Schemadefinition

SchemaDefinition is a formal specification that describes the structure, content, and constraints of data within a software system. It defines the shape of data objects, the permitted data types, the required and optional fields, and the rules that data must satisfy. By providing a machine-readable contract, a schema definition supports validation, interoperability, and change management across components and services.

Schemas are expressed in schema languages or formats appropriate to the domain. Common examples include JSON Schema for JSON data, XML Schema Definition (XSD) for XML, and SQL data definition language for relational databases. Other domains use interface or data-model definitions such as OpenAPI components, Avro, or Protobuf definitions. A typical schema specifies type constraints, allowed value sets, constraints like minimums or patterns, relationships between entities, defaults, and whether fields are required.

The primary purpose of a SchemaDefinition is to enable runtime validation of data, generation of documentation, and automated client or server code generation. They support data governance, versioning, and compatibility checks when schemas evolve. Validation is performed by schema-aware validators that enforce conformance and reject non-conforming data.

Lifecycle and evolution are central to SchemaDefinition. Schemas are usually versioned and may include migration rules or compatibility guarantees to preserve existing data. Deprecation and extension are common strategies for evolution, with tooling to map old data to new forms.

Example: a User schema may require id and email, allow name as a string, age as a non-negative integer, and status as an enumeration of 'active', 'inactive', or 'suspended'.