Chapter 3

The Interaction

3.1 Choose two of the interaction styles (described in Section 3.5) that you have experience of using. Use the interaction framework to analyze the interaction involved in using these interface styles for a database selection task. Which of the distances is greatest in each case?


There is no single answer for this exercise, so we will provide an example of the style of answer that is suitable and the level of analysis that is appropriate.

You should be aware that, although the term distance is used, we have not associated any real measures to any of the translations in the interaction framework.

As a result, this analysis can only be informal and at this point is mainly informed by ones intuition and experience with various interaction styles.

As was stated in Section 3.2.3, assessment of any interaction with the interaction framework can only be relative to some task. For this example we will choose a common database selection task -- selecting records from an online library database. The two interaction styles we will analyze are a natural language interface and a command line interface.

The task is to select a set of references from the library database that satisfy some search criteria. Once the task has been formulated in the user's task language (for instance, the user wants to see all of the books written by Alan Dix since 1990), that task must be articulated in the input language.

A natural language interaction style would allow the user simply to type in the selection query exactly as they think of it. The articulation distance is small both because it is easy to articulate (possibly even easier if a spoken interface is provided rather than typing), and because the coverage is total (the user is allowed to articulate anything as a query). On the other hand, for a command line interface, the limited vocabulary of the input language makes it more difficult for the user to articulate a task even though the limited language provides complete coverage in terms of possible queries allowed.

The real difficulty for a natural language interface is how the system translates the input expression into the actual query that accesses the library records. This performance translation will be much easier for the command line interface since it may not even require any translation of an input expression, that language having already been constructed with the database engine in mind.

Therefore, we can see that for a natural language interface the performance distance is greatest, whereas for a command line interface it is the articulation distance that is greatest.

However, the above analysis only really deals with the execution translations. On the evaluation side, a natural language interface must try to present the results of the database query in the form in which the user phrased the question. This can in general be a difficult translation for the system as it attempts to answer questions in the style in which an arbitrary user has posed them.

Having accomplished that, the observation by the user should be easy to perform. For a command line interface, there is no guarantee that the result of the query will be displayed automatically, and the user may have to request a display explicitly (and they may have to express how the display be formatted).

Neglecting that point, presentation by the system is made easier, as the output language can be very constrained. Observation is made more difficult, as the user must translate the output into the terms of their original task formulation. For example, having asked for books by Alan Dix published after 1990, the user may have a difficult time locating author name and year of publication to determine if the resulting records match their expectations.

For evaluation, a natural language interface has a greater presentation distance and a command line interface a greater observation distance. In general, therefore, we would expect that a natural language interface would be easier from the user's perspective but more difficult from the system builder's perspective. The opposite should hold for a command language interface.

There are some issues that we haven't addressed in this example, such as displaying a large set of records that satisfy the query, and being able to reuse the output of one query as the input to another in order to compound searches easily.

Since the performance translation is so difficult for a natural language interaction style it is important for a natural language interface to present the results of the query in such a way that the user is able to determine if the system understood the original query in the way the user intended. This would involve the presentation translation reiterating both the user's query and the selected records simultaneously. In our example, since the user was interested in the author and date of publication, it would help if that information was prominently presented in the result set.

We have not considered, either, what effect experience with the system provides. As users become more comfortable with the syntax and semantics of a command language, its perceived difficulty will decrease. Another problem is that a verbose natural language output may limit the number of records it is possible to display from a result set.

The moral of the story is that despite their intuitive allure, such informal analyses as suggested by this exercise cannot be the last word on analysis of an interactive system. Ultimately, our judgements must be made more precise and concrete.

3.2 Look at some or all of the following objects: a book, a pair of scissors, a cup, a corkscrew. Discuss the affordances of the objects and the constraints that these place on their use.


Book: hand-sized suggests you can pick it up. Covers and spine operate in such a way as to aid opening it, whilst softer pages allow it to be flicked through.

Scissors: holes in handles suggest positions for fingers, especially when shaped specially. Visible blades suggest cutting - restrained motion of hinge means that when fingers move blades move appropriately. Thin pointed nature of blades suggest sharpness and cutting.

Cup: hand-sized for picking up, particularly with handle which suggests fingers go through hole. Space inside suggests it can contain something, whilst flat base means you know you can stand it down again.

Corkscrew: twisted bottom part suggests twisting, echoed by handles on top. Not put-downable - no resting position; it's a dynamic tool, no use when resting on the table.

3.3 Find out all that you can about natural language interfaces. Are there any successful systems? For what applications are these most appropriate?


This exercise is intended to encourage personal research in the form of a brief literature survey. Appropriate places to begin such a search would be: general text books on artificial intelligence (e.g. Janet and Alan's An introduction to Artificial Intelligence), which will include basic information on natural language processing and famous systems such as SHRDLU; proceedings from conferences such as the AAAI and specialist journals, which will have more up-to-date research papers in the area; proceedings of HCI conferences such as CHI, Interact and HCI, which will include natural language systems particularly geared towards the interface.

Other likely sources are popular journals such as BYTE and personal computer magazines, which are likely to review commercial systems. The student's response to the second part of the question will depend upon what is unearthed, but it is likely that the systems that they find out about operate in very constrained domains and that the natural language used is restricted. There are as yet no general purpose natural language interfaces.

3.4 What influence does the social environment in which you work have on your interaction with the computer? What effect does the organization (commercial or academic) to which you belong have on the interaction?


The aim of this exercise is to explore the social and environmental influences that affect interaction, often without the user being aware of them. The particular influences will vary from environment to environment, but we encourage you to consider some or all of the following.

In each case consider what influence there may be on the interaction. It may be helpful to consider other possible environments in order to identify how the interaction would differ under these different circumstances. For example, if you currently share a machine with colleagues, would your interaction practice change if you were given a personal machine?

Chapter 14 also discusses the influence of groups of workers within an organization on interaction, and is suggested as further reading material on this topic.

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