Service-Oriented ComputingBasic Technologies

SOC and SOA

Service-oriented architecture (SOA) An architectural approach for software integration A coarse grained and loosely coupled approach Support better reuse and dynamic adaptivity More focused on software services

Web service A set of XML based standards defined to realize SOA

Service-oriented computing A more general concept than SOA, consider any form of services

Such as services provided by hardware devices or even human

Semantic web Theories and techniques to specify the web Can be applied to SOC for service specification and discovery

Basic Service Infrastructure

ServiceBroker

ServiceProvider

ServiceRequesto

r

Invocation(SOAP)

Discover(UDDI)

Publish (WSDL)

Registry

Web Service Stack (W3C)

Service Oriented Computing

Topics Service specification

Specifies the service and its I/O (WSDL) Is it sufficient?

Service publication and discovery Is UDDI based centralized approach sufficient?

Service composition and orchestration Specification of the composition and process (BPEL, OWL) Discovery and adaptation (allow interoperations) It is still a very challenging area

Service invocation Invocation protocol (SOAP) Is it sufficient? How about continuous interactions?

Service Oriented Computing

Topics Semantic web

Achieve better service specification, discovery and composition

Service mediation Solve mismatches (data, protocol, process) among the services in

different domains

Quality of service (QoS) How to specify QoS, how to satisfy QoS requirements, …?

Dependability and security issues WS-Security, WS-Trust, …

Service Invocation

SOAP (Simple Object Access Protocol) Designed on top of HTTP for remote procedure call or simply message

exchange

Include three parts Envelope: define the message to be a SOAP message Encoding rules: for expressing instances of application-defined

data types Body: information for the actual invocation and response

SOAP Request Example

POST /temp HTTP/1.1Host: www.socweather.comContent-Type: text/xml; charset="utf-8"Content-Length: xxxSOAPAction: "http://www.socweather.com/temp"

<?xml version=“1.0”?><env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/" env:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/> <env:Body> <m:GetTemp xmlns:m="http://www.socweather.com/temp.xsd"> <m:City>Honolulu</m:City> <m:When>now</m:When> </m:GetTemp> </env:Body></env:Envelope>

HTTP header followed by a mandatory blank line

Web service URL and method nameInput parameters

SOAP Response Example

HTTP/1.1 200 OKContent-Type: text/xml; charset="utf-8"Content-Length: xxxSOAPAction: "http://www.socweather.com/temp"

<?xml version="1.0"?><env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/" env:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/> <env:Body> <m:GetTempResponse

xmlns:m="http://www.socweather.com/temp.xsd"> <m:DegreesCelsius>30</m:DegreesCelsius> </m:GetTempResponse> </env:Body></env:Envelope>

Service Specification

WSDL Define transmission protocol, services, standard data type

definition file, etc. Define the service name and URL (service) Define all publicly available functions (operation) For each function, define all message requests and message

responses Example

<wsdl:service name="HelloWorldService"> <wsdl:port binding="impl:urn:HelloWorldSoapBinding"

name="urn:HelloWorld"> <wsdlsoap:address

location="http://localhost:8080/axis/services/urn:HelloWorld" />   </wsdl:port></wsdl:service> Define service name and location

Service Specification

<wsdl:portType name="HelloWorldService">

<wsdl:operation name="sayHello" parameterOrder="in0 in1">

  <wsdl:input message="impl:sayHelloRequest" name="sayHelloRequest" />

  <wsdl:output message="impl:sayHelloResponse" name="sayHelloResponse" />

  </wsdl:operation>

</wsdl:portType>

<wsdl:message name="sayHelloRequest">

  <wsdl:part name="in0" type="tns2:string" />

  <wsdl:part name="in1" type="tns2:string" />

  </wsdl:message>

<wsdl:message name="sayHelloResponse">

  <wsdl:part name="sayHelloReturn" type="tns2:string" />

  </wsdl:message>

Define functions and bind their request/response definitions

Define I/O parameters and types

Service Publishing and Discovery

Directory service in distributed systems (Name server) For distributed file systems Maintain the file names, their locations, …

UDDI Universal Description, Discovery, and Integration Provide directory service for web services It is a Web service itself (access to UDDI is SOAP based)

WSDL UDDI UDDI register information specified in WSDL

UDDI

UDDI registry Each entry is an XML document composed of:

businessEntity: A description of the organization that provides the service, can be a company, a group, a person, etc.

businessService: A list of all services offered by the business entityo Support projection: reference to services provided by other organizations

o Include name, description

o categoryBag: a list of business categories (e.g., which industry, which product category, which geographic region)

