Pattern-driven Model-based User-Interface Development

tasks Tasks which require complex activities whose performance cannot be univocally allocated. A user session with a system. The phases three to five are supported by the Teresa (Transformation Environment for Interactive Systems Representations, [Mori et al. 2004]) environment, a software tool for semi-automatic design of user-interfaces beginning with a CTT task specification. It provides suggestions for the next design steps or can perform some of them automatically according to heuristics and predefined settings. The “One Model Many Interfaces Approach” is a user-interface modeling approach with three different levels of abstraction: Task, AUI and CUI level. Early in the development process, starting with the task modeling phase, different models for different target platforms are specified. Whereas task, abstract and concrete user-interface model are explicitly described, a domain and dialog model are implicitly included in these models. Especially the CTTE task modeling tool and corresponding notation are widely used and referenced in the HCI community. 2.3. User-Interface Modeling Notations As outlined in the beginning of this chapter modeling contains a modeling method, some have been introduced in 2.2, and a modeling language. The modeling language itself contains a notation and syntactic, semantic and pragmatic rules for its use. The notation can be of graphical, e.g. the graphical CTT notation as introduced in 2.2.3, or a machinereadable type. In this section some machine-readable notations will be outlined that correspond to the methods of section 2.2. Machine-readable notations formally capture 2. Model-based User-Interface Development 24 the user-interface model information in a persistent and transportable format. The information can be retrieved later on for further refinement, reuse or reengineering. The notations introduced in this section are, like most of the user-interface modeling notations, XML (Extensibel Markup Language, [W3C 2006]) based and thus share the common advantages of all XML formats. That are foremost the system-independency, the structured data representation and the wide acceptance and support [W3C 2006]. In general there exist various XML-based notations for user-interface specification purposes. [Luyten 2004] gives an overview and mentions AUIML, RIML, Teresa XML, useML, ISML, UIML, XIML and UsiXML as representatives. However, most of the languages capture only specific user-interface models and thus are not intended to describe user-interfaces on various levels of abstraction. AUIML (Abstract User-Interface Markup Language) and RIML (Renderer Independent Markup Language) focus mainly on the presentation model. UseML (Useware Markup Language) considers primarily the task model. ISML (Interface Specification MetaLanguage) concentrates on a sophisticated presentation model. UIML (User-Interface Markup Language) can be used as a notation for the presentation model and partially the domain or application model. In the following XIML (Extensible Interface Markup Language), UsiXML (User-Interface Extensible Markup Language) and Teresa XML that support describing user-interfaces on various levels of abstraction are discussed in more detail. 2.3.1. XIML (Extensible Interface Markup Language) XIML (Extensible Interface Markup Language, [XIML 2006]) aims to be a standard representation for interaction data, the data that defines and relates the relevant elements of a user-interface. These elements are abstract, concrete or relational interface data items. Abstract aspects are for example the context, in which the interaction takes place, concretes ones are for instance specific widgets and relational elements, which are used to link data items within the language. XIML captures the definition of the userinterface, whereas the rendering can be left up to the target device. In doing so, a single interface definition can be used for multiple devices, each representing it according to its specific characteristics. XIML includes seven different predefined model types: task, domain, user, dialog, presentation, preference and workstation models. Additional a generic model component 2. Model-based User-Interface Development 25 is provided for purposes which are not captured by the other models. It is possible to define and use custom relations and attributes at the interface, model component or model element level. Relations are used to link single model elements. Attributes define properties of elements to which a value can be assigned. On the one hand defining custom attributes and relations offers extended flexibility. On the other hand it thus lacks standardization and interoperability. Every user-interface specification has to contain these definitions, what inflates their file size. The intended meaning of a self-defined element is often lost. 2.3.2. UsiXML (User-Interface Extensible Markup Language) UsiXML (User-Interface Extensible Markup Language, [UsiXML 2006]) is a user-interface description language that aims describing user-interfaces at various levels of details and abstractions, depending on the context of use [Limbourg et al. 2004]. UsiXML is structured according to the Cameleon Reference Framework as described in 2.2.1. UsiXML includes task, domain, context, abstract and concrete user-interface, mapping, transformation and resource models. The task model is based on the ConcurTaskTree (CTT, [Paternó 2000]) notation as introduced in 2.2.3. The domain model represents the domain objects in similar way like UML (Unified Modeling Lanuage, [Booch et al. 1999]) class diagrams. The context model describes all the entities that may influence carrying out the interactive user tasks with the intended user-interface. It consists of a user, a platform and an environment model. The user model decomposes the user population into stereotypes and sub-stereotypes. The platform model captures relevant attributes for each couple software-hardware platform that may significantly influence the contextsensitivity. The environment model describes any property of interest of the physical environment where the user is using the user-interface. The mapping model contains mappings between models or elements of models. The transformation model represents model transformations as proposed by the Cameleon Reference Framework introduced in 2.2.2. The resource model contains resource definitions like for instance language information. UsiXML is supported by an active community. Various tools have developed and are available at [UsiXML 2006].