Habitats, Activities, and Signs

Martin Brynskov1 and Peter Bøgh Andersen2

1Department of Computer Science, University of Aarhus, Aabogade 34, DK-8200 Aarhus N, Denmark

brynskov@daimi.au.dk 2Department of Information and Media Studies, University of Aarhus,

Helsingforsgade 14, DK-8200 Aarhus N, Denmark pba@imv.au.dk

Abstract. Digital habitats is a framework for designing and modeling envi-ronments for activities that involve mobile and embedded computing systems. This paper 1) introduces the basic concepts of the framework, i.e. activity, the-matic role, and the three ‘dimensions’ of a habitat: physical, informational, and pragmatic, 2) proposes a notation, and 3) sketches a method and exemplifies ar-eas of application using authentic cases from hospital work, primary school education, the maritime domain, and other areas.

1 Introduction

This paper will present a framework for designing and modeling environments for nomadic, collaborative work that includes elements of pervasive computing, i.e. mo-bile and embedded digital media. It is called digital habitats and is based on the bio-logical notion of a habitat.

Computers used to be machines that sit on a desktop. While this is to a large extent still true, the widespread adoption of mobile computing devices is beginning to have an impact on the kind of information systems that are developed and used, and this, in turn, seems to change the way users perceive and interact with those systems.

Technically, computers – or microcontrollers – have been embedded in all kinds of appliances like cars and washing machines for years, but although the amount of embedded microcontrollers produced today vastly outnumbers ordinary computers [1], they have been well hidden in stand-alone artifacts and have not really been per-ceived as computing devices. A washing machine is still a washing machine as long as it just takes care of the laundry. However, as network technologies have allowed devices to be increasingly open to exchange of information and interaction with other systems – e.g. a car obtaining weather information, or a refrigerator that allows the user to check the inventory while shopping in the supermarket – we may see a change away from a single/closed-system perspective towards a more diffuse environmental and experiential perspective. Computing (or information) processing ‘power’ is be-coming a feature of a physical space, just like electricity in the woodwork; and that is called pervasive or ubiquitous computing.

Pervasive computing systems are more integrated into the context of the use situa-tion, thus, ‘the system’ becomes a combination of physical space, information, and

people. Habitats address this integration by offering a ‘holistic’, yet structured per-spective.

Section 2 presents the framework and notation and illustrates it with examples; Section 3 suggests ways of describing the genesis of habitats and illustrates variations of the habitat concept, some due to problems of scale, and some due to non-overlapping physical and informational habitats. Section 4 describes an authentic case of habitat emergence from a hospital, and finally Section 5 suggests simple design guidelines for habitats, and illustrates them with a post-mortem analysis of a real project on context-sensitive mobile technology.

2 The Framework

2.1 Activities and Roles

In this framework, the governing concept is the activity consisting of a number of actions subsumed under a common goal. An action can again be broken into a number of elements, thematic roles, that are required for the activity to take place. This is much like a sentence, where an activity is described by filling a number of slots with different types of words playing different roles. It can be observed linguistically that different languages have different devices for marking roles – e.g. inflection (case, number, tense, mood, voice), syntax (word order), lexicon (e.g. particles), or pronun-ciation (prosody) – but in spite of the huge variation, a number of identical roles seem to be representable in many languages. They include, among others, the general activ-ity (verb), persons involved in the activity (agent, patient), objects (target, instru-ment), and a number of relations and movements in time and space (e.g. location, proximity, origin, destination, and directed movement). The spatial-temporal relations have often developed abstract meanings as well (already in ancient times), which is evident from the etymology of many words, e.g., prefer (from Latin, prae in front of + ferre bear) or hypothesis (from Greek, hypo under + tithenai to place). An example of a device for expressing roles in natural language is the eight Proto-Indo-European noun cases that mark the role of substantives: nominative (subject), vocative (ad-dressee), accusative (direct object), genitive (possession, source), dative (indirect object, receiver), ablative (separation from), locative (location), and instrumental (instrument) [2].

In the following we shall use Table 1 as our repertoire of thematic roles.

Table 1. A list of thematic roles. Authentic examples from the maritime domain. Adapted from Jurafsky & Martin [3]

Agent The volitional cause of an event: Can we berth her without a tug? Experiencer The sentient being that senses an event: Maybe we can see the

‘Gudrun’ from here. Force/Cause The non-volitional cause of an event: As she goes full speed at shal-

low water, then she creates a water wave Theme The participant most directly affected by an event: Can we berth her

without a tug? Material The thing that changes identity in an event: Isn’t that the only place

where we get a copy of those receipts? Result The final identity of the material: We make a three sixty (maneuver) Content The proposition or content of a propositional event: I said to him that

as soon as you were finished steering, you would come down so that we could get it in

Instrument The tool used in an event: Can we berth her without a tug? Beneficiary The non-Agent that benefits from an event: I said to him that as soon

as you were finished steering, you would come down so that we could get it in

Source The start location of the Theme of a transfer event: I really thought he came from Rotterdam

Goal The end location of the Theme of a transfer event: ‘Gudrun’ must sail before we can get in.

