Modiquitous 2011 Proceedings A Context Taxonomy Supporting Public System Design Romina Kühn, Christine Keller, Thomas Schlegel Technische Universität Dresden Nöthnitzer Str. 46, Dresden {Romina.Kuehn, Christine.Keller, Thomas.Schlegel}@tu-dresden.de ABSTRACT To do so, the context of usage must be captured and then Context awareness is the basis for a system’s ability to adapt correctly classified. Based on the captured context, the sys- to changing conditions of its environment. This ability is es- tem then must be able to adapt the interaction with the user. pecially important in the public domain where a variety of Depending on his location, a user for example needs differ- systems is used, so-called public systems. Public systems ent data and based on his abilities, he needs to interact using perform in public spaces and are available to all people, in- speech based interfaces, for example if he is blind. Based stead of focusing on specific user groups. They also often in- on this context classification, the system’s behaviour can be tegrate many different devices. Thus, they need to be highly modeled. In our previous work, we have developed a method context-adaptive in many ways. However, it is very difficult to model interactive systems on the basis of the technique of to determine what context is. None of the existing defini- Use Cases. Our method allows to model interactive compo- tions can serve as a guideline throughout the whole process nents and to modify the provided interactions according to of system development. Context relevant features need to be context. In this paper, we want to describe a context taxon- determined from scratch for each new system, making sys- omy that models contexts and context criteria of ubiquitous tem design error-prone, costly and time-consuming. To sup- public systems. We also describe how these context criteria port easy development of context-aware systems and appli- can be substantiated for different kinds of public systems. cations, we propose a reusable taxonomy of context features for the public domain. Related Work Most of the existing information systems that perfom in pub- Author Keywords lic systems are concerned with public transportation, often Context taxonomy, Context awareness, Public system specialized for example, for the blind people [5, 2]. Another kind of public system is focusing on tourists [11, 13]. As INTRODUCTION ubiquitous technologies became popular, they were also ap- plied in the public domain, for example integrating public Ubiquitous technologies are highly applicable in spaces, where displays and mobile devices or stationary information termi- many people need to access certain services. The first vi- nals [17, 21]. sion of ubiquitous systems by Mark Weiser introduced the idea of an pervasive work environment, where many people The idea of modeling context for ubiquitous systems is not a can work together, supported by invisible and intelligent sys- brand new topic [8]. Early context-aware systems are mostly tems that surround them [23]. But the “smart office” is not location based or consider location and additionally physi- the only application of ubiquitous technologies. Recent re- cal conditions as a system’s possible context [22, 4]. In re- search efforts explore the usage of ubiquitous systems in the cent years, the view on “context” has changed from a mainly public, like hospitals, public transport systems or other pub- physical to a broader view. Some choose to consider tasks lic spaces [9, 5, 7]. In public spaces, many people have to or activities of a user as the system’s context to take into ac- access many different services, different data and use differ- count, too [18, 16]. In public systems, all of these variations ent devices to do so, like personal mobile device or public of context have to be considered, but there are additional displays. Ubiquitous technologies can be used to integrate views on context that can become relevant. There is, for those different devices and the different services that are pro- example, also a social context that may be important for the vided in public space. Such ubiquitous public systems have usage of public systems. We developed a reusable taxonomy to be context-aware and to adapt to the requirements of many of context criteria that are typically found in the public do- different kinds of users or environments. main and we therefore consider essential for public systems. This paper is organised as follows. In the next chapter, we want to present the aforementioned method for modeling in- teractive public systems we developed in our previous work. We will describe how this method allows to easily model such systems in a context-adaptive way. The following chap- ter then describes, how we modeled our context taxonomy. First, we want to describe our perception of context and the R. Kühn, C. Keller, T. Schlegel: A Context Taxonomy Supporting Public System Design. 45 Proc. of 1st International Workshop on Model-based Interactive Ubiquitous System 2011, Pisa, Italy, June 13, 2011, http://ceur-ws.org/Vol-787 Modiquitous 2011 Proceedings terms we use to derive specific context types from relatively context criterions in the iterative development of Interaction- abstract context criteria. We then present the user-centered Cases and allows step-by-step refinement of contexts from context taxonomy we developed. We also present exemplar- coarse-grained contexts to fine-grained context types. We ily modeled Interaction-Cases that builds on our context tax- will describe this structure and the context taxonomy for onomy. We conclude the paper discussing our approach and ubiquitous public systems in the following. describing work that is planned for further research efforts. A CONTEXT TAXONOMY FOR THE PUBLIC DOMAIN MODELING INTERACTIVE UBIQUITOUS PUBLIC SYSTEMS The public domain has special requirements towards infor- In order to support the seamless integration of various de- mation systems and a variety of contexts are possible. There vices and services in ubiquitous public systems, these sys- are different users with a different background, different cul- tems must be properly designed and modeled. Persona and ture, knowledge etc. and a wide range of devices such as scenarios can serve as a basis to define the user’s require- mobile devices, public displays, but also