Can someone please explain to me when is it a good idea to have <include> or <extend> in use cases?

This file contains the responses I received to a message I sent on January 21, 2000 to the TECHWR-L and WINHLP-L discussion lists. It was posted on the Techwhirl website for awhile but was removed during a reorganisation of the site. Other people’s comments are included with their permission.





Here is my original message:





Can someone direct me to a plain English explanation of “use cases” and “user scenarios” as used in designing, programming and documenting software applications?





I have some superficial experience with them, but find that I can’t explain them in plain English, or at least not beyond the superficial. I’ve found some definitions on the net, but the definitions were all in techno-speak and made little sense to me. If there’s anything in the archives of either of these lists, it eluded me.





The context is: writers can use them to help build task lists from which to build online help and user guides.





But what exactly do the terms “use case” or a “user scenario” mean, and how do they fit into the software development cycle?





I saw Anthony Markatos’ comment (on a different thread), “But Use Cases are just stripped-down Data Flow Diagrams… a currently very popular book on Use Cases [is] Larry Constantine’s ‘Essential Use Cases’,” but I would prefer not to buy a book. I don’t need to know this in depth (I hope) but I do need an overview. “Just the executive summary, please!”





Any leads, preferably online ones, gratefully received!