Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!decwrl!ucbvax!hplabs!hp-sdd!nick From: nick@hp-sdd.hp.com (Nick Flor) Newsgroups: comp.cog-eng Subject: Task Trees and consistency, was Re: consistency Keywords: consistency, desktop metaphor, interfaces, computing environments Message-ID: <1748@hp-sdd.hp.com> Date: 12 Feb 89 19:41:49 GMT References: <714@cogsci.ucsd.EDU> <1465@thumper.bellcore.com> <83@sundown.ACA.MCC.COM> Sender: news@hp-sdd.hp.com Reply-To: nick@hp-sdd.hp.com.UUCP (Nick Flor) Organization: Hewlett-Packard, San Diego Division Lines: 82 In article <83@sundown.ACA.MCC.COM> grudin@sundown.ACA.MCC.COM (Jonathan Grudin) writes: > When examined carefully, his [Ralph Hill's] >position reduces to "consistently do the best thing in every situation" >-- we can all agree on that but it isn't useful. ... >But if you are determined to defend "consistency," here is one possibility: >"Consistently maximize user efficiency and satisfaction." Because in order >to do that, you will have to focus your attention on the users' work, which is >where your attention is most usefully focused. Well... but what is maximum "user efficiency and satisfaction"? I assume when you say maximize user efficiency you mean that the software tool together with its user interface must be efficient with respect to the time required to mentally specify AND physically accomplish a goal. Anyways, I view the whole consistency/efficiency issue as follows: If we can believe that users when presented with a task involving the use of a software tool, use the problem solving techniques of abstraction and decomposition to break up the task into more manageable pieces, we can envision a mental task tree -- where all subtrees of a node must be satisfied before the task the node represents is satisfied, [yeah, I know damn those CS metaphors]. At the top of the tree is the root node which represents the overall task, at the bottom - the physical actions necessary to accomplish the overall task. We can use this task tree as the basis for discussing efficiency and consistency. If the task trees for two separate software applications are similar, then the two applications are said to be totally consistent with each other. If they differ in just the leaf nodes, then the user interface is inconsistent. Given two different users and the same application, if the root node and the leaf nodes are the same for both users, but the depth differs, then the user with the smaller depth is the more expert of the two. So, the morphology of the task tree is important. To be efficient you want to minimize both breadth and depth. Minimizing depth amounts to creating a software tool that is easy to use. Minimizing breadth amounts to cutting down the amount of actions necessary to carry out a task. As a user becomes more expert, the level of the tree decreases. The expert user goes from root node to leaf nodes. The time it takes to decrease the levels in the task tree, i.e. transitioning from user to expert user, is the learning period. If you try to cheat on the the number of action nodes, at the expense of depth then you are not being more efficient. If you try to make your application ultra-friendly, you decrease the depth of the tree at the expense of breadth -- also not very efficient. So clearly, or not so clearly, there is this breadth/depth tradeoff to consider when designing a software tool. Now the consistency issue boils down to this: given a software tool that is similar in function to another software tool, to what degree is it's task tree smaller than the other tool. You then can assign consistency thresholds, so if the consistency threshold is, say 1/2, and your tree is 1/2 the size of the other tool then why bother being consistent, since the efficiency gained outweighs the need to be consistent. One last thing before I shut up, it's important to not just look at the user interface because this amounts to examining just the action nodes. Minimizing depth, i.e. learning time, can be critical, especially for beginners. I'd like to say more, and cover all holes (like how to you get this task tree from a user onto paper, how is the consistency threshold determined, and so on and so forth), but it's five minutes until the NBA all star game, and after that INCOME TAX!!!. I can't think after doing income tax. But, I'm sure the net will correct me if I'm wrong. Nick -- + Disclaimer: The above opinions are my own, not necessarily my employer's. + + Oh, sure. Sure. I'm going. But I got | Nick V. Flor * * o * * + + your number, see? And one of these | Hewlett Packard SDD * * /I\ * * + + days, the joke's gonna be on you. | ..hplabs!hp-sdd!nick * * / \ * * +