June 2010 Edition
Computer Science Department, University of Cape Town
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Whereas HTA is concerned almost entirely with procedures, KB analysis focuses on the things (at least in a loose sense) in the task domain, namely objects and actions. KB analysis involves creating taxonomies, or hierarchies, of objects or actions. Such taxonomies can be used in interface design – for example, by ensuring that related objects or actions are grouped together sensibly, and that all important objects are represented at the interface.
Again, we will start with the simple example introduced earlier: writing a letter and preparing it for posting. Initially we consider the description of Linden's activity:
| Description of task | Objects | Actions |
|---|---|---|
| First, we observe Linden, who has no computer support, performing this task in her office. She finds a sheet of paper, a matching envelope and a pen, and settles down at her desk to write. |
Paper Envelope Pen |
Find |
| She starts by putting her own address in the top right-hand corner, then picks up her address book (which is lying on the desk beside her) and flicks to the page containing the addressee’s address information. She copies the addressee’s address to the paper (left-hand side), then writes today’s date and starts on the body of the text: “Dear …”. When she has finished, she signs the letter |
Address (sender) Address (addressee) Address book Page Date Body text Signature |
Pick up Open & flick Write Sign |
| & then reaches for the envelope, writes the name on it and copies the address from the address book onto the envelope, & |
Envelope Address (addressee) |
Pick up Write |
| & folds the letter, puts it into the envelope and seals the envelope. Task completed. |
Letter Envelope |
Fold Insert Seal |
Looking at this list, we can immediately see that there are two kinds of objects: the physical objects with which Linden is working, and the component parts of the letter (the bits of writing that turn a blank sheet of paper into a letter). Arguably, there are other distinctions – for example, between the address that is a kind of thing-in-the-world (as used, for example, by the postal service) and the address as a small portion of text that contains information about the corresponding thing-in-the-world. Conversely, maybe the actions ‘find’ and ‘pick up’ are essentially the same for this task: both are concerned with the user being in possession of the associated object.
A first attempt at a taxonomy might look like this. We are using the terms AND, OR and XOR to indicate whether an object can be or have all the sub-components at the same time. Here, AND means ‘all of’, OR means ‘any number of’, while XOR means ‘exclusive or, exactly one’.
Letter-writing object XOR
Physical object XOR
Paper XOR
Blank sheet
Letter
Pen
Envelope
Address book
Page (lots!)
Portion of text XOR
Address AND
Owner XOR
Sender
Addressee
Location XOR
Letter
Envelope
Date
Body text
SignatureIn this particular case, there are no ‘OR’ objects: most parts of the taxonomy are XOR (e.g. the address owner is either the sender or the addressee, and we are not considering the possibility that these might be the same), while we are also saying that an address has both an owner AND a location (where it is written). There are some quirks – for example, that a sheet of paper is either blank or a letter; we might wish to add a third option (partially written). We will not develop this taxonomy further, but quickly present the corresponding taxonomy for actions:
Letter-writing action XOR
Gain possessionof
Find (e.g. locate address in address book)
Write XOR
Write header information
Write general text
Sign
Fold
Insert
SealAt this level of description, the action taxonomy is neither interesting nor revealing. However, at a finer grain of detail it could be very valuable. Consider, for example, the pull-down menus implemented within word processors such as MS Word. If you look at the organisation of the menus under the top-level headings (‘file’, ‘edit’, ‘insert’, etc.), the groupings of items within each menu, and the options made available, you will see that there is a strong taxonomic basis to the organisation. See, for example, the Figure below. You can go one further and identify places where the taxonomic structure might be open to challenge (e.g. where should ‘insert table’ be located? And why does this ambiguity arise?).
 |
As discussed for HTA, the level of detail required depends on the purpose. In this figure, we see a fine grain of detail (listing out all the most common closing phrases for letters), which is useful for this level of implementation. In other cases, the challenge may be just to create a taxonomy of the physical objects in the domain to support reasoning about design alternatives, or to support the generation of overview documentation.
Compare the KB description of Linden's task of handwriting a letter to the informal description (presented earlier) of Remi's task of word-processing one. Modify the object taxonomy presented for handwriting to describe the word-processing version of the task. Are there important design points that come out of this?
Answer at the end of the chapter.
Select three e-commerce sites (e.g. a bookseller, a travel agent, a financial services supplier) and probe them to see whether you can identify any underlying knowledge based structure. What are the concepts the user has to work with? What actions are available to them? Are actions and objects grouped appropriately at the interface, or within the overall site?
A Discussion on this activity can be found at the end of the chapter.
What are the core concepts expressed in a KB analysis?
Answer at the end of the chapter.
KB analysis can be used to guide the design of manuals to support activity. True or false?
Answer at the end of the chapter.