- Can be used to help search in terms of category

bindingTemplate: the specifications of the services being offeredo bindingKey, serviceKey, description

o accessPoint: the URL of the service being provided (actually can be anything, e.g., an e-mail address or even a phone number)

tModel (technical model)

UDDI

tModel A tModelis is a document with a short description of the technical

information and a pointer to the actual information It contains

A pointer to the

WSDL description Description of the

business protocol

and conversations tModelKey, Name, overviewDoc (URL) categoryBag …

UDDI

Business UDDI IBM, Microsoft, SAP, NTT has provided public UDDI registry

since 2000, and cumulated approximately 50,000 service entries But they discontinued in 2006

Problems with UDDI No semantic information

Can add OWL-S related specifications, but not completely compatible with the semantic information

No structure, difficult to imposed security constraints E.g., cannot support role based access (cannot map roles to entries)

No management protocols Difficult to maintain and evolve

AXIS

Remote procedure call From shared memory to message passing to RPC

Axis Support web service infrastructure

Tools to generate wrappers for client and server (same as RPC) Tools to generate WSDL from methods Web server

Network + DNS

Server-sideDriver

Method

Client-sideStub

Client

Web Server

AXIS

Problems Static binding, client invokes a fixed service

Some solutions Making URL a reference

Fixed function and syntax in the invocation Dynamically bind to the service with matching WSDL

Data flow model Output of one service is linked to input of another service

Which solution is preferable Any other possibilities?

Service Composition

BPEL A language for specifying business process based on Web services A standard for Web service composition by OASIS Specification of partner link

BPEL describe the business process The partner link links a node in the process to a Web service that can

be invokedo Partner Link Type

- The portTypeof the process and the portTypeof the service

o Partners: a group of Partner Links (this is an optional element)

- A partner link can only point to one partner

o Partner Link: the actual link to the service

Service Composition

BPEL Description of basic activities

<receive> allows the business process to do a blocking wait for a matching message to arrive.

<reply> allows the business process to send a message in reply to a message that was received through a <receive>

o <receive> and <reply> form a request-response operation for the composed process

<invoke> allows the business process to invoke a request-response operation offered by a service or process

<throw> generates a fault in the business process <wait> Insert a wait for a given time period or until a certain time

Service Composition

BPEL Specification of structured activities

<sequence>: an ordered sequence of activities <switch>: case-statement <while>: loop <pick>: execute one of several alternative paths <flow>: parallel steps

Semantic Web Service

Deficiencies in original web service framework WSDL only support syntactical description Service discovery capability is limited No support to automate service composition No specification of interaction with services

Semantic web Support specification of information that contains machine-

processable and machine-understandable semantics

Semantic web service Semantic web technology Semantic and QoS models for web services Mediation (WSMO)

Semantic Web Service

Semantic Web stack Language models

SWRL (Rules)

XML (Extensible Markup Language)

RDF (Resource Description Framework)

RDFS (RDF Schema)

OWL ([DLP], Light, DL, Full)

OWL-S (Services)

RDF

RDF (resource description framework) Data model

Resourceso Named by URI (universal resource identifier)

Propertieso Define characteristic of a resource

Value Example:

<rdf:Description rdf:about="http://www.w3schools.com">  <si:title>W3Schools</si:title>  <si:author>Jan Egil Refsnes</si:author>

</rdf:Description>

RDF statement (triple) Specifying facts using subject/predicate/object

RDF Schema

RDF Schema Defines new RDF vocabulary Light-weight ontology specification

RDF Schema example: rdfs:Class and rdfs:subClassOf

Specifying a class of resources and the class hierarchy

rdfs:Resource (all things in RDF are resources) All resources are an instances of “class”

rdfs:Literal Literal values such as strings and integers

rdfs:Property (is also an instance of rdfs:Class) rdfs:domain & rdfs:range

Define restrictions on the resources that have a given property (domain) and the set of valid values for that property (range)

RDF Schema

Reasoning Validation

Class

Property

Person

type

Fish

type

owns

type

WandaWendy

type

owns

range

domain

Person

Fish

type

type

Or, Wanda can be a person and a fish (a mermaid)

OWL

Web ontology language (OWL) Build on top of RDF and RDF Schema Add more vocabulary for describing

Relations between classes (e.g., disjointness) Cardinality (e.g., "exactly one") Equality Richer typing of properties Characteristics of properties (e g symmetry) Enumerated classes

