Pervasive Web Application Architecture. History Scalability Availability Development Application Architecture

Transcription

1 Pervasive Web Application Architecture History Scalability Availability Development Application Architecture

2 It support multiple devices, such as PCs, WAP phones, PDAs and voice-only phones enables to access web servers through voice gateways. The architecture addresses the special problems associated with pervasive computing, including diversity of devices, markup languages and authentication methods.

3 History The problems that application programmers initially faces when implementing web applications with browser access from PCs have, to a large degree, been resolved. Various technologies are available that allow application programmers to create transactional web applications in a straightforward manner, supported by a large number of tools.

4 The advent of pervasive computing, application programmers now face many new challenges. Users have many different devices that look and behave in very different ways. Different user interfaces Different markup languages Communication protocols Authentication protocols Web applications that support pervasive computing should adapt to whatever device their users are using. Application must provide in a form that is appropriate for the user s particular device WML, VoiceXML, HTML and so on.

5 As a consequence, architectures for pervasive computing application must not allow for filtering of unnecessary information, and for output targeted to different flows of interaction depending on the user s device. Another challenge that is posed by pervasive computing is increased scalability and performance requirements. The frequency of users accessing the application from mobile phones will be higher than that of PC users, as the phone always available. Pervasive computing web applications need to scale to larger numbers of users than classical OC-only web applications.

6 Scalability Given the ever-growing number of pervasive computing devices, scalability of pervasive computing applications is a very important issue. An example, large telecommunication companies expect millions of users to subscribe for some applications.

7 Availability It is of particular importance in the pervasive computing environment. For example, most users of pervasive computing devices and applications will neither understand nor accept comments like server currently down for maintenance if a service is not available when they need it, they will assume that it does not work, and will stop using the application or switch to another service provider.

8 Both the scalability and availability issues can be resolved by system topologies that employ parallelism and redundancy.

9 Firewall Firewall WAP Gateways Voice Gateways Authentication Proxies Network dispatcher Authentication Credential directory Server Application Server Back-end applications PDA Gateways Demilitarized zone Network dispatcher Database Server Scalable topology for PCWA

10 Development To implement web applications, four roles are in a team as follows Business logic designers functions and application flow to be performed. User interface designers responsible for look and feel, and good usability. Application programmers work with web applications such as HTML, JSPs, etc. Experts for existing legacy database and transaction systems for implementing the application logic and connectivity to database and transaction systems in the back end.

11 In addition to the above team a pervasive computing specialist, who knows about the capabilities of devices and the infrastructure required to support pervasive computing applications. For ex: WAP gateways, Voice gateways and gateways for PDAs. Generally WML, and VoiceXML, which normally cannot be handled well by traditional web designers.

12 Pervasive application architecture The Model View Controller is a good choice when implementing web applications. The controller is implemented as a servlet. The model implemented as a set of EJBs. The views as JSPs.

13 MVC The simplest way to implement Web applications generating dynamic content is to use JSPs that receive a request. It invoke application logic to perform the required operations on the server side. Finally create and return and appropriate response. Client Request Response JSP Application logic

14 Limitations with simple MVC It is too inflexible for real-life web applications. It does not provide appropriate separation of responsibilities between Java programmers and Web designers.

15 1.Request Controller 2.Execute Command Beans 3.Access Model Model Ex: EJB Client 4. Pass request with reference to command bean 6.Response Views Ex: JSP 5.Get result properties The Web Application based on the MVC

16 Action Action MVC pattern applied to pervasive computing applications Command Bean - 1 Command Bean - 2 Model-1 PC Controller Command Bean - 3 Model-2 Web Application (Server) WAP Controller Model-3 Voice Controller WAP View-1 Model-4 WAP View-2 PC View-1 Voice View

17 Session DB DB DB Application Application Application Security State Security State Bean Security Policies Secure access Content Delivery Content Authentication servlet Device connectivity infrastructure Secure pervasive architecture

18 3..Invoke authentication Device specific authentication (servlet or web server) PC PKI smart card authentication WAP WIM authntication Form-based authentication Form-based authentication (WML) 5.Establish session 6 Session (2, 7) Check 1.Request 11.Response Proxy 8.Check policy 9.Invoke application 10.Response Application Security Policy Form-based authentication with a WAP phone (first request)

19 Session 1.Request 11.Response Proxy (2) Check 4.Invoke application 5.Response Application 3. Check policy Security Policy Form-based authentication with a WAP phone (subsequent requests)

20 Secure MVC application Secure JSP application Interaction between the authentication servlet and application servlet via the session object Components used by the secure pervasive access framework