Purpose The intention of the Agent of the event: Well, down to about 7.5 meters draught, you need that in order to run properly with the top of the tunnel.

Time The time of the event: he will not sail until two o’clock. Location The place of the event: we are still lying here waiting Manner The manner in which the event is performed: Shall we start turning

slowly now?

Thematic roles like these form part of the interpretation of an action. The action can be realized in two kinds of behavior: we can enact it and we can talk about it. The hypothesis is that the thematic roles control both types of behavior, not only the talk-ing (as evidenced above) but also the doing [4].

The roles in Table 1 belong to the individual action. We can define macro-roles as-sociated to an activity by means of thematic roles: a macro-role denotes the rights and obligations of its filler to play a number of specified roles in a specified set of actions. For example Bækgård [5], a borrower has the right to be the beneficiary of the action The library lends the borrower a book and the duty to be the Agent of the action The borrower returns the took to the library. Macro-roles are useful in describing activi-ties qua a set of actions subsumed under a common goal.

Our objective in the following is to develop some concepts as well as a notation that allow us to describe some essential roles and features when modeling activities and actions that include mobile digital media. We start out with the notion of a habi-tat.

2.2 Habitats

The habitat was introduced as a design metaphor in pervasive computing by May and Kristensen [6] as an attempt to grasp the new challenges that arise when information systems become (even more) embedded in the physical environment. The idea is parallel to similar holistic trends within other fields and has affinities to older tradi-tions such as ‘time geography’ (invented by the Swedish geographer Torsten Häger-strand, cf. [7]) and ‘space syntax’ [8], both used in urban planning and transportation research. Habitats as a framework for description has subsequently been evaluated in specific domains, including trains [9] and hospitals [10].

A habitat is defined as an environment that supports and mediates the activities of its inhabitants – presents a set of affordances in the sense of Gibson [11]. Not all places are habitats, and not all entities are inhabitants. Only actors whose activities are supported by the habitat are its inhabitants, and only environments that support an actor is a habitat for it. An arbitrary part of the North Sea is not necessarily a habitat for maneuvering a ship; however the presence of buoys near a harbor indicates that the harbor is indeed a habitat. Also, there must be a stable relation between habitat and inhabitants. In other words, the inhabitants’ habits must reflect the habitat. How-ever, a fundamental feature of this relationship is that habitat and inhabitant influence each other and adapt to each other’s changes. Thus, habitats evolve over time.

Actors can be people, robots or digital agents, and they can be inhabitants in more than one habitat. Likewise, habitats can support many types of actors.

Instead of viewing a habitat as an indiscriminate whole, we divide it into three ‘dimensions’: a physical, an informational, and a pragmatic dimension (adapted from May et al. [12]. However we have replaced their term conceptual habitat with prag-matic habitat). These three dimensions are three perspectives on the world (Fig. 1). We can describe features of habitats in each of these dimensions, thus, we talk about physical habitats, informational habitats, and pragmatic habitats. Habitats can be grouped and nested.

Fig. 1. The three ‘dimensions’ we use to describe habitats

Physical habitats. A physical habitat is a section of physical space/time. By viewing places as habitats we get a broader perspective than the mere empty, abstract space as a mathematical model in four dimensions (three physical dimensions + time). A physical habitat is a tangible and everyday thing: a kitchen, a bus terminal or a hospital ward. This means that it changes and evolves over time as a result of the ongoing interaction with the activities of its inhabitants; thus, if we do no longer have

Physical dimension

Informational dimension informational habitats

Physical dimension physical habitats

The world habitats

Pragmatic dimension pragmatic habitats

time to cook, we install a micro oven in the kitchen. Physical habitats can be nested. A good example is a train: the train as a whole is a habitat for the traveling activity (embarking, showing tickets, disembarking), but a part of it, the compartment, is a habitat for work activities (reading, writing on a laptop, telephoning, cf. [9]). The work activity is subordinate to the travel activity, since the latter can interrupt the former, but not conversely.

Notation: A physical habitat is denoted by a black outline shape. It can be an abstract shape (Fig. 2a), or it can correspond to the actual physical space (Fig. 2b), just like maps [13].

Fig. 2. Simple notation of a physical habitat, as an abstract form focusing on accessibility (a) or

as a more iconic representation of physical space (b).

Informational habitats. Informational habitats need a bit more explanation, or at least justification. An informational habitat is a well-defined combination of informa-tion and media that support certain inhabitants’ information and communication needs. Information is a result of interpretation, and communication is the exchange of information by peers. Since the model encompasses all kinds of information and all kinds of interpreters, i.e. both digital (digital media and digital agents) and non-digital (non-digital media and people), we find it useful to distinguish between informational habitats as the context for people’s interpretation (Peirce’s interpretant) and com-puters’ algorithmic determination [14]. Thus, we use ‘communication’ about peers exchanging information, i.e. human-human or agent-agent, and we name non-peer exchange, i.e. human-computer or vice versa, ‘mediation’.

It is possible to conceive information as a space defined by accessibility relations [13]. However, the resulting ‘space’ is not equivalent to Euclidean space, since it is not metric. Distance in a metric space must be symmetric – the distance from A to B must be the same as the distance from B to A. But if we define informational distance as the minimal number of nodes necessary to get from point A to point B, then infor-mational distance is asymmetrical, because the number of links needed to go from A to B may be 100, whereas B may contain a direct link back to A.

