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Constantine Stephanidis
Institute of Computer Science
Foundation for Research and Technology - Hellas
Science and Technology Park of Crete
Heraklion, Crete, GR-71110 GREECE
Email: cs@ics.forth.gr 
Website: http://www.ics.forth.gr/proj/at-hci/cs.html

Today, software products support interactive behaviors which are biased towards the "typical", or "average" able-bodied user, familiar with the notion of the "desktop" and the typical input and output peripherals of the personal computer. This has been the result of assumptions (by product developers) regarding the target user groups, the technological means at their disposal and the type of tasks supported by computers. Thus, the focus has been on able, "knowledgeable" workers using technology mainly in the work environment, excluding, inevitably, people with disabilities from the cutting edge of technological development.

Though the Information Society is still in its infancy, its progressive evolution has already invalidated (at least some of) the assumptions in the above scenario. The fusion between information technologies, telecommunications and consumer electronics has introduced radical changes to traditional markets, and has complemented the business demand with a strong residential component. At the same time, the type and context of use of interactive applications is radically changing, due to the increasing availability of novel interaction technologies (e.g., personal digital assistants, kiosks, cellular phones and other network-attachable equipment) which progressively enable nomadic access to information.

The above paradigm shift poses several challenges: users are no longer only the traditional able-bodied, skilled and computer-literate professionals; product developers can no longer know who their target users will be; information is no longer relevant only to the business environment; and artifacts are no longer bound to the technological specifications of a predefined platform. Instead, users are potentially all citizens of an emerging Information Society, including people with disabilities, thus requiring accessibility and usability by anyone, from anywhere, at anytime.

The Unified User Interface Concept

In traditional efforts to improve accessibility, the driving goal has been to devise hardware and software configurations (or alternative access systems) which enable disabled users to access interactive applications originally developed for able users. There have been two possible technical routes to alleviate the lack of accessibility of interactive software products. The first is to treat each application separately and take all the necessary implementation steps to arrive at an alternative accessible version (product-level adaptation). The second alternative is to "intervene" at the level of the particular interactive application environment (e.g., MS-Windows, X Windowing System) in order to provide appropriate software and hardware technology, so as to make that environment accessible in alternative ways (environment-level adaptation). In effect, with the latter option, the scope of accessibility is extended to cover potentially all applications running under the same interactive environment, rather than a single application.

Despite recent progress, the prevailing practices aiming to provide alternative access systems, either at the product- or environment-level, have been criticized for their essentially reactive nature. The critique is grounded on two lines of argumentation. The first is that reactive solutions typically provide limited and low quality access; something that has already been identified in the context of non-visual interaction, where it is argued that non-visual user interfaces should be more than automatically generated adaptations of visual dialogues [Savidis & Stephanidis, 1995]. The second line of critiquing concerns the economic feasibility of the reactive paradigm to accessibility. In particular, it is argued that continuing to adopt prevailing practices within the software industry leads to the need to reactively develop solutions for interactive computer-based products, accessible to users with situational, temporary, or permanent disability. Clearly, this is sub-optimal for all parties concerned and renders the reactive approach to accessibility inadequate and inappropriate in the long run. Instead, what is required is a proactive approach to cater for the requirements of the broadest possible end-user population.

In contrast to the above approaches, Unified User Interfaces [Stephanidis, 1995; Stephanidis, Savidis & Akoumianakis, 1997; Stephanidis, 2000] seek to convey a new perspective on the development of user interfaces which provides a principled and systematic approach towards coping with diversity in the target users groups, tasks and environments of use. In other words, Unified User Interfaces provide a pathway towards accommodating the interaction requirements of the broadest possible end-user population. The notion of a Unified User Interface originated from research efforts (see Acknowledgments) aiming to address the issues of accessibility and interaction quality for people with disabilities. The intention was to articulate some of the principles of Design for All in a manner that would be applicable and useful to Human-Computer Interaction (HCI), which gave rise to the concept of User Interfaces for All [Stephanidis, 1995]. Subsequently, these principles were extended and adapted to depict a general proposition for HCI design and development, which was complemented by specific methodologies, techniques and tools.

