Tracker: Ideas for future changes to data structure and metadata

[dgkuester-nist]

This is to track ideas for future breaking changes in the structure of saved data.

Output dataset field names

• if_headroom -> mixer_headroom (this better describes the meaning for a typical hardware architecture)

Input specification field names

• Sweep.options -> Sweep.flow (these all seem to configure the execution sequencing)

Structure

• Explore use of DataTree to clean up namespaces #81
• Redefine capture specs as containing both waveform and analysis specs #101