As with physical habitats, informational habitats can be grouped and nested. It is often practical to view a collection of media or information services as one medium. The individual components part can then be addressed if need be.

Examples of informational habitats are mobile phones, conferences, meetings, wireless network services, or bookshelves.

Physical habitat

b a

Physical habitat

Informational habitats are essentially semiotic by nature. They provide and mediate signs. It is therefore useful to distinguish between the representation (Peirce’s repre-sentamen) and the object of the sign. Thus, we distinguish between the representing part, the access area, and the represented part, the reference area, of an informational habitat. The access area is where the inhabitants have access to the information, and the reference area is the object of the information. The reference area might include anything from physical artifacts to mental entities.

Notation: Informational habitats are drawn with dashed lines. The access area is the location that gives access to information about objects located in the reference area. An arrow connects the two spaces. The label on the arrow indicates the medium used (Fig. 3).

Fig. 3. Informational habitat.

Pragmatic habitats. A pragmatic habitat is a shared mental space (consensus) that sets the boundaries for the inhabitants behavior (including interpretation, reasoning, communication, and collaboration). Thus, pragmatic habitats describe the socially stabilized demands to skills, knowledge, obligations and rights required by the fillers of the roles to make an activity possible.

A bit of explanation is in place before we simply claim that sets of concepts and behavior can form habitats: we assume that human cognition functions in such a way that we relate new experiences to concepts and behaviors previously learned [15]. Therefore, we are inclined to choose some interpretations rather than others depend-ing on our immediate context.

This is true in language as well as in behavior. If we hear an utterance we cannot immediately understand, we will first choose a habitual or contextually appropriate meaning before considering more exotic meanings. Or, driving a car, we would re-spond to any danger by moving our right foot to the brake – we do not first consider the huge spectrum of possible actions we could also take; otherwise riding a car would be a risky business (more than it is already). Such a ‘mental space’ is a ‘mode’ that we are currently in, a set of concepts matching certain expectation, thus making certain interpretations and behavior more likely than others. In linguistics, such ‘rep-ertoires’ are known as registers [16]. Although these chunks of behavior may be idio-syncratic for one person, it must be shared in order to become a pragmatic habitat.

In our definition, a pragmatic habitat cannot be separated from intentions and ex-pectations. Therefore a pragmatic habitat is something that exists in people, whether in the management or in the people actually performing the work. We can find repre-sentations of pragmatic habitats in manuals etc., but the habitats as such are embedded in people – or digital agents, if such are used.

We use the term glue to describe the relations between roles and fillers (actors) in pragmatic habitats. If one of the activity’s roles lacks a filler, the activity is potential

Access area Reference area M

edium

but not realized. In computer science terms, we can say that the activity is defined as a pattern or a class of activities that are not instantiated fully and are not executed until all roles have been filled.

Glue describes the ability, knowledge, obligations, and desires required of the filler to fill its role. During its life as a potential activity (for examples, see [17]), the activ-ity lacks fillers, the glue binding a filler to a role is too weak, or it involves conflicts. For example, in the cardiac arrest example in Section 4, the telephone call increases the doctor’s obligation to assist in the resuscitation activity, but he may not immedi-ately be able to comply, since he is in another ward with other obligations, and there-fore unable to immediately join the resuscitation team.

The potential activity exists as different stakeholders’ goals and expectations. These exist as the routines and competences of a group of workers, e.g. doctors and nurses, and perhaps backed up by a written description of the activity; in the case of a hospital, potential activities are extensively documented. In case of a digital agent, the potential activity is described by the algorithms governing its behavior. The members of a potential pragmatic habitat are the inhabitants (persons or digital agents) that meet the requirements in terms of skills, knowledge, and authority to fill a role. Two or more inhabitants may join skills to meet the requirements.

A realized activity exists as the behavior of actual fillers of roles, i.e. actors (peo-ple or digital agents) performing the activity, chunks of information, different media (digital and analog), objects, instruments etc. Members of a realized pragmatic habitat are the actual inhabitants filling the roles.

The pragmatic habitat depends on the activity but it does not float free in the aether. It is constantly reinforced as well as changed. In a hospital, there are strict regulations behind the procedures and goals that make up activities, so here the prag-matic habitat will to a large extent be explicit in written material and formal educa-tion. But people are not robots that mechanically carry out orders, they internalize the work routines, through actual work and collaboration, thus the actual pragmatic habi-tat at a hospital ward may be quite different from the formal descriptions of it. The pragmatic habitat may also change as a result of feedback from the inhabitants as they adapt their work routines, and in turn this may even change the activity. An example of this is the changing of procedures at a hospital ward because everyday work has highlighted some strength or weakness. The following diagram illustrates the dialectic relationship between an activity, a pragmatic habitat, and its inhabitants:

Fig. 4. The ontological status of a pragmatic habitat.

