Web technologies short list

Client-side processing

How to provide interactivity on client side ?

Some processes require quick response to user requests. This requires processing on the client. There are two big options :

1. Script based dynamic HTML generation

scripts can be nested in HTML pages and executed on client side

impossible to reach the server from a pure script

simple actions only : suitable e.g. for form validation

two platforms :

• JavaScript and standard HTML Document Object Model : largely accepted standard (including Microsoft)
• VBScript/JScript and Microsoft HTML Document Object Model : only with Microsoft Internet Exporer

2. Integration of various executable objects in the HTML page

when the HTML scripts do not allow the achieve the right results, it is possible to embed objects developed with other tools or languages; the objects embedded in an HTML page are executed within the browser by an external engine

ability to write arbitrary complex applications and to reach the server

two platforms :

• Java platform :
• • objects are called java applets and compiled in a pseudo-code targeted to the Java Virtual Machine (JVM)
  • implementations for the JVM exist on any major platform, including Microsoft, Linux, Mac, Unix... so applets are sure to run on every client browser
  • JVM is isolated of its host platform (e.g. restricted access to the filesystem, ...) so users can trust Java applets even if they dont know its supplyer
  • Java applets should be written in Java - no other compiler exists at the time of writing.
• Microsoft platform
• • the objects are developed by tools supporting the generation of ActiveX controls and compiled in native executable code, targeted only to Windows operating systems (95/98/NT/2000 on Intel 32-bit)
  • • Visual Basic, C++
  • objects will not run on Mac, Unix, ...
  • objects will have the same rights on the system that local applications, i.e. they will run with the user's rights : users will not trust ActiveX controls excepted if they know their suppliers
  • there exist many good tools to write ActiveX controls

 

Objects nested in a web page may be accessed by page scripts, which enable a mixed solution : using both scripts and objects. This could be done, for instance, to retrieve raw datas from the server with an object, and to perform the HTML styling and insertion by scripts.

Note: some browsers (only the lastest version of Microsoft Internet Explorer on the time of writing) can perform runtime XML stylesheets transformations, which reduces data transfers between client and server.