In libsecret a schema allows to define the structure of the attributes stored with a secret.

It also allows to request all the items of an app (if the schema ID is unique to the app), because it sets the xdg:schema attribute with the schema ID when the app is not sandboxed.

In Rust it could be a trait that allows to provide a struct instead of a HashMap for the attributes, by making the trait implementors provide conversion methods. There could even be a derive macro that implements the conversion for a simple struct.