This diagram illustrates the relationship between an activity, its pragmatic habitat, and the participating inhabitants (actors A1-A3). The pragmatic habitat is a projection of each individ-ual’s mental space and competences (circles and dashed lines) that are required to fill the roles of the activity. The double arrows denote reciprocal influence over time, both between inhabi-tants and habitat, and between habitat and activity. The pragmatic habitat – i.e. the competences and traditions that the doctor and nurses expect in this activity – takes the form of an inde-pendent entity because they can refer to it and communicate about it. The collaboration and common routines in this activity helps strengthen the externalization of the pragmatic habitat. The resulting reification can be even stronger in the shape of manuals, teacing material, and legislation. Thereby the pragmatic habitat is conceived as an entity separate from the individual subjects; and indeed they are separate since pragmatic habitats do not depend on single persons. A pragmatic habitat is comparable to a register [16, 18].

In the diagram above, the glue is left out. But very often it is not enough to have the required skills to fill a role to actually be allowed to do so. Not any doctor can walk in from the street and participate in the work at a ward (unless it is an emergency). Nor-mally potential fillers of roles need a formal authorization to be granted the right to become inhabitants in realized habitats, they need a contract (glue). In a structured work setting as a hospital, this would be in the form of education, certification, and employment. Also, in this case, rights are followed by duties: the person filling the role of “doctor” in the cardiac arrest example in Section 4 is not only a person li-censed to do it, it is also a person whose duty it is, i.e. the doctor on duty.

In a less informal environment, e.g. a private home, rights may be granted in the form of some kind of authorization by the owner of the habitat: guests are invited to use the guest room for a delimited period of time.

The authority to grant and deny rights in a habitat, i.e. to define the glue between certain roles and fillers, is closely related to the purpose of the activities. In some habitats, e.g. the bridge of a large container ship, there is a very explicit hierarchy, complete with powerful rights backed by law. In other settings, e.g. in a public politi-cal forum, these rights are much less explicit, or even absent to a large extent, and are negotiated ad hoc by the participants.

A1 Nurse

Activity

Prag-matic

Habitat

A2 Doctor

A3 Nurse

A similar situation exists with the priority of activities. In some situations, priority will be well-defined, but not in others.

Notation: An empty role is marked by a white circle; fillers are marked by a black circle. If there is a glue specifying that an absent filler is obliged to fill a particular role (e.g. via a watch schedule), the filler will begin to move into the habitat if this is possible (Fig. 4). We use the following four types of changes of ability, knowledge, obligation, and desires (cf. [19]): * = creation; † = destruction, \ = suppression, / = maintenance.

Change of glue with respect to a role in one activity is often caused by the filler having participated in another role in another activity. The doctor’s obligation to act as the doctor in the resuscitation activity is created by his participating as the ad-dressee in the telephone call done by the nurse. This makes him hurry to the ward. Other examples are: if X participates as the buyer in the action The railroad company sells a ticket to X, he acquires the right to participate as the agent in a traveling event X travels from Y to Z by train.

*obl

F

ActivityRole: R

R

X

ResuscitationDoctor: D

D

Telephone callAdressee: A

A

*obl

Fig. 5. Pragmatic habitat. Filler F moves to the habitat in order to fill the role.

Fig. 6. A telephone call creates glue that obliges the doctor on duty to play the role of “doctor” in the re-suscitation activity.

2.3 Default notation

In order to make the notation as simple and powerful as possible, some default as-sumptions are made: By default, the access area and reference area of the informa-tional habitat coincide with the physical habitat. Everyone in the physical habitat has access to information about the surface of objects located in the habitat. However, by default they neither have access to information about content of containers, nor to the space surrounding the physical habitat. Inaccessible parts are marked by gray. If all elements belong to the same activity, there is no need to indicate to which pragmatic habitat the empty roles belong.

R

ActivityRole: R

a b

Fig. 7. Graphical notation of an activity, with (a) and without (b) the default assumptions explicitly marked.

We can still use the explicit notations if need be, e.g. to denote access to information that would otherwise be inaccessible, or to distinguish roles of different activities. In our framework, the authority to grant and deny rights is by default inherent in stati-cally defined glue between the roles of the activity and potential fillers. Priorities of activities are by default absolutely defined on the system level to avoid deadlocks. However, handling priorities is a potentially difficult task if the system is to have some degree of autonomy.

3 Genesis of Habitats

This chapter deals with different types of habitats and the reasons for their genesis. We have found it convenient to formulate these reasons in terms of deviances from the default situation. In the default situation, activities are going on in exactly over-lapping habitats in all three dimensions. This situation is stable in the sense that noth-ing further needs to be done in order for the activity to be executed. Also it seems to be the most frequent situation in everyday life. In my office, I can see most of the things I need from every place in the office (if we leave out the contents of cupboards and drawers). The idea is now, that deviation from this standard situation in one di-mension must be compensated by a change in the other dimensions. For example, disjoint physical habitats require changes in the informational habitat. The reason for having disjoint physical habitats could be a desire to make better use of scarce re-sources (e.g. doctors) or the need to separate activities physically (e.g. in a chemical plant).

In the following, we describe various situations of this kind and we also discuss the difficult problem of entering, leaving and crossing habitats.

