Web Services and Their Protocol Stack

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Web Services and Their

Protocol Stack

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• The Model of SOA

• Overview of Web Services

• XML and XML Schema

• The Communication Protocol

• Web Services Description

• Web Services Flow Description

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• As a distributed computing architecture, Web Services are the most important implementation for SOA.

• SOA Model is Web Services Concept Architecture.

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Concept in SOA Model

• Role – Services Provider – Services Requestor – Services Registry • Operation – Publish – Find – Bind • Key Component – Services – Services Description

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Core Standards in SOA Model

• Some Standards

– Web Services Description Language (WSDL)

– Universal Description, Discovery and Integration (UDDI)

– Simple Object Access Protocol (SOAP)

– Web Service Flow Language

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Process in SOA Development

Business Component Analysis Services Identification

Services Specification Component Identification Component Specification Services Realization Decision SOA Implementation

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The Level Model of SOA Development

Existing Application Resources Components Services Business Process Services Provider Services Consumer

Qos Security Management

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Relationship Between SOA and Web

Services

• Based on open standard and flexible implementation, Web

services is natively applicable to SOA implementation.

• The Relationships between Web services and SOA are:

– Web services provide an open standard and machine-readable model (WSDL) for creating explicit, implementation-independent descriptions

of service interfaces.

– Web services provide communication mechanisms that are location-transparent and interoperable.

– Web services are evolving through BPEL4WS, document-style SOAP, and WSDL, and emerging technologies such as WS-ResourceFramework to

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Web Services

• The Web: Flexible human-machine interaction

• Web Services: Web services are a recent set of technology

specifications that leverage existing proven open standards such as XML, URL, and HTTP to provide a new system-to-system

communication standard.

• Working Definition: Network-resident software Services accessible via standardized protocols

– Simple Object Access Protocol (SOAP): very flexible remote procedure call

• Lots of interest in trade press, academic community, standards bodies, . . .

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Categories of Web Services

• Business-Oriented Web Services

– ERP,CRM，

– Application system integration

• Consumer-Oriented Web Services

– B2C website, across multi B2C systems

• Device-Oriented Web Services

– Support the services across different kinds of services. E.g weather report, email service

• System-Oriented Web Services

– Authentication

– Monitoring

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The Processes of Web Services

Simplify and/or automate web Services

• Discovery

– What properties should be described? – How to efficiently query against them?

• Composition

– Specifying goals of a composition

– Specifying constraints on a composition – Building a composition

– Analysis of compositions

• Invocation

– Keeping enactments separated – Providing transactional guarantees

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Web Services Standard Stack

XML messaging layer: SOAP , WS-Addressing, WS-Notification, WS-Eventing,

WS-Enumeration, WS-MessageDelivery, WS-Reliability,WS Reliable Messaging, WS-Resources WS-Transfer

Services Description Layer: WSDL, WSCL, WSCI,WS-MetadataExchange, WS-Policy Web Services composition: WSFL,BPEL4WS WS-CDL WS-CAF Publishing and discovery: UDDI, WSIL , WS-Discovery Web Services Transaction: WS-Coordination WS-Transaction WS-AtomicTransaction WS-BusinessActivity Web Services Management: WSDM, WS-Manageability SPML, WS-Provisioning Web Services Security: XML-Encryption XML-Signature WS-Security WS-SecureConversatio n WS-SecurityPolicy WS-Trust

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Data Type Interface Behavior Message BPEL

Web Service Standards Implementation Platforms

WSDL SOAP

XML Schema

XML _{Sun J2EE}

Web Service Core Standards

Microsoft .Net

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The structure of XML

• Tag: label for a section of data

• Element and Subelement: section of data beginning with <tagname> and ending with matching </tagname>

Elements must be properly nested

– Proper nesting

• <account> … <balance> …. </balance> </account>

– Improper nesting

• <account> … <balance> …. </account> </balance>

– Formally: every start tag must have a unique matching end

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– Every document must have a single top-level element

