Web Services

Presented By : Noam Ben Haim

Agenda

Introduction What is a web service Basic Architecture Extended Architecture WS Stacks

Introduction

The Need: The expanding WWW is not able to communicate correctly.

Distributed Systems – Maturity in the enterprise, only born in WWW.

Failure of COM and CORBA to interoperate, lots of security issues over the web.

Introduction

The opportunity: evolve of several Web Technologies such as SOAP, XML and WSDL.

What is a Web Service

Software system Identified by URI Defined and described using XML Can be discovered XML based messages over internet

protocols

Web Services are an Architectural Evolution.Web Services are an Architectural Evolution.

Main Frame

IBM

Main Frame

Data Base

2 Tier

Data Base

3 Tier

Web Server

Web

Internet

Web Server

N Tier

Internet

ApplicationServer Web Server

Internet

ApplicationServer

ApplicationServer

Web Server

Technology Evolution

XMLXML

ProgrammabilityProgrammabilityConnectivityConnectivity

HTMLHTML

PresentationPresentation

TCP/IPTCP/IP

Technology

Technology

Innovation

Innovation

FTP,FTP, E-mail, Gopher

E-mail, GopherWeb Pages

Web Pages

Browse Browse the Webthe Web

Program Program the Webthe Web

Web Services

Web Services

Some Terminology SOAP: Simple Object Access Protocol (remote invocation)

WSDL: Web Service Definition Language (service characteristics)

UDDI: Universal Description, Discovery, and Integration (directory)

XKMS: XML Key Management Specification (under development)

XML: Extensible Markup Language

XLANG: Transactional support (under development)

ebXML: (e-business XML)

Basic Architecture

Various components that comprise a WS “Stack”Exchanging messagesDescribing Web servicesPublishing and Discovering WS description

The Basic architecture defines an interactions between SW agents

Basic Architecture (cont.)

Models interactions between three roles:Service providerService discovery agencyService requestor

Models three operations:PublishFindBind

Basic Architecture (cont.)

Service Request

or

Service Provider

Discovery Agency

Discovery Agency

Client

Service

Service Description

Service Description

find

Interact

Publish

Basic Architecture (Cont.)

Typical scenario: Service provider hosts a network accessible software

module (an implementation of WS) The service provider defines a service description and

publishes it. The service requestor uses a find operation to retrieve

the description from the Disco Agency The Service requestor uses the description to bind

with the service provider.

Basic Architecture (Cont.)

Requestors and Providers interact using Message Exchange Patterns (MEP’s)

The description includes data types, MEP info and address of the service provider.

Basic Architecture (cont.)

The Components:The Service:

the implementation of the WS whose description is the interface.

A software module deployed on the network. It exists to be invoked or to interact with service

requestor It may also act a a requestor using other WS in its

implementation

Basic Architecture (Cont.)

The Components:The Service Description:

Contains the details of the interface and implementation

Data types, Operations, Binding info, network locations.

Metadata : Categorization, etc. Published to a requestor directly or to a Disco

Agency

Basic Architecture (Cont.)

The Roles:Service Provider:

The platform that hosts access to the service. Acts as a server for the requestor in the MEP

Service Requestor: The application that interacts with the service. Can be played by a browser operated by human or

by a program with no UI. Acts as a client.

Basic Architecture (Cont.)

The Roles:The Discovery Agency:

A searchable set of service descriptions. Centralized or Distributed. Can be push or pull. Support static and dynamic binding for apps.

Basic Architecture (Cont.)

The Operations:Publish:

The service publishes its description such that the requestor can find it.

Find: The service requestor retrieves a service

description directly or queries the registry. Can be involved in the design time or run time.

Basic Architecture (Cont.)

The Operations: Interact:

The service requestor invokes or initiates an interactions with the service.

Single Message One Way, Broadcast, Multi Message conversation, etc.

Synchronous or Async.

Extended Architecture

Extends the basic architecture with additional features and functionality, extending the technologies and Components.

Extended Architecture (Cont.)

List of Features (Partial):A sync. MessagingAttachments – packaging of multiple docs

together, binary data, etc. (SOAP with Attachments and DIME)

CachingLong running transactionsMessage Authentication – HTTP auth, x.509

Extended Architecture (Cont.)

List of Features (Partial):Message Confidentiality – SSL/TLS, SOAP

encryptionMessage Integrity – digital signature with

SOAPManagement messagesSession

Web Services Stacks

The “stack” of technologies create the protocol.

WS Stacks – Wire Stack

Wire StackEncapsulates the concepts and technologies

needed for the actual, physical exchange of information between the roles mentioned before.

Network transport Message packaging Message extensions

WS Stacks – Wire Stack

WS Stacks – Wire Stack

Transport:HTTP is the de facto standard network

protocol for internet available web services. Intranet domains may use MQSeries,

CORBA, etc.The choice of network technology can be

made transparent to the developer and consumer of the service

WS Stacks – Wire Stack

Packaging:SOAP is the de facto standard for XML

messaging. Relatively simple, thin layer on top of existing

network technologies (HTTP). Extensible, allows solutions to be incrementally

applied as needed. Based on XML, enjoys a broad support from the

community More on SOAP later.

WS Stacks – Wire stack

Extensions:Provides a framework that allows additional

information to be attached to WS messages.SOAP defines a mechanism to incorporate

orthogonal extensions (features).A broad collection of features are already

standard, and more to come…

WS Stacks – Wire stack

WS Stacks – Description Stack

WS Stacks – Description Stack

A stack of description documents defined using XML Schema.

Through the service description a service provider communicates all the specifications for invoking the web service.

Uses WSDL for base level service desc.

WS Stacks – Description Stack

Interface and implementation: The messages

the service expects and returns, and how to encode the messages and where to send them to.

Minimum service description.

WS Stacks – Description Stack

Policy: defines business context, QoS, security req,

etc. Presentation:

how to render the input/output messages on screen for different devices/

WS Stacks – Description Stack

The upper levels of this stack are somewhat left for the user to guess…

WS Stacks – Discovery stack

WS Stacks – Discovery stack

The discovery stack can be implemented with a range of solutions.

Service discovery depends on service publication.

Any mechanism that allows the service requestor to gain access to the service description and make it available to the application at runtime qualifies as service discovery

WS Stacks – Discovery stack

Publication:Several tools exist that help the developer to

produce the service description.Direct publish : send description directl to the

user (email, ftp, etc)UDDI Registry: business context and

toxonomies.

WS Stacks – Discovery stack

Discovery and publication:Service requestors can retrieve a service

description at design time or run time, from a web page (URL), repository or UDDI registry.

The service requestor uses the description to create SOAP requests to send to the service.

WS Stacks – Discovery stack

Inspection: Inspection technologies such as WSIL provide a de-

centralized service discovery method Local service discovery for ‘local’ web service

applications (micro SOAs that don’t leave the box… all else is the same except it limits where it looks for services).

Application integration. Discovery agents populated by crawlers looking for

WSIL documents. Management topologies of available services (but its

not a discovery source).

WS Stacks - Summary

Questions

Bibliography

W3C Web services architecture: http://www.w3.org/TR/ws-arch/

W3C Web Services Glossary: http://www.w3.org/TR/ws-gloss/

Web Services Architecture Usage Scenarios :

http://www.w3.org/TR/ws-arch-scenarios/