R

Activity Role: R

3.1 Disjunct physical habitats

All activities take place in one or more physical habitats. Therefore, all informational habitats are located in a physical habitat. Or, phrased more precisely, the access area of the informational habitat must be located in a physical habitat inhabited by the people participating in the activity; the reference area, the object, may be anywhere, even nowhere, as in fiction. Similarly, pragmatic habitats are dependent on informa-tional habitats, otherwise collaboration is impossible. Actors must therefore have access to an informational habitat, implicitly or explicitly. This requires physical access to the medium, the access area of the informational habitat. In conclusion, whichever dimension of a habitat an actor wants to enter, he must always enter a physical habitat.

The effect of these dependencies is that if one or more of the conditions fail, we should seek solutions to (1) restore the standard conditions, or (2) provide alternative configurations that still make it possible to realize the activity.

(1) Restore standard conditions. A typical situation is when an event triggers a new activity with higher priority than other current activities; this requires some roles to be filled at a certain location that is different from the current location of the potential filler. This filler could be a person needed for the agent role (e.g. a doctor) or it could equipment needed for the instrument role (e.g. resuscitation equipment). If a filler happens to be outside the physical habitat where an activity requires him/her/it to be, the simplest solution is to move him/her/it into the physical habitat (Fig. 5, cf. also Section 4). If for some reason this is impossible, as in the following case with an ambulance where the doctor is in his office, something else must be done.

(2) Provide alternative configurations. A man falls ill on the street and the by-standers call an ambulance. The ambulance arrives with two paramedics. The patient is unconscious and would benefit from an instant diagnosis, which is something the paramedics are neither allowed nor capable of providing. At the hospital sits a doctor on duty in his office. The paramedics call him on the videophone and brief him. Apart from video and audio from the phone, the doctor could use some information about the patient’s vital data. Therefore, the paramedics place some sensors on the patient, sending scope data from the patient to the doctor’s computer. The doctor can now give a temporary but much safer diagnosis and instruct the paramedics how to pro-ceed.

Scope

telep

hone

FirstAidParmedic: PDoctor: DPatient: Pt

P Pt

D

hospital

ambulance

Scope

D

patient

hospital

ambulance

Fig. 8. Collaboration between a doctor at a hospital and a paramedic in an ambulance.

Fig. 9. The doctor has access to in-formation about (in) the patient that is not available to the paramedic (unless similar equipment is in the ambu-lance).

Fig. 8 shows how the situation with two disjoint physical habitats is overcome, not by moving all fillers physically into the same physical habitat, but by letting two actors (the doctor and the paramedic) join to fill one role by means of a shared informational habitat (the phone). However, this diagram is not sufficiently precise since it only asserts that the scope gives the doctor access to the surface of the patient. In reality the doctor has access to the interior of the patients’ body. Therefore Fig. 9 is a more precise diagram.

3.2 Sub- and Super-Human Scale

Disturbance of the standard situation may also be caused by the fact that the access and the reference areas of an informational habitat have different scales. The access area must always be of human scale, while the reference area may be much smaller or much larger. Lemke [20] discusses the notion of scale at length, and claims that sys-tems where meaning plays an important part are characterized by the phenomenon of scale heterogeneity:

I will propose that when relations of meaning as well as of material interaction co-determine the dynamics of a system, we must take into account scale heterogeneity or scale-mixing as well. If system processes at very different scales are tightly coupled with one another, we may need new paradigms for system analysis and a somewhat different interpretation of the meaning and significance of ‘downward causation’. (Lemke, 2000: 181)

Meaning and the use of signs is the vehicle that establishes links between the human world and worlds of smaller or larger scale:

Meaning is the link between matter and history; making the material meaningful potentially links the scale of humans, artifacts, and other same-scale ecological partners to the larger scales of their diverging histories and the dynamical processes that determine those histo-ries. (Lemke, 2000: 193)

Since the basic element of the informational habitat is the sign, we should expect the informational habitat to display scale heterogeneity, and this is indeed the case.

Sub-human scale: Microsurgery. Haase et al. [21] describe microsurgery as taking place in two habitats of different scales: the operating theatre is a habitat of human scale, whereas the location of the operation is of sub-human scale, only accessible via media like the operating microscope or the endoscope. Their main point is that the knowledge, skills, and abilities of the surgeon performing a micro-operation are dif-ferent from those needed to perform a macro-operation, since the two activities take place in two different habitats.

Fig. 10 shows the two habitats of microsurgery: in the operating theatre the activity is “operation” which involves surgeon and nurse (plus other professionals); a part of this activity involves the activity of “microsurgery” that takes place in a sub-human scale habitat that is normally inaccessible from the macro-world. However, the micro-scope is used as a medium that enables informational access to the microscopic part of the patient which is the work object of the microsurgeon.

MicrosurgerySurgeon: S

MicroscopeS

N

Patient

OperationSurgeon: SNurse: N

Fig. 10. The access area of the informational habitat is the small area around the microscope. The reference area is a small part of the patient. The part-whole relation between the operation

as a whole and the microsurgery part is denoted by the aggregation symbol from UML

Super-human scale: Maneuvering. But there are also many examples of the opposite, namely represented habitats that are much larger than the habitat where the represen-tation is accessed. This is true for space as well as for time. A simple example is shown in Fig. 11. The human-scale habitat is the ship bridge where the representation is accessed. The work object of the officer is much larger than the bridge; in fact it is the ship, the volumes of water surrounding it, and other ships. The main point is that only one ship at a time can occupy a given volume of water; volumes are a scarce resource, and therefore ships have to cooperate in order not to collide. The radar is a medium that represents this work object of super-human scale, and whose representa-tion is accessible from the bridge.

