There's no single way to do this kind of verification. Different applications will have different 'roots of trust' for the authenticity of database data. For e

There's no single way to do this kind of verification. Different applications will have different 'roots of trust' for the authenticity of database data. For example, for Wikipedia, we could imagine the Wikipedia site serving the PIR themselves (they are already the entity you trust to decide what is on Wikipedia). A third party wishing to mirror Wikipedia over PIR might try to get some kind of digital signature over the contents of each article from Wikipedia or another trusted source. For blockchain queries, there are more technical solutions. For Bitcoin, for example, we could include a Merkle tree proof-of-inclusion for the transaction (a la BIP 37).