Service Oriented Architectures Semantics, Processes, Agents

Based of Book by:(Munindar P. Singh, Michael N. Huhns)

Ben SnivelyEEL6938

Classroom: Eng I - 388 Class Hours: Tues, Thurs 10:30 - 11:45

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Outline

Breadth over SOA Technologies

Leveraging a SOA

Agents/Multi-agents

Agent integration into a SOA

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Service Oriented ArchitectureBreadth Overview

SOA is an Architectural Approach of Designing, Implementing, and Deploying Services.

So what’s a Service…

Services are Course Grain, Loosely Coupled, and Distributed components. More concrete definitions to follow…

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Services

Services must have a well defined interface. Understand parameters/complex types to the service.

Discoverable and Stateless entities. Find a Service that matches my need.

Shared Communication Models Understand how to call the service.

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Services

Producer (Service Implementation) and Consumer (Caller of the Service) interact the well-defined interfaces.

Hiding the Implementation.

Service becomes independent of Language, Platform, and Location.

Consumer Producer

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Service Review

Services are Course Grain Loosely Coupled Distributed Well Defined Interfaces Discoverable Shared communication Model

Independent of Implementation Standards Based.

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Services – Side note

Everything should not be made a service. Service explosion occurs

So what should be a service: Cost of doing job by client should be much greater

than the cost of calling service + service doing it. Why send a request to do 2+2, when overhead to

send the request is more than calculating result.

Re-usable components.

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Our Sample for Today - eBay

We’ll use eBay as an example that we can all relate to.

Candidates to be a Services: eBay Services

Bid Service – User Bid on Item Auction Item Search – User Search Auction Item Description – Pull Description

PayPal Services SendPayment – Send Payment

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Web Services

Web Services is NOT Web Pages. “Web” since it often operates over HTTP/HTTPS

Advantage: HTTP “naturally open” for firewall ports.

Type of Service Framework

Standardized ways for Communication (providing Shared Communication Model)

SOAP Interface Definition (providing Well Defined Interfaces)

WSDL – Web Service Definition Language Discovery

UDDI

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Web Service Model

Consumer Producer

Registry (UDDI)

1. Registers/Publisha Service (WSDL)2. Request Service

for requirement.

3. Invoke/Bindto Service

(SOAP)

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WSDL – Interface Definition

XML Document that defines Parameters to the Service

Parameters are sent in the form of ASCII XML. Binary sent either through:

Pointers Attachments BinaryASCII Encoding

Methods Location/Port of the Service

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Invoking the Service

Since it’s XML Document sent as the Message.

Sender responsible for transforming it’s data type into XML Called Marshalling

Receiver responsible for transforming the XML back into the data type Called Un/Demarshalling

Allows for heterogeneous environment (Java talking to C++, C, etc..)

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Services and Agents

ConsumerReactive

Agent

Often times:Distributed Services are implemented

using Distributed Reactive Agents(which need to be discovered/etc..)

ReactiveAgent

ReactiveAgent

SOAP SOAP

Sensor

Actions

KB

StrategyGoals

SOAP SOAP

Actuators

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Now What

We have all the course grain services – how do we get anything done.

Services become “Building Blocks” for doing complex tasks and processing.

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Achieving Business Goals

Processes execute series/parallel of services/agents.

Services used by multiple processes.

Manufacturing Example: Automobiles Companies share components between different

models (i.e. Engines, Frames, etc). Multiple “Assembly Lines” reuse these components

to product different products.

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Types of Processes

Orchestration Central composer organizes/controls flow and calls

Choreography Control is shared between participants, having

agreement ahead of time. Collaboration

Choreography, with ability to enter relationships, such as contracts and obligations. Participants become Business Partners.

Workflow Human-oriented tasks

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Process Example

eBay Example:

Automatic bid/purchase of auction item1. Bid X number of dollars

right before end of auction WS CALL2. IF (WON)

a) Complete eBay Checkout WS CALLb) Send PayPal Payment WS CALLc) Send Client notification of Won Item WS CALL

3. ELSEa) Send Client notification that Item not won. WS CALL

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Issues with SOA

Web Service pattern does not work – Discovery issue. Has become development time task of selecting

correct service.

Standard simply define the syntax and means to communication.

Missing semantics of the service, parameters, contracts – which are required for machine to understand service.

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Adding Semantics

Web Service Standards An XML Schema document gives us syntactic

details. Doesn’t identify the content represented by a

document. User Schemas allow multiple representations for the

same content Example: CustomerID and Customer_ID in two schemas

may refer to the same entity. RDF expresses the content itself, adding

meaning to the elements in the document.