The information service provided by the VHF radio creates an even larger informa-tional habitat, but this habitat turns out to be too large: the officers receive irrelevant information about defect buoys many hundred nautical miles away.

Radar

ManeuveringOfficer: OO

Ship

Bridge

Fig. 11. The bridge as the human-sized habitat, and the surrounding water as a super-human

habitat.

3.4 Time and space

The access and reference areas of the informational habitat may not only be separated in physical space or because of scale, but may also be separated by time. In process control, for example, statistics and trend curves give access to a larger temporal and spatial habitat than a human can span. Therefore we need to represent habitats with a temporal as well as spatial boundary since most activities are limited both by spatial and temporal boundaries. A good example is the monitors placed in railway stations and airports ([15], Fig. 12). They typically show trains and airplanes departing from this station or airport within the next hours from now. Thus, the information is contex-tually bound to place as well as time. The habitat itself has changed from being an object to becoming a process developing in time (cf. similar concepts in [22], Ch. 10); however, by our natural senses we can only access the small time-window defined by the present.

Space

Time

Station

Monitor

Fig. 12. Informational habitat on a railroad station. Monitors make the future state of the station accessible from the present state. Note that the monitors can only be accessed from the station,

so that the information is contextually bound to space (“here”) and time (“now”).

3.5 Non-human inhabitants

Some habitats do not have human inhabitants but houses mechanical or informational agents (robots or software agents). The reasons may be that the habitat is unhealthy for the human body (nuclear power plants), that it is not physically accessible for humans (the Mars robots), or that replacing humans by automation saves money. In these cases it makes sense to say that the inhabitants are mechanical or informational agents – an agent being a device that possesses actuators and sensors and which can act autonomously in the environment where it is placed. Mechanical agents typically demand specific properties of their physical and informational habitats.

Traditional control loops in process control can be reinterpreted as agents. For ex-ample, a sensor measures the water level in a tank and controls a valve that ensures that the level is maintained at a desired value. Fig. 13 shows an agent that controls the water level of a tank placed out in the plant. Its activity is “maintaining water level”. This activity is a part of the larger activity of process control performed by the opera-tor. The operator in the control room can control the setpoints of the agent, and can see what its sensors can see.

The main idea in Fig. 13 is that automatic systems are viewed as role fillers in ac-tivities also involving the operator. Thus the water level controller acts as the agent of the action of maintaining water level which is a part of the process control activity. This requires us to view automatic systems as intentional systems – not in the anthro-pomorphic sense, but in the sense that the automatic system cannot be understood without understanding the intentions of the engineers that designed it. Lind [19] pre-sents an elaborated method for describing automatic systems along these lines. An-dersen [4] suggests another, but related, way of doing it.

Process controlOperator: O

O

Control room

Plant

control +screen

A

Maintain water levelAgent: AWater

tank

Fig. 13. Process control involving manipulating and inspecting an agent placed remotely in the

plant.

One of the expectations of ubiquitous computing is that mechanical agents will no longer be confined to the production sphere, but will enter domestic life too. At pre-sent we have only simple agents with simple control loops that hardly can be consid-ered autonomous: washing machines, coffee machines, ovens, the heating system. Agents with the ability to sense their environment and act accordingly seem a present mostly used to help habitat crossing (automatic door openers) and prevent it (burglar alarms, electronic door control, electronic firewalls, virus protection. See Hollnagel [23] for a classification of such barriers).

3.6 Habitat crossing

In many cases the access area of an informational habitat is duplicated outside the habitat, the purpose being to help or prevent people from entering the habitat and participate in its activities. For example, airports or railway stations may have moni-tors displaying bus departures in the neighboring bus station, and shops place adver-tisements on the pavement outside. Similarly, “no entry” signs prevent cars from driving into a one-way road. Such devices influence the glue binding a potential role filler of the habitat’s activities: his ability, knowledge, desires, and obligations to participate. See Fig. 14 for an example. Fig. 14 makes it clear that our diagrams must adopt the perspective of one of the participants. Fig. 14 is a true representation of the information the person located in the airport can access; but it is does not represent what the passenger located inside the bus terminal sees, since he obviously can see the monitors in the terminal.

P

Airport

Mon

itor

Travel by buspassenger: P

Busstation

Mon

itor

Fig. 14. From the airport, the potential bus passenger will normally not have access to informa-tion about bus departures. In order to ease the transition from airport to bus terminal, an extra

representation is placed outside the bus habitat.

