwestbrook]

Having the starting coordinate information well integrated into the data model
is an feature both for using the specification as a working format and in the
data processing, validation and analysis operations that may be performed
downstream. The starting coordinate category is fully integrated with the
definition of the molecular system of the IHM.

The provenance of the starting coordinates is separately important and is
also captured along with mapping information to integrate these data.
If it is more convenient for your application to process this data remotely
then this option is available to you. For other use cases, accessing and transforming
the remote data may be not be desirable or possible.

As the specification supports both access patterns, this seems complimentary
rather than redundant.

[brindakv]

Update from Feb 23, 2017 meeting: Starting model files compliant with the PDBx/mmCIF dictionary can be made mandatory at deposition (either deposited in the PDB or the Model Archive or linked via a DOI) so that these are available for all I/H models and can be used by Chimera and other visualization software. The ihm_starting_model_coord category is an archive requirement and can be populated by the archive from these external objects.