A Unified User Interface is defined as an interactive system which comprises a single (i.e., unified) interface specification, targeted to potentially all user categories and contexts of use. Such a specification can be built using either a traditional programming language, or a dedicated language which allows the construction of the Unified User Interface as a composition of abstractions at different levels.

The distinctive property of a Unified User Interface is that it can realize alternative patterns of interactive behavior, at the physical, syntactic or even semantic level of interaction, by automatically adapting to accommodate specific user- and context-oriented requirements. Typically, such alternative interactive behaviors encompass interaction elements available in different toolkits or interaction platforms (e.g., Windows95, toolkit for non-visual interaction), suitable for the different target user groups (e.g., sighted and blind users respectively).

Unified User Interface Development

Unified User Interface design entails an early account of the broadest possible range of end-user requirements and contexts of use, so as to develop effective representations depicting the global task execution context [Savidis et al., 1997; Stephanidis, Akoumianakis & Paramythis, 1999]. Unified implementation, on the other hand, requires the capability to encapsulate design alternatives into suitable dialogue patterns and to map abstract design components to corresponding implemented (interaction platform-specific) options [Savidis & Stephanidis, 2000a].

Two distinctive requirements characterize Unified User Interfaces [Savidis & Stephanidis, 2000b]. The first is the requirement for an analytical design activity leading to the representation of the design knowledge required to reveal and differentiate amongst plausible design alternatives. The second requirement is that of encapsulation of the corresponding dialogue patterns into a (conceptually) single interactive entity. In this context, representation implies the use of suitable notations to capture and encode both design artifacts and accompanying design rationale. On the other hand, encapsulation entails the use of suitable dialogue specification techniques (programmatic, declarative, etc.) to manipulate interactive artifacts in a manner that is not dependent on a particular target interaction platform (e.g., by avoiding direct "calls" to the platform's interactive facilities).

The design of a Unified User Interface entails three iterative tasks, namely enumeration of design alternatives, abstraction towards reusable unified design components and rationalization of the design space [Stephanidis, Akoumianakis & Paramythis, 1999]. Enumeration of design alternatives can be attained through techniques which foster an analytical design perspective (such as design scenarios, envisioning, ethnographic methods) and facilitate the identification of plausible design options for different user groups (i.e., design space). Abstraction in design entails the identification of abstract interaction components that can be used to encapsulate alternative concrete artifacts. Such abstract components are de-coupled from platform, modality, or metaphor specific attributes to provide a kind of reusable design "library". Abstract components may be used to compile composite interface elements suitable for different users and contexts of use. Finally, rationalization of the design space implies the explicit encoding of the rationale for mapping an abstract design element (e.g., an abstract selector) to a concrete artifact (e.g., a menu, or a 3D acoustic sphere). This is typically achieved by assigning criteria to design alternatives and providing a method for selecting the maximally preferred option.

To facilitate encapsulation of the designed alternatives in a single interactive artifact, Unified User Interface development requires techniques that enable: (i) the grouping of alternative dialogue patterns (e.g., implemented design alternatives, catering for different user requirements) on the basis of an abstraction model; and (ii) the context-sensitive mapping of abstract components to suitable concrete artifacts. To this effect, the process of Unified User Interface implementation involves: (a) the construction of a Unified User Interface as a composition of abstractions at different levels of interaction; (b) the manipulation and management of the physical resources (e.g., various toolkits); and, (c) the establishment of the relationships between the involved abstractions and the available physical resources. More details can be found in [Savidis & Stephanidis, 2000a].

The Unified User Interface development paradigm is supported by a set of development tools, which have been built to provide an integrated framework that efficiently supports the design and implementation of Unified User Interfaces [Savidis & Stephanidis, 2000b]. The main characteristics of this framework are: (i) platform independence, intended to address the pluralism of interaction platforms and graphical environments (e.g., MS-Windows™, the X Windowing System), offering the versatility required for the management of different environments; (ii) metaphor independence, so as to cater for the interaction needs and characteristics of diverse target user groups, which may necessitate the coupling of different interaction metaphors to different categories of users and usage situations; (iii) automatic adaptation capabilities, so that the resulting user interfaces are adaptable and adaptive to the individual user (dis)abilities, requirements, skills and preferences; (iv) unified interface specification, which aims to reduce the overall development costs for Unified User Interfaces through the introduction of specification-oriented (rather than implementation-oriented) interface construction techniques.

