DataContract

A data contract is a formal agreement that specifies the structure of data exchanged between distributed software components. It defines the data types, member names, and serialization rules used when messages are produced and consumed by a service or API. Data contracts are commonly used in service-oriented architectures, web services, and microservices to enable interoperable communication across different platforms and programming languages.

In practice, a data contract is implemented by marking data structures with serialization attributes and by enumerating the members that may be serialized. In the .NET framework, the DataContract and DataMember attributes mark a class and its fields or properties as part of the contract, with the DataContractSerializer handling the serialization. A data contract can also specify optional and required members, order, and whether default values should be emitted, aiding compatibility across versions.

Versioning is a central concern, since clients and services may evolve independently. Data contracts support version tolerance through mechanisms such as replacing members with new ones, providing KnownTypes for polymorphism, and avoiding breaking changes like renaming serialized members. Best practices include maintaining a stable external name for members, using default values, and accommodating forward and backward compatibility.

Data contracts contrast with implementation contracts, which describe internal class structure rather than serialized form. They also relate to other contract-based approaches, such as OpenAPI for REST APIs or protocol-specific schemas like Protocol Buffers and gRPC. A well-defined data contract improves interoperability, testability, and client generation, at the cost of additional annotation and careful version management.