The most detailed description of graphd, the metaweb storage engine
“Giving every piece of data a fixed identity, is radically different from the relational model which deals only with sets of values and leaves the notion of identity up to the application. Working with identities as a first-class notion is essential if schema is to be flexible. Long before we can agree on the exact shape of the data used to represent a person or a building, we can agree that individual people or buildings exist and that they have certain obvious attributes that we might want to record: height, address, builder, etc.”