Web Services - Chinese University of Hong Kong › ~ect7010 › Materials › Lecture ›...

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merce Technologies Edited by Christopher C. Yang

Web Services

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‧Web services facilitate the collaboration of e-businesses–e-business applications communicate with each other (App-to-App

Communication)• Web services is

– Platform independent– Language independent– Location independent

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Web Services are Different…• UNIX RPC – Requires binary-compatible UNIX

implementation at both ends• CORBA – Requires compatible ORBs• RMI – Requires Java at each endpoint• DCOM – requires Windows at each endpoint

Web Services are Language-independent, Component Model-independent, Location-independent, Firewall friendly

Web services enable App-to-App communication

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• Web Services Characteristics– Self-describing– Easy to integrate the services provided– Interoperability– Ubiquity– Low Barrier to Entry

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What is Web Services?

• Web services is different from application service providers (ASPs)– Application Service Providers (ASPs) are third-party entities that manage

and distribute software-based services and solutions to customers across a wide area network from a central data center.

– ASPs allow companies to outsource some or almost all aspects of their information technology needs.

• The ASP model is based on application rental (as opposed to purchase)• Key: Web Services could be a way ASPs deliver their

services/applications.ASP Web ServicesBusiness Model Technical Architecture

Mainly Complete Applications

Mainly Modular & Data Oriented

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• W3C Definition: Web service is a software system identified by a URI, whose public interfaces and bindings are defined and described using XML. Itsdefinition can be discovered by other software systems. These systems may then interact with the Web service in a manner prescribed by its definition, using XML based messages conveyed by Internet protocols

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“Web Services is a standards-based software technology that lets programmers and integrators combine existing and new systems or applications in new ways over the Internet, within a company’s boundaries, or across many companies. Web Services allow interoperability between software written in different vendors, or running on different operating systems or platforms”(IDC, Web Services: Analyst: Sophie Janne Mayo, March 2002)

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Web Services• Web services is both a process and set of protocols for

finding and connecting to software exposed as services over the Web

• Web services = repository + client + provider• Three major aspects:

– Service provider– Service requester– Broker

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Collaboration Environment

• Web services builds on SOAP’s capability for distributed, decentralized network communication by adding new protocols and conventions that expose business functions to interested parties over the Internet from any Web-connected device. – SOAP is not a stand-alone technology, but the result of synergies between

XML and HTTP.• Web services satisfies the need for a flexible and efficient business

collaboration environment.– It links loosely couple systems using technology that doesn’t bind them to

a particular programming language, component model, or platform.

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What does Web Services includes?

• Web services (WS) includes– Describing: WS describes its functionality and attributes so that other

applications can figure out how to use it.– Exposing: WS registers with a repository that contains a white page

holding basic service-provider information, a yellow pages listing services by category, and a green pages describing how to connect and use the services.

– Being invoked: When a WS has been located, a remote application can invoke the service.

– Returning a response: When a WS has been invoked, results are returned to the requesting application.

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Basic Conceptual Architecture

Component View

Web Services consist of a set of messaging protocols, programming standards, and network registration and discovery facilities that expose business functions to authorized parties over the Internet from any web-connected device.

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Service View

Subscriber Publisher

Three major aspects:•Service provider : provides an interface for software that can carry out a specified set of tasks•Service requester : discovers and invokes a software service to provide a business solution.

•The requester invokes a remote procedure call on the service provider, passing parameter data to the provider and receiving a result in reply.

•Repository or broker : manages and publishes the service

Broker

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Components of Web Services • Service

– software module deployed on network accessible platforms provided by the service provider

– It exists to be invoked by or to interact with a service requestor– It may also function as a requestor, using other web services in its

implementation• Service Description

– contains the details of the interface and implementation of the service – includes its data types, operations, binding information, and network location – include categorization and other meta data to facilitate discovery and utilization

by requestors – realized as a set of XML description documents

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Roles in Web Services• Service Provider

– From a business perspective, this is the owner of the service – From an architectural perspective, this is the platform that hosts access to the service – also referred to as a service execution environment or a service container – role in the client-server message exchange patterns is that of a server

• Service Requestor– From a business perspective, this is the business that requires certain function to be

satisfied – From an architectural perspective, this is the application that is looking for and invoking

or initiating an interaction with a service – played by a browser driven by a person or a program without a user interface – role in the client-server message exchange patters is that of a client

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Roles in Web Services• Discovery Agency

– a searchable set of service descriptions where service providers publish their service descriptions

– can be centralized or distributed – support both the pattern where it has descriptions sent to it and where the

agency actively inspects public providers for descriptions – Service requestors may find services and obtain binding information (in the

service descriptions) during development for static binding, or during execution for dynamic binding

• For statically bound service requestors, the service discovery agent is in fact an optional role in the architecture, as a service provider can send the description directly to service requestors.