<bank>

<name> Hayes </name> <street> Main </street> <city> Harrison </city> <account>

<account-number> A-102 </account-number> <branch-name>Perryridge </branch-name> <balance> 400 </balance> </account> <account> … </account> </customer> . . </bank>

The structure of XML

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The structure of XML

• Attribute

– Elements can have attributes

<account-number> A-102 </account-number> <branch-name> Perryridge </branch-name> <balance> 400 </balance>

</account>

– Attributes are specified by name=value pairs inside the starting tag of an element

– An element may have several attributes, but each attribute name can only occur once

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The structure of XML

• Differences between element and attribute

attributes cannot be nested

<account-number> A-102 </account-number> <branch-name> Perryridge </branch-name> <balance> 400 </balance> </account> <account> … </account> </customer>

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The structure of XML

• Well-Formed XML Documents

–

There is only one outermost element in the

document (called the root element)

–

Each element contains an opening and a

corresponding closing tag

–

Tags can not overlap, as in

<author><name>LeeHong</author></name>

–

Attributes within an element have unique names

–

Element and tag names must be permissible

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The structure of XML

• The Tree Model of XML Documents

–

_{There is exactly one root}

–

There are no cycles

–

_{Each node, other than the root, has exactly}

one parent

–

Each node has a label. Element or attribute

–

The order of elements is important

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Namespace

• XML data has to be exchanged between organizations

• _{Same tag name may have different meanings in}

different organizations, causing confusion on

exchanged documents

• _{Specifying a unique string as an element name avoids}

confusion

• _{Better solution: use}

_{unique-name:element-name}

• _{Avoid using long unique names all over document by}

using XML Namespaces

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Namespace

<Schema name="mySchema" xmlns="urn:schemas-microsoft-com:xml-data" xmlns:dt="urn:schemas-microsoft-com:datatypes" xmlns:myNS=http://www.xml_step_by_step.edu\ns.xml > Three namespaces: schema namespace datatype namespace myNS namespace

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XML Schema

• Database schemas constrain what information can be stored,

and the data types of stored values

• schemas are very important for XML data exchange

– Otherwise, a site cannot automatically interpret data received from another site

• Two mechanisms for specifying XML schema

– Document Type Definition (DTD) – XML Schema

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XML Schema

• XML Schema Supports

–

Typing of values

• E.g. integer, string, etc

• Also, constraints on min/max values

–

User defined types

–

Is itself specified in XML syntax, unlike DTDs

• More standard representation, but verbose

–

Is integrated with namespaces (reuse and refine)

–

Many more features

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<xsd:schema xmlns:xsd=http://www.w3.org/2001/XMLSchema> <xsd:element name=“bank” type=“BankType”/>

<xsd:element name=“account”> <xsd:complexType>

<xsd:sequence>

<xsd:element name=“account-number” type=“xsd:string”/> <xsd:element name=“branch-name” type=“xsd:string”/> <xsd:element name=“balance” type=“xsd:decimal”/> </xsd:squence>

</xsd:complexType> </xsd:element>

….. definitions of customer and depositor ….

<xsd:complexType name=“BankType”> <xsd:squence>

<xsd:element ref=“account” minOccurs=“0” maxOccurs=“unbounded”/> <xsd:element ref=“customer” minOccurs=“0” maxOccurs=“unbounded”/> <xsd:element ref=“depositor” minOccurs=“0” maxOccurs=“unbounded”/> </xsd:sequence>

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XML Schema

• Element Types

<element name=". . ."/> with possible attributes: – ‘ type’ attribute

define the element type of this element: type=". . ." (more on types later)

– cardinality constraints:

• minOccurs="x", where x may be any natural number (including zero)

• maxOccurs="x", where x may be any natural number (including zero) or unbounded

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XML Schema

<element name="email"/>

<element name="head" minOccurs="1"

maxOccurs="1"/>

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XML Schema

• Attribute Types

<attribute name=". . ."/> with possible

attributes

–

type=". . ."