The AVANTI Web Browser Case Study

The AVANTI project (see Acknowledgments) aimed to address the interaction requirements of individuals with diverse (dis)abilities, skills, requirements and preferences (including disabled and elderly people), using Web-based multimedia applications and services. AVANTI advocated a new approach to the development of Web-based information systems, putting forward a conceptual framework for the construction of systems that support adaptability and adaptivity at both the content and the user interface levels. The AVANTI Web Browser [Stephanidis et al., 1998], which acted as the front end to the AVANTI information systems, was developed following the Unified User Interface Development paradigm and demonstrated the feasibility of employing the related approaches, methods and techniques for the development of a user interface that supports able-bodied users, users with various degrees of motor impairment and blind people.

Following the principles of Unified User Interfaces, the AVANTI Web browser employs adaptability and adaptivity to attain accessibility and high-quality interaction for all the target user groups. In this respect, adaptability is mainly targeted to ensuring that the initial instance of the interface with which users come in contact is automatically tailored to fit their particular (dis)abilities, skills, requirements and preferences, as these are defined in their profile. This profile can be derived from initialization files, smart cards, or a brief question-answer dialogue (carried out by means of an interactive component that is concurrently accessible by all target user categories). Adaptivity, on the other hand, seeks to further enhance the interactive experience of the user, by making use of knowledge about the user and the context of use that becomes available dynamically (i.e., at run-time) and is derived mainly from interaction monitoring data.

To better illustrate the practical implications of interface unification and the employment of automatic adaptation techniques to ensure accessibility, let us consider the exemplary instance of the browser presented in Figure 2. In that particular instance, the browser has adapted itself for single switch- based use, by motor-impaired individuals. Adaptations visible in this figure include: (a) a window manipulation toolbar enabling users to minimize/maximize/restore, move and resize the window, without the need for any type of mouse emulation; (b) an on-screen keyboard for text input, which may have alternative key layouts to better suit the users' needs and experience; and, (c) the scanning highlighter, part of the (automatically activated) scanning interaction technique.

Figure 2: An instance of the AVANTI browser adapted for motor-impaired users

The AVANTI Web Browser was evaluated in the context of the project by users belonging to all target categories (i.e., able-bodied, motor-impaired and blind) [Andreadis et al., 1998]. Users within each of the categories were further differentiated by a number of factors, including but not limited to: native language; experience in computer use in general and the Web in particular; the context within which they used the browser (e.g., at home to do Web browsing in general, at public information kiosks to gain access to the AVANTI information systems); their preferences regarding interaction media, modalities, and target; etc.

The results of the evaluation were encouraging, both in terms of user acceptance of the characteristics of the interface, and in terms of the fulfillment of the initial goals of developing a Unified User Interface. In particular, adaptations addressing accessibility issues for the various end-user groups proved quite successful, as each user category conceived the interface as having been specifically developed to cater for their particular requirements. The results were similar for the non-disability related categories in which users were classified (e.g., according to their computer expertise).


The emergence of the Information Society necessitates a shift in the way product and service developers approach their prospective users, as it is no longer possible to realistically design for the nonexistent "average" user. Rather, the diversity in the user population (whether it is attributed to (dis)abilities, skills, domain-specific knowledge, cultural background, etc.) must be understood and addressed from the early phases of design and throughout the development life-cycle of interactive products and services.

Unified User Interfaces provide a set of methodologies, techniques and tools that enable developers to move beyond the traditional reactive paradigm of addressing the requirements of people with disabilities. The underlying concept fosters the creation of single interactive artifacts that encapsulate the alternative interaction elements required for the different users categories and contexts of use. This approach is proactive in nature, has been proven feasible even when employed in large-scale, mainstream user interfaces (as was the case of the AVANTI Browser), and has the potential to deliver even better results than "dedicated" development for particular categories of disabled people, both in terms of accessibility and interaction quality, and in terms of economic efficiency and efficacy in the long run.


The R&D work reported in this paper has been carried out in the context of the TIDE - ACCESS (TP 1001) project "Development Platform for Unified Access to Enabling Environments" (January 1994 - December 1996) and the ACTS - AVANTI (AC042) project "Adaptive and Adaptable Interactions to Multimedia Telecommunications Applications" (September 1995 - August 1998), both partially funded by the European Commission.

