Soap and the Future of Distributed Processing on the Internet

Mohammed El-AffendiDept of Computer Science, CCIS, PSU

Topics Covered What is a distributed application? Evolution of distributed applications. The famous RPC. Architectures of distributed systems and

applications. CORBA and COM: interoperability. XML and SOAP. WEB services

What is a distributed application? A distributed application is an

application that runs on several interconnected machines, but appears to its user as if it were running on a single machine.

This is called a true distributed application.

Network Applications? In network applications, the

network is transparent. The user knows that he is using a

network. Transparency is the major

difference between distributed and network applications.

Architecture of distributed systems and applications: Distributed systems may be based

on existing OS’s and protocols or built from scratch. (Distributed Unix versus Amoeba).

They may be based on monolithic or thin kernels.

Function Calls in Distributed Systems: The Famous RPC: Remote Procedure Calls (RPC’s):

ClientProgram

ServerProgram

MarshallStub

Transport Transport1 0 01 1

Client Calls Functions

unmarshall

The CORBA Standard and Distributed Objects: The OMG designed CORBA as a

standard for interoperability between distributed objects.

The main motivation is to allow applications to call functions implemented by other distributed applications using a standard interface specification.

COM and DCOM: Microsoft introduced a similar de facto

standard commonly known as COM. The main motivation behind COM is to

allow binaries to interoperate through exported interface specifications, in a manner independent of the programming language and platform.

COM and DCOM: Another motivation is to allow

applications to control each other easily.

COM assumes that the interoperating applications are on the same machine.

DCOM is an extension of COM across networks and the Internet.

DCOM clients may call procedures and functions implemented by DCOM servers on other machines.

DCOM Clients and Servers: The user should not worry about

communication details:

Client Server

Problems with COM and CORBA: One problem with COM and CORBA

is that they are competing standards which are not compatible.

Another problem is that in many cases they may not be able to cross firewall boundaries.

Enter SOAP: Due to the above problems, people

have been looking for a more versatile solution acceptable by all.

The answer has been “SOAP”. SOAP stands for “Simple Object

Access Protocol” In one sentence: SOAP=XML +

HTTP.

SOAP: The main idea behind SOAP is to utilize

two widely accepted standards to facilitate interoperability across the Internet.

The first of these is the XML standard for describing data (I will explain shortly).

The other standard is nothing but the widely accepted WEB protocol: the famous HTTP.

SOAP: In what follows, I will briefly

describe XML and the HTTP and then come back to SOAP.

However, one point to remember is that the HTTP is one of the very few protocols that can cross firewalls.

XML: XML is all about structured, self-

describing data Data which must be structured are

the method calls and return data Many implementations available to

process XML

What is XML XML stands for “eXtensible Markup

Language” XML Language is a text-based format that lets

developers describe, deliver and exchange structured data between a range of applications and clients for local display and manipulation.

XML also facilitates the transfer of structured data between servers themselves.

XML resembles and complements HTML. XML describes data, while HTML defines tags

that describe how the data should be displayed.

XML: XML, however, allows developers to

define an unlimited set of tags, bringing great flexibility to authors, who can decide which data to use and determine its appropriate standard or custom tags.

HTML uses a frozen set of tags that are difficult to extend.

XML example: The following simple example shows how

XML is used to describe a weather report: <weather-report> <date>16, Sept, 2001</date> <time>12:45</time> <area> <city> Sharjah </city> <region> North. Reg</region> <country> UAE </country> </area>

XML Example: <measurements> <skies>partly cloudy</skies> <temperature>46</temperature> <wind> <direction>SW</direction> <windspeed>6</windspeed> </wind> <humidity>40</humidity> <visibility>10</visibility> </measurements> </weather-report>

Why XML XML is simple

Text-based and human readable Open, Standards Based

Much like TCP/IP, HTTP, HTML XML makes data more important than code

and is good for describing data XML enables powerful Web applications and is

available on (almost) all platforms XML will be the format and the data model for

all information flowing across applications, via messages, and through the web

Namespaces

Solves the “naming” and “sharing” problems Makes XML very extensible

Enables developers to mix data described by multiple schemas in one XML instance

Schema components are reusable in other schemas Qualifies data elements uniquely

<B:Title>Learning XML</B:Title> <C:Title>Dr.</C:Title>

Namespaces

URI’s are used for Scoping. Uniform Resource Identifiers (URIs)

Uniform Resource Name (URN) Location Independent, need not equate to

anything. Uniform Resource Locator (URL)

Location hints are embedded in identifier

Using Namespaces

To define a namespace for an element: Define the xmlns attribute and

assign it a Uniform Resource Identifier (URI)

<root><bk:BOOK

xmlns:bk="urn:BookStore.org:BookInfo" xmlns:money="urn:Finance:Money"> <bk:TITLE>A Suitable Boy</bk:TITLE> <bk:PRICE>22.95</bk:PRICE>