3.7 Conventional habitats

Some places are used for some activities and not for others, although there is no func-tional reason for this. Consider a house: there is a functional explanation for the fact that cooking is done in the kitchen and bathing in the bathroom: the oven affords cooking and the shower cabinet affords showering. But why do some households rule that eating must done in the dining room or the kitchen, but not in the hall, or that guests are not entertained in the bedroom, although it would be physically possible? There seems to be a need for the notion of conventions too. It is not “proper” or “cosy” that the teenage son uses the coffee table for repairing the moped, while grandmother sits there too with her coffee and cakes. One cause of conventions could in fact be that certain activities mutually disturb one another. The reason for trains to have “quiet compartments”, where speech is forbidden, is that conversation disturbs reading or working.

3.8 Emergent habitats

Humans are both inhabitants of physical and informational habitats: they are physical bodies that move, but they are also sources of information. Therefore a random as-sembly of a few persons may attract another person in search of information – a self-perpetuating process. This newcomer is himself a new source of information which makes the emerging informational habitat even more attractive. If such spontaneous assemblies become a habit and are regularly associated with a specific place, then the place may come to house an informational habitat, even if it does not support access to information in any other way. You know you have a chance of getting information if you move to that place; and your presence attracts other people that want to use you as a source of information.

Examples of such emerging informational habitats at the hospital are the coffee room and the nurses’ shared desk at the ward. Although both places are already in-

formational habitats – the coffee room has a notice board on the wall, and at the desk there is an extensive array of information sources – the fact that people assemble there produces another kind of convenient informational habitats. It is often faster to ask your colleagues than to seek out some more authoritative source of information, e.g. a secretary or a medical reference book.

It is possible that informational habitats by nature are emergent to some degree. For example, natural language is not designed, but patterns evolve as a consequence of language usage. Damsgaard and Truex [24] claim that EDI-standards to some de-gree should be allowed to emerge “bottom up”.

4 Case: Cardiac Arrest Procedure

The following is an example of emerging habitats at an intensive care unit at the Uni-versity Hospital of Aarhus. It evolves around four phases of the activities triggered by cardiac arrest in a patient.

The ward has a number of rooms with two beds each (Fig. 15). All patients are monitored electronically for a number for parameters (e.g. heart rate and respiration) and the data is sent to displays at the bed and at the shared desk (cf. Section 3.7) in the corridor (Fig. 16). In ‘surveillance’ wards, a nurse or assistant must always be physi-cally present. The ‘intermediary’ patients are checked in person by the nurses now and then, otherwise their condition is monitored remotely from the desk.

Fig. 15. Floor plan of Intensive Care Unit B. Black dots are people engaged in different activities.

Fig. 16. The nurses’ desk with monitors

This case concerns an intermediary patient: The alarm is sounded by the monitors at the desk. It consists of a bell sound and a flashing red rectangle on the screen. This triggers the first part of the activity: making sure that the alarm is real and initiate the cardiac arrest procedure. This phase is carried out by the closest nurse who hurries in to the patient to see what caused the alarm, an emergency or a false alarm (e.g. a sen-sor slipping off a finger). If the alarm is real, she manually turns on the cardiac arrest alarm in the corridor. This triggers phase two: notifying people on duty to hurry to help with the resuscitation.

The notification is done in two ways, with two kinds of informational habitats: (1) by sound and blinking lights at the ward and coffee room (for people present at the

ward), and (2) by use of a dedicated phone (‘the heart phone’, located at the desk) that automatically calls up people with mobile phones, i.e. those who are not necessarily present at the ward (e.g. doctors, porters, and people carrying special equipment) (Fig. 17).

Fig. 17. Informational habitats required to notify staff of a cardiac arrest (simplified).

The information access perspective is that of the nurse at the desk. The phone call and verifica-tion creates the glue (cf. Fig. 6) between the doctor and the empty role in the pragmatic habitat needed by the resuscitation activity. Similarly, the nurse in the coffee room gets the alert be-cause of the ambient alarm.

All of these people will most likely be otherwise engaged in other activities around the hospital, but a cardiac arrest has higher priority than anything else so they must drop whatever is in their hands and run to the patient’s room. Nurses, assistants, and porters more or less flock together around the room, making certain that enough hands are present, whereas the more specialized staff, i.e. doctors and carriers of equipment, all enter the room. As people arrive, the third phase begins: resuscitating the patient. After the outcome – the patient either survives or dies – there is actually a fourth phase in which the participants exchange a few words with their colleagues and return to their other duties.

The circumstances of the activities related to the cardiac arrest procedure can be seen as the creation of new habitats and the destruction, or at least suspension, of others. When a nurse confirms that an alarm is real (thus moving from phase one to phase two), she instantiates a new pragmatic habitat and creates the appropriate glue

Doctor’s office

Patient room Nurses’ desk

Coffee room

P N1

D

N3

N2

Alarm Phone

Alarm D

Notify staff Nurse: N1 Doctor: D Patient: P

Resuscitation Doctor: D Nurse: N2, N3 Patient: P

N3

between empty roles and potential fillers (cf. Fig. 6), using the two kinds of informa-tional habitats (ambient alarms vs. phones). At the same time, this destroys or weak-ens the glue between those fillers and other pragmatic habitats they were engaged in before being summoned, thus leaving those habitats defect and waiting to be filled, either when the same person returns or by others. When the glue has been created, the physical movement is simple (illustrated below in Fig. 18).

