Support cross-agency identifier field such as for the California POST id

[nn35007]

It would be great if OpenOversight would support an additional identifier that allows tracking the same cop across multiple agencies, such as the California POST id. Maybe the identifier should be scoped to a particular state.

The California POST Commission is responsible for tracking certifications across most (but not all) law enforcement agencies in California. It issues a unique identifier, the POST id, to officers and tracks which agency an officer works for and their rank. This POST id is stable across rank changes and even POST member agencies, so if e.g. an officer transfers from LAPD to San Diego PD, or if they transition between full-time and reserve officer, their POST id remains the same. POST also is responsible for certifying and decertifying cops. Over 250,000 California officers across almost 800 agencies have a unique POST id.

California POST ids are strings, apparently of the format [A-Z][0-9]{2}-[A-Z][0-9]{2}, so for example B09-M46.

It would be great if users could query by this unique POST id across agencies, so e.g. list all entries for a certain POST id across all agencies (maybe of a certain state).

Many other states have POST agencies or equivalent bodies, but I am not familiar with any unique identifiers they may have or publish. It's not clear to me what identifiers the federal data bases (National Law Enforcement Accountability Database, National Law Enforcement Accountability Database) use, but their data isn't publicly accessible either way.

Ideally this identifier could be used to query the same officer across agencies — so e.g. "query all California POST agencies for the officer with California POST id B09-M46".

I have not dug in enough into the OpenOversight database model (this file, right?) to make an intelligent suggestion for how to implement this :-)