Current Trends in Network- Based Application Developments Bill Chu Department of Software and...

Current Trends in Network-Based Application Developments

Bill ChuDepartment of Software and

Information SystemsUNC Charlotte

© Bei-Tseng Chu Oct 2002

Web Service Likely the next architecture for

internet based business computing A web service communicates over

a network to supply a specific set of operations (methods) that other applications can invokes


Web service and screen scrapping Many early web services

implementations are deployed to replace “screen scrapping”

Rather than pulling data off web sites with the implicit understanding of the data format, which is subject to change, web services can obtain data in XML and application standards


Architectural difference Current Web applications (including

servlets) are based on a client-server architecture When a servlet talks to another servlets, one is

taking on the role of a client Web services are equal, or peer to peer Three-tier model with key differences

Loosely coupled Based on ubiquitous architecture The promise of open standards


Multi-tire architecture

Web serverWeb application

serverBrowser

Data baseBusiness

object

Business

object

Business

object

Business

object

Business

object

Business

object

Web services


Web service examples www.xmethods.net, www.salcentral.com Ziplocator service Dollar Rental Car Zagat Survey (restaurant and hotel info) Credit authorization Human Resource outsource service


Brokering Architecture

Client

ServiceBroker Service

Provider 1

Service Provider 2

Subscribe: service description




Client


Provider 1

Service Provider 2



Recommend: service description

Service Provider 2



Client


Provider 1

Service Provider 2

Request

Response


XML-RPC: forerunner to SOAP XML formatted message Using HTTP Post to transmit the message Enable any web service with CGI

interface to accept the message Universal acceptance, even through

firewalls! Many implementations: www.xmlrpc.com


An example XML-RPC RequestPOST /RPC2 HTTP/1.0User-Agent: Frontier/5.1.2 (WinNT)Host: someserver.comContent-Type: text/xmlContent-length: 181

<?xml version=“1.0”?><methodCall>

<methodName> lookup.getStateFromAreaCode </methodName><params>

<param> <value> <int> 512 </int> </value></param>

</params></methodCall>


An example of Response to the RequestHTTP/1.1 200 OKConnection: closeContent-length: 158Content-Type: text/htmlDate: Fri, 17 Jan 2001 11:50:13 GMTServer: UserLand Frontier/5.1.2-WinNT<?xml version=“1.0”?><methodResponse>

<params><param> <values> <string>Texas</string></value></param>

</params></methodResponse>s


SOAP (Simple Object Access Protocol) SOAP defines XML based format for sending

messages Envelope Data encoding RPC convention

Unlike XML-RPC, SOAP tries to be neutral to transportation protocol

HTTP SMTP Java Message Service

.Net also uses SOAP as the RPC mechanism


A generalized SOAP architecture

HTTP

SMTP

FTP

JMS

Others

SOAPEnvelope

SOAPServer

ServerApplication


Deployment Descriptor (APPACHE)<isd:service xmlns:isd=“http://xml.apache.org/xml-soap/deployment”

id=“urn:Publications”><isd:provider type=“java”

scope=“Application”methods=‘getPubCount getModDate getByCode”>

<isd:java class=“com.lanw.soapsrvr.PubsServer” static=“false”/></isd:provider><isd: faultListener> org.apache.soap.server.DOMFaultListener</isd:faultListener></isd:service>


Java methods for the serverpackage com.lanw.soapsrvr;

Import java.util.*;Import org.w3c.dom.Element;

Public class PubsServer {

//….

Public Element getByCode( String code) throws SOAPException {//….}/….}


Client using the service//….

URL url = new URL(“http”, “www.soap.uncc.edu”, 8080, “soap/servlet/rpcrouter”);

Call call = new Call();call.setMethodName(“getByCode”);

Vector params = new Vector();Params.addElement(new Parameter(“param”,String.class,”1234”,

Constants.NS_URI_SOAP_ENC));call. setParams(params);

Try {resp=call.invoke(url, “ “);

} catch (SOAPException e) { //…}


Universal Description, Discovery, and Integration (UDDI)

Directory for web services XML formatted information for

Contact points “white page” Industry classification “yellow pages” Web service discovery “green page”,

technical information UDDI registry


Web Service Description Language (WSDL) Defines a web/network service

End point Accepts messages

Key elements of a web service Documentation – English description Types – data type (e.g. structure) Message – message format PortType – Java class and their operations Binding – protocols for message or portType Service – Specifies web addresses

WSDL description may be automatically generated based on Java class definitions


Microsoft .Net A framework for network-based

application development Provides a middleware for web-services

to communicate with each other Specifically designed to address the

following problems Lack of consistent access Proprietary data formats Isolation of information


.Net components Cross language interoperability

Allows components written in different programming languages to work with each other

Use Inheritance

Self-describing components Common Type System Application domain

Unit of processing and security policy enforcement .NET My Service

Streamline the use of authentication information


Example of cross language interoperability: Box Class in C#Public class Box{

Public Double Length, Width, Height;Public Box () {

Length=0; Width=0; Height=0; print();}public void print() {

System.Console.WriteLine(“Length=“+Length.ToString()+”Width=“Width.ToString()

+”Height=“Height.ToString());}} VB.NET Simple InheritancePublic Class Car : Inherits Box

Private iAxils as IntegerProperty Axils as Integer

Get Axils=iAxils End GetSet iAxils = Value End Set

End PropertyEnd Class


.net: Microsoft Intermediate Language (MSIL) All .net applications are compiled

into this language Preserves metadata about the

components Verified for type safety JIT compiled into native assembly

language for execution


ASP.NET Solve the following problems of

classic ASP Interpreted ASP/VB scripts Lack of maintainability as all

components are contained in one file State Management Use of COM objects/lack of

interoperability


.NET My Service User store identity information in the Passport. Web services can cooperate and share information under the control

of information owner Routing: specify the routing path of a SOAP message and also what

part of the message is intended for which receiver Referral: how a SOAP intermediary can modify the routing Security: SOAP does not address message security.

Credentials: authenticate the origin of the message Integrity: verification of message integrity (digital signature) Confidentiality: encryption of SOAP messages

Microsoft Passport Provide a single Internet identity accepted by many sites User authentication by sites can be handled indirectly through MS Passport

server system A single passport ID and password can get one into multiple sites

Current Trends in Network- Based Application Developments Bill Chu Department of Software and...

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