Authors: Preece, Rogers & Sharp
Case Studies
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Interaction Design: beyond human-computer interaction  
Case Study 1: Using XP to Develop Context-Sensitive Adverts for the Web


This case study focuses on the visual design of a context-sensitive advert for the Web. It is one output from a participant observation study of a company that produces such adverts. The approach to development they use is different to any described in our book; they use eXtreme Programming (XP), one of a number of 'agile' methods that are gaining popularity among some software developers.

After a brief introduction to the company, Connextra, and XP, we describe the visual design and development of one context-sensitive advert. We end by summarising the design issues raised by the case study, and offering some observations of the XP approach to development.


Connextra ( is a web development company that specialises in bringing contextually-relevant information to the user's desktop. They use the eXtreme Programming (XP) approach to development, which is one example of a set of methods, called 'agile' methods. These methods challenge many of the principles underlying traditional software engineering lifecycle models and take a code-centric, people-oriented approach. Connextra has developed a number of technologies that analyse the content of what the user is browsing, and then use that knowledge to display relevant information. One such technology is the ActiveAd. This case study focuses on the visual design of an ActiveAd.


An ActiveAd analyses the content of a webpage and identifies some key terms. These are then translated into parameters that define the advert to be shown. For example, an article on careful parenting may discuss the advantages and disadvantages of different buggy designs. An advert to be displayed on this page would highlight the sale of buggies and related equipment. If the article is later replaced by one about car safety seats, then the advert would automatically change accordingly. ActiveAds are 'clickable' and can link through to any webpage specified by the client. For example, an advert for a bookmakers (i.e. someone who takes bets on horses etc.) might link through directly to the online betting slip on the client's site; the buggy advert above may link to an online catalog showing different models and their price.

ActiveAds work from a feed of data sent by the client, they parse the data to pick out the information that is required, and display the relevant advert on the target webpage. The information in the feed is updated periodically, e.g. every 15 minutes, and the advert will change accordingly. The frequency of the change depends on the nature of the information to go in the advert.

If an ActiveAd cannot be displayed for some reason, e.g., Connextra's server experiences connection problems, then the host website needs to know what to display in its place. It clearly is not desirable for an error message to appear on the screen. So, each ActiveAd is associated with a 'panic', i.e., a default graphic that will be displayed if ActiveAd is not available.

eXtreme Programming

eXtreme Programming is a new approach to software development which takes a code-centric view of the activity. There is a lot to say about XP, but this section is confined to a brief introduction. Further information can be obtained from the references listed at the end of this case study, or from our other online resources.
XP is different from traditional approaches in many ways:

  1. XP involves short, tight iterations of building and releasing software. In our case study company these iterations were 3 weeks long, but others have used 2 weeks. At the end of this time something new has been released.
  2. Requirements are gathered in terms of 'stories'. These usually begin with 'I want…' or 'We want…'. These are produced by the customer or client. The developers look at the stories and estimate how long they think it will take to satisfy them. Developers and customers negotiate what requirements can be delivered in the time available. This exposes the customer to developers' estimates, and encourages them to prioritise their requirements since it is not possible to do everything in one iteration. The activity of estimating and prioritising to see what can be done in the next iteration is called the planning game.
  3. The customer is on site and is part of the development team.
    4. Once the iteration has started, developers work in pairs. No development is done by a single individual. All development is jointly owned. This is a surprisingly successful element of XP. Further information on this aspect is in Williams et al (2000).
  4. A 'test-first' philosophy prevails. In XP you write the test to show that the code will work before you write the code. Testing and coding are performed together. Before any new software is released, the whole test suite is run to ensure that it does not break any other component of the system.
  5. Some principles underlying the people aspects of XP are: work no more than 40 hours a week, be courageous, take responsibility and share ownership.
  6. Some principles underlying code production are: keep it simple, have one shared metaphor to guide system development, regularly restructure the system to improve it (refactoring), continuously integrate and test, and follow coding standards.

The Betabet case study

This case study focuses on the (re-)design of an ActiveAd for one of Connextra's existing clients, Betabet. Betabet run a portal website which allows punters to place bets
with independent bookmakers via the Internet. The advert developed by Connextra displays the betting odds for the outcomes of various sporting fixtures such as football games and horse racing. The specific odds to be displayed are determined by the contents of the rest of the user's webpage. The advert is designed to sit on host websites ( and link directly to Betabet's site.

Here, we focus on the work of the graphic designer, Elena, who designed the visual appearance and produced the working html. Behind the visual appearance is Java code which processes the data feed, handles the website content analysis, and provides the other infrastructure necessary for the ActiveAd to keep running.