OWL extends RDF to add richer meaning

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OWL – Web Ontology Language

includes Descriptions of classes Class properties Relationships between classes/instances Restrictions and Axioms

OWL is designed for use by applications that need to process the content of information instead of just presenting information to humans.*

(* from Wikipedia)

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OWL Entities and Relationships

rdfs:subClassOf

owl:equivalentClass

owl:disjointWith rdf:domain

owl:inverseOf

owl:equivalentProperty

rdfs:subPropertyOf

rdf:range

x

rdf:subPropertyOf

owl:equivalentProperty

owl:TransitiveProperty

owl:SymmetricProperty

owl:DatatypeProperty

rdf:Property

owl:ObjectProperty

owl:Class

rdfs:Class

rdfs:Datatype

owl:DataRange

owl:FunctionalProperty

owl:InverseFunctionalProperty

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OWL Inference

Information from different sources references the same object (URI) are automatically combined. We can declare

No Person can have more than one mother Mary is John’s mother Jane is John’s mother

Normal data constraints cause integrity violation

OWL reasoner infers Mary = Jane (John is referenced using ID/not Name)

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Combing SOA and OWL

Web Ontology Language – Services (OWL-S)

OWL-S Adds Semantics to the Web Service Framework,

extended it’s syntactical standards.

Allowing for service selection and understanding by Computers/Programs

Page 318

Goal: “MAKE WEB SERVICES AMBIGIOUSLY

INTERPRETABLE BY A COMPUTER/AGENT”

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OWL-S Explained

Describes Declarative Properties and Capabilities (for

Discovery) Declarative APIs Declarative Descriptions

Inputs, Outputs, Preconditions, Effects ** Used for Composition and Interoperation.

Allows systems to programmatically use services.

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OWL-S Service Ontology

Service function, applicability, quality of service, preconditions

communication protocol, message formats,

port numbers

use of service, semantic content of requests,

outcome conditions,SERVICE REALLY WHAT

MATCHES NEEDS

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Agents for Service Oriented Computing

Unlike Basic Services, agents Know about themselves, and could know

about their users and their competitors Use and reconcile ontologies or other forms

of Knowledge base Extends the simple stateless service.

Learn Are proactive (in some cases) Form commitments and communicate Can be cooperative

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Multi-Agent Systems

Tradational thought: 1 Server 1 Solution

Examples includes Services, Processes (which could be made up from other distributed services)

Collaboration Agents/Services Retain identity, but more explicitly interacts

with other services.

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Collaboration Agents/Services

They must Operate Asynchronously Allow choice between services Engage in negotiations Describable through declarative means

NOT PROCEDURAL.

WebSem WebSrvcAgentsMulti-Agents

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Combining Agents with Traditional Web Services

WebService Agent

Gateway

Web ServiceClient

SOAPRequest

SOAPResponse

Agent

ACLRequest

ACLInform

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Service Composition as Planning

Service composition solved implemented as an automatic planning problem:

States of the world (current and desired or goal) can be represented formally through Ontology and Knowledge structures.

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Actions

Actions are activated through Service calls – rather than actuators. OWL-S allows for the agent to quickly

Find Services Make sure they semantically implement what

need to get done Which define: Inputs, Outputs, Pre-conditions, Post-

conditions, and other characteristics of the service.

Actions could have reward functions/etc

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Planning

Plan becomes a set of services that are invoked. Called under suitable constraints of control and data

flow

Agent designs could be applied depending on situation. Could use:

MDP, POMDP, Rules-based, Case-based, BDI, etc…

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Two Patterns for Engineering Service Applications

Task1

Task2

Task3

Task4

Task5

Task6

Task7

WebService1 WebService2 WebServiceN. . .

Discovering, Matching, Planning, Composing

Repository/Directory of Services

Discovering, Matching, Planning, Composing

Goal

Subgoal

Subgoal

Subgoal

Subgoal

Subgoal

Subgoal

Subgoal

SubgoalSubgoal

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eBay Example

Deal-finder Agent Rather than saying – bid max on price on Item X, of type

Product Y.

Give me the best price on Product Y Start learning, acting, and re-acting it’s environment – through

the set of composite services. End up getting Product Y for a customer at the best price

available. Could build similar agent to buy, sell goods, with the

goals to make a profit and operate on their own. Get Auction Items would be used in both buying and selling

agents.

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Questions?

Questions?