This document discusses using protocols and Codables to build REST APIs in Swift. It introduces Encodable and Decodable protocols which allow objects to be encoded to and decoded from data. This enables sending objects over REST without serialization code. Commands define API requests and responses. ObjectType is a protocol for objects that can be saved and fetched. Extensions add saving and fetching methods. The SDK handles encoding/decoding and executing requests on a background queue for asynchronous access to APIs.