We should probably make sure that the difference for storage and logging is clear; storing is only for operational use, and requires quick lookups of subject identifiers. Logging is what should be used for data analysis, and requires an append-only / stream to write to, e.g. a log file, or Kafka, or an insert-only database table.

It's technically possible to run an experiment without any storage defined (although this comes with several drawbacks), but logging is required in order to analyze the results. We may want to rename "log" to "audit trail", because that name shows the importance of the log better.