Time Scalability Single User Unlimited Users 100s of Users Several Users PC based Single user Late 1980sNow PC based, file-level locking Single user or Peer-to-Peer LAN based Max users depends upon file-handles 2-tier Client/Server user=process 3-tier Internet Client/Server pooling connection n-tier Internet Client/Server Business components, servlets s of Users Mainframe Mid-1990s 3-tier Internet Client/Server single stateless connection per CGI call Client/Server File-sharing Database scalability eras

Time Scalability Single User Unlimited Users 100s of Users Several Users Dataease, Paradox, Dbase... Late 1980sNow Access, Paradox Oracle Forms application on internal network Coldfusion, ASP Java applications, applets etc 1000s of Users Mid-1990s Common Gateway Interface: Perl scripts... Many early web-enabled apps Client/Server File-sharing Database scalability eras CRUD tutorials

Internet TCP/IP Early Internet Client/Server Server HTML Documents Clients Web Browsers 1) Select URL 2) Send HTTP3) Wake up and process request 4) Return required HTML 5 ) Browser interprets HTML

Data aware Internet Applications 1) Select URL 2) Send HTTP3) Wake up and process request 5) Return required HTML with data embedded 6 ) Browser interprets HTML Dbms Web Server 4) get some data CGI or Web-server extender module

BC4J Alternative (simplified) Browser AppserverDB server(s) HTTP JSP Runtime Environment BC4J Application Module View Object One or more physical servers

Issues with web-enabled databases Statelessness is a big issue: –How do you carry information between forms? –How do you carry information throughout a session? –How do you recognise a user? –How do we keep down the connection overhead?

Issues with web-enabled databases Where do we do: –data management –data manipulation –business logic –input validation –presentation processing

Issues with web-enabled databases GUI Server-side processing of business logic: triggers, stored procedures... Thin Client Applications GUI Serving the data Fat Client Applications Application logic

Jargon-busting 3-tier –In the current incarnation: Database Server Application Server Client –Advantages: separation of business logic Scalability Robust

Jargon-busting Web Server –aka HTTP Server – piece of software which basically acts as a document handler typically in tier2 –You ask it for one of its HTML documents by requesting its URL using HTTP –Examples include Microsoft IIS, Apache

Jargon-busting HTTP Server extension modules –Allow for the creation of dynamic HTML, especially useful for handling getting data from (or to) a DBMS –The modules are actually DLLs –Administrator configures.conf file to include the extensions –Examples include: ColdFusion, ASP

Jargon-busting Servlet Engines –Do much the same as an extension does in that they handle non-HTML URLs and allow for the creation of dynamic HTML –An environment for running Servlets, and compiling JSPs –Written in Java for running Java code –Examples include: Jserv, JRun

Jargon-busting Applet –An application with its arms tied behind its back! –“inside the sandbox,” means must run from within a browser and not make OS I/O calls –Is called from, and killed by, the Browser –should have an Init(), not a main() –Its more sub-classing a GUI than writing an application

Jargon-busting JavaBean –“A reusable software component that can be manipulated in a builder tool” –blackbox interface that permits users to interact with the Bean –Can be GUI related or non-visual objects Enterprise JavaBean –EJB TM is a server-side component model –the EJB server itself handles the underlying transaction management

Learn How To CRUDing With......series: –ASPASP –ColdfusionColdfusion –PerlPerl Connecting –Steve Broadbridge's linksSteve Broadbridge's links