The partners of the ACCESS consortium were: CNR-IROE (Italy) - Prime contractor; ICS-FORTH (Greece); University of Hertforshire (United Kingdom); University of Athens (Greece); NAWH (Finland); VTT (Finland); Hereward College (United Kingdom); RNIB (United Kingdom); Seleco (Italy); MA Systems & Control (United Kingdom); PIKOMED (Finland).

The AVANTI consortium comprised the following partners: ALCATEL Siette (Italy) - Prime contractor; CNR-IROE (Italy); ICS-FORTH (Greece); GMD (Germany); University of Sienna (Italy); MA Systems (UK); MATHEMA (Italy); VTT (Finland); ECG (Italy); University of Linz (Austria); TELECOM ITALIA (Italy); EUROGICIEL (France); TECO (Italy); Studio ADR (Italy).


Andreadis, A., Giannetti, L., Marchigiani, E., Rizzo, A., Schiatti, E., Tiberio, M., Pentila, M., Perala, J., Leikas, J., Suihko, T., Emiliani, P.L., Bini, A., Nill, A., Sabbione, A., Sfyrakis, M., Stary, C., and Totter, A. (August 1998). Global evaluation of the experiments. ACTS AC042 AVANTI Project, Deliverable DE030.

Savidis, A., and Stephanidis, C. (2000a). The Unified User Interface Software Architecture. In C. Stephanidis (Ed.), User Interfaces for All (chapter 20), Lawrence Erlbaum Associates, Mahwah, NJ, ISBN 0-8058-2967-9, to appear in 2000, 850 pages.

Savidis, A., and Stephanidis, C. (2000b). Development Requirements for Implementing Unified User Interfaces. In C. Stephanidis (Ed.), User Interfaces for All (chapter 22), Lawrence Erlbaum Associates, Mahwah, NJ, ISBN 0-8058-2967-9, to appear in 2000, 850 pages.

Savidis, A., and Stephanidis, C. (1995). Developing Dual User Interfaces for Integrating Blind and Sighted Users: the HOMER UIMS. In Proceedings of the 1995 ACM Conference on Human Factors in Computing Systems (CHI'95), Denver, USA, 7-11 May 1995, pp. 106-113. Stephanidis, C. (2000). The concept of Unified User Interfaces. In C. Stephanidis (Ed.), User Interfaces for All (chapter 19), Lawrence Erlbaum Associates, Mahwah, NJ, ISBN 0-8058-2967-9, to appear in 2000, 850 pages. Stephanidis, C., Akoumianakis, D., and Paramythis, A. (1999). Tutorial on "Coping with Diversity in HCI: Techniques for Adaptable and Adaptive Interaction". Tutorial no 11 in the 8th International Conference on Human-Computer Interaction (HCI International '99), Munich, Germany, 22-26 August. Available on-line: http://www.ics.forth.gr/proj/at-hci/html/tutorials.html. Stephanidis, C., Paramythis, A., Sfyrakis, M., Stergiou, A., Maou, N., Leventis, A., Paparoulis, G., and Karagiannidis, C. (1998). Adaptable and Adaptive User Interfaces for Disabled Users in AVANTI Project. 5th International Conference on Intelligence in Services and Networks (IS&N '98), "Technology for Ubiquitous Telecommunications Services", Antwerp, Belgium, 25-28 May 1998. Savidis, A., Paramythis, A., Akoumianakis, D., and Stephanidis, C. (1997). Designing user-adapted interfaces: the unified design method for transformable interactions. In Proceedings of the ACM Conference on Designing Interactive Systems: Processes, Methods and Techniques (DIS '97), Amsterdam, The Netherlands, 18-20 August 1997, 323-334. Stephanidis, C., Savidis, A., and Akoumianiakis, D. (1997). Unified Interface Development: Tools for Constructing Accessible and Usable User Interfaces. Tutorial 13, HCI International '97 Conference, San Fransisco, USA, August 1997. Available on-line at: http://www.ics.forth.gr/proj/at-hci/html/tutorials.html. Stephanidis, C. (1995). Towards User Interfaces for All: Some Critical Issues. In Proceedings of the HCI International '95 Conference, Tokyo, Japan, July 1995.

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