stationary informa- ments and the system’s behaviour [12, 1]. Based on infor- tion terminals. In order to capture the possible contexts that mally described scenarios, Use Cases can be derived that de- influence the interaction between a user and the ubiquitous scribe the system’s behaviour from a user’s perspective. Use public system, we focused on the user and the situations that Cases describe the system’s requirements in a more formal can arise in ubiquitous public systems. We do not claim that way. our context taxonomy is complete, but it can serve as a start- ing point for further refinement. Which contexts are relevant In our previous work, we proposed the method of Interaction- and which are not depends on the system’s characteristics, Cases for modeling interactive systems [20]. Interaction- its structure and its purpose. The structure of our context Cases can be used to describe the interaction between user taxonomy supports easy refinement of the contexts that are and system in a semi-formal way. Types of Interaction-Cases relevant for the task at hand. can be predefined, they are therefore reusable. Interaction- Cases can already be defined when requirements are deter- Structure of the Taxonomy mined in early phases and then be substantiated up to a very We based our perception of context on the definition given specific level, that can be linked directly to Use Case dia- by Dey and Abowd [8]: grams and code fragments. Context is any information that can be used to charac- In order to develop context-aware ubiquitous systems, the terize the situation of an entity. An entity is a person, contexts must be modeled in advance and depending on these place, or object that is considered relevant to the inter- contexts, the context-adaptive behaviour of the system needs action between a user and an application, including the to be modeled, too. We therefore refined our Interaction- user and applications themselves. Case method, allowing these Interaction-Cases to be context- adaptive [19]. In early design stages, an Interaction-Case For the usage of context with Interaction-Cases and for iter- can be marked as context-adaptive to a certain context. The ative refinement of relevant contexts, we describe context as Interaction-Case and the context definition may be very coarse- different context criteria that are organized in a hierarchical grained at first. In those early phases, the specific context taxonomy. These can be used as a first overview on possible features that lead to system’s adaptations may not be known, context dimensions for public systems. We then describe dif- but the general context criteria that influence the interaction ferent context types, that can be specified and derived from process between system and user can already be anticipated. a certain context criterion [14]. Context specifications can Therefore, it should be possible to refine the context criteria then be substantiated from context types by allowing a sys- as the specification of the system proceeds. tem’s architect to subsequently define values or value ranges for which certain context types are laid out in his system’s Using context-adaptive Interaction-Cases, it is possible to context design. A possible structure of such a hierarchy is define the interaction process between system and user in a shown in figure 1. different way for different situations. If the system observes, for example, that the ambient noise level is very high, it can • Context is information that characterizes situations or cir- adapt its audio volume. Another example is, that if the user cumstances of an entity like a person, a place or an object is blind, it is necessary to switch to audio interaction instead [8]. The complete context a system is able to capture in of visual. a specific situation, is most likely combined of different types of context features and different values of these fea- The development and modeling of interactive ubiquitous pub- tures. A complete system’s context can, for example, be lic systems becomes easy and less time-consuming using combined from a temperature of 20 degrees celcius, the Interaction-Cases. The method depends, however, on a prop- availablility of visual and audio output and a certain time erly modeled context hierarchy, that serves as a basis for and location. development of context-adaptive scenarios and interactions. We therefore propose a context taxonomy for contexts in • Context criteria are different categories in which context ubiquitous systems. It models contexts that can occur in the can be defined. The context criteria are criteria that may public domain and are of possible interest for public sys- influence a system’s context and are defined on a rela- tems. The structure of the taxonomy reflects the usage of the tively abstract level. Context criteria can be hierarchi- 46 Modiquitous 2011 Proceedings cally organized. Examples of context criteria are “Cli- mate” and “Temperature” but also “Perceptive Context” and “visual”. Socio-technical Context Physical Context • A context type is a sub-category of a context criterion. From context criteria on an abstract level, several context types can be derived that describe features of this context criterion on a specific level. As an example, from the con- Interaction Context Task Context text criterion “visual”, a system designer can define the context types called “blind” and “visually impaired”. • Context types can be specified directly by defining values User or value ranges. These are called context specifications. A context specification for the context type “visually im- Temporal Context Spatial Context paired” may be a value range capturing vision from 20% - 70% or from 71% - 99% as shown in figure 1. Figure 2. User-centered context Context Level Interaction Context output options. In between these steps, the system processes Perceptive Context Criterion the given input. According to this, our context criteria for Context Criterion the system’s interaction context are the following: Level visual • Input: For the context criterion of input, context types can be defined that describe the abilities of the system to get Context Type Level blind visually impaired input at all. Some devices used in public systems, for example like tourist information terminals in cities, are Context equipped with keyboards and sometimes