WS Choreography v.0-1
Overview
This is work-in-progress
David Burdett, Commerce One
18 June 2003
Topics
 Feature Overview
 XML Structures
 What’s missing
 Issues
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Feature Overview
Features
 Reusability
 A choreography definition is reusable in different contexts with
different software and different message formats
 State Driven
 Processes or organizations that take part in choreographies
maintain their state in the choreography
 Cooperative Organizations
 Describes how independent organizations or processes
cooperate
 Verifiable
 Choreography definition can be used to verify that a
Choreography is being followed correctly (How not yet defined)
 Multi-Party
 The specification allows Choreography Definitions with any
number of organizations or processes involved
 Modular
 An "import" facility allows separately define components to be
imported
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Reusability
 Roles
 Describes the type of a process/organization behavior e.g. a
Buyer or a Seller
 States
 Identifies the point within a choreography a Role has reached
e.g. a Buyer State could be OrderSent after sending an Order
 Interactions
 Communicating information from one Role to another for a
reason. e.g sending an Order to request a purchase of goods
 Message Families
 The set of messages that serve the same or similar purpose. e.g
a RosettaNet Order, a UBL Order, an EDI Order, are all the same
 Processes
 Occurs as a result of some event such as a change of State
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Why Reusability is important
Big Co ($$$$$)
1. Work my way or you
don’t get my business!
5. Big Co doesn’t realize the benefits
of automation as they can’t extend all
the way down the supply chain
2. OK
Medium Co ($$$)
3. Work Big Co’s way or
we can’t do business!
4. STOP!!!!
I can’t afford to implement all these
ways. I’ll just continue with fax!
Small Co ($)
3a. Work Bigger Co’s way
or we can’t do business!
Medium Co 2
3b. Work even Bigger Co’s way
or we can’t do business!
Medium Co 3
3c. Work Mega Co’s way or
we can’t do business!
Medium Co 4
Developing reusable ways of doing business* that are based on common standards
are a pre-requisite to bringing smaller businesses into widespread eCommerce
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*Choreography definitions are just one of the essential parts!
State Driven
Buyer
New Order
Created
Seller
Order
Sent
Send Order
Order
Received
Check Order
Order
Checked OK
Order Error
Message Checked
Process Order
Error
Order Error
Received
Legend
Interaction
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State
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Process
Send Order Error
Order Error
Sent
Order Checked
Rejected
Order Checked
Error
Interactions, Reliable Messaging
and Signals
The Choreography definition
defines just the messages that
cause the state to change …
Buyer
Seller
Interaction
Order
Sent
Reliable
Messaging
Signals
Send Order
Reliable Messaging Ack.
Message Checked OK
Message Processing Started
Message Processing Complete
… the other messages are
implementation dependent
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Order
Received
Check Order
Cooperative Organizations
Private
Process
… but they both have
to agree how they will
cooperate …
Private
Process
Buyer
Seller
xxx
New Order
Created
Order
Sent
Send Order
Check
Order
Received
Order
Order
Checked
OK
xxx
Order Checked
Rejected
xxx
xxx
xxx
Order Error
Message Checked
Process
Order Error
Order Error
Received
The Buyer can’t
control what the Seller
does and vice versa …
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Send Order Error
Order Error
Sent
Order Checked
Error
… which means they must have
a shared understanding of what
each will do!
Checking Choreography Progress
Buyer
Choreography
Definition
Shared Common
Choreography Definition
Seller
Choreography
Definition
State Errors
ERP
Record
State
Order
Sent
Send Order
Order
Received
ERP
State
DB
State
DB
Check
State
State Errors
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Check
State
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Order Error
Received
Send Order Error
Order Error
Sent
Record
State
Other Features
 Multi-Party Choreographies
 Any number of roles can take part
 One definition for all roles – makes sharing easier
 Importing Definitions
 Allows reusability of individual definitions, e.g. messages, roles,
etc
 Extending Choreography Definitions
 Allows one Choreography to extend another … perhaps should
be composition instead!