As in all development at Connextra, Elena works in a pair with a colleague, although as the only graphic designer in the team, she is the main driver for most graphics work. What follows is a description of the work as observed by the participant observer.

Early design

The starting point for this design, as for all work conducted at Connextra, is the story, as described above. This was raised by the client via one of Connextra's sales representatives, Scott. The story in this case was very simple:
"We want an improved design for Betabet"

Connextra had previously produced an ActiveAd for Betabet, but the design needed improving. On clarifying the story with Scott, Elena discovered that the advert should show the winnings for a £10 bet, based on the odds displayed. In addition, the size of the advert was to be increased to 120x120 (pixels), and the client wanted more of the advert to be clickable.

The first stage of the design was to develop some sketches, capturing both detailed decisions such as the size of the columns and rows, and broader issues such as what the banner across the top should contain. These mockups were discussed with Scott, and refined.

Figures 1 and 2 show these preliminary sketches. Figure 1 shows some initial ideas for the banner to go at the top of the advert, and the Betabet panic. The three boxes on the left hand side are banner lines that will be animated and displayed alternately; on the right is the Betabet panic (the 'blob' over 'BET' represents a sketch of the Betabet logo).

Figure 1. Ideas for Betabet banner and panic
Figure 1: Ideas for Betabet banner and panic

Figure 2 shows some detail for the main advert. You can see the rows and their contents, and also where Elena has worked out the height of each one (the overall height must be exactly 120). The sketched advert shows the case where the outcome 'Liverpool wins by 3-1' is given the odds of 5 to 1. This translates a £10 bet into £50 winnings.

Figure 2. Detailed planning for the main advert
Figure 2: Detailed planning for the main advert
Photoshop mockup

A Photoshop mockup based on these initial ideas was produced. This allowed Elena to experiment with colors, typefaces, sizes, positioning etc from a purely visual perspective, before getting involved in using style sheets or html. Although Photoshop does not produce exactly the same look and feel as html, it is sufficiently accurate for her to get more detailed feedback from Scott. Figure 3 shows a printout of this mockup together with some evaluation notes.

Figure 3 The Photoshop mockup and accompanying notes from evaluation discussions
Figure 3: The Photoshop mockup and accompanying notes from evaluation discussions


Creating the advert

Once Elena was happy with the mock-up, she set about designing the executable version. Some elements of the advert are animated, i.e., move or change over time, such as the banner shown in Figure 2, and the names of the teams and their odds. But some elements remain static. These static elements were developed first and the animated elements were superimposed on top of the background at a later stage.

The background itself was made up of a series of layers. The first was the black background. Then came the other colored sections, and the animated banner across the top. Superimposed on this was an 'invisible' table structure to hold the other elements of the design. As you can see from the background, the spaces to display the animated features of the advert are of different sizes. It would have been possible to design one table to fit over the background, with different sized columns for each row, but this kind of structure in which table cells are 'spanned', or merged to make larger cells can cause problems in some browsers. Instead, each element was defined individually.

Figure 4 shows the complete background for the Betabet advert. The dimensions were based on the original sketch that Elena produced early on, but the process of choosing colors and exact sizing went through a number of iterations before the final decisions were made.

Figure 4: Static background for Betabet ActiveAd

Figure 4: Static background for Betabet ActiveAd

As a first step towards testing the advert, without linking to the live data feed, some values for the teams and their odds entered directly into the html. This final advert is shown in figure 5, and the panic is shown in Figure 6.

figure 5: The final ActiveAd, containing some dummy data

Figure 5: The final ActiveAd, containing some dummy data


Figure 6 The 'panic', i.e. default display, for the Betabet ActiveAd

Figure 6: The 'panic', i.e. default display, for the Betabet ActiveAd


Testing against a 'real' webpage

Having produced the correct html, Elena wanted to check that the proposed advert would look good on a sample page. Looking at a relatively small image like this out of context is different from seeing it pasted onto a real page. To do this, she chose a webpage that contained Betabet's existing advert, took a copy of it offline, and pasted in her new design. The result is in Figure 7. Note that the context-sensitivity feature of ActiveAd is not being shown here, i.e., the article talks about Manchester United although the advert displays prices for Leeds and Arsenal. This is because at this stage the details are hard-coded and the webpage was taken offline.