–

use="x", corresponds to #OPTIONAL and #IMPLIED

in DTDs

–

use="x" value=". . .", where x may be default

or fixed

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XML Schema

<attribute name="id" type="ID"

use="required"/>

<attribute name="speaks"

type="LanguageType" use="default“

value="en"/>

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XML Schema

• Data Types

–

Numerical data types, including integer, Short,

Byte, Long, Float,Decimal

–

String data types, including string, ID, IDREF,

CDATA, Language

–

Date and time data types

• user-defined data types

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XML Schema

• Complex data type and extension data type

– defined from already existing data types by defining some attributes (if any) and using sequence, all and choice.

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XML Schema

• <element name=“lecture” type=“lectureType”>

<lecture title=“associate professor”> <firstname>gang</firstname> <lastname>Huang</lastname> </lecture>

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XML Schema

Data Type Extension: existing data types can be

extended by new elements or attributes

</sequence>

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XML Schema

• Restriction data type and simple data type

be defined by restricting existing data types

<element name="firstname" type="string" minOccurs="1" maxOccurs="2"/>

</sequence>

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XML schema

• Simple data types can also be defined by

restricting existing data types.

<simpleType name="dayOfMonth">

<restriction base="integer">

<minInclusive value="1"/>

<maxInclusive value="31"/>

</restriction>

</simpleType>

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The Communication Protocol

(SOAP)

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Why

S

imple

O

bject

A

ccess

P

rotocol

• SOAP is an XML messaging protocol that is independent of any specific transport protocol.

• Light weight replacement for complicated distributed object technology

• Originally for BizTalk (Microsoft/UserLand/DevelopMentor )

• Now a W3C standard

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SOAP Message Structure

• Envelope contains – Header – Body • Header is optional – Out-of-band information such as… • Authentication information • Message routes • Logging • Transaction flow

SOAP Envelope

SOAP Header Header Block Header Block . . . SOAP Body Body Block . . .

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SOAP Example

<?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-ncoding"> <soap:Body> <m:GetPrice xmlns:m="http://www.w3schools.com/prices"> <m:Item>Apples</m:Item> </m:GetPrice> </soap:Body> </soap:Envelope>

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SOAP Example

<?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"> <soap:Body> <m:GetPriceResponse xmlns:m="http://www.w3schools.com/prices"> <m:Price>1.90</m:Price> </m:GetPriceResponse> </soap:Body> </soap:Envelope>

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Web Services Description Language

(WSDL)

• WSDL is an XML-based interface definition language

that separates function from implementation, and

enables design by contract as recommended by SOA.

• WSDL defines

–

What does Services do –

interface

–

Access specification –

how

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Ingredients of WSDL

Operation

Port Type

Message

Binding

Port

Services

Supports

Input & Output

Provides How to encode Formats & Protocols

How to invoke

Implements

Interface

Access

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Main Structure of WSDL

<definitions namespace = “http://… ”> <types> XML schema types </type>

<message> definition of a message </message> <portType> a set of operations </portType>

<binding> communication protocols </binding> <Services> a list of binding and ports </Services> </definitions>

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Types

• <types> define data types used in defining messages

• XML Schema, DTD, and etc.

• XML Schema must be supported by any vendor of WSDL

conformant products

<types>

<schema targetNamespace=“http://example.com/stockquote.xsd”

xmlns=“http://www.w3.org/2000/10/XML Schema”>

<all>

<element name=“tickerSymbol” type=“string“

minOc cur = “1” maxOccur=“10”/>

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WSDL Messages

• A <message> element defines the data elements of an operation

• Each message can be the input or output of an operation, and may consist of one or more parts

• A part resembles a parameter of a function <message name=“GetLastTradePriceInput”>

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WSDL PortTypes

• The <portType> element is the most important WSDL element: it defines

– a web Services

– the operations that can be performed, and – the messages that are involved

• The <port> defines the connection point to a web Services, an instance of <portType>