</bk:BOOK> </root>

<root><bk:BOOK

xmlns:bk="urn:BookStore.org:BookInfo" xmlns:money="urn:Finance:Money"> <bk:TITLE>A Suitable Boy</bk:TITLE> <bk:PRICE>22.95</bk:PRICE>

</bk:BOOK> </root>

HTTP Internet’s Request/Response

Protocol Ubiquitous cross-platform/language

support Highly scalable server-side

implementations are available Simple and Extensible protocol Typically the only thing allowed

through firewalls

A basic HTTP scenario User-Agent establishes TCP connection

to Server Typically over port 80

User-Agent sends HTTP request message to Server

Server processes request and sends back HTTP response message

An HTTP endpoint is identified by a Uniform Resource Locator (URL):

http://www.affendi.net/test/mmm.asp

HTTP operations HTTP 1.1 supports several built-in

methods GET and POST most common POST requests typically contain a

body used to pass information along with request

GET can only pass information using a Query String

HTTP messages HTTP request and response messages have

headers & optional body Headers contain method (GET/POST), URL and

HTTP version. Headers are text-based name:value pairs Headers are CRLF delimited Body starts after CRLFCRLF sequence Content-Length/-Type headers indicate size and

MIME type

Sample HTTP messages

POST /test/display.asp HTTP/1.1

Host: WWW.affendi.NET

Content-Length: 12

Content-Type: text/plain

Hello, World

GET /test/mmm.asp HTTP/1.1

Host: WWW.affendi.NET

HTTP responses HTTP responses begin with a status line

containing a numeric code and description 2xx: Success 4xx: User-Agent Error – Request contains bad

syntax or cannot be fulfilled 5xx: Server Error – The server failed to fulfill

an apparently valid request Also 1xx and 3xx codes.

HTTP/1.1 200 OK

Content-Length: 12

Content-Type: text/plain

Hello, World

Back to SOAP: Now Back to SOAP.

SOAP version 1.1 Specifies a simple and lightweight

XML messaging protocol for exchanging structured and typed information. Designed as an RPC mechanism

Bindable to many transports HTTP is currently the primary transport

Extensible Based upon its envelope structure

SOAP Spec consists of 4 parts An extensible envelope (XML) expressing

what is the message and what are its features whether the features are optional or mandatory.

A set of encoding rules for data Defines how data is represented in XML.

A convention for representing Remote Procedure Calls Defines how calls and returns are packaged in

XML. A protocol binding to HTTP

What SOAP messages over HTTP look like

SOAP HTTP Message Structure

SOAP Message

SOAP Envelope

SOAP Header

SOAP Body

Message Name & Data

Headers

HTTP Headers

XML Encoded SOAPXML Encoded SOAPMessage Name & DataMessage Name & Data

<Body> contains SOAP<Body> contains SOAPMessage Name & DataMessage Name & Data

Individual headersIndividual headers

<Header> encloses headers<Header> encloses headers

<Envelope> encloses payload<Envelope> encloses payload

Standard HTTP and SOAP HTTP HeadersStandard HTTP and SOAP HTTP Headers

The complete SOAP MessageThe complete SOAP Message

A Simple Request Example: < : : =" : -SOAP Envelope xmlns SOAP urn schemas

- : . 1">xmlsoap org soap v    < : ></ : >SOAP Header SOAP Header    < : >SOAP Body        < : m GetSalesTax

: =" : / : ">xmlns m urn myserver soap TaxCalc         < >100</ >SalesTotal SalesTotal        </ : >m GetSalesTax    </ : >SOAP Body</ :SOAP Envelope

A Simple Response Example: <SOAP:Envelope xmlns:SOAP="urn:schemas-xmlsoap-org:soap.v1">    <SOAP:Header></SOAP:Header>    <SOAP:Body>        <m:GetSalesTaxResponse

xmlns:m= "urn:myserver/soap:TaxCalc">            <SalesTax>4</SalesTax>        </m:GetSalesTaxResponse>    </SOAP:Body></SOAP:Envelope>

Sample SOAP (HTTP) Message

POST /sample/soapdemo.asp HTTP/1.1

Host: www.ctmsdev.net

Content-type: text/xml

Content-length: nnn

SOAPAction: Some-uri#MethodName

<SOAP-ENV:Envelope

xmlns:SOAP-ENV=http://schemas.xmlsoap.org/soap/envelope/

SOAP-ENV:encodingStyle=http://schemas.xmlsoap.org/soap/encoding/>

<SOAP-ENV:Header>

</SOAP-ENV:Header>

<SOAP-ENV:Body>

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

SOAP Headers Headers are optional

Associate special processing instructions with the request

Open-ended set of header entries Can be used for security, transactions, etc… Or any other special information that applies

to processing this message Individual header entry can be

optional/mandatory mustUnderstand=“1” indicates the recipient

must understand this instruction and obey it or fail processing.

