Defines the API that validator schema instances have to implement. Schema objects are results of parsing of input that defines validation rules; things like DTD files, W3c Schema input documents and so on. Schema instances can not be directly used for validation; they are blueprints for constructing such validator Objects. Because of this, they are also guaranteed to be thread-safe and reusable. One way to think of this is that schemas are actual validator factories instead of XMLValidationSchemaFactory instances.

One note about creation of validator instances: since the validation may be invoked from wide variety of contexts (from parser, from serializer, from processing pipeline etc), the validation context is abstracted as ValidationContext. Instances may make use of additional knowledge about actual implementing classes if they can safely determine the type runtime, but should gracefully handle the cases where the context is created by a caller that is not part of the same StAX implementation as the validator.