Application-to-application communication and Web services

1. Application-to-application communicationand Web services ISD3

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, resources, standards; processes • In Computer systems , reuse is about use of generic software components – classes, functions • Hosted applications (Blogger, Flickr, 37Signals, Del.icio.us) is about reuse of entire applications

5. Two different Web architectural styles • Web services with SOAP or other protocol • REST with just URLs over HTTP • Amazon's web services have both SOAP and REST interfaces, and 85% of the usage is on the REST interface. (He 2004)

6. 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

7. 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)

8. 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.

9. Simple GET Interaction • Request/Response pattern server client Get Request (+ parameters) function Response

10. 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.

11. 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.     • URLs can be • Bookmarked perhaps using del.icio.us • Stored in a database • Communicated e.g. if I want another lecturer to check on a programme structure, I email the URL with a comment (instead of giving her instructions about how to find this resource using a given navigational interface) • POST, Frames , Flash, Java Applets all defeat simple URLS

12. Example • The currency converter example was set up as a server.  • The SMS server is the client in this connection, the calculator script the server • cursms.xql

13. Simple Interaction • Request/Response pattern SMS server Currency script On $host cursms.xql $message= CUR 100 USD NZD $from=4478678777 • $response = • file(“$host?text=100+USD+NZD&code=CUR8&from=4478678777”); text=100+USD+NZD&code=CUR8&from=4478678777 convert Reply: 100 US Dollars is 130 NZ Dollars print $response; e.g. $host=“stocks.cems.uwe.ac.uk:8080/exist/servlet/ChrisWallace/calulator”

14. 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 requires tricky programming using pattern-matching 

15. XML responses • Define a schema for the response • Publicise this schema as part of the interface to the SMS server • Return all replies as XML • Program can use generic XML parser to read <Reply> <action>Send</action> <message> 100 US Dollars is 130 NZ Dollars</message> </Reply>

16. RESTRepresentational State Transfer • An architectural Style (or Pattern) whose name was suggested by Roy Fielding in 200 • Key ideas • Every resource has a unique URI – Logical not Physical • Request uses HTTP GET with simple URI • Reply is an XML document, a summary of the resource, with links to related resources • State of interaction is held only by the Client • Client can fetch further detail as the user selects links • no need for session • Use HTTP operations (GET, POST, PUT, DELETE) to provide a CRUD interface to the information resources

17. Example : Modules and Programmes • Request data about a module www.uwe.ac.uk/Module/UFIEKG-20-3 this may be re-written to become : www.uwe.ac.uk/fold/module.xql?code=UFIEKG-20-3 But this is transparent to the client, allowing changes in server implementation • Receive XML document <module id=“UFIE8V-20-3> <title>Information systems development 3</title> <credits>20</credits><level>3</level> <specification link=“www.uwe.ac.uk/ModuleSpec/UFIE8V-20-3”/> <run link=“www.uwe.ac.uk/ModuleRun/UFIE8V-20-3&version=2006/1”/> </module> • Reply is a summary of data, with links to related resources • Client will present this and provide navigation

18. Server • Need to decide on • the Resources to be provided • Module • Run • Collections can also be resources • All Modules in a Field for a given Year • The granularity of the data • Slow reveal, not everything at once • The schemas for the ‘representation’ • Provide mapping (de-referencing) from URI to internal calls • Provide access to the schemas themselves

19. Client • Client may be • Running Server side, constructing a static HTML page for the end user • Running Client-side, with JavaScript code to unpack the XML and dynamically construct pages • End users obtain client code from the service provider • AJAX enables complex Client-side scripting

20. Example • New site isbn.com • http://isbndb.com/ • http://isbndb.com/data-intro.html • Create an account • Create an access key http://isbndb.com/api/books.xml?access_key=TRE9KNJB&index1=isbn&value1=156592262X Response is <?xml version="1.0" encoding="UTF-8" ?> - <ISBNdb server_time="2006-03-09T07:17:03"> - <BookList total_results="1" page_size="10" page_number="1" shown_results="1"> - <BookData book_id="java_in_a_nutshell_a01" isbn="156592262X"> <Title>Java in a Nutshell</Title> <TitleLong>Java in a Nutshell (The Java Series)</TitleLong> <AuthorsText>David Flanagan,</AuthorsText> <PublisherText publisher_id="oreilly">O'Reilly</PublisherText> </BookData> </BookList> </ISBNdb>

21. REST sources • wikipedia entry • http://en.wikipedia.org/wiki/Representational_State_Transfer • Roger Costello • http://www.xfront.com/REST-Web-Services.html • Roy Fielding’s PhD (2000) • http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm • Hao He, 2004 Implementing REST Web Services: Best Practices and Guidelines • http://www.xml.com/pub/a/2004/08/11/rest.html • They are all here and may be updated (and a great Rest example): • http://del.icio.us/perdika/rest

22. Web services via SOAP • 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.

23. 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 can 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.

24. 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 ISBN for UML Distilled by Martin Fowler • Run my simple client

25. 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

26. SOAP and Java • Object-orientation is at the heart of all modern approaches 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

27. Web services as information services • WSDL defines (part of ) the formal interface • But what defines the information quality of the 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?

28. 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 • Web2.0 is based on • sharing • trust