=Paper=
{{Paper
|id=Vol-149/paper-6
|storemode=property
|title=xLink: Context Management Solution for Commodity Ubiquitous Computing Environments
|pdfUrl=https://ceur-ws.org/Vol-149/paper06.pdf
|volume=Vol-149
|dblpUrl=https://dblp.org/rec/conf/ubipcmm/SadiM05
}}
==xLink: Context Management Solution for Commodity Ubiquitous Computing Environments==
https://ceur-ws.org/Vol-149/paper06.pdf
ubiPCMM 2005 35
xLink: Context Management Solution for
Commodity Ubiquitous Computing
Environments
Sajid H. Sadi and Pattie Maes
this capability. Weiser also noted that the acceptance of the
Abstract—In this position paper, we present xLink, a system for vision of Ubicomp depended, perhaps more than other areas, on
managing context information and marshalling service queries reaching a critical mass, or in other words, on the technology
and data flow. The repeated re-invention of context management becoming commodity. By “commodity technology” we mean
systems remains a perennial phenomenon in context aware and
ubiquitous computing. Often, these systems are integrated into
that the technologies are commonly available at the consumer
applications to accommodate the low level requirements of the level, much as cellular phones or televisions are today.
underlying devices. We hope to address this issue by providing a Additionally, we imply high accessibility by the general public,
framework that allows a clean, API-based separation of device, and low initial and recurring cost, such that individuals may use
context, and service management functionalities without them not as luxuries, but as part of their daily lives. This implies
curtailing the capabilities of any segment. xLink is designed to that devices must be low cost, interchangeable, and easily
allow commodity ubiquitous computing devices, particularly
devices with highly constrained computational capabilities, to
duplicated, manufactured, and used. These constraints in turn
interface directly at a low level to the context management bound what can be expected of these devices in terms of
framework, while still providing a clean and versatile service processing power, memory, reliability, and adherence to
Application Programming Interface (API) that allows protocols.
applications maximum expressive freedom. We also present a In looking at the history of ubiquitous computing, it is clear that
usage scenario for technologies based on xLink, and discuss the researchers have often been forced to develop special purpose
strengths and shortcomings of our approach in relation to other
context and information flow management strategies.
context management systems to address their needs [1, 2, 6, 11].
In many instances, the low level integration of the application
Index Terms—context management, context modeling, to the physical devices has essentially led to applications which
ubiquitous computing, interoperability. have context management embedded, thus limiting the
applicability as a commodity technology. We believe that this
situation is a side effect of the fact that no uniform and
I. INTRODUCTION expressive API exists to provide a clean separation between
device, service, and information flow management.
U biquitous computing (Ubicomp) presents a compelling
vision of environments, objects, and even people
augmented with technological and computational resources for
In this paper, we present an implementation of this claim:
xLink, a system of context management that offers a general
providing information “just-in-time”, or when and where the purpose environment which is capable of handling the needs of
information is needed and best applied [1, 11]. In introducing special purpose, low-capability devices without sacrificing a
this area of investigation, Mark Weiser of Xerox Parc also uniform service model. xLink is designed to support both
suggested some critical areas in need of investigation. One of continuously-running and on-demand applications in a
the primary technological challenges noted by Weiser is the seamless way, thus allowing application development
context management problem, that is, the need for methods of independent of the context and device management models.
managing and coordinating the flow of information between The system helps bridge the gap between general purpose data
the nodes and services available in the augmented environment flow management systems and low level “drivers” that allow
[11]. The omnipresent interface envisioned by Ubicomp simple devices to interact with such systems. xLink is designed
requires that devices act concertedly to support the user’s to be “close to the hardware,” and provides APIs for low level
current actions [3], and context management forms the basis of interfaces to be built directly above the flexible information
routing core. This feature allows us to integrate commodity
Manuscript received June 14, 2005. hardware directly into the context management backend
S. Sadi is a graduate student at the MIT Media Lab, Cambridge, MA 02142 without intermediary layers, while allowing services to interact
USA (phone: 617.253.9706; e-mail: sajid@ media.mit.edu). uniformly with devices without sacrificing low-level access.
P. Maes is an associate professor with the Media Arts and Sciences Program,
MIT Media Lab, MIT, Cambridge, MA 02142 USA (e-mail: Finally, the xLink system incorporates implicit and explicit
pattie@media.mit.edu). invocation of services, which allows for autonomous behavior
Sajid H. Sadi and Pattie Maes 36
while still allowing the user control over the interaction and C. The InConcert Middleware Layer
information flow. We have designed xLink to be a “room The InConcert middleware layer was produced by the
operating system” — a context management solution which can Microsoft Research Labs to serve, among other things, as a
be configured to support the specific purposes of an area, middleware layer for the EasyLiving Project [2]. It is, by design,
allowing shared infrastructure between disparate services, highly specialized for automation and control of living spaces.
while retaining the freedom of design and expressivity required Like UPnP, it is a protocol based system using XML message
by particular applications. schemas. As with JINI, a directory node within an augmented
physical location is used to register and track all other nodes [2].
