Application-to-application communication and Web services

1. Application-to-application communicationand Web services ISD3 Lecture 9

2. 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

3. Silos to SOA

4. 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

5. 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

6. 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)

7. 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.

8. Simple Interaction • Request/Response pattern server client Request (+ parameters) function Response

9. 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.

10. 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.     • . 

11. Example • The currency converter example was set up as a server.  • The SMS server is the client in this connection, your script the server

12. Simple Interaction • Request/Response pattern SMS server Currency script /~astudent/cur.php $message= CUR8 100 USD NZD $from=4478678777 • $response = file(“http//www.cems.uwe.ac/~astudent/cur.php? • text=100+USD+NZD&code=CUR8&from=4478678777”); text=100+USD+NZD&code=CUR8&from=4478678777 convert Reply: 100 USD = 130 NZD print $response;

13. 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.

14. 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.

15. 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.

16. 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

17. ISBN Web Service The 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: AUTHOR FULLTITLE SHORTTITLE ISBN DATE SUBJSECT PUBLISHER

18. 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

23. 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?

24. 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