Application-to-application communication

and Web servicesISD3

Lecture 9

Connecting Information Systems• Application silos

– Typically applications in a company are build with all three layers coupled together, perhaps with a web presentation layer

• Personnel (HR)• Project Management (PM)• Payroll• Purchase Order processing

– Application interactions• PM needs access to staff details• Job sheets are information about projects and payroll• PM system generates and tracks purchase orders

– Applications may be in different organisations:• Purchase Order processing in company X • To Order processing in supplier Company Y

• Service Oriented Architecture– Enabling the use of data and services in each application within

and between organisations

Silos to SOA

Reuse

• In Information Systems reuse is about use of existing information and information services - objects

• In Computer systems , reuse is about use of generic software components - classes

Creating a web service• For the client:

– Discovering an information service which provides the required information– Understanding the data quality supported.– Understanding the communication protocol– Writing the client and converting the information

• from the form it which it is provided • to the form in which it will be used. 

• For the server – Recognising a common service requirement– Establishing the right to disseminate the information.– Understanding the legacy system– Developing the service– Describing the interface to the service– Publishing the information– Gaining financial or other benefits from the service– Ensuring the security and reliability of the service

Web services in practice

• www.webservicex.net provides a range of free services. We will use a few of these in the workshop next week.

• Another collection of web services is Xmethods.  Here there is also a simple interface to try a service.

• Other web services will require a payment to use. • Web services used within an organisation to provide a

clean interface between information providers and information requirers.

• Web services can be put on top of legacy systems to enable integration of existing systems.

• Web services lead to a Service Oriented Architecture (SOA)

Mechanisms

• These are all variations of the simple interaction protocol – one request with parameters sent, one reply returned.

• The differences lie in– the underlying communications protocol used

(these are all HTTP based) – in the way in which parameters are packaged

for sending and reply.

Simple Interaction

• Request/Response pattern

client server

function

Response

Request (+ parameters)

Simple URL

• Client-side– Parameters passed using GET with a formatted reply– Parameters are send in name=value pairs, each

value URL-encoded (space replaced by ‘+’,  odd characters replaced by %hex value).

– Limited data structuring available (but names can be repeated). 

– One or more parameters might be used to specify which operation to perform. 

• operation=query means execute a query• operation=update means add a record to the database.

– The reply is a page whose structure is determined by the server.  The client will be responsible for parsing the input to extract the information. This might range from a simple string to a complex XML document.

Simple URL

• Server-side– Script is invoked just as if it had been the target of a

link on a page or a form. – In PHP the parameters themselves can be accessed

by :• $name (if the installation variable register_globals is set) • $_GET[‘name’]  or $_POST[‘name’].

– Reply can be any string whose structure is determined by the service application

• Testing and testing scripts are easy to set up.    • . 

Example

• The currency converter example was set up as a server. 

• The SMS server is the client in this connection, your script the server

Simple Interaction• Request/Response pattern

SMS server

Currency script

/~astudent/cur.php

converttext=100+USD+NZD&code=CUR8&from=4478678777

$message= CUR8 100 USD NZD

$from=4478678777

Reply: 100 USD = 130 NZD

$response = file(“http//www.cems.uwe.ac/~astudent/cur.php?text=100+USD+NZD&code=CUR8&from=4478678777”);

print $response;

Page scraping

• HTTP get as before• Server is unaware that the client is another application,

not a browser. • The information in the reply is contained in a normal web

page• Complex parsing of the result is required to dig out the

required information.• This ‘html-scrapping’ is common but there is no

guarantee that the format of the page or its location will remain stable, so it’s a very risky approach. 

• Parsing the html page and the data is also difficult.•  

Web service• Web services are a response to the problems of the simple URL based

mechanism.  – The main problem is the formatting of the sent and received data. If there was a

standard way of formatting both, and a standard way of describing that format, life would be much easier. 

• Web service interaction– an XML file sent using HTP POST – response is also an XML document– the client has to parse the returned XML document to discover what information

has been provided.  • Parsing XML is not a simple task, but with the increased use of XML, it is a

routine task, for which many packages already exist.  PHP has built-in support for XML parsing. 

•  • The convention for the structure of both the sent and returned data is called

SOAP Simple Object Access Protocol).•  • There also needs to be a way of describing the structure of both documents,

there is a third use of XML – in the Web Service Definition Language WSDL.

Web services and PHP

• Creating a web service at a low level is a bit complicated but packages are available in most languages such as PHP, Perl and Java to simplify the task of writing a client or server.

• We will use a package for PHP called nusoap.  It can be downloaded from here, and just needs to be unzipped into a suitable directory to use. . It is an open source project under Sourceforge.

• SOAP is included in PHP5 and the interface is slightly different, but this package works fine with PHP4.

ISBN application

• One of the free web services is a service to locate book details given the ISBN – International Standard Book Number

• 0-201-32563-2 is the ISB for UML Distilled by Martin Fowler

• Run my simple client

• Show the script

ISBN Web ServiceThe interface is defined by the WDSL for this service. Service URI:

www.webserviceX.NET/isbn.asmx

Operation: GetISBNInformation

 Parameters:  

Code Output:

An XML structure with fields for:AUTHORFULLTITLESHORTTITLEISBNDATESUBJSECTPUBLISHER

 

SOAP and Java

• Object-orientation is at the heart of all modern approachs to systems development – Java, .NET, Object-oriented databases…

• SOAP is object-oriented but it has a much simpler model than Java and other object oriented languages.

• The following slides contrast the two

Feature Java SOAP (Simple Object Access Protocol)

unit object object aka service

encapsulates.. state and behaviour state and behaviour

reference to object internal hidden pointer URL

scope all objects in the same program

the entire web

message format layer

JVM SOAP

transport layer JVM HTTP (and others)

interface methods operations

method categories adhoc service

direct access to state possible but inadvisable no

Feature Java SOAP (Simple Object Access Protocol)

request procedure call sending a SOAP package with parameters expressed in XML

example myDictionary.get ('0-201-72219-4')

<soap:Envelope ..><soap:Body><getbyISBM><Code>0-201-72219-4</Code></getByISBN></soap:Body></soap:Envelope>

Feature Java SOAP (Simple Object Access Protocol)

response value or object reference a SOAP package with data in XML

example a (reference to) another object e.g. a Dictionary

<soap:Envelope ..><soap:Body><getByISBNResult><author>Budgen</author><title> Software Design</title>..</getByISBNResult></soap:Body></soap:Envelope>

human readable no yes

object creation within program external

object deletion garbage collection external

classes extensive base class library + application libraries

no classes

Feature Java SOAP (Simple Object Access Protocol)

description of interface

the class definition WSDL (Web Service Definition Language)

interface checking at compile time at runtime

class reuse yes in base library no

locating suitable object

no or adhoc published service describe by UDDI (Universal Description, Discovery Integration)

object reuse Java Beans ? service is unit of reuse

lifetime runtime of program (if not saved to disk)

Persistent

speed 1 100

security is an issue no yes

Web services as information services

• WSDL defines (part of ) the formal interface• But what defines the information quality of he

service?– Which are books in the ISBN service – what’s the

coverage of the service?– How current is the data? – How accurately has the data been collected?– Who is responsible for the content of the service?– What guarantees of service availability?– How stable is the defied interface?

Web Service Security issues

• Web services open up an application to the web and to malicious access– Accessing confidential data– Unauthorised interaction with a core system– Denial of service attacks