OWL

OWL class can be constructed Explicitly By set operators

IntersectionOf, unionOf, complementOf Example

<owl:Class rdf:ID='SweetBread'>

<owl:intersectionOf rdf:parseType='Collection'>

<owl:Class rdf about '#Bread'/>

<owl:Class rdf:about='#SweetFood'/>

</owl:intersectionOf>

</owl:Class>

OWL

Restrictions A unique feature of description logics Key primitives

someValuesFrom a specified class allValuesFrom a specified class hasValue equal to a specified individual or data type minCardinality and maxCardinality

Examples<owl:Restriction>

<owl:onProperty rdf:resource="#hasFather"/>

<owl:maxCardinality rdf:datatype="xsd:nonNegativeInteger"> 1 </owl:maxCardinality>

</owl:Restriction>

<owl:Restriction>

<owl:onProperty rdf:resource='#bakes'/>

<owl:someValuesFrom rdf:resource='#Bread'/>

</owl:Restriction>

OWL

Axioms Common primitives

rdfs:subClassOf owl:equivalentClass

Example<ex:Country rdf:ID='Iran'/>

<ex:Country rdf:ID='Persia'>

<owl:sameAs rdf:resource='#Iran'/>

</ex:Country>

Inference Based on restrictions and/or axioms Statements from different documents about the same URI are

automatically conjoined

OWL-S

OWL for services An OWL ontology defined for (formally) describing properties

and capabilities of Web services

Upper ontology

OWL-S

Profile Capabilities description (functional properties)

Inputs, outputs, preconditions, effects May be a subset of process model IOPRs

Service descriptors (non-functional properties) Provenance Quality of Service

o Response time, quality guarantees, etc.

Security and policies Domain-specific characteristics

o E.g., geographical region, class of service

Some do not have adopted standards yet

OWL-S

OWL-S

Process Description of service behavior Interaction patterns (read/write messages)

Tells service user how and when to interact

Include Inputs, outputs, preconditions and effects (IOPE)

Can be Atomic processes or composite processes

Composition processes can be defined by Control flow Data flow

OWL-S

OWL-S

Process Description of service behavior Interaction patterns (read/write messages)

Tells service user how and when to interact

Include Inputs, outputs, preconditions and effects (IOPE)

Can be Atomic processes or composite processes

Composition processes can be defined by Control flow

o Loop, condition

o Sequence, choice, parallel

Data flow

OWL-S

Grounding Information for accessing the service

Message formatting, transport mechanisms, protocols, serializations of types

Builds upon WSDL

OWL-S

Added capabilities Define ontology-based specification frameworks for describing

Web Services and related aspects (Web Service Description Ontologies)

Support formal specification of the semantic behavior of the web services Facilitate composition

In service profile, pre-conditions and effects can be defined to specify the functional behavior of the service

Support the definition of service ontology Describe the relations among services

Define ontologies for underlying data models to allow machine supported data interpretation (Semantic Web)

WSMO - Web Service Modeling Ontology

OWL-S An ontology to describe Web services and data Facilitates composition, but does not specifically model it OWL-S is grounded in WSDL and it has been mapped into UDDI

WSMO Ontology based model for Web services, data, as well as

composition aspects Core elements: Ontologies, Web Services, Goals, Mediators Language for semantic element description (WSML) Reference implementation (WSMX) Popular in Europe

Mediation as a key element Every resource description is based on ontology Every data element interchanged is an ontology instance

WSMO

Goals Objectives that a client wants to achieve Clear separation of requester and provider Use ontological relationships & mediators to link goals to web

services, but there is no good solutions either

Goal specification Ontology based goal specification

Support goal ontology Can reuse an existing goal ontology or build on top of existing ones

Requested Capability (desired service functionality) Requested Interface

Describes communication behavior supported by the requester (Choreography)

Restrictions/preferences on orchestrations of Web services

WSMO

Mediation Resolve mismatches on data, service, and process

WSMO

Data mediation Solving terminological mismatches by ontology mapping,

merging, alignment

Functional mediation Solving functional mismatches between goals and/or web services Used during service discovery and semantic matchmaking

Exact, plug-in, subsumption, intersection, no-match

Process mediation Solving communication

mismatches

WSMO

OO Mediators Data level mediation, resolve mismatch terminologies

GG Mediators Data/Function/Process level mediation Goal does not involve the communication mechanisms

WG Mediators Match a Web Service to a Goal and resolve mismatches Data/Function/Process level mediation

WW Mediators: Enable interoperability of heterogeneous Web Services Data/Function/Process level mediation

OWL-S and WSMO

OWL-S Profile = WSMO capability + Goal + Non-functional properties OWL-S uses Profiles to express service capabilities and desired

capabilities WSMO separates provider (capabilities) and requester points of

view (goals)

