= Schema

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Most applications need to integrate with other apps in the enterprise.
To facilitate such integration scenarios, Apache Causeway defines a number of standard XSD schemas:


* the xref:refguide:schema:mml.adoc[metamodel] schema, which allows the internal metamodel to be exported in a canonical fashion

* the xref:refguide:schema:cmd.adoc[command] schema, which captures the __intention__ of a user to invoke an action or edit a property

* the xref:refguide:schema:ixn.adoc[interaction execution] schema, which captures the actual execution of an action invocation/property edit

* the xref:refguide:schema:chg.adoc[changes] schema, which captures which objects have been created, updated or deleted as the result of an execution of an action invocation/property edit

These each use XSD types defined by the xref:refguide:schema:common.adoc[common schema] (most notably the `oidDto` complex type which identifies a domain object).

The xref:userguide:commandlog:about.adoc[Command Log] extension, xref:userguide:executionlog:about.adoc[Execution Log] and xref:userguide:executionoutbox:about.adoc[Execution Outbox] extensions all persist these objects, eg for auditing or integration purposes.

The sections below discuss these schemas in more detail.