even a mouse- specification 20 % - 70 % 71 % - 99 % like device. Many public information systems nowadays Level vision vision use touch screens, sometimes in addition to keyboards [15]. From the input context criterion, it is possible to de- Figure 1. Example of a specific context including context criteria, types rive context types that can be used to classify the possible and specifications inputs of a system. CONTEXT IN UBIQUITOUS PUBLIC SYSTEMS • Processing: The main task of an information system is to process data. The processing context criterion can capture Central to the description of context in ubiquitous public sys- the circumstances of processing in ubiquitous public sys- tems is the user, as shown in figure 2. These systems adapt to tems that may influence the system’s interaction towards the context they perceive in order to provide an optimized in- the user. Small devices, like mobile phones, have less terface for the many different users that use them. We there- processing power than devices connected to a processing fore started to collect the requirements of users in public sys- server, for example. The processing capabilities affect the tems. Based on these requirements, we differentiated sev- possible interactions with the user and can therefore be eral contexts that can be useful in modeling context-aware modeled using the processing context criterion. ubiquitous public systems. These context served as starting points for further refinement. In the following sections we • Output: The output context criterion captures the abilities will therefore explore these categories and the possible use of the system to pass information to the user. In public in modeling interactions in ubiquitous public systems. systems, all kinds of public displays are known [10, 6]. Thus, most ubiquitous public systems have visual output Interaction context abilities. But additional output modalities are also possi- By modeling context-adaptive Interaction-Cases, it is pos- ble, for example speech output or haptic output interfaces. sible to model the interaction processes a ubiquitous public system provides. Our first step is therefore to capture con- Interaction on part of the user begins with perception. The text criterions that directly affect the interactive process be- perception abilities of the user may require the ubiquitous tween users and systems. Ubiquitous public systems consist public system to adapt and, for example, provide different of different devices that provide different interaction modali- output modes. After perceiving information, a user pro- ties. The user may have different abilities to interact with the cesses the information, just like the system itself does. The system, too. We modeled the different context criteria that user also acts in order to input information to the system or are involved in interaction context by mapping the interac- to request information from the system. We therefore cap- tion process on part of the system and on part of the user as tured the interaction context on the part of the user using the shown in figure 3. The system possesses input options and following context criteria: 47 Modiquitous 2011 Proceedings • Perception: This context criterion captures how a user can • Sociological context criterion: With the sociological con- perceive input. A person can perceive using his senses. text criterion we describe the rules which people in pub- Regarding the interaction with computer systems, sight, lic systems are following. These rules allow us to model hearing and touch are the main perception channels. Con- possible scenarios for different sociological contexts and text types derived from this context criterion can grasp the so affect the usage of ubiquitous computing in public sys- perceptive abilities of a user. tems. For example, it is a common rule not to disturb other people in surroundings like churches with mobile phones • Cognitive: The cognitive abilities of a user can be grasped or other devices or to request people’s personal data where using the cognitive context criterion. Children, for ex- others can see it. ample, have other cognitive abilities than adults. A sys- tem can then adapt to these cognitive abilities, if they are • Organizational context criterion: The organizational con- known, and present information, for example, in simpler text criterion describes a third party like organizations which form. are somehow involved in public systems. This context cri- • Action: The abilities of the user to act towards the system terion can model the different conditions and possibilities can be modeled using the action context criterion. A user of, for example, public transport organizations, supplier can act using gestures, voice, facial expression or move- or other organizations that are associated with public sys- ment. The cognitive context criterion can be used to cap- tems. ture the acting abilities of a user, analogous to his percep- tive abilities. Besides the user-centered context criteria there are two sys- tem’s socio-technical context criteria which are described as follows: Output Context Criterion • Operational context criterion: In public systems there is a multitude of processes, procedures and activities which Processing Context Criterion are not directly visible to a user. These operations can be summarized in the operational context criterion. For ex- Input Context Criterion ample, activities or procedures like to operate the turnout in a control center can affect this criterion. Interaction Context Perceptive Context Criterion • Technical context criterion: Another system centered cri- terion is the technical context criterion. It includes all Cognitive Context Criterion technical abilities of a system, for example, the ability to show real-time data or just data which can not be updated automatically. Acting Context Criterion Organizational Context Criterion Figure 3. Interaction context The different sides of interaction context are comparable. From a certain point of view, the input context criterion and Sociological Context Criterion the acting context criterion capture the same type of context, for example, speech input. The same is true comparing out- Socio-technical Context put and perception context, capturing, for example, visual Operational Context Criterion input. We distinguished a system’s