Information About the Environment

As shown in figure5.3, eachContextis associated with zero or moreUser, PlatformandEnvi- ronmentclasses. The environment class contains details on the surroundings and other external factors which are present when the user accesses the web application. The model includes those factors which may influence the user experience (for example, the surroundings may repeatedly distract the user), the user’s expectations from the system (for example, causing him to be less patient than usual) or the behaviour of the device (for example, there is too much noise for the user to hear any audible output).

The requirements for an environment model for usability and accessibility tool support are contradicting: On one hand, the model should describe the situation of use well, and allow the representation of any aspects which might affect the users’ ability to reach their goals. On the other hand, the model should be simple enough to permit it to be specified quickly by the de- veloper, and to allow tools to extract information relevant for them. The solution of making the model easily extensible is not ideal, as any existing tools will not be able to make use of information added via a later extension of the model.

With regard to related work, some existing models choose the approach of detailed modelling. For instance, with SOUPA there is a set of core concepts like persons, actions or space, a number of existing extensions for situations such as “meeting”, and a way to supply further extensions for specific circumstances. In contrast to this, theenvironmentclass in UsiXML simply restricts the conditions in the environment to a very small number of parameters, namely noise, lighting level and how stressing the environment is. While such a model will be easy to interpret both by humans and programs, it may not be able to describe the environment accurately enough.

The environment model proposed below tries to balance the advantages and disadvantages of a simple and a more complex model. Due to the fact that only the web application running on the device is of interest, it is possible to follow UsiXML’s general approach and only to model theinfluenceof the environment on the use of the web application, rather than the environment itself. At the same time, the model is more elaborate than UsiXML’s: There is more fine-grained control over which human senses are affected by a particular environment, and some additional parameters can be represented, such as how concentrated the users are. In general, the model is fairly abstract, which makes it applicable to many types of environment. If more detailed infor- mation is required for a specific environment, it is possible to extend the classes with additional attributes, or to assign meaning to additional string tag values. Figure5.7shows an overview of the attributes of theEnvironmentmetaclass.

id A developer-supplied name for the environment. Similar to the user and platform IDs, the name can help the developer to organize different platforms, and it can be used by tools for error reporting and related purposes.

partialAbility, fullAbility A set of tags with the same meaning as those in the user model’sno- Ability,partialAbilityandfullAbility, which lists the types of abilities which are supported or partially supported by the current environment. For instance, theseeability will not be present in this model if the application is intended for use while the user is driving a car, or while carrying the device in his pocket. (If the device is used both with and without looking at it, this can be modelled by two different contexts, which are also distinguished via different user goals.) Tools can form an intersection of this set of tags with the ones in theUserandHardwarePlatformclasses to find the senses that are available in a particular context.

requirement A set of tags, each of which is a description of certain constraints or requirements imposed by the environment on the use of the application. Tools may check for the pres- ence of specific tags and enable a set of special checks if a supported tag is found. This can be used to further describe the activity of the user with tag values liketravelling,driv- ing, athome or onholiday – any tool which makes use of the model in this way needs to document which tag values it recognizes, as well as the resulting changes in the tool’s behaviour.

However, this attribute also serves to record legal requirements which are related to acces- sibility or usability: While the targeted user group of an official government institution may not include people with disabilities, the institution may nevertheless be required by law to apply measures to support access by the disabled (see section 2.2.2). Suggested values for guidelines include the following: wcag1-a, wcag1-aa, wcag1-aaa, wcag1(identical towcag1-aaa), wcag2-a, wcag2-aa,wcag2-aaa, wcag2(identical towcag2-aaa),bitv,

section508,stanca-actor generallyaccessibility-law-xxwherexxis a two-letter country code likede.

stressed, stressedDeviation A measure of how much at ease the users are the moment they use the application, or how stressed they are. A value of −100 indicates that they are com-

pletely at leisure, or even bored, with no time pressure at all, +100 means they are ex- tremely stressed and may only have a few seconds of time to use the application. Programs interpreting the model should combine this value with the generalpatiencelevel of a user group to estimate the actual level of patience. For instance, a simple heuristic would be to demand that the web application fulfils the stricter of the two values. For a tool which measures the response time of a database query, this would mean that short response times are required if a user group is impatient by nature or if the environment is stressful. Longer response times are only allowed ifboth the users are patient and the environment is not stressful.