The general CPPA 3.0 extensibility approach is to exploit substitution
groups, while preserving the complex type structures of version 2 cpp or cpa
instances
When using substitution groups, the alternatives must have a
type that is a subtype of the substitutable element’s type (the
“substitution group head’s type”)
One design impact of this constraint when applied to
refactoring an old schema is that the original version 2 element can be made a
subtype of the actual substitution group head’s type. Then the head
element can have a type that allows both the old element and the new element to
be in the same substitution group. Following this procedure gives us greater
flexibility for the extension points created version 3.0 schema.
So, the following alternatives are proposed to accommodate
ActionContext2 to track the choreographic context of a reference in a
BusinessTransactionActivity to a BusinessTransaction pattern.
The point for ActionContext extensibility is currently
within the ActionBindingType or FlatActionBindingType
So for the old ActionBindingType we have in the content
model the extension point “ActionContextHead” [ActionContextHead is
actually declared abstract and cannot occur in a valid instance. Only elements
in the substitution group of ActionContextHead (that satisfy the subtype
constraints) can occur in an instance. The two non-abstract elements in the
substitution group are named “ActionContext” and
“ActionContext2”]
(Diagrams from Oxygen)
So, ActionContext retains its version 2 type.
while ActionContext2 is tentatively
Aside from the differences in attributes, note that the
CollaborationLevelHead has been introduced as an extension point within
ActionContext2. Note that at the moment the schema does not alter ActionContext
to permit substitution group extensions.
The CollaborationLevel element (in the substitution group of
CollaborationLevelHead) is used to track “nesting” arising from
reuse of BusinessCollaborations (using the CollaborationActivity element) or to
track nesting (of the BTA) arising from use of
ComplexBusinessTransactionActivities.
At each level, at present, only the name of the BusinessCollaboration
or the ComplexBusinessTransactionActivity is recorded as a trace of the
nesting.
First question for the TC: should we add any more information to the
level?
Final question for the TC: is the use of the role attribute value
(in ActionContext2) now sufficient to capture the role value in the context of
the BTA’s Performs assignment?
There are also some minor other issues that might come up depending on
how the first two questions are resolved. For example, should we put
CollaborationActivity into a substitution group with CollaborationLevel (and
then allowing them to be mixed in the track of the nesting?)