Figure 7: A mockup of how the advert will look against a real webpage

Figure 7: A mockup of how the advert will look against a real webpage

Testing on different platforms

Further testing stages were undertaken before it was linked to the live feed, including running the advert on a series of different platforms, and using different browsers. One change had to be made as a result of this testing. The original design used the Verdana typeface, but when the advert was displayed on a Mac, the text was too large and expanded beyond the boundaries of the design. When the typeface was changed to Arial, however, this problem disappeared.


Further and ongoing testing

The next stage of testing (not observed on this occasion) is to move the advert to a test server which uses the live data feed, but is not publicly accessible. This is visible to the client Betabet who can give the final approval for it to go live. Before this can happen, however, there needs to be some liaison with those working on the Java code to ensure that the processing of the data feed is compatible with the display requirements of the advert, e.g., that the date arrives in the correct format.
Once the advert is live, further testing is performed to determine the advert's effectiveness, i.e., how many 'click-through's to Betabet's own site does it result in. These statistics are collected and monitored on an ongoing basis.

"No user testing is mentioned explicitly here, although there is close liaison with the client, and there is ongoing monitoring of the advert's efficacy. Do you think that user testing should be performed on this ActiveAd?"

Some conclusions and observations

Design issues

Although quite a small endeavour, this case study raises a number of interesting design issues, which we summarise below:

  • The need to include a 'panic' gif in case the main advert can't be displayed.
  • The need for careful planning of the row sizes to make the overall advert just the right size; the height of rows needs to be specified in pixels.
  • The choice of typeface is significant to ensure that the advert is viewable on different platforms and using different browsers. Sans serif typefaces (e.g., Arial) are more appropriate than serif typefaces (e.g., Times) for reading material on a screen. Elena prefers to use Verdana or Tahoma, but not everyone has Tahoma. If it proves necessary, as it did in this case, she will switch to Arial.
  • When considering the detailed mock-up, Elena needed to check that the likely values for the 'live' data would fit in the space she had provided. For example, the Betabet advert includes the date and time of the event to be bet upon. Displaying a date as 12 January requires more space than 12 Jan or 12/01; a time could be displayed in the 24-hour clock style, such as 19.30, or as 7.30pm. In addition to fitting in the space, the format for display also had to be consistent with the data format as supplied from the underlying Java code.
  • What elements of the design should be made clickable? What elements is it possible to make clickable? How do you balance these two?
  • The need to take into account different platforms, and to test on different platforms. In Connextra, this testing stage was automated, i.e., no-one had to sit and manually try the advert on each platform.
  • The use of mock-ups both for communication with the client, and for Elena herself to try out alternatives.

Using XP

The following observations are drawn from the participant observer study:

  • XP in Connextra works well. We cannot comment on how well it would work in a different organisation or with a larger software effort. The articles in IEEE Software mentioned below will give some insights here.
  • Working in pairs can cause some problems for client support. For example, if a client needs a swift response to a problem or query, it is not possible to interrupt just one developer, a pair must be disturbed, and this can result in one developer sitting idly while the other addresses the support issue. This has knock-on effects for the iteration time planning.
  • Working in a pair all the time can become claustrophobic. To stop developers becoming bored, each developer at Connextra is allowed two 'gold cards' a month. These are days when he or she can work on something on their own.
  • The graphic designer, Elena, sometimes pairs with a Java programmer to work on Java code. Although she is not as knowledgeable about Java and is not skilled in producing these programs, she finds it useful in helping her understand the wider system context.
  • Elena has two gold cards a month, like everyone else, but she finds that she needs more space some times to consider designs, and to surf the web looking at alternative designs.
  • Clients appreciate the fast and reliable response that working under XP allows.

Some resources to find out more about XP

These are in addition to the other online resources for XP given elsewhere on this site:

Beck, Kent (2000) eXtreme Programming Explained: embrace change, Addison Wesley.
This was the first book to be produced about XP. It explains the rationale behind XP, and discusses the underlying principles and values, but it does not provide great detail about how to go about applying XP. Another book, eXtreme Programming Installed by Jeffries, Anderson and Hendrickson is better from that perspective. A number of other books have been written on the subject from different angles. These are all published as part of the Addison Wesley XP series.

IEEE Software (2001) Reports from the field, November/December
This contains a number of articles exploring XP's deployment in a range of projects, both large and small, and for different stages of the lifecycle.

Williams, L. et al (2000) Strengthening the case for Pair Programming, IEEE Software, 17(4), 19-25.

"eXtreme Programming Pros and Cons: what questions remain?" IEEE Computer Soc Dynabook, J. Siddiqi (ed) Nov 2000;

  Copyright 2002