 Choreography Dependencies
 Once choreography can only execute after another, e.g. You can
only query the state of a choreography if there is another
choreography instance to query
 Semantic Definitions
 Two ways of defining semantics: in the XML, or at a URL
 Multi-lingual
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XML Structures
Note all attributes are required unless
stated as optional
Choreography
Definitions
in multiple
languages
Import definitions from other
files (works like WSDL)
Define the roles
involved
Define the
Message Families
Define the
Interactions
The same definitions
can be reused in
multiple choreographies
Define one or more
Choreography
Definitions
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Choreography XML
Default language for
content of Description
elements
<Choreography defaultLanguage="us-en" xmlns="..."
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
...
</Choreography>
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Description XML
Optional. If present, overrides default language for
content
Optional. If present is
URL of more detailed
readable specification
<Description language="en-uk"
ref="http://www.example.com/ChorSpecs/en-uk/OrderManagement.htm">
This section contains a set of choreographies for Order Management
</Description>
Semantic definitions
Description elements can always occur
zero or more times. Each occurrence
must be for a different language
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Import XML
<Import namespace="http://example.com/chor/OrderManagement/Roles"
location="http://example.com/chor/OrderManagement/Roles"/>
Import works in the same way as a
WSDL Import
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Role & State
A Role may have one or more states
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Role & State XML
A Role name must be
unique within a
choreography file
<Role name="Seller">
<Description>This role represents the seller of goods or services
</Description>
<State name="OrderReceived"/>
<State name="OrderCheckedOK"/>
States can also have a
...
Description (not shown)
</Role>
State names must also
be unique within a
choreography file
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Message Family
Message Family name
must be unique within a
choreography file
URN uniquely identifies the
Message Family
<MessageFamily name="Order"
urn="http://example.com/MessageFamilies/OrderManagement/Order">
<Description>Messages in this family contain information to convey
a request to purchase goods or services
</Description>
</MessageFamily>
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Interaction Definitions
Sending
Role
The name of the
Interaction
Receiving
Role
What’s
being sent
<InteractionDef name="SendOrder"
fromRole="Buyer" toRole="Seller" messageFamily="Order">
<Description>Send the order From the Buyer to the Seller
</Description>
<InteractionEndStates
fromState="OrderSent" toState="OrderReceived"/>
</InteractionDef>
State of the sending
role after the
message is sent
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State of the receiving
role after the
message is received
Interaction End States
Receiving
Role
Sending
Role
Buyer
New Order
Created
Order
Sent
From
State
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Seller
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Send Order
Order
Received
Check Order
To
State
Choreography Definition
Allows one Choreography
Definition to be the extension
of another
Declares a Choreography can
only be followed if another
choreography has been
followed first
Identifies the states that
indicate the start and end of a
choreography
Defines the usage of
an interaction
Interactions and
processes can occur
in any order
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Defines a process
Choreography Definition (XML)
Unique name
Unique URN
<ChoreographyDefinition name="OrderManagementChoreography1"
urn="http://example.com/choreographies/OrderManagement1">
<Description>A simple Order Management Choreography that includes
the sending of an order from a Buyer to a Seller and the Seller
returning an error if a problem is found.
</Description>
List of start and
end states
<StartEndStates>
...
List of Interactions
</StartEndStates>
and Processes in
<Interaction ... />
any order
<Process ... />
...