– It can be compared to a function library (or a module, or a class) in a traditional programming language

– Each operation can be compared to a function in a traditional programming language

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Operation Types

• The request-response type is the most common operation

type, but WSDL defines four types:

– One-way: The operation can receive a message but will not return a response

– Request-response: The operation can receive a request and will return a response

– Solicit-response: The operation can send a request and will wait for a response

– Notification: The operation can send a message but will not wait for a response

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Operation Types

One-way:

• <message name="newTermValues"> <part name="term" type="xs:string"/> <part name="value" type="xs:string"/> </message>

• <portType name="glossaryTerms"> <operation name="setTerm">

</portType > Request-response ：

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• Binding defines how message are transmitted, and the location of the Services

• <binding> element has two attributes: – type: the port type

– name: name of the binding

• <soap:binding> has two attributes: – style: either “document” or “rpc”

– transport: protocol to use, e.g., “http”

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Binding

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<Services name=“StockQuoteServices”> <documentation> My first Services </documentation> <port name=“StockQuotePort” binding=“tns:StockQuoteBinding”> <soap:address location=“http://example.com/stockquote” /> </port> </Services>

Services

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Summary of WSDL

• Types

• Message

• Operation

• PortType

• Binding

• Port

• Service

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Business Process Execution Language

• Define business processes as coordinated sets of Web Services interactions

• Define both abstract and executable processes

• Enable the creation of compositions of Web Services

• Where it comes from:

– Strong roots in traditional flow models

– Concepts from structured programming languages

– On the top of WSDL and core XML specifications

– Merges WSFL and XLANG concepts

• The OASIS WS BPEL Technical Committee is advancing the

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Structure of a BPEL Process

• Web Services the process

interacts with

• Data used by the process

• Used to support asynchronous

interactions

• Alternate execution path to deal with faulty conditions

• Code to execute when

“undoing” an action

• What the process actually does <process ...> <partners> ... </partners> <messageExchanges> ... </ messageExchanges > <correlationSets> ... </correlationSets> <faultHandlers> ... </faultHandlers> <compensationHandlers> ... </compensationHandlers> (activities)*

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• A partner is accessed over a WS “channel”, defined by a Services link type

• A SLT defines two roles and the portTypes that each role needs to support

Partner Definitions and Links

<partner name=“...” ServicesLinkType=“...” partnerRole=“...” myRole=“...”/> <ServicesLinkType name=“...”> <role name=“..."> <portType name=“...” />* </role> <role name=“...”> <portType name=“...”/>*

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Containers Definition

<containers>

<container name=“…"

messageType=“…"/>

<container name=“…"

messageType=“…"/>

</containers>

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• Invokes an operation on a partner

• Receives invocation from a partner

• Sends a reply message in partner invocation

• Data assignment between containers

<assign> <copy>

BPEL Basic Activities

<invoke partner=“...” portType=“...” operation=“...”

inputContainer=“...” outputContainer=“...”/>

<receive partner=“...” portType=“...” operation=“...” container=“...” [createInstance=“...”] />

<reply partner=“...” portType=“...” operation=“...”

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• Detects processing error and switches into fault processing mode

• Pull the plug on this instance

• Execution stops for a specified amount of time

• Do nothing; a convenience element

More Basic Activities

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• A <sequence> activity contains one or more activities that are performed sequentially.

• The <pick> activity waits for the occurrence of exactly one event from a set of events, thenexecutes the activity associated with that event.

• The <flow> activity provides concurrency and synchronization.

• The<swith>activity provides optional activity.

BPEL Structured Activities

<flow standard-attributes>activity+</flow>

<sequence standard-attributes>activity+</sequence>

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• The <while> activity provides for repeated execution of a contained activity.

• The <repeatUntil> activity provides for repeated execution of a contained activity.

• The <if> activity provides conditional behavior.

