E-mail from Brad:

Conceptual definitions of tables:

observation: permanent attributes of a unit or area of observation, in particular geographic location. Can be areas or points. Contains one or more observationEvents.
observationEvent: a single sampling event at a particular place (observation) and time. Contains one or more taxonOccurrences.
observationMethod: set of methods used to make a taxonObservation. Can also be applied to entire observations (plot or subplot) or observationEvents. Unites criteria of size classe, growth form, strata, and sampling area used to include the taxonObservations (and hence to exclude others). We should consider having more method lookup tables linked to observationMethod (growth form criteria, for example), or take a more ontological approach and use sets of generic rules such as `inclusionCriterionName`, `inclusionCriterion`, `inclusionCriterionUnits`, etc. Let me know if you think this is already adequately modeled by current VegBIEN schema.