• service requestors can obtain a service description from other sources besides a service registry, such as a local filesystem, FTP site, URL, or WSIL document.

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Operations in Web Services• Publish

– a service needs to publish its description such that the requestor can subsequently find it

• Find– the service requestor retrieves a service description directly or queries the

registry for the type of service required – find operation may be involved in two different lifecycle phases for the service

requestor • at design time in order to retrieve the service's interface description for program

development • at runtime in order to retrieve the service's binding and location description for

invocation

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Operations in Web Services

• Interact– the service requestor invokes or initiates an interaction with the

service at runtime using the binding details in the service description to locate, contact, and invoke the service

– Examples of interaction• single message one way, broadcast from requester to many services, a

multi message conversation, or a business process – Synchronous or asynchronous

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What to do?

• When a company want to take advantage of WS technology, what does it need to do?

1. Decide on the service it wants to provide.2. Pick a registry for uploading its information.3. Decide how to list its services at the registry.4. Define explicitly how users can connect to its service.

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WS Architecture

• Three major aspects:– Service provider : provides an interface for software that can carry

out a specified set of tasks– Service requester : discovers and invokes a software service to

provide a business solution. • The requester invokes a remote procedure call on the service provider,

passing parameter data to the provider and receiving a result in reply.– Repository or broker : manages and publishes the service

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Key Technologies

• UDDI– A protocol for describing WS components that allows business to register

with an Internet directory• WSDL

– Built around an XML-based service Interface Definition Language that defines both the service interface and the implementation details

• WSDL details may be obtained from UDDI entries that describe SOAP messages needed to use a particular WS.

• SOAP– A protocol for communication with a UDDI service

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SOAP

• Simple Object Access Protocol (SOAP) is a XML-based protocol that offers platform, language, and transport independence for data exchange between partners and suppliers.

• SOAP provides a decentralized, distributed environment.• SOAP defines an XML envelop for delivering XML

content and specifying a set of rules for servers to follow when they receive a SOAP message.

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SOAP Protocol

• SOAP is a text-based protocol that uses XML– IIOP for CORBA are binary protocols– SOAP is easier to move across firewalls than IIOP because it is

text-based.– SOAP is standard-driven rather than vendor-driven because it is

based on XML.

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SOAP Message Structure• SOAP Envelope : root of the XML document that defines a SOAP message.• SOAP Header : (optional) provides a modular way of directing SOAP servers to do

processing before passing the SOAP message on. E.g. instructs a server to add transaction or authentication information.

• SOAP Body : where the transported XML is loaded.

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Example

• ZwiftBooks opens the server up to collectors who wish to notify ZwiftBooks about books they have for sale.

1. Define a top-level element and related subelements that will trigger processing of the book availability data by the SOAP server.

2. Define a schema (DTD or XML Schema) that dictates the form of the XML that will arrive from collectors.

3. Specify a namespaces that is unique to ZwiftBooks. (e.g. the ZwiftBooks Web site or URI)

4. Configure the server to return a fault if the incoming SOAP message is not one of the special elements defined in Step 1.

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• Message paths– Messages may be routed from server to server along a so-called

message path.

• SOAP Intermediaries– Intermediaries act in different roles, including proxies, caches,

store-and-forward hops, and gateway.

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UDDI– Universal Description, Discovery and Integration

• Standards based specification for service description and discovery

• Programmatic descriptions of business and services they support

• Publishing APIs• Inquiry APIs

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UDDI Registry3 categories

White Pages Yellow Pages Green Pages

-Directory of names-Provider info-Contact info

-Directory of Domains-Specific Search using Context such as location, service type

-point to White pages

-Directory of Biz info-Info about Biz Model-Technical details of provided service

-Info Business Process

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UDDI

• UDDI stems from a cooperative agreement among Microsoft, IBM, and Ariba on an XML-based specification for establish a registry of business and services on the Internet. (began in August 2000)

• UDDI defines a layer above SOAP in an interoperability stack that builds on TCP/IP, HTTP, and XML.