As a result, the system is more centralized, with a central unit
II. RELATED WORK
coordinating inter-device communication, though the actual
As mentioned previously, there is a great deal of communication takes place via asynchronous message passing
fragmentation in the area of context management, with many between individual devices [2]. Like xLink, InConcert provides
systems existing only as parts of applications. This section high level lateral linkage support, but depends on a relatively
provides a non-comprehensive sampling of stand-alone context “heavy-weight” protocol (XML over IP) that hinders use in
and device management systems in order to present and low-capability devices without the use of additional hardware
contrast some other approaches to context management. and software resources. One interesting feature of InConcert is
A. Universal Plug and Play its internal topological model of the environment [2]. This
highly specialized extension improves upon its intended
Universal Plug and Play (UPnP) is a discovery-based
functionality, which is bound to home automation and control,
protocol for connecting devices originally developed by an
but at the cost of generality. Nonetheless, the intrinsic
industrial consortium led by Microsoft Corporation. It is meant
understanding of device relationships at the lowest level allows
for spontaneous discovery and configuration of
for interesting possibilities that are more difficult with the more
network-connected devices [10]. The communication protocol
generic device model of xLink.
uses IP as a transport layer, which is generally a complex and
resource-intensive protocol to implement with minimal D. The Dartmouth “Solar” System
hardware. Additionally, message passing and discovery is done The “Solar” system is a message simplification scheme
with XML messages [10], which provides high generality but based on directed acyclic graphs. The graph is used to route
also high latency and resource cost. As such, it is more events to graph operators that incrementally reduced messages
appropriately considered for sharing pieces of context, as to a form which can be consumed by applications [3].
opposed to a system for actual management of context, since Applications use a context-sensitive subscription model to
devices retain their own context information. While meant for acquire data [3]. One of the primary problems with ubiquitous
the commodity market, it is too resource intensive for the computing, evident from its earliest [11] days, is the sheer
lowest level devices that the xLink project is designed for. volume of data produced [4]. The Solar system efficiently
Additionally, the peer-to-peer structure, in contrast to the star compresses this volume by applying aggregating services to
topology of xLink, makes implementation of flow policies incrementally refine information. The high data resolution at
highly client-dependent. However, it remains well suited for the leaves [3] can also lead to performance issues, since the
interfacing devices with greater computational capacity. structures are currently geared towards a scenario where
B. JINI Extensible Remote Invocation System subscribing application have information pushed to them. Also,
the collaboration of various devices, and additionally the
JINI, an analogue to UPnP created by Sun Microsystems for
sharing of information between services which operate in
the Java platform, is also a discovery-based service [10].
parallel (lateral linkage within the data flow graph) is
Unlike UPnP, JINI does use a lookup service to mediate the
ill-defined. In contrast, xLink features well-defined lateral
discovery process, and the actual discovery involves finding
linkage between devices and services at the same level in the
the service in the first place. All subsequent calls are made via
overall hierarchy, but does not focus on data aggregation, thus
Remote Method Invocation (RMI) and serialized Java objects,
allowing easier inter-device and inter-service collaboration
which is understandable given the tight platform bindings. Due
capabilities at the cost of scalability.
to the requirements of the Java Virtual Machine, JINI is by
definition a relatively demanding protocol-oriented method of E. The EventHeap Model
managing context. The design is tightly bound to a client-server The EventHeap model is a middleware layer designed for the
model of interaction that considerably limits its expressive Stanford iRoom, and allows the multiple input and output
capability. However, the ability to push code from a server to a surfaces of the room to function as a ubiquitous computing
client is clearly a very powerful capability enabled by the environment [7]. It is based on an API model, though internally
homogenous execution environment, which allows JINI to the implementation does use a protocol to communicate
support greater low-level interaction between devices than between targets. The API model differs from the xLink model
UPnP and to achieve some of the low-level interface in that it is meant for programming devices themselves, and not
capabilities of xLink. links to devices. This suggests a level of capability with is
ubiPCMM 2005 37
easily available within the iRoom, but cannot be presumed for allows a coordinated privacy policy to be implemented, even
the scope of xLink. The message passing strategies of both though multiple systems are used, so Rodger only has to
systems are also similar, though unlike xLink, EventHeap tends authorize the system to allow access from a single location.
