During the past years, a lot of user interface description languages, most of them based on XML, have been introduced. At the same time, the use of formal ontologies for describing user interfaces has been discussed for a number of use cases. This paper discusses the di erences between a formal ontologies and user interface description languages and and points out how both research directions can bene t from each other.
In parallel, various UI description languages have been
proposed, most of them XML based [
Although ontologies and software models are related,
they are not essentially the same. Software models and
ontologies are di erent by nature. An ontology claims
to be a generic, commonly agreed upon speci cation of
a conceptualization of a domain [
Taking this thought to the domain of user interfaces and interactions, models are used to de ne particular user interfaces (e.g. with the goal of generating code implementing those interfaces), while a formal ontology would capture the nature of things that exist in the domain, e.g., which types of user interfaces exist, and how they are related.
Due to those di erences, we argue that developing a formal ontology on user interfaces will not lead to yet another user interface description language, but to a formal model with di erent intentions and usages. In the next sections, we will discuss how the two worlds can bene t from each other.
A lot of research work has gone into the development of di erent user interface description languages. Those research e orts can be and should be taken into account when developing an ontology of the domain.
Most methodologies for ontology engineering foresee the capturing of key concepts and relationships as one of the rst steps. This can be done by conducting interviews
Software Model -respimrepsliecnittyatoiovner precise - task-specific approach - prescriptive Different goals lead to different models
shared conceptualization of a domain
- generic approach
- precise representation
- descriptive
over simplicity
with domain experts, scanning books and other
material, and/or reusing parts of other ontologies [
As discussed above, ontology engineering aims at providing a complete, comprehensive formal description of a domain. However, assessing the completeness of an ontology is not always an easy task. Here, user interface description languages can once again help by providing a benchmark for the ontology's completeness. Such a benchmark can be performed in di erent ways. On the meta-model level, the number of concepts contained in the meta model (e.g., tags and attributes in an XML schema) which have a counterpart in the ontology can be determined. On the model level, one can check whether given models in a user interface description language can be expressed using only the terms given in an ontology, either informally, or formally, e.g., in RDF. Thus, user interface description languages can provide a measure for the completeness of an ontology of the domain.
Once an ontology of the domain of user interfaces and interactions has been created, it can be used to improve the development and usage of new and existing user interface description languages as well.
In an analysis of user interface description languages,
we have found that terms are often used di erently in
di erent standards. An example is the term dialog. In
XIML, for example, a dialog element is de ned as
being \like a command that can be executed [...] It is the
more concrete instantiation of a task." [
Mapping a user interface description language to a formal ontology capturing the semantics of those terms can avoid such misinterpretations. With the example term dialog, a formal ontology can help resolving the ambiguity by indicating that the languages imply di erent top-level categories such as Process, Plan, or Software Component as super-category for Dialog.
XML based languages usually use a xed set of tags. In order not to be too strictly limited for practical use, many of those languages provide some extension mechanisms such as universal general purpose tags that can be used for user-de ned concepts (e.g. the ELEMENT tag in XIML). These extension slots are then lled with arbitrary strings.
Arbitrary strings, however, are dangerous. They lead to extensions that are incompatible with each other, interpreted di erently by di erent people and systems - concept collection
ark forpleteness ontology com - benchm Modeling Language - d-ie-sxactmoecmnbosipngiabvureialiisrttsyiooinonnaonfdterms relying on di erent conventions and external documentations, and, in the end, foil the overall idea of having a standardized modeling language.
A formal ontology can help here by providing a standardized vocabulary which can be used to ll such extension slots. Thus, it can be assured that there is an unambiguous interpretation of the extensions.
When bringing together di erent development teams,
information systems, or organizations, it is likely that
models created with di erent user interface description
languages already exist. Using a mediating ontology for
annotating the models is a common way of establishing
comparability between models, not only user interface
models [
Once models are annotated and can be compared using a common ontology, automatic conversion of models can be long-term objective. For the moment, a common ontology can at least support developers in understanding each other's models and assist them in unambiguously transferring their contents between modeling languages manually.
With these considerations in mind, we have started to develop a formal ontology of the domain of user interfaces and interactions. The goal is to end up with an ontology that is comprehensive at least with respect to the expressivity of current user interface de nition languages, that is universal enough to be extendable to future user interfaces that do not exist at the moment. Furthermore, to support valuable reasoning on user interfaces and provide meaningful semantics, the ontology should be highly axiomatized. To end up with a comprehensive ontology, we have analyzed several user interface description languages in order to collect a maximum set of relevant terms. We have used UsiXML, XIML, UIML, Maria, XUL, LZX, WAI ARIA, and XForms as a basis for identifying the core concepts.
In order to build upon well-acknowledged roots, we have
chosen the top level ontology DOLCE [
This position paper has discussed the di erences between UI description languages and a formal ontology of the domain of user interfaces and interactions. Furthermore, We have given insight into the development of a comprehensive formal ontology of the user interfaces and interactions domain. In the long run, we are con dent that formal ontologies and UI de nition languages will both have their places, and that both will bene t from each other.
We have presented a number of potential improvements where developers employing user interface description languages could bene t from those languages being mapped to a formal ontology of user interfaces and interactions. Thus, our claim is that organizations providing user interface description languages could improve the usability and acceptance of those languages by providing such a mapping.
As a long-term objective, such a mapping could even
facilitate automatic conversion between models developed
with di erent user interface description languages. To
that end, more sophisticated mapping approaches than
simply relating elements form a modeling language to a
category in an ontology are needed [
A formal ontology will not replace user interface description languages, but be a valuable enhancement. Due to the conceptual di erences between software modC D
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els and ontologies, user interface description languages
do a better job, e.g., when developing user interfaces
in model based approaches. Although there have been
attempts for UI code generation from ontologies [
The work presented in this paper has been partly funded by the German Federal Ministry of Education and Research under grants no. 01IA08006 and 13N10711.