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Technologies

Technologies. For use on different layers. Technologies. Client tier Client tier to middle tier protocols Middle tier technologies Middle tier to data tier technologies. But first…what is a protocol?.

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Technologies

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  1. Technologies For use on different layers

  2. Technologies • Client tier • Client tier to middle tier protocols • Middle tier technologies • Middle tier to data tier technologies

  3. But first…what is a protocol? • ‘In computing, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of communication. Protocols may be implemented by hardware, software, or a combination of the two. At the lowest level, a protocol defines the behaviour of a hardware connection.’ – www.wikipedia.org

  4. Wikipedia.org… • Protocols are generally used to define real-time communications behaviour. Most protocols specify one or more of the following behaviours: • Detection of the underlying physical connection (wired or wireless), or the existence of the other endpoint or node • Handshaking • Negotiation of various connection characteristics • How to start and end a message • How to format a message • What to do with corrupted or improperly formatted messages • How to detect unexpected loss of the connection, and what to do next • Termination of the session or connection

  5. Client tier • Client applications • Human to human communications: • E-mail, instant messaging, USENET news, chat. • File transfer or file swapping. • Remote login. • Proprietary applications (e.g. a multi-user game). • Clients hosted in a Web browser can use the following: • HTML forms. • JavaScript. • Proprietary plug-ins (e.g. Flash). • ActiveX controls. • Java applets.

  6. Client tier protocols • IMAP for e-mail • AIM for instant messaging • HTTP/CGI for HTML forms • Browser Apps and plug-ins can be written in: • Java, C++, Eiffel, Fortran, even Cobol. • Need a compiler for your chosen language that will put the code into a DLL (MS Windows) or shared library (UNIX).

  7. HTML • Visually rich and widely supported. • Forms are primitive and not automatically validated on the client. • Not visually pleasing ( step through pages, each of which flashes white before it is drawn).

  8. JavaScript • Permits some programming on the client side. • E.g. data validation. • Interpreted, so slower than compiled code. • Not purely object-oriented. • Different browsers provide different levels of support.

  9. Plug-ins and ActiveX • Plug-Ins • Can provide client interaction. • Need to be downloaded and installed. • Each one requires different programming expertise. • Must be ported by supplier to each new platform. • ActiveX controls • These are 32-bit Windows binaries, hosted by a web browser. They can only run on Windows. • Controls such as clocks and calendars can be added to forms.

  10. Java and new clients • JAVA • Simple • Pure object-oriented language. • Prohibits access to resources on the local machine without user authorisation. • New clients • Mobile phones • PDAs (Personal Digital Assistant) • Most of the technologies have a version for these.

  11. Client tier to middle tier protocols • Communicates between the client and the server. • Layered: • At the bottom, TCP/IP • SSL (Secure Socket Layer) which encrypts and decrypts information for privacy and integrity (optional layer). • Secure HTTP (HTTPS), allowing a client to request a document by URI and get back the contents of that document (e.g. Squirrelmail) (optional layer). • JRMP (Java Remote Method Protocol) allows Remote Method Invocation (RMI), allowing an object to send a method to a remote object.

  12. aClient aServant JRMP HTTPS (Optional) SSL (Optional) TCP/IP How RMI can use a network After O’Docherty, M.,’Object-Oriented Analysis and Design’, p245, Wiley, 2005

  13. Continued… • Commonly used protocols can be specialised and general: • Specialised: • IMAP (e-mail) • AIM (AOL Instant Messaging) • NNTP (USENET news) • HTTP / CGI (HTML forms) • FTP (File transfer protocol) • Telnet (remote login) • General: • TCP/IP (low level transport, also known as sockets) • JRMP (for Java-to-Java communications) • IIOP (for CORBA communications • Like RMI, but lots of different languages.

  14. Middle tier technologies • This tier (layer) is reached when the user’s interaction with the system is accepted and has been passed on to a server. • Server applications may be multi-threaded and designed for high capacity. • A server application ‘listens’ to a port (connection point) for clients to connect. • Applications can be stand-alone or can be run from a web-server.

  15. Stand-alone applications • Mail, messaging, news, chat servers. • FTP daemon • A daemon is a type of housekeeping task, that is used by the operating system in a multitasking environment, to ensure that all tasks are properly initiated and ended. • Telnet daemon • Naming services • These allow clients to find the server object by name E.g.: • CORBA registry • RMI registry or • Java Naming and Directory Interface (JNDI) server ( a general name-to-thing mapping service) • Proprietary server (e.g. a process hosting CORBA or RMI objects, an EJB client or a .NET client).

  16. Server code • Hosted by a web server: • JSP (Java Server Pages) for building Web pages. • Raw HTML interspersed with Java code. • ASP (Active Server Pages) (VB version) • CGI scripts • Textual files written in a command language (e.g. PERL – usually invoked by HTML) • Servlets (Java server objects that are instantiated on demand by applets, JSPs or HTML forms).

  17. Middle tier to data tier technologies • To access the data tier, either: • Include database-client code on the middle tier, sot we can access a DBMS running on the data tier (e.g. using Java and JDBC (Java Database Connectivity)) • Use same protocols as for client-to-middle tier • Use some non-TCP/IP protocol (legacy system) • Include Enterprise Java Beans (EJB) client code in our middle-tier server and access the data tier via EJBs (see next slide) • Include .NET code in the middle tier server. (Microsoft version of EJB)

  18. Enterprise JavaBeans • The Enterprise JavaBeans (EJB) specification is one of the several Java APIs in the Java Platform, Enterprise Edition. • EJB is a server-side component that encapsulates the business logic of an application. The application server provides: • persistence • transaction processing • concurrency control • events using Java Message Service • naming and directory services (JNDI) • security • deployment of software components in an application server • remote procedure calls using RMI-IIOP or CORBA • Additionally, the Enterprise JavaBean specification defines the roles played by the EJB container and the EJBs as well as how to deploy the EJBs in a container. • Wikipedia.org

  19. How they fit together

  20. Client tier

  21. Middle tier

  22. Data tier

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