to treat devices and services essentially as peers, since within Lastly, the output of the system is seamlessly transformed and
the EventHeap’s scope devices and services are generally routed to output devices, including the headset, the terminal,
intertwined. and the receipt printer at the counter, as needed. Input is also
gathered from multiple devices to feed services such as the buy
service, which requires an additional signature input. With this
III. SCENARIO AND CASE STUDY scenario in mind, we shall outline the design choices that
In order to motivate the system design, we would first like to support this interaction.
present a short scenario. Though this is a fictitious usage
scenario, the devices and technologies discussed are the
outcome of research projects completed by our group using IV. SYSTEM DESIGN
xLink as the context management system. A central goal of the xLink system is to provide a local-scale
Scenario — “Rodger walks into the local bookstore, hoping generalized framework for connecting commodity devices. As
to find a good book on yoga. The bookstore is enabled for his such, we chose to create a system which is based on an
ReachBand — a wireless Radio Frequency Identifier (RFID) API-based plug-in design instead of protocols, so as to ensure
and gesture sensor worn on the wrist [5] — and headset, and he overall generality and “instant-on” capability for new device
quickly scans the placard at the entrance to enable his devices. types. In exchange, the system gained the ability to have highly
The store had already detected the wristband, and by reading device-specific behaviors that allow for easy modifications and
the RFID tag on the placard, Rodger gives explicit permission additions at the interface without requiring changes to the
for the store system to interact with his devices. As he walks internal workings of the core software. In a protocol based
around, a book catches his eyes, and he picks it up. As he is system, for example, the store system would have had to
flipping though the book, the ReachBand scans the tag on the communicate with the wristband via some standard protocol,
book, and he hears a slight audio notification on his headset that which would also then have to accommodate all similar devices,
information of that book is available. He finds the book or suffer from myriad parallel protocols catering to different
outwardly interesting, so he makes a slight gesture of his wrist, systems. Instead, by supporting a pluggable interface, we are
which accesses the list of services. The system has retrieved his able to support a very minimal communication system between
profile from his phone, and knows he likes the New York the ReachBand and xLink, while retaining flexibility for the
Times reviews when possible, so when he selects reviews, the services. As Cohen points out [4], this is an important goal in
system checks and tells him that there is a New York Times creating a system which can survive unanticipated
book review available. He chooses to listen to the review. The requirements, and the API-based interface also supports this
review plays over the headset as he continues to flip through the easily. If, in the next year, a different model wristband becomes
book. He then chooses to listen to the Ambient Semantics [9] common, it is simple to install another pluggable module and
service, which tells Rodger that several of his friends are necessary transceiver to support the new device without
interested in getting into yoga exercises, opening the possibility requiring modifications to the core xLink system.
for working out together. He also notices that a review selected The principal purpose of the system is to mediate interaction
by the system recommends a different book for beginners. between input and output devices, which may physically be
Rodger is in a rush, so after finding the other book, he scans the instantiated as objects, rooms, or even conventional computer
tag on a public access display, which shows the menu he had displays, and services. To this end, we designed the internal
been listening to. He quickly accesses and scans the review, representation of the input of devices and the output of services
and chooses to buy the new book. He simply selects the buy to attain flexibility, and focused on allowing a high level of
option, and authorizes use of the card he has in his profile. He adaptability for interfacing physical devices to the system. This
signs the store receipt on-screen, but if he had not been at the can be seen in the seamless transitions between display and
terminal, the clerk would simply have had the receipt ready for interaction modes, which reflect the flexibility of the internal
him at the counter. The security system has been made aware representation. It is important to note that though it is often
that the book now belongs to Rodger, and automatically handled within the realm of context management, the
disarms the security tag as he walks out.” management of object identity and metadata is implemented as
Within the above scenario, the xLink instance for the store regular services within our system, and is accessed like any
has coordinated the experience so that the sensor and output other service as needed.
devices that Rodger brought with him, and embedded systems
and services within the store work in coordination to produce a
seamless experience. The system invokes both local services,
such as services to buy books, detect gestures, disarm a security
tag, and read back information as well as remote services, such
as the New York Times book review search. The system also
Sajid H. Sadi and Pattie Maes 38
Tuple-Set::ReachBand detail ordered by depth. This is a “soft” requirement, which
name values
may be ignored if necessary. For example, if there is some
device ReachBand minute detail of high interest, it may be placed at a higher level.
id 17:32:54:af:7b:92 Additionally, resource-expensive or highly specialized services
payload 64:8c:d4:56:b3:9f:7a:14 1118990279918 can opt to send a request link indicating their availability
gesturedata 73,44,3,35,23,34,23,5,623,23,42,42,34,23,
23,4,23,54,2,52,35,23,3,42,3,42,34,23,42,
instead of the actual output. This, for example, allows the New
3,5,14,56,82,34,82,0,3,57,2,85,90,31,48, York Times search service to reply with links to several articles,
75,12,37,89,567,34,90,57,34,8,9,0,67
without having to send all of them. Links to content rendered in
Figure 1: Typical tuple-set from a scanner device in the shared data
space after processing by link module.
different formats can also be embedded in the tree, which can
then be retrieved by devices capable of rendering the link. As a
result, images of the book suggested by Ambient Semantics can
A. Internal Representation
be displayed by the terminal, but easily ignored by the headset.