Fig. 18. The persons dispersed around the hospital (cf. Fig. 15) leave their current positions and

run to or into the patients room.

5 Design of Informational Habitats

It is too early to set up detailed design guidelines. However, the following steps fol-low naturally from the theoretical framework:

1. Draw a map of the location. 2. Annotate the map with activities associated to particular places. 3. Divide it into habitats according to the activities. 4. Determine the information which the individual roles need in order to partici-

pate in the activities. 5. Provide representations that are accessible from the places where the activity

needing the information takes place.

If we take a closer look at places like highways, railroad stations, and airports, we can see that the designers of the static monitors and signposts must have followed similar guidelines, often very skillfully. The only new in mobile context-sensitive technology is that here the medium of representation (e.g. a location sensitive PDA or a mobile phone) moves with the user, and information on its screen is exchanged as a result of

this movement. In both cases, we need information telling us where to check in when we move into the entrance hall of an airport. We also need information about depar-tures in case we are late. When we come into the departure hall, we need to know the gate number and how to get to the gate. At present this information is provided by static monitors and signposts located at the strategic locations. A mobile technology would make these signposts superfluous and present the required information when close to the positions of the now outdated signposts. However, if the airport system is allowed access to the PDA and its electronic flight ticket, it can make the information even more precise, since it can make a very good guess at the activity which the pas-senger is engaged in, i.e. exactly which flight he is to take. It means that it does not need to present information about all departures, as we see it now, but can focus on that particular flight and give walking directions leading to its particular gate. A huge reduction of information indeed!

In the following we give a post-mortem reconstruction of a small experiment with mobile technology one of the authors participated in the HyCon project [25]. The purpose was to support schoolchildren during a field trip to Vestergade, a particular street in Aarhus. The children were to experience the real street and collect informa-tion about its past while on the spot. Later, back at school, they were to prepare a presentation to be shown to their classmates.

1. Draw a map of the location: an existing map of Aarhus was used. 2. Annotate the map with activities associated to particular places. The children

are to collect information about the houses they can see. 3. Divide it into habitats according to the activities. The streets were chosen as

habitats. 4. Determine the information which the individual roles need to participate in the

activities. The map is annotated by pictures and texts informing of the past of the houses of the street. Pictures and text are associated to the individual houses.

5. Provide representations that are accessible from the places where the activity needing the information takes place. The medium chosen was a location sensi-tive (GPS) tablet PC with access to a remote server and the internet. Pictures and texts show up on a map when the tablet is in the vicinity of the actual houses. In addition, a location sensitive internet search facility was provided that only produced results related to the location of the tablet. The tablet also anno-tates the map with the locations visited, and in this respect is self-describing. The purpose of this is to help the children remember where they had been, and which parts of the city the pictures and texts refer to.

PresentationPresenter: PAudience: A

PA

Field tripSchoolchildren: S

time

Place

tablet S

20031930

tabletprojector

Vestergade

School

Fig. 19. The setup of the HyCon project

Fig. 19 shows the whole setup, using our notation. Vestergade is a process beginning a couple of hundreds years ago and since then occupying a part of the space of Aar-hus. Only the present section of the street is accessible to the children with their naked eye. However, the tablet provides access to the location as it was in the past, e.g. in the thirties. In the classroom in the school another activity takes place, namely a pres-entation involving a presenter and an audience. Information about the information gathered in Vestergade can be accessed via the tablet connected to a projector (in the real project, the information was edited before it was presented. It is not shown in Fig. 19).

In addition to providing access to “old times”, the tablet also provided access to a larger part of the city by displaying a map where its present location was shown. As shown in Fig. 20, this means that the tablet, like other locators, is self-referring, since the access area (the locator) is inside the reference area (the city of Aarhus). Fig. 21 shows another interesting feature, namely chains of access and reference areas. The projector in the classroom refers to the pictures and text that appeared on the tablet in Vestergade; and the tablet in its turn referred to Vestergade in 1930; in this case, we may infer that the projector too referred to Vestergade in 1930, since the meta-reference involves simple copying and editing. Essentially, the projector quotes and comments what was previously on the screen of the tablet. However, this is not true of all meta-references, so the inference is not true in these cases.

tablet S

tablet

tablet

tablet +projector

tablet +projector

Vestergadein 1930

The tablet

The classroom

Fig. 20. Self-reference provides an overview. Fig. 21. Chains of access (representing) and reference (represented) items.

The HyCon project incidentally underlines the fact (cf. Section 3.1) that informational habitats are parts of physical habitats. One of the problems encountered was that one of the mobile phones connecting a tablet PC to the internet broke down because of rain!

6 Conclusion

In this paper, we have presented digital habitats as a simple framework for modeling activities involving mobile and embedded digital media. The framework consists of a set of concepts, a notation and a method sketch. Its main strength is that is provides a theoretically motivated connection between activities, locations, information needs, and information access. It is a work in progress and many aspects are still tentative, but we believe that habitats will be useful for 1) representing essential features of activities in a form that allows designers to make important design decisions, and 2) for providing a fairly smooth (although not trivial!) transition from analysis and de-sign to implementation when developing mobile and embedded digital media.

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