Web Service Architecture Part I- Overview and Models (based on W3C Working Group Note Frank Yung-Fong Tang System Architect Services Infrastructure, AOL

Roadmap Introduction Format Overview Relationships Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

What is 'Web Service'? Designed to support interoperable machine-to- machine interaction over a network. Has an interface described in a machine- processable format (specifically WSDL). Other systems interact with it in a manner prescribed by its description using SOAP messages Typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards

Key Standards for WS WSDL SOAP HTTP XML

Service / Agent / Messages Service- Abstract notion with interface definition. Agent- Concrete implementation of a service Message- Agent receive and send messages

Requester Provider

Requesters and Providers Requester Entity (person or organization) Requester Agent (software) Agree BOTH Semantics and Mechanics of the message exchange Messages  Provider Entity (person or organization) Provider Agent (software ) Agree BOTH Semantics and Mechanics of the message exchange  Messages

Semantics of Web Service Shared expectation about the behavior of the service Response to the messages that are sent to it "Contract" Purpose & Consequences of the Interaction How and Why of the interaction Maybe explicit or implicit, oral or written, machine processable or human oriented, legal or informal.

Overview of Engaging a Web Service

Roadmap Introduction Format Overview Relationships Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

Concepts & Relationships Concepts- Noun-like things Relationships- Verb-like things Associations between concepts ConceptA predicate conceptB Ex: "An agent" IS a B, "A message" HAS C Concept Maps- informal & graphical way to illustrate key concepts and relationships

Models and Conformance Models- larger scale meta-concepts Coherent subset of architecture on particular aspect Conformance Web Services Architecture conformance is imprecise than language specifications or protocol specifications.

Roadmap Introduction Format Overview Relationships Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

Relationships Is A Describes Has A Owns Realized Contains

Roadmap Introduction Format Overview Relationship Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

Architectural Models

Message Oriented Model Focus on messages, message structure, message transport Agent: sends & received messages Message HAS Message headers Message body

Service Oriented Model A service is implemented by an agent, and used by another agent Services are mediated by message exchange between provider agent and requester agent Meta-data (Description)- document the aspect of the service

Resource Oriented Model

Policy Model Focus on constraints on the behavior of agents and services Policies are about resources Policies are apply to agents that may attempt to access those resources Policies are established by people May represent security, QoS Management, application concerns.

Roadmap Introduction Format Overview Relationship Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

Message Oriented Model (simplified)

Message Oriented Model (complete)

Message Oriented Model- 1/5 Address Delivery Policy Message May be part of a "message sequence" May be described by a "service description language" Message Body Is contained by the "message envelope" Is application-specific content

Message Oriented Model- 2/5 Message Correlation Association of a "message" with a "context" Maybe realized by including message identifiers Message Envelope

Message Oriented Model- 3/5 Message Exchange Pattern (MEP) Should have a unique identifier Realize "message correlation" May describe a "service invocation" MPE <= Choreography Message Header Message Receiver

Message Oriented Model- 4/5 Message Reliability Maybe realized by a combination of message ack and correlation Maybe realized by transport mechanism Message Sender Message Sequence

Message Oriented Model- 5/5 Message Transport Has zero or more "capabilities" Is constrained by various delivery "policies" Must know sufficient "adderss" information

Roadmap Introduction Format Overview Relationship Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

Service Oriented Model (simplified)

Service Oriented Model (complete)

Service Oriented Model- 1/8 Action May result in a desired "goal state" Maybe the sending of message Maybe the processing of receiving messages Agent

Service Oriented Model- 2/8 Choreography Define the pattern of possible interaction between agents Maybe expressed in "a choreography description language" Defines the relationship between exchanged message and tasks of a service. Differ from orchestration- how one web service invokes other web services for a particular function

Service Oriented Model- 3/8 Capability Has a identifier Has a description of its semantics Goal State Desirable state of service / resources Provider Agent Provider Entity

Service Oriented Model- 4/8 Requester Agent Requester Entity Service Has a service description Has a service interface Has service semantics Has one or more service roles May have one ore more policies

Service Oriented Model- 5/8 Service Description Is a machine-processable description of a "service" Is a machine-processable description of a "service's interface" Contains a machine-processable description of the "messages" that are exchanged by the "service" May include a description of the "service's semantics"

Service Oriented Model- 6/8 Service Interface Defines the messages relevant to the service Service Intermediary Is a web service that transform messages in a value-added way Service Role Is a set of "service tasks"

Service Oriented Model- 7/8 Service Semantics Is the contract between the provider and requester concerning the effects and requirements to the use of a service Describes the "intended effects" Should be identified in a "service description"

Service Oriented Model- 8/8 Service Task Is an action or combination of actions Is associated with one or more intended "goal states"

Roadmap Introduction Format Overview Relationship Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

Resource Oriented Model (simplified)

Resource Oriented Model (complete)

Resource Oriented Model- 1/3 Discovery Is the act of locating a "resource description" Involves matching a set of functional and other criteria with a set of resource description May be realized by using a "discovery service" Discovery Service Is a service Is used to publish "description" Is used to search for "resource description"

Resource Oriented Model- 2/3 Identifier Should be realized by a URI Identifies a resource Representation Is a data objects that reflect the state of a resource. A resource may have a representation

Resource Oriented Model- 3/3 Resource Maybe governed by zero or more "policies" Resource Description Contains the "resource identifier" May reference a "policies" May reference the "semantics" applicable to the resource.

Roadmap Introduction Format Overview Relationship Overview of Architectural Models Message Oriented Model Service Oriented Model Resource Oriented Model Policy Model

Policy Model (simplified)

Policy Model (complete)

Policy Model- 1/5 Audit Guard Is a policy guard May monitor one or more resources May monitor actions relative to one or more services May determine if an agent's obligation have been discharged

Policy Model- 2/5 Domain Is a collection of agents and/or resources Defines the scope of application of one or more policies Obligation Is a kind of policy May require an agent to perform one ore more actions May require an agent or service to be in one ore more allowable states May be discharged by the performance of an action or other event

Policy Model- 3/5 Permission Is a type of policy May enable one or more action May enable one or more allowable states Permission Guard Is a policy guard Is a mechanism that enforces permission policies May control one ore more resources Enable actions relative to one or more services

Policy Model- 4/5 Person or Organization May own an agent May belong to a domain May establish policies governing resources that they own. Policy Is a constraint May have an identifier May be described in a policy description May define a capability

Policy Model- 5/5 Policy Description Describes a policy Policy Guard

What is NEXT? Part II- Web Services Technologies