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Existing web engineering approaches either include a presentation model which specifies the ma- jor components that make up pages of a certain kind (e.g. UWE), or a template document with the same purpose which can be transformed into such a model (e.g. WebML). For some of the tool concepts outlined in other chapters, this model needs to be augmented with additional in- formation. For example, model-based usability analysis of the final implementation may include a test which checks for the presence of a de-facto standard page layout, with e.g. a navigation menu at the left side of the main content.

Adding Context Information to Presentation Classes

As already explained above, for any model which describes the contents of a page or the naviga- tion layout, it must be possible to attach a context class with information about the users, platform and the environment. Figure5.8shows that this is achieved in the metamodel by introducing the abstract metaclassUiModel, which supports the appliesTo association. The UWE metaclasses likeNavigationalClassare then derived from theUiModelclass.

Assigning Meaning to Areas on the Page: “role”, “importance”

Furthermore, it must be possible for tools to perform a mapping from an area on the final HTML page to the functionality which is provided in this area, e.g. “this area of the page is the navigation menu”. This information needs to be added to the metaclass which represents one page area – in the case of UWE,PresentationClass[Hennicker01Modeling]. For this purpose, as shown in figure 5.8, the abstract metaclass PresUiModelis derived from UiModel. Its role attribute is a string which describes the purpose of the page area, andPresentationClassinherits the attribute. Sometimes, functionality is distributed in a finer-grained way inside a page area – for instance, the role of a single text field may differ from that of its parent page area. To avoid the need for the developer to introduce«presentation class»classes in this case for the sole purpose of assigning a role to them, theUI Elementmetaclass (whose instances like«text»make up the content of a UWEPresentationClass, see figure3.3on page45) inherits fromPresUiModelas well.

For the keyword string stored in the role attribute, the following values have a predefined meaning. In part, they were inspired by the proposed XHTMLroleattribute [W3C-XHTMLrole]:

usability UWE UiModel UI View PresentationClass UI Element PresUiModel role : string importance : int Context 0..* appliesTo 0..*

Figure 5.8: Extensions to the presentational models (e.g. assigning roles like “navigation menu” to page areas) are introduced via the metaclassesUiModelandPresUiModel.

main The main text (or other content) of the page

seealso Additional content whose topic is related to the main content, e.g. an

abstract in a sidebar.

secondary Additional content which is not related to the main content, e.g. infor-

mation about other parts of the site or a “weather forecast” box in a news article

logo The logo of the company or website

ad Advertisement in the form of banners or animations, or in the form of text links (so-called “sponsored links”)

empty Empty space on the page, uniformly coloured or at most showing a faint,

unobtrusive background image

ornamental Space on the page which is not empty, but which serves no purpose other

than contributing to the visual page design

navigation Links for navigating the document or site. If possible, the more specific

values below should be used.

navigation-menu The main menu of navigation links, possibly with multiple hierarchy

navigation-bar A secondary, shorter navigation menu – this includes “tab bars” with links to major parts of a large site, and breadcrumb links

navigation-other Other navigation aids on the page, such as tag clouds. In an online shop, this can also be a “related items” section or the shopping cart

search A field to search the site, or a link to a search page

login User account management options, including “login” and “register user”

help A link to a help page, or a section with instructions on how to use the site

contact A link or other element to contact the site maintainer

other Other content, which does not fit the categories above or which should

be ignored by tools

Other values may be used by developers, and programs may include special support for ad- ditional keywords. For instance, a tool which specializes on analysis of the text on a page could potentially support keywords which classify different types of text content.

With the ornamentalkeyword, a facility exists to declare parts of the page as ornamental. This value is mostly useful to assign to images which act as spacers, rules or graphical frames around areas. It is also appropriate for “mood images” which are intended to attract the curiosity of a sighted reader, but which are not essential for understanding the content.

As described at the beginning of section 5.2, tools should ignore (i.e. treat as type other) values they do not understand, unless an encountered value is a known value followed by “-” and further characters. For example, a program which works withmainpage areas should also treat anymain-textarea like amainarea.

Finally, the role value can also be the empty string (which is not to be confused with the value “empty”). For nested user interface elements, the empty string indicates that the developer did not assign a role value to the UI element in question, but only to one of its parent objects (a page area that contains the element). Thus, the element itself can be considered to be part of the implementation of the higher-level area. For example, a “search” button will usually have an emptyrolevalue because the screen area which contains the search field and the button will already have been assigned thesearchfunctionality.

Theimportanceattribute is intended to be used by the developer to assign more importance to those areas of the page which he considers central for the web application, and for which usability problems are less acceptable than elsewhere. Similar to the importance attribute of contexts (section5.2.1), the positive integers stored in this attribute represent the relative impor- tance of one area over another, with higher values indicating higher importance. Tools can use this information e.g. for ordering the results of their analysis so that important areas are listed first, or possibly to increase their demands for the usability-related properties of this part of the user interface. For example, the developer of an online shop may assign the highest importance value to the online shopping cart, and this may cause his web engineering tool to require that a keyboard shortcut is assigned to the respective link on the page.