Guaranteeing Type Consistency in Collective Adaptive Systems.

Collective adaptive systems whose entities are loosely coupled by their exchange of complex data structures became a very common architecture for distributed web-based systems. As HTTP-based APIs transfer data as plain text, this exchange is very error prone: API changes and malicious data modifications may remain unnoticed. GraphQL addresses this concern at the server side with strong typing but leaves the clients untouched. In this paper we present an approach to align the type schemas provided by GraphQL and type definitions at the client side on three levels during the systems’ life cycles: At generation time by verifying queries against the GraphQL schema, at compile time by leveraging TypeScript’s type system, and at run time by using decoders to validate payloads. Key to our solution are a functional, type-safe domain-specific language for the definition of GraphQL queries and a corresponding generator implementation providing the GraphQL queries and TypeScript artefacts. Together they ensure that clients become aware of and are able to react to changes of the (evolving) GraphQL schema, a precondition for maintaining the consistency of the overall collective adaptive system. We will illustrate our approach along a popular GitHub-based, collaborative development scenario.