More Structured Activities

<if standard-attributes>standard-elements <condition>…</condition>activity <elseif>*<condition>…</condition>activity</elseif> <while standard-attributes><condition>..</condition>activity</while> <repeatUntil standard-attributes>activity <condition>…</condition></repeatUntil>

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execute activities sequentially

<flow>

execute activities in parallel

<while>

iterate execution of activities until condition is violated

<pick>

several event activities (receive message, timer event)

scheduled for execution in parallel; first one is selected and corresponding code executed

A Activities Use Case

Flow Seq Seq Seq While <sequence> <receive .../> <flow> <sequence> <invoke ... /> <while ... > <assign> ... </assign> </while> </sequence> <sequence> <receive ... /> <invoke ... /> </sequence> </flow>

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Web Services Publication and

Discovery

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UDDI

• UDDI servers act as a directory of available services

and service providers. SOAP can be used to query

UDDI to find the locations of WSDL definitions of

services, or the search can be performed through a

user interface at design or development time.

• Data structure specification describes what kind of

data is stored in UDDI.

• The programmer’s API specification contains how a

UDDI registry can be accessed.

• The replication specification contains descriptions of

how registries replicate information among

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UDDI

• Three basic functions

–

publish：how to register a web service

–

Search: how to find a specific web service

–

binding: How to connect to a web service

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UDDI Registries

UDDI registries contains information about

businesses and the Services these businesses

offer.

–

Public registries

–

Private registries

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Public Registries

• IBM Public registry Registration:

https://uddi.ibm.com/ubr/registry.html

inquiryURL= https://uddi.ibm.com/ubr/inquiryapi publishURL= https://uddi.ibm.com/ubr/publishapi

• Test registry Registration:

https://uddi.ibm.com/testregistry/registry.html

inquiryURL= https://uddi.ibm.com/testregistry/inquiryapi publishURL= https://uddi.ibm.com/testregistry/publishapi

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Public Registries

• HP Registration: http://uddi.hp.com inquiryURL = http://uddi.hp.com/ubr/inquire publishURL = https://uddi.hp.com/ubr/publish • Microsoft Registration: http://uddi.rte.microsoft.com inquiryURL=http://uddi.rte.microsoft.com/inquire publishURL=https://uddi.rte.microsoft.com/publish • SAP Registration: http://udditest.sap.com

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Private UDDI Registries

• Operate your own registry for testing purposes

• Establish your own registry of Services for your own organization

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Summary

• As a distributed computing architecture，Web Services are the most important implementation for SOA;

• Web Services: Flexible machine-machine interaction;

• XML is a powerful language to describe data. It’s construct rules is defined by XML Schema.

• SOAP is a light weight replacement for complicated distributed object technology which we use to wrap Web Services message; • The function and interface of Web Services is open by WSDL

and the interaction between Web Services is presented by BPEL;

• Universal Description, Discovery, and Integration (UDDI) is a technical specification for describing, discovering, and

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Reference

•SOA & Webservices.http://www-900.ibm.com/developerWorks/cn/ webservices

•WebServices. http://www.w3.org/2002/ws/

•Ueli Wahli ,Thomas Kjaer…“WebSphere Version 6 Web Services Handbook Development&Deployment”,http://www.redbooks.ibm.com

/redbooks/pdfs/sg246461.pdf,2005

•Stan Kleijnen,Srikanth Raju.An Open Web Services Archiecture.NewYork: ACM Press,2003

•XML.http://www.w3.org/TR/xml/

•XML Schema. http://www.w3.org/TR/xmlschema11-1/

•XML Schema. http://www.w3.org/TR/xmlschema11-2/ •WSDL. http://www.w3.org/TR/wsdl

•Tony Andrews, Francisco Curbera…Business Process Execution Language for Web Services Version 1.1.http://download.boulder.ibm.com/

ibmdl/pub/software/dw/specs/ws-bpel/ws-bpel.pdf

•The Stencil Group.” The Evolution of UDDI ,UDDI.org White Paper” http://www.uddi.org/pubs/the_evolution_of_uddi_20020719.pdf