interaction context from the user’s interaction context. Using two different “sides” of interaction context means, that it is possible to perceive that the user is blind, which is a context type deriving from the Technical Context Criterion perception context criterion. At the same time, it is possi- ble that the system is only able to give visual output (output context criterion). This situation can only be observed us- ing a perceptive context that is distinguished from an output context. Figure 4. Socio-technical context Socio-technical context Another interesting aspect of context is the socio-technical Further contexts context in figure 4. We identified four socio-technical con- Beside the contexts we described above, there are some fur- text criteria [19] which we divided, depending on their focus, ther contexts that affect the usage of ubiquitous systems in in user and system modelling context criteria. The following the public domain. We briefly characterize these in the fol- social-technical context criteria are user-centered. lowing paragraphs. 48 Modiquitous 2011 Proceedings Physical context board input to acquire the departure information. It is shown Physical context of ubiquitous public systems captures, for in figure 6 on the right. example, temperature, humidity, ambient noise level or bright- ness. The context criterion “ambient noise level” can be rel- evant, for example, for adapting the output volume of speech output as the ambient noise level raises. Task context There are several approaches to capture task or activity based context [18]. The task the user wants to complete, does in- fluence the interactions he pursues. We therefore plan to capture different task-based contexts for public systems in our future work. Figure 6. General Interaction-Case and context-adaptive derivation Spatial context The spatial, or location-based, context is described in other However, if the user of the system is blind, he is not able to projects and papers e.g. by Bauer et al. or Bellavista et al.[3, use a normal keyboard to provide the departure information. 4]. Spatial context can, for example, capture the location of In this case, the system should switch to audio interaction. a user but also the user’s movements, which means whether The Interaction-Case in figure 6 is therefore modeled for the the users walks or stands. context-type “blind” and the system adapts the input modal- itiy to audio. Using this modeling technique and our context Temporal context taxonomy for public systems, it becomes possible to model As already described in our previous work, the temporal context-adaptive interactive ubiquitous public systems eas- context contains absolute and relative time [19]. Time as- ily, already beginning in early design phases using pen and pects can, for example, affect the presentation of data both paper. on a mobile device and public displays. Further contexts re- lated to time are conceivable. We will explore these aspects CONCLUSION AND FUTURE WORK and their possible use in ubiquitous public systems in future In this paper we presented a structure for a context taxonomy work. that supports modeling and development of context-aware ubiquitous public systems. Using a context taxonomy for USAGE OF CONTEXT FOR MODELING INTERACTION the public domain as a basis and implementing the method of modeling Interaction-Cases, it becomes possible to de- In this section, we want to give a short example of the usage fine interactions between system and user in an iterative way. of context-adaptive Interaction-Cases. Given the context hi- The structure of context we proposed also supports the step- erarchy in figure 1, the input of data in a public system can be by-step refinement not only of Interaction-Cases, but also modeled in different ways. Our example of a public system of the involved contexts, as shown exemplary in the previ- is a public transport system. In such a setting, people want ous section. We also presented a context taxonomy for the to retrieve information on timetables of buses or trains. We public domain that can be used as a starting point to model therefore modeled the Use Case retrieveTimetable- contexts for ubiquitous public systems. Information, as displayed in figure 5. In order to request information on a timetable, the user needs to specify the lo- Our goal is to enlarge the taxonomy we described above and cation and time of departure. The Use Case thus contains an to refine the context criteria in the future. It is, for exam- Interaction-Case enter departure information. ple, possible, to refine the input context criterion within the interaction context with respect to the data type that can be entered via the different input channels. Some input chan- nels may, for example, only be relevant or active for input of special data types. We also want to explore the possibil- ities of deriving context-adapted Interaction-Cases automat- ically using rule-based substitution of certain Interaction- Steps. We hope to further improve the modeling method and Figure 5. Use Case retrieveTimetableInformation and associ- the underlying context taxonomy and therefore to improve ated first Interaction-Case and facilitate the development of ubiquitous public systems. The system we modeled as an example should adapt to the ACKNOWLEDGEMENTS perceptive abilities of its users. The Interaction-Case enter Part of this work has been executed under the project IP- departure information is therefore modeled context- KOM-ÖV funded by the German Federal Ministry of Eco- sensitive. It can be adapted regarding the context criterion nomics and Technology (BMWi) under the grant number “visual”. We modeled two Interaction-Cases that implement 19P10003O. the given Interaction-Case for two different context criteri- ons. The first is the “normal” Interaction-Case that uses key- 49 Modiquitous 2011 Proceedings REFERENCES 12. Kazman, R., Abowd, G., Bass, L., and Clements, P. 1. Aoyama, M. Persona-scenario-goal methodology for Scenario-based analysis of software architecture. IEEE user-centered requirements engineering. Requirements Software 13, 6 (1996), 47–55. Engineering, IEEE International Conference on 0 (2007), 185–194. 13. Klante, P., Krösche, J., and Boll, S. Accessights - a multimodal location-aware mobile tourist information 2. 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