What is a data contract in API-based data exchange and what elements does it typically include?

• A. Describes the network topology and routing rules between services.
• B. Defines the shape and constraints of data exchanged: field names, types, required/optional, formats, validation rules, and error semantics.
• C. Lists the available API endpoints and their URLs only.
• D. Represents a legal agreement detailing service levels and penalties.

Answer: (B)

A data contract in API-based data exchange defines what data will be exchanged and how it is structured. It lays out the shape of the payload: the field names and their data types, which fields are required versus optional, the formats to use (such as specific date or string patterns), and the validation rules that data must satisfy. It also specifies how errors are represented and communicated when data doesn’t meet those constraints. This contract gives both producer and consumer a shared, machine-checked understanding of what to send and what to expect, enabling reliable validation, client generation, and safe evolution over time. In practice, you’ll often see data contracts expressed through schemas or interface definitions in formats like JSON Schema, OpenAPI, Protocol Buffers, or Avro. The other items describe where data travels or legal terms, not the data’s structure and constraints, so they don’t define the data contract.