Sample SOAP Message -- Header

<SOAP-ENV:Envelope

xmlns:SOAP-ENV=http://schemas.xmlsoap.org/soap/envelope/

SOAP-ENV:encodingStyle=http://schemas.xmlsoap.org/soap/encoding/>

<SOAP-ENV:Header>

<mynms:CurrIndex xmlns:myns=“My-uri”

SOAP-ENV:mustUnderstand=“1”>3</myns:CurrIndex>

</SOAP-ENV:Header>

<SOAP-ENV:Body>

…

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

SOAP Body Always mandatory This is where the method call and

response are encoded Errors can be reported on the response

Sample SOAP Request<SOAP-ENV:Envelope

xmlns:SOAP-ENV=http://schemas.xmlsoap.org/soap/envelope/

SOAP-ENV:encodingStyle=http://schemas.xmlsoap.org/soap/encoding/>

<SOAP-ENV:Header>

…

</SOAP-ENV:Header>

<SOAP-ENV:Body>

<m:MethodName xmlns:m=“Some-uri”>

<x>3</x>

<y>4</y>

</m:MethodName>

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

Sample SOAP ResponseHTTP/1.1 200 OK

Content-Type: text/xml

Content-Length: nnn

<SOAP-ENV:Envelope

xmlns:SOAP-ENV=http://schemas.xmlsoap.org/soap/envelope/>

<SOAP-ENV:Body xmlns;m=“Some-uri”>

<m:MethodNameResponse>

<return>24</return>

</m:MethodNameResponse>

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

SOAP Types SOAP specification specifies Simple as

well as Compound Types Simple types are defined in the section of

“Built-in data types” of “XML Schema Part 2: Datatypes”

String, int, boolean,float, etc… Compound Types are either Structs or Arrays

In Structs, the element names distinguish the different elements

In Arrays, the Ordinal postion serves to distinguish among the elements

WEB Services: SOAP made it possible to

implement RPC’s across the Internet.

Using SAOP, an application may transparently call a function implemented in server somewhere on the Internet.

Companies are now utilizing this feature to provide “WEB Services”.

WEB Services: A WEB service is simply a WEB

application or method callable across the Internet.

The vehicle is of course SOAP.

What is the Significance of this? The main significance of this is that the

Internet is being transformed from a network system into a huge global distributed system that may host a wide variety of distributed applications.

Users may now build distributed applications that consists of components that reside on other machines and platforms.

What is the Significance of this? Software may now be provided as a

subscription service. You license an application for a period

of time rather than buying it. Users may be able to control their

environments and do a wide range of things that were not possible before.

A huge amount of services will shortly be available across the Internet.

Current web applications

OS, Core Services

and Data

App Code

Web app developers took advantage of these local services and used HTML to “project” the UI to lots of clients.

Web app developers took advantage of these local services and used HTML to “project” the UI to lots of clients.

Browsers

Browsers

Internet

Historically, most development efforts have been directed toward building apps using rich local services.

Historically, most development efforts have been directed toward building apps using rich local services.

The Web Services View

OS andLocal

Services

App Code

Application SpecificWeb Services

Building BlockWeb Services

Vertical and PortalServices

DevicesBrowsers

Internet

Web Services are building blocks that enable developers to build and aggregate applications and services from local and remote resources for a range of clients.

Web Services are building blocks that enable developers to build and aggregate applications and services from local and remote resources for a range of clients.

What are Web Services? A web-addressable resource that

provide data and functions for programmatic access.

WEB Services:

ClientProgram

ServerProgram

Proxy Stub

Transport Transport1 0 01 1

SOAP

WSDL

UDDI -DISCO

Building Block Standards XML

Standard way to represent information

Used to build all other protocols HTTP

Transport Layer Scalable

Web Service Protocols Simple Object Access Protocol (SOAP)

Remote Procedure Calls Web Services Description Language (WSDL)

Describe Web Services Discovery Protocols

DISCO Tied to a particular URL

UDDI Universal Description Discovery and Integration Building Web Service catalogs and finding Web

Services from central repositories

RoutingRouting

XMLXML

Web Service Infrastructure

CommunicationCommunication DescriptionDescription DiscoveryDiscovery

SOAPSOAP(XML Protocols)(XML Protocols)

DiscoDisco

Service Service DescriptionDescription

(WSDL)(WSDL)

Process Process Orchestration Orchestration

(XLANG)(XLANG)

PackagingPackaging

HTTPHTTP

XMLXML

XMLXML

XML SchemasXML Schemas

SecuritySecurity

ReliabilityReliability

Directory (UDDI)Directory (UDDI)

