RE: [ebxml-bp] ActionItem 26 Nested Collaboration Logic Gap, first draft

["Dale Moberg" <dmoberg@cyclonecommerce.com>]

Discussion: OASIS.ebBP.WI26-NestedCollaborationsAndRoles;
Topic|Referring,Roles,Reusability;
Point|<Performs> BPSS-like content model for Performs

dwm@

BPSS usually seems to like using attributes for nonrepeating elements
when it can. So a more stylistically consistent Performs pattern might
be:

<Performs initiating="true" bindingBy="name" inScopeRole="A"
bindsToRole="Buyer"  />

Other attributes might be useful too in reworking this syntax, as we
proceed through the use cases. 

dwm@

In the following I assume we accept Martin Robert's proposals concerning
specializations of BusinessTransaction, and also some form of JJ
Dubray's proposal that the main containers (elements) for complex flow
control include BinaryCollaboration, MultipartyCollaboration, and
possibly CollaborationActivity. BinaryCollaborations and
MultipartyCollaborations can basically have very similar content models
in JJ's view, except that the number of "locally declared Roles" will
differ. I will be discussing "references" made to the above items [the
complex flow containers] and also references to the specialization
siblings of BusinessTransaction made in BTAs.

One of the difficulties that CPPA has had with aligning with BPSS is
that CPPA needs to pick out of BPSS the BusinessTransactions that a
given party will support, and also select from the global view of BPSS
the Role perspective of one participant (party) (for a CPP). The problem
is like finding a projection of 1-dimensional curves out of some
n-dimensional model, and is a little tricky. What CPPA intends to do is,
starting with some complex flow's entry point, trace a toplevel Role's
trajectory through all the referenced complex flows to the baseline
specializations of business transasction. What CPPA needs to do is to be
able to track the Role in one flow container/businesstransaction down to
the primitive collaboration patterns (Notification, RequestResponse, and
so forth). Ideally explicit (and _uniform_) syntactical constructs,
rather than implicit semantic conventions in the BPSS text, will mark
out the "connections" through the flow constructs so that implementers
can have a reasonably simple task to trace trajectories.

BPSS, on the other hand, rightly demands that the containers it defines
be reusable, and that different complex flows can refer to (and thereby
reuse) the same syntactical units (possibly flow containers themselves
but in the simple case, the specializations of BusinessTransaction). So
reusability and reference rightly go together. 

Now the problem has so far been that if we put Role trajectory
connections "in" a container, the container becomes far less reusable.
Hence there has been a tension between the design requirement from CPPA
for Role trajectories, and the design requirement from BPSS for
reusability. I think there is a resolution for these apparently
conflicting requirements that applies to all flow containers, and that
is _uniform_.

Here are the features of the proposed resolution:

1. There can be both "local" and "global" Role declarations. That is,
Role elements can occur at the toplevel and can also occur within
complex flow containers (current). The global Role elements are really
BusinessPartyType declarations that can get associated with a toplevel
flow starting container by being bound to its (local) Role values. For
uniformity, all bindings use Performs elements, so the content models at
various points will need to be expanded to allow sequences of Performs
elements. [Adding global Roles to indicate BusinessPartyTypes is
indicated by Anders recent model. It is actually an optional feature,
but one I like.)


2. The connection between Roles currently visible and those in a
referred to construct occurs where the reference is made using either
IDs or names. I think this design is, more or less, the way we currently
do it. But our current syntax is neither uniform nor does it generalize
to the MC case. Let me take some time to expand this with some unusual,
but possible use cases.

a. Suppose we want to reuse a JJ-style MC flow involving a
credit-approver, a seller, and a buyer. Suppose we want to reuse it from
a BC with a buyer and seller Role defined locally. We want the
localseller to bind to the MC seller, the local seller to the MC
credit-approver, and the local buyer to the referenced buyer. Three
Performs constructs within the BC's Transition element's content model
would accomplish assoiating local Roles with referenced Roles.
Reusability supported. If we need to indicate which is the initiating
Role, an attribute on Performs could mark that. [That allows the reused
MC container to not have a fixed initiating Role-- it always picks that
up from the Referencing context.]

b. Suppose we want to loop around a choice (XOR) over BTAs. Let the
Referencing context have two local roles, A and B, and the Referenced
BTA be in a context with two roles, counterProposer, proposalResponder.
To alternate A with B for the Role of counterProposer, we would just
alternate the Performs associations, viz., 

<Performs><Local>A</Local><Remote
initiating="true">counterProposer</Remote></Performs><Performs><Local>B<
/Local><Remote>proposalResponder</Remote></Performs> 

 with

<Performs><Local>B</Local><Remote
initiating="true">counterProposer</Remote></Performs><Performs><Local>A<
/Local><Remote>proposalResponder</Remote></Performs>.

c. As these examples illustrate, the formal analogy here is that of
actual parameters and formal parameters that are used to hook up a
function invocation with a function declaration. The locally "visible"
Roles are analogous to the actual parameters in the call, and the
declared Role values in a flow container declaration are analogous to
the formal parameters. IMO, it would be nice to have an attribute on
Performs called "bindingBy" with two values, "name" or "ID" That way we
would not need to have the repetitive attributes such as "fromRoleId"
and "fromRoleName" all the time. Also, the whole "fromRole" "toRole"
attribute apparatus would disappear in 2.0. These distinctions are
inherently limited to a "BinaryFlow" perspective, and don't generalize
well to Multiparty flow control. Also while initiating is an important
property, I would like to see it placed within the content-model of
Performs.

d. Different initiator flag (to accomodate Martin's different "entry"
mode use case) e. Distributor (Haugen/Fletcher style) cases. f. Yunker
multiparty cases

[I will try to do these other use cases if I get more time this
weekend.]

One implication of the above approach is that, for example, constructs
containing a forward reference (such as, BusinessTransactionActivity,
(OperationActivity if it is added), Transition, Start,
CollaborationActivity) will have content-models expressing Role
associations, which I have assumed to be provided by sequences of
Performs, the uniform Role connection construct. The Success and Failure
states also have references pointing back. I think we could probably use
Performs here also. I think it is a separate small point that needs
investigation though. How to mark the toplevel flow constructs (use a
Start state?) is another pending item. A final issue is whether we
should dispense with CollaborationActivity in Referencing
BinaryCollaborations. Minimally, I think CollaborationActivities should
allow me to feference either a MultipartyCollaboration or
BinaryCollaboration. I am not certain what is allowed at present.


@dwm

@dwm