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User Models target at helping designers and developers to maximize the level of usability and accessibility of products and services by providing appropriate user properties for adaptation purposes. User Models are intended to be used for the generation or adaptation of user interfaces during runtime. This proposal is based on the work being done by a cluster of European funded research projects "VUMS: Cluster on Virtual User Modelling and Simulation" 
User Model, Standardization, Interoperability, User Preferences, Adaptation, User Profile.
A user model can be seen from a functional/procedural point of view or from a more declarative point of view. In the first case the focus is laid on processes and actions. In the second case the focus is set on definitions and descriptions. The first view is dynamic the latter is static. A procedural approach would start from asking about user tasks and activities. This again is highly depending on the use case. A declarative approach would start from the question, what a user is. Thus for communication about interoperability a more declarative approach seems to be more suitable. Therefore, it is proposed to focus in standardization of user models on a declarative approach and to separate the user model strictly from the task model or any other models like device model or environment model.
User models can be considered as explicit representations of the properties of an individual user and can be used to reason about the needs, preferences or future behavior of that user. One of the main problems is to integrate user profiles supporting different user models in one service/application, or migrating profiles stemming from one application to another. This can be attributed to incompatibilities in user profiles due to differences in scope of modeling, source of modeling information, time sensitivity of the model or update methods (static vs. dynamic model) and so on. In some cases physical (mechanics and control) as well as cognitive processes that underlie the users’ actions are relevant in user modeling. Additionally, the differences between the user's skills and expert skills, or the user's behavioral patterns or preferences can be reflected in a user model specification, too. Finally, user modeling approaches also differ regarding whether they model individual users or whole communities or groups of users.
In general one can conclude that user modeling covers many different aspects, including the interaction of the user with interfaces and devices, the analysis of user tasks and the analysis of user characteristics (sensory, physical and cognitive abilities, psychological and behavioral characteristics). So it is necessary to put efforts into finding similarities among modeling approaches and making user profiles portable. A common standard for user model interoperability could be an approach to achieve this. Application and nature of user models are of course very heterogeneous among different contexts, and this has to be reflected in the standardization activities. The goal is therefore not to create a new common user model standard, but to make user models interoperable through standardization of common aspects and creation of interfaces between them. This will then support the exchange and sharing of user profiles among different services and contexts. It is commonly accepted that usable and accessible interfaces of software applications, AAL services (Ambient Assisted Living) and consumer products depend upon the adaptation and customization of content and presentation of these interfaces to user needs expressed usually in user models and implemented through user profiles.
There are a plethora of systems developed in human computer interaction during the last three decades that are claimed to be user models . Many of them modeled users for certain applications - most notably for online recommendation and e-learning systems. There is a bunch of application-independent models which merges psychology and artificial intelligence to model human behavior in detail. In theory they are capable of modeling any behavior of users while interacting with environment or a system. This type of models is termed as cognitive architecture and has also been used to simulate human machine interaction to both explain and predict interaction behavior. A simplified view of one of these cognitive architectures is known as the GOMS model  and still now is most widely used in human computer interaction though it does not consider people with disabilities or non-expert users in detail.
The emergence of mobile devices showed the need for a description of device characteristics so content providers could customize their offers to capabilities of devices. The World Wide Web Consortium developed the Composite Capabilities/ Preference Profiles framework . CC/PP offers the possibility to define user and device profiles for an adequate adaptation of content and presentation for Internet services. CC/PP is based upon  a general-purpose metadata description language. RDF provides the framework with the basic tools for both vocabulary extensibility, via XML namespaces, and interoperability. RDF can be used to represent entities, concepts and relationships in the Web. So far, the only practical implementation of CC/PP is the User Agent Profile (UAProf) , developed by the Open Mobility Alliance (formerly the WAP-Forum) and targeted to mobile devices. This approach was extended by further developments by W3C groups in the W3C Delivery Context Ontology; it provides a formal model of the characteristics of the environment in which devices interact with the Web or other services. The Delivery Context includes the characteristics of the Device, the software used to access the service and the Network providing the connection among others. The Universal Remote Console - URC Standard (ISO/IEC 24752) the goal of URC technology is to allow any device or service to be accessed and manipulated by any controller. Users can then select a user interface that fits their needs and preferences, using input and output modalities, and interaction mechanisms that they are familiar with and work well with them.