What are Web Services? Building blocks for constructing

distributed applications Independent of platform, object model and

language Based upon open Internet Standards Internet or Intranet Loosely coupled

Higher levels of application integration Software as a service

The programmable web

Access dataAccess data

CommerceCommerce

TransactTransactbusinessbusiness

Leverage yourLeverage yourexperienceexperience

Web ServicesWeb Services

PublishPublish

CollaborationCollaboration

SecuritySecurityChasmChasm

BusinessBusinessChasmChasm

IntegrateIntegrate the Web with the Web with business systemsbusiness systems

TransformTransform the way you the way you conduct businessconduct business

Get yourGet yourinformation oninformation onthe Webthe Web

VVAALLUUEE

Illustrating the Idea: A Simple LookUp Example:

LookUp

Methods:

• FindPerson

• GetPersonList

Web Service Specifications HTTP – transport XML – packaging SOAP – method/response formatWSDL – services and types UDDI and DISCO

(Web) Services Description Language Need a way to describe Web

Services As documentation for the Web

Service For Tools / Platforms to automate the

details of communication WSDL 1.0 is a new standard for

doing this.

A Service Description fragment – Service Description

<serviceDescription xmlns:s0="http://tempuri.org/main.xsd" xmlns:s1="" name="WebService1" targetNamespace="" xmlns="urn:schemas-xmlsoap-org:sdl.2000-01-25">

<soap xmlns="urn:schemas-xmlsoap-org:soap-sdl-2000-01-25">

<service>

<addresses>

<address uri="http://localhost/websx/webservice1.asmx"/>

</addresses>

<requestResponse name="FindPerson“ soapAction="http://tempuri.org/FindPerson">

<request ref="s0:FindPerson"/>

<response ref="s0:FindPersonResult"/>

</service>

</soap>

A Service Description fragment -- Types

<schema targetNamespace="http://tempuri.org/main.xsd" xmlns="http://www.w3.org/1999/XMLSchema">

<import namespace="http://www.w3.org/1999/XMLSchema"/>

<element name="FindPerson">

<complexType> <element name="strEmail" type="string" nullable="true"/> </complexType>

</element>

<element name="FindPersonResult">

<complexType> <element name="result" type="s0:Person"/> </complexType>

</element>

<complexType name="Person">

<element name="strEmail" type="string" nullable="true"/>

<element name="strFirstName" type="string" nullable="true"/>

<element name="strLastName" type="string" nullable="true"/>

</complexType>

Discovery Used to locate a Web Service’s description DISCO is targeted discovery

Looking directly at a particular site Web crawlers

UDDI is a centralized services directory Geared toward finding standard services from a

centralized registry UDDI defines an API executed via SOAP UDDI hold pointers to the details (WSDL or

DISCO) Let’s look at DISCO a bit further

DISCO in practice

http://resource

<discovery> information about resource</discovery>

HTTP request

Sample DISCO Documents<?xml version="1.0" ?><discovery xmlns="http://schemas.xmlsoap.org/disco/"><contractRef ref="/calc/Calc.asmx?sdl" docRef="/calc/Calc.asmx"

xmlns="http://schemas.xmlsoap.org/disco/scl/" /></discovery>

<?xml version="1.0" ?>- <discovery xmlns="http://schemas.xmlsoap.org/disco/"><discoveryRef ref="/CPPWS/CPPWS.disco" /><discoveryRef ref="/Calc/Calc.disco" /><discoveryRef ref="/CalcForm/CalcForm.disco" /><discoveryRef ref="/Calculator/Calculator.disco" /><discoveryRef ref="/CPPWS/CPPWS.disco" /><discoveryRef ref="/WA1/WA1.disco" /><discoveryRef ref="/WS1/WS1.disco" /><discoveryRef ref="/WS2/WS2.disco" /></discovery>

The SOAP Toolkit

Local Services

SOAP

App Code

Application SpecificWeb Services

Building BlockWeb Services

Vertical and PortalServices

DevicesBrowsers

ROPE

The Toolkit enables you to: • Expose Web services by generating

an XML service description from a COM component’s type library

• Consume Web services automatically in VB by turning the contract into a programmable proxy with a Remote Object Proxy Engine (ROPE)

• Receive SOAP requests from a SOAP client (e.g., the proxy) with an ASP or ISAPI “listener”

The Toolkit enables you to: • Expose Web services by generating

an XML service description from a COM component’s type library

• Consume Web services automatically in VB by turning the contract into a programmable proxy with a Remote Object Proxy Engine (ROPE)

• Receive SOAP requests from a SOAP client (e.g., the proxy) with an ASP or ISAPI “listener”

SD

LSD

LSD

LA

SP

ASP

ASP

Thanks Thank you for attending and

listening. WaSalamu Alaikum Wa Rahmatu

Allah.