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Scenario of interaction for connection to a company server usingUDDI discovery

1. A company is interested in writing a software to connects to several book-service providers and comparing price and delivery times for each.

2. It needs a program that can connect to the UDDI business registry via either a Web interface or a tool that use the Inquiry API.

3. After a lookup based on an appropriate yellow pages listing, thecompany obtains a businessEntity that represents a book-service provider, ZwiftBooks.

4. Using the businessEntity, the client can either drill down for more detail or request a complete businessEntity structure. The objective is to obtain a bindingTemplate that provides the information about how to connect to ZwiftBooks WS.

5. Based on the details of bindingTemplate, the company sets up its program to interact with the ZwiftBooks WS.

6. At runtime, the program invokes the WS based on the connection details provided in the bindingTemplate.

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WSDL – Web Services Definition Language• A description language to define web

service interfaces and how to invoke them. (how to connect to Web service providers)

• Allows both the message and the operations on the messages to be defined abstractly in XML

• An XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-orientated information - WSDL specification

• Where does WSDL appear?– Reside in UDDI or directory

services– Provided via configuration or other

means such as in the body of SOAP request replies

http://www.w3.org/TR/wsdl

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WSDL schema

• A WSDL schema includes:– Service, Types Message,

Operation, Port Type, Binding, Port

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Value of Web Services

Simple•HTML-like simplicity for App-to-App Communication•Platform Independent•Development language Independent

Standards-based ( Interoperability)•Broad agreement on core standards: SOAP, WSDL, UDDI•Broad supported by major platform providers (IBM, Microsoft, Oracle, etc)

Business Driven•New application/revenue models•Strengthen relationships with customers•Optimize business process / Reduce costs

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Web Service scenario

WorkflowEngine ERP Adapter

2.Locate Suppliers

3 RequestQuotes

4 Sort Responses

5 Obtain Approval

6 Generate andSend Order

7 Delivery,Update inventory

SOAPAdapter

1. low inventoryStart workflow

PrivateUDDI

PublicUDDI

HTTP

2.Locate Suppliers

WSDL

WSDL

fi rew

all

3 RequestQuotes

3 RequestQuotes

6 Generate andSend Order

7 Delivery,Update inventory

By using Web Services and related repositories, company is able to streamlineand automate its request for quote (RFQ) and order fulfillment process.

Factory

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Business Benefit• Expand markets

– Web service can be decentralized and distributed over internet and access by wide variety of communication device

– Attract new business by extending application to much more audience

• Smooth B2B integration– Create once, expose to many customers– Provide affordable, easy-to-implement, end-to-end application integration solution

• Discovery of business partner that meet the business need– E.g search for cheapest web services by system

• New business – New subscription or pay-to-use model– Web services can combined to build a new web services– Assembly of new applications by linking existing internal and external third-party Web Services (Web

Services Aggregators)

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Pricing Service

Order EntryService

InventoryAvailable Service

Tax CalculatorService

Negotiated PricingService

CurrencyConversion

ServiceBusiness Benefit

• Enhance business automation by combine web services at run time• Increase visibility by enabling real-time connections among

operational systems– Significantly increase managers’ visibility into a data-centric business processes

• Increase productivity– Web Services are self-describing business function– Allow system to trigger the business process automatically

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Technical Benefit

• Improve efficiency of application development by assembly

• Save development effort by re-use of web services• Support both applications and people with the same Web

Service• Lower maintenance cost and easy management

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Technical Benefit

• Neutral platform – Highly compatibility between various operating systems

– Universally Agreed Specifications

• Strong industry support– All major vendors support– Available solution for most platform

• Flexible in development

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Technical Benefit• Extend legacy application functionality

– Ease of legacy system integration– Develop SOAP/XML Wrapper– Look like a regular services from customer view

SERVICE

Legacy System

SOAP/XML Wrapper

Components

SOAP/XML Wrapper

UDDI Registry

Application

WSDLServices“Yellow Page”Tool

XML/ SOAP (static lookup)

XML/SOAP(dynamic lookup)

XML over SOAP /ebXML

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Barriers on Applying Web Services

• Lacking of Standard– Security :

• OASIS (Organization for the Advancement of Structured Information Standards) proposes SAML

• WS-Interoperability proposes WS-Security

– Routing SOAP messages :• Microsoft releases WS-routing• IBM has no plan to support and will push another protocol

– Workflow : • Microsoft - XLANG• IBM - WSFL (Web Services Flow Language)• Team to develop BPEL (Business Process Execution language)

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Barriers on Applying Web Services• Performance

– XML has lengthy data format– Estimates the size of a typical XML document at 10 times of an equivalent EDI transmission.

