1. An interactivity creation and customization computer system including a hardware processor comprising: an interactivity builder including: an Interaction Model Library comprising a plurality of Interaction Models that respectively define a plurality of interactivities, each Interaction Model having: (1) a data XML component including (a) a parameter section comprised of one or more parameters, wherein at least one of said parameters contains attribute data, and (b) a description section containing story text with hyperlink references to parameters corresponding to words that act as hyperlinks, (2) an executable component receiving (a) a data path for locating the data XML component, (b) a media path for locating media assets, and (c) a mode value indicative of a play mode, a select mode or an edit mode, said executable component including a play-mode user interface programmed to a desired interactivity functionality, a select-mode user interface programmed to capture mouse pointer clicks on parts of the interactivity, an edit-mode user interface programmed to allow a user to perform customization operations, and an input processor for locating the data XML component using the data path, reading contents of the data XML component, and parsing contents of the data XML component, and (3) media assets; an interaction model selector that allows a user to select an Interaction Model from the Interaction Model Library, thereby creating an interactivity for accessing available Interaction Models; an interactivity editor for modifying the interactivity of the selected Interaction Model according to user inputs to create a modified interactivity, said interactivity editor allowing a user to select a parameter of the interactivity for modification; and an output generator for generating an output file for the modified interactivity, said output file having a format appropriate for use in an authoring application.
2. An interactivity creation and customization computer system as claimed in claim 1 , wherein at least one of said plurality of Interaction Models models a learning interaction appropriate for use in a training course in an electronic format.