OWL-S Process = WSMO Service Interfaces OWL-S Process model describes operations performed by Web

Service, including consumption as well as aggregation WSMO separates Choreography and Orchestration OWL-S formal semantics has been developed in different

frameworks such as Petri Nets and Pi-calculus WSMO service interface model with ASM-based formal semantics

OWL-S and WSMO

OWL-S Grounding is similar to WSMO Grounding Both map to WSDL WSMO also aims at an ontology-based grounding to avoid loss of

ontological descriptions throughout service usage process

Mediation External to OWL-S, performed in the orchestration process WSMO regards mediators as key conceptual elements

Support mediator reuse

Some Other Concepts

WSIF: Web Services Invocation Framework Similar to the tasks performed by Axis, but only for the client, and

involves binding as well as invocation Support dynamic binding and asynchronous invocation

WSCL: Web Services Conversation Language Defines the overall input and output message sequences of a web

service using a finite state machine over the message types WS-Coordination

Support the specification of a service whose job is to coordinate the activities of the Web services that are part of a business process

WS-Transaction Support transaction execution on composite services Support conventional transaction protocols, such as 2PL E.g., travel agent, airline, hotel together perform transactions

WSCL Example

<<ReceiveSend>>Registration

in: RegistrationRQout: RegistrationRS

<<ReceiveSend>>Login

in: LoginRQout:ValidLoginRS

out: invalidLoginRS

<<ReceiveSend>>CatalogInquiryin: CatalogRQout: CatalogRS

<<Send>>Shipping

out: ShippingInformation

<<ReceiveSend>>Logout

in: LogoutMessage

InvalidLoginRS

InvalidLoginRS

ValidLoginRS

<<ReceiveSend>>Quote

in: QuoteRQout: QuoteRS

InvalidPaymentRS

<<ReceiveSend>>Purchase

in: PurchaseRQout: PurchaseAcceptedRSout: InvalidPaymentsRS

out: OutOfStockRS

PurchaseAcceptedRS

OutOfStockRSInvalidPaymentRS

<Conversation name="StoreFrontServiceConversation" … <ConversationInteractions> <Interaction interactionType="ReceiveSend" id="Login"> <InboundXMLDocument id="LoginRQ"/>

hrefSchema=“http://conv1.org/LoginRQ.xsd” <OutboundXMLDocument id="ValidLoginRS"/>

hrefSchema=“http://conv1.org/ValidLoginRS.xsd” <OutboundXMLDocument id="InvalidLoginRS"

hrefSchema=“http://conv1.org/InvalidLoginRS.xsd”/> </Interaction> … <Interaction interactionType="Empty" id="Start" /> <Interaction interactionType="Empty" id="End" /> </ConversationInteractions> <ConversationTransitions> … <Transition> <SourceInteraction href="Login"/> <DestinationInteraction href="Registration"/> <SourceInteractionCondition href="InvalidLoginRS"/> </Transition> <Transition> <SourceInteraction href="Logout"/> <DestinationInteraction href="End"/> </Transition> </ConversationTransitions></Conversation>

WS-Coordination

A coordination service is an aggregation of three services: Registration: for parties to register with the coordinator Activation: to create an instance of a coordination context Coordination protocol: to define the specific protocol to be

followed

Coordinator

ActivationService

RegistrationService

ProtocolService X

ProtocolService Y

CreateCoordinationContext Register

Protocol YProtocol X

SOC

SOC Offers a new paradigm for system development and deployment Can integrate hardware/software/other services through the same

service composition concept and technologies But real-world system development is still a major challenge

How to integrate services into systems The technologies still remain in the syntactical level, semantic

information has not shown revolutionary contributions The foundation of discovery is specification Semantic technologies help better describe services But the actual specification technologies is still far from satisfactory

o E.g., how to properly specify the functionality of Linux (or differentiate it with Windows)

SOC

How to integrate services into systems Still the same old barrier: software component specification

In SE research, this has been investigated for 3 decades Will a sophisticated ontology really help?

o Take the Linux example, how to use ontology to achieve a better specification?

Will we ever be there?

Best practice: design patterns Has been an effective technology for software design Now being considered in SOA (service patterns) In a way, it is already in SOA

o In OWL-S, a service can be composition of existing services

But service pattern can make is more explicit and flexible

Planning and reasoning May provide some help in service composition as well

SOC

Evolution in software development First evolution: From hardware/assembly to high level languages Second evolution: From basic language constructs to high level

components/objects/services Many models have been provided, a lot of improvement, but software

development is still time/cost/effort intensive

Future evolution: Need revolutionary techniques SOC may some additional help, but is still far from the solution