Changes

The changes ("chg") schema defines the serialized form identifying which objects have been created, updated or deleted as the result of invoking an action or editing a property. It also captures a number of other metrics counts (number of objects loaded, number of object properties modified), useful for profiling.

An instance of the DTO (corresponding to this schema) is used within the ExecutionSubscriber SPI, identifying changed objects that are to be published (as per @DomainObject#publishing() or equivalent).

changesDto

The changesDto root element is defined as:

<xs:schema targetNamespace="http://isis.apache.org/schema/chg"                                  (1)
           elementFormDefault="qualified"
           xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns="http://isis.apache.org/schema/chg"
           xmlns:com="http://isis.apache.org/schema/common">

    <xs:import namespace="http://isis.apache.org/schema/common"                                 (2)
               schemaLocation="../common/common-1.0.xsd"/>

    <xs:element name="changesDto">                                                              (3)
        <xs:complexType>
            <xs:sequence>
                <xs:element name="majorVersion" type="xs:string"                                (4)
                            minOccurs="0" maxOccurs="1" default="1"/>
                <xs:element name="minorVersion" type="xs:string"
                            minOccurs="0" maxOccurs="1" default="0"/>

                <xs:element name="transactionId" type="xs:string"/>                             (5)
                <xs:element name="sequence" type="xs:int"/>                                     (6)
                <xs:element name="completedAt" type="xs:dateTime" minOccurs="0" maxOccurs="1"/> (7)
                <xs:element name="user" type="xs:string"/>                                      (8)
                <xs:element name="objects" type="objectsDto"/>                                  (9)
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    ...
</xs:schema>
1 the changes schema has a namespace URI of "http://isis.apache.org/schema/chg". Although URIs are not the same as URLs, you will find that the schemas are also downloadable from this location.
2 uses complex types defined in the "common" schema.
3 definition of the changesDto root element. The corresponding XML will use this as its top-level element.
4 each instance of this schema indicates the version of the schema it is compatible with (following semantic versioning)
5 unique identifier for the transaction in which this interaction is being executed. The transaction Id is used to correlate back to the command that represented the intention to perform this execution, as well as to the interaction that executes said command.
6 uniquely identifies this set of changes within the interaction. Can be combined with transactionId to create a unique identifier (across all other changed object events and also any interaction executions) of this particular set of changed objects.
7 the date/time that the transaction that dirtied this objects completed
8 the user that executed the (top-level) action invocation/property edit.
9 identifies the objects that have changed.

The ChangesDto DTO corresponding to the changesDto root element can be marshalled to/from XML using the ChangesDtoUtils class.

objectsDto

The objectsDto complex type actually identifies the objects created, updated or deleted. It also captures additional metrics counters:

<xs:schema targetNamespace="http://isis.apache.org/schema/chg" ... >
    ...
    <xs:complexType name="objectsDto">
        <xs:sequence>
            <xs:element name="loaded" type="xs:int"/>                                           (1)
            <xs:element name="created" type="com:oidsDto"/>                                     (2)
            <xs:element name="updated" type="com:oidsDto"/>
            <xs:element name="deleted" type="com:oidsDto"/>
            <xs:element name="propertiesModified" type="xs:int"/>                               (3)
        </xs:sequence>
    </xs:complexType>
</xs:schema>
1 the number of objects that were loaded, in total, by the interaction.
2 the identities of the objects that were, respectively, created, updated or deleted within the transaction.
3 the number of objects' properties changed, in total, by the interaction.

The interaction schema also provides metrics on the number of objects loaded/changed, but is more granular, each figure relating to a single (sub-)execution within an interaction.