1. A mechanism for enabling a developer to create a software application for execution on a network having a plurality of tiers, the mechanism comprising: specifying means for enabling the developer to specify a plurality of executable components; and means for enabling the executable components to be associated with at least one hypertext-based document, such that the executable components are executable in response to requests for the at least one hypertext-based document, and such that an executable component of the plurality of executable components can be automatically and dynamically assigned to an appropriate tier for execution at run-time in response to a request for an associated hypertext-based document or can be specified to execute on a particular tier using an applet tag specifying the tier within the associated hypertext-based document.