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COMCIFS / Powder_Dictionary

CIF definitions for powder diffraction
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Need a pd_diffractogram category #21

Closed jamesrhester closed 1 year ago

jamesrhester commented 1 year ago

Dependence of a piece of data on a particular diffractogram would normally be expressed in CIF by adding a child of some diffractogram identifier to the category containing that data. Currently pdCIF simply uses the block identifier as a proxy for the diffractogram identifier, with a system of block pointers linking particular data to particular diffractograms. There is no need to change this system. By adding a PD_DIFFRACTOGRAM category with identifier (and that identifier being made equivalent to the block_id) it will be possible to express the relationships between diffractograms and data in a way that is robust, plays well with other dictionaries, and is mathematically rigorous, while not changing the current "pointer" system

This will also allow various schemes for distributing powder data over data blocks to be formally described in terms of categories, with PD_DIFFRACTOGRAM corresponding to diffraction data just as PD_PHASE corresponds to phase.

jamesrhester commented 1 year ago

Just a note on the interaction between _pd_block.diffractogram_id and pd_meas/proc. _pd_block.diffractogram_id should point to data blocks containing a diffractogram. It is possible that this block could contain both a pd_meas loop of raw(ish) data, and a pd_proc loop of processed data (see example in IT Vol G 3.3.7.1). So both pd_meas and pd_proc should contain children of a notional pd_diffractogram.id.