With the explosion of the Web, and e-commerce in particular, several commercial user modeling tools appeared in the market with the objective of adapting content to users’ preferences. Standards and recommendations in this area had to cope with the spread of service-oriented architectures in ubiquitous environments and to cover workflow and user interface aspects e.g. UsiXML , EMMA (Extensible Multi Modal Annotation mark-up language) and MARIA XML in all these frameworks contains a user model component but does not cover all user modeling aspects. Another major source for the development of user models was the E-Learning sector, here we mention IMS AccLIP (Access For All Personal Needs and Preferences Description for Digital Delivery Information Model) and AccMD, which have been internationalized in the ISO/IEC JTC1 Individualized Adaptability and Accessibility for Learning, Education and specification for the User Modeling software Training (ISO/IEC 24751-1:2008).
There is additional need in user models for awareness of context, location and emotional state, as well as seamless roaming and portability , the key issue here is as well the need to cope with demands of different granularity requirements as in applications at design time (simulation), where detailed information are required and runtime adaptations, where less detailed information are sufficient.
All these developments show the need for developing standard user models that can respond not only to everyday scenarios nowadays, but also can be flexible enough to cope with future scenarios coming from ubiquitous, wearable computing and Ambient Assisted Living.
Considering all these approaches together, it becomes challenging to define what a user model actually is. This lack of definition also makes the interoperability of user models difficult. On the other hand, there was a plethora of standards about human factors, user interface design, interface description language, workplace ergonomics and so on that can be used to develop user models. In this context the aims should be to develop
- A standard user model considering people with different range of abilities
- Common data storage format for user profiles
- Common calibration / validation technique
- Collaboration on ethical issues
- Ensuring sustainability by making them available within a standard
- Mechanisms for exchanging user profile data between sources
- Protection mechanisms for privacy issues
- Control mechanisms for user profile data exposure
This work is being successively worked on by the VUMS cluster, which initiated its work by defining a common glossary of terms  which enable user model developers to exchange concepts. Later it proceeded to define a set of variables to describe a user .
- VUMS: Cluster on Virtual User Modelling and Simulation
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- G. Klyne, F. Reynolds, C. Woodrow, H. Ohto and M. H. Butler (eds.) (2002). Composite Capability/Preference Profiles (CC/PP): Structure and Vocabularies, W3C Working Draft 08 November 2002. World Wide Web Consortium. Available at: http://www.w3.org/TR/CCPP-struct-vocab/ , Accessed on 12th December, 2012
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- Peissner, M., Schuller, A., & Spath, D. (2011). A Design Patterns Approach to Adaptive User Interfaces for Users with Special Needs. . In: J. Jacko (Ed.) Human-Computer Interaction. Design and Development Approaches, LNCS 6761, Berlin: Springer-Verlag. S. 268–277.
- Biswas P., Langdon P. & Robinson P. (2012) Designing inclusive interfaces through user modelling and simulation, International Journal of Human Computer Interaction, Taylor & Francis, Vol 28, Issue 1 DOI:10.1080/10447318.2011.565718
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- Pierre T. Kirisci, Patrick Klein, Markus Modzelewski, Michael Lawo, Yehya Mohamad, Thomas Fiddian, Chris Bowden, Antoinette Fennell, Joshue O. Connor: Supporting Inclusive Design of User Interfaces with a Virtual User Model. HCI (6) 2011: PP 69-78. The four-volume set LNCS 6765-6768
- VUMS white paper
- VUMS Terms Definition
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