</ChoreographyDefinition>
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Start End States
A state that indicates
the start of the
choreography
A state that may be a
last state for a Role in
the choreography
A state that is a
last state for a Role
in the choreography
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Start End States exampleThere is one Start state, but each Role
must have one or more end states
Start
State
Conditional
End State
Buyer
New Order
Created
Order
Sent
End
State
Seller
Order
Received
Send Order
End
State
Order Error
Message Checked
Process Order
Error
Order Error
Received
Check Order
Order
Checked OK
Order Error
Sent
Send Order Error
End
State
Order Checked
Rejected
Order Checked
Error
End
State
<StartEndStates>
<Start state="NewOrderCreated"/>
<ConditionalEnd state="OrderSent"/>
If the Seller finds no problems with the
<End state="OrderCheckedOK"/>
Order, then OrderSent is the Buyer’s
<End state="OrderCheckedRejected"/>
final state. But if problems are found
<End state="OrderErrorSent"/>
then OrderErrorMessageChecked is
<End state="OrderErrorMessageChecked"/>
the Buyer’s final state
</StartEndStates>
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Interactions and Processes
A Boolean expression of
states that must be true for
the Interaction to occur
A Boolean expression of
states that must be true for
the Process to occur
A list of the possible end
states for a process
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Interaction and Process XML
Buyer
New Order
Created
Seller
Order
Sent
Send Order
Order
Received
Check Order
Order
Checked OK
Order Checked
Rejected
Reference to
Interaction Definition
<Interaction name="SendOrder">
<Description>Send the order to the seller</Description>
<PreCondition condition="NewOrderCreated"/>
Role that executes
</Interaction>
the process
<Process name="CheckOrder" role="Seller">
<Description>The seller checks the order.</Description>
<PreCondition condition="OrderReceived"/>
<ProcessEndState state="OrderCheckedOK"/>
<ProcessEndState state="OrderCheckedRejected"/>
<ProcessEndState state="OrderCheckedError"/>
</Process>
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Order Checked
Error
Complete Choreography Example
<ChoreographyDefinition name="OrderManagementChoreography1" urn=“...">
<Description>In this Choreography Definition, a Buyer sends an Order to a Seller. The Seller returns
an Error Message, if the Order cannot be processed</Description>
<StartEndStates>
<Start state="NewOrderCreated"/>
<ConditionalEnd state="OrderSent"/>
<End state="OrderCheckedOK"/>
<End state="OrderCheckedRejected"/>
<End state="OrderErrorSent"/>
<End state="OrderErrorMessageChecked"/>
</StartEndStates>
<Interaction name="SendOrder">
<Description>Send the order to the seller</Description>
<PreCondition condition="NewOrderCreated"/>
</Interaction>
<Process name="CheckOrder" role="Seller">
<Description>The seller checks the order.</Description>
<PreCondition condition="OrderReceived"/>
<ProcessEndState state="OrderCheckedOK"/>
<ProcessEndState state="OrderCheckedRejected"/>
<ProcessEndState state="OrderCheckedError"/>
</Process>
<Interaction name="SendOrderError">
<Description>The order was in error - send an error</Description>
<PreCondition condition="OrderCheckedError"/>
</Interaction>
<Process name="ProcessOrderErrorMessage" role="Buyer">
<Description>Buyer Processes Order Error Message</Description>
<PreCondition condition="OrderErrorReceived"/>
<ProcessEndState state="OrderErrorMessageChecked"/>
</Process>
</ChoreographyDefinition>
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What’s Missing from the spec
 Choreography Bindings to WSDL and SOAP
 Handling errors
 e.g. Message (document) errors, Process timeouts, transmission
errors, etc
 Composing new choreographies out of existing
choreographies
 Relationships to Reliable Messaging, signals and other
protocols such as BTP and WS Transaction
 How Imports work
 Detailed schema validation rules, e.g. interdependencies
 Guidance on how to do run-time checks that a
choreography is being correctly followed
 Inquiring on another role’s choreography state
 Recovering from a failure of the choreography
… this list is definitely not complete …
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Issues
 Import
 Should also allow imports of process definitions
 Handling name conflicts between imports
 Roles & States
 “name” attributes are “ID’s”, should probably make
them unique just within their scope
 Roles should also be identified by a URI
 Processes
 Should be independently defined and importable
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