• Difficult to build trust between a Consumer & Web Service Developer

• Dependency– If server from an external party goes down, your application will be affected

• Company Scale – Small business cannot afford the cost in developing web services

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Barriers on Applying Web Services

• Critical mass of deployments– Without enough web services, company still need to create

applications themselves

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Keep Their Legacy System

• Overview:– One of the most popular department stores in the United States – They want to improve communication between Nordstrom's e-commerce

site and its other application– Since the Nordstrom.com uses Microsoft software– but the company’s enterprise resource planning (ERP) applications

which it employs to check inventory, place orders and organize company resources run on Hewlett-Packard UNIX servers, and the inventory data resides on IBM mainframes

– At first, the company considered connecting these systems using traditional middle-ware product. But finally, the management decided that the available solutions were too expensive and time-consuming.

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Keep Their Legacy System (cont.)

– Nordstom is using Web services to connect its e-commerce site to its gift-card-management and cosmetics-replenishment applications, which reside on legacy systems. Customers can redeem Nordstrom gift cards through the Web Services that link nordstrom.com to the gift-card management systems

Legacy system

Gift-card management Cosmetics-replenishment

Nordstom.com

Gift CardWeb Service

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Keep Their Legacy System (cont.)

– Another Web services implementation is designed to improve Nordstrom's cosmetics-inventory system. When a customer purchases a cosmetics product from nordstrom.com, a Web service automatically updates the cosmetics replenishment application to reflect the changed inventory.

Legacy system

Cosmetics inventory

Nordstom.com

Purchase order

InventoryWeb Service

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What does it contribute?

• Meet the management need, since they don't want to reinvent the wheel

• Enable cost cutting, and better customer service, since customer don't need to wait a queue for redeem their gift cards and no longer need too many staff for inventory control.

• As nordstom.com concern about the security problem of Web service, so they just deploy Web services on the company's private network.

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Other Examples:

• Search information e.g using Google API• Validation e.g. credit card number, e-mail address and

check spelling …..• Get specified information e.g networking related

information, weather, news or stock price …..• Translation: translate from one language to another

language

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Search by Google API in my site

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Validate the e-mail address

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Validate my Spelling

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Query IP information

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Translation

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Goolge WSDL

<definitions name="GoogleSearch" targetNamespace="urn:GoogleSearch" xmlns:typens="urn:GoogleSearch" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns="http://schemas.xmlsoap.org/wsdl/">

Web Service URI

All Namespaces

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<types><xsd:schema

xmlns=http://www.w3.org/2001/XMLSchematargetNamespace="urn:GoogleSearch">

<xsd:complexType name="GoogleSearchResult"><xsd:complexType name="ResultElement"><xsd:complexType name="ResultElementArray"><xsd:complexType

name="DirectoryCategoryArray"><xsd:complexType name="DirectoryCategory">

</xsd:schema></types>

XML Schema

DataType

http://www.w3.org/2001/XMLSchema

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<message name="doGoogleSearch"><part name="key" type="xsd:string" /><part name="q" type="xsd:string" /><part name="start" type="xsd:int" /><part name="maxResults" type="xsd:int" /><part name="filter" type="xsd:boolean" /><part name="restrict" type="xsd:string" /><part name="safeSearch" type="xsd:boolean" /><part name="lr" type="xsd:string" /><part name="ie" type="xsd:string" /><part name="oe" type="xsd:string" />

</message><message name="doGoogleSearchResponse"><part name="return" type="typens:GoogleSearchResult" />

</message>

Data Unit

Request Parameter

Return Parameter

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<portType name="GoogleSearchPort"><operation name="doGetCachedPage"><operation name="doSpellingSuggestion"><operation name="doGoogleSearch">

<input message="typens:doGoogleSearch" /><output message="typens:doGoogleSearchResponse" />

</operation></portType>

Methods opened for remote calling

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<binding name="GoogleSearchBinding" type="typens:GoogleSearchPort"><soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http" /><operation name="doGetCachedPage"><operation name="doSpellingSuggestion"><operation name="doGoogleSearch">

</binding><service name="GoogleSearchService">

<port name="GoogleSearchPort" binding="typens:GoogleSearchBinding"><soap:address location="http://api.google.com/search/beta2" />

</port></service>

Communication style

Web service endpoint

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