understanding information in ios photos.sqlite database

I'm trying to make sense of a sqlite database. Does anyone have a cheat sheet for what the following column names mean, and what the values mean?

Z_PK = Primary Key. Is this the name of the file?
Z_ENT = ?
Z_OPT = ?
ZISAVAILABLE = Seems self explanatory
ZISLOCALLYAVAILABLE = Whats the difference between this and ZISAVAILABLE?
ZTYPE = ?
ZCLOUDMASTER = ?

I have searched google and can't find anything that really answers my questions.

Thanks