Imagine you're Amazon and you receive data from vendors. It's not enough to authenticate the sender, you still need to check that the payload is at least syntac

Imagine you're Amazon and you receive data from vendors. It's not enough to authenticate the sender, you still need to check that the payload is at least syntactically valid before starting to process it. You can write custom code, of course, but after writing lots of it you're likely to start naturally splitting it into a declarative part and a universal processor that checks incoming data against the declaration. It's harder to come up with a declarative way from the start, but it's a natural tendency, because declarative form is much simpler than procedural: declarations are data, and data are easier to understand than a process. This is what schema, transforms, and paths are: they're a declarative way to address these tasks in XML. It's natural there will be attempts to reinvent them for JSON.