Internally, the system operates on “tuple-sets” – unordered Within the design constraints of the system, this allows for a
sets of n-tuples, with each tuple consisting of a name as the first reasonable range of output modalities without requiring a
entry, and n-1 data values as the remainder. A representative highly annotated output structure.
tuple-set is shown in Figure 2. The overall schema is very
similar to the system originally used in the Linda system [6] and B. Device Model
later explored in the EventHeap system [7]. Each tuple-set has a All devices within the scope of the system are classified as
required field, “id,” which identifies the logical device that logical output or input devices. For example, the headset or the
originated that tuple-set uniquely within the context of the terminal screen are logical output devices in our scenario, while
system instance. This accommodation is made so that devices the RFID sensor and the security tag sensor are input devices.
like the wristband in our scenario, with limited communications Accommodations are made for complex (multi-modal) devices
capabilities, may still identify themselves without having to such as the terminal, which are internally represented as a
expend precious bandwidth transmitting a universally unique collection of logical input and output devices. Since we expect
identifier (UUID). Additionally, the link layer can attach a to have commodity devices from a variety of sources and with
family identifier to the actual identifier received to partition varying levels of complexity and capability interact with the
device families. Therefore, in Figure 2, it might be that the system, very few assumptions are made about devices. Each
device model itself only received the very last byte from the family of devices is allowed its own plug-in “link module,”
ReachBand, and provided the rest locally. If necessary, the which is responsible for translating data to or from a format the
device model can also send commands directly to the core device can accept. Link modules communicate to the devices
system using tuple-sets. This allows the device model to through shared “connector modules,” allowing for sharing of
communicate with the system without incurring additional API resources among devices using the same communication
overhead. medium, but differing protocols or information transformation
The communication is generally analogous to the needs. For example, several different phone clients can be
“tuplespace” concept introduced by [6], but using tuple-sets in supported, all over the same Bluetooth connector module, but
the same way as EventHeap [7]. Our implementation allows for via different link modules for different manufacturers. The
sets of tuples, without imposing the temporal constraints of interaction between various parts of the device model and the
EventHeap. Instead, depending on the device type, certain xLink core context management system is shown in figure 1. As
fields are required in each tuple set to identify the source and shown in the figure, all connections between logical
provide a means of “replying” to a message. The tuplespace subsystems are by default bidirectional, allowing modules to be
methodology depends on matching of key sets against the both data producers and consumers. As such, link and
requisite key sets of a service [7], which is analogous to the connector modules may act as local services, consuming input
service selection system used within xLink. Tuples with no or carrying out other operations independently as required by
consumers, if marked ephemeral, are simply discarded. the device. For example, the wrist gestures can be consumed
Devices may economize bandwidth and lower overhead by directly by a display link module lacking a keyboard, without
storing fragments of data streams into fields. In figure 2, the posting it to the event pool. In addition, this allows for the
ReachBand has stored accelerometer data for gesture detection creation of low-latency links between input and output devices,
in this way, sending several records in one tuple. The entire thus bypassing the internal tuple-set pool for time-critical
tuple [, ] can then be consumed by a gesture
translation service which converts the data into a single
tuple-set [, ], retaining
the same identifier as the original.
The output of services that is meant for display devices is
internally represented as structured trees, which are
contractually constrained to provide information in increasing
ubiPCMM 2005 39
Figure 2. Overview of the xLink linkage model, showing interconnections between different module families and object encapsulation. The core xLink
functionality is indicated by segment marked “xLink Core” and is responsible for the message routing and service querying functionality at the heart of xLink.
As stated previously, for input devices, the link module should they wish to remain within the network of devices. In
simply translates to the tuple-set format. In addition, the link our implementation, a garbage collection system discards stale
module can perform any transformation on the incoming data, displays after a considerable delay. These devices, if active,
thus providing the ability to augment the actual data sent by the then automatically reconnect to the system. This method of
device. In our scenario, this allows the wristband to use a very connection management is optimized for the expected
short ID’s and reserve the majority of the packet space for communication modes of the input and output devices, with
RFID or gesture data. In the case of the display link modules, inputs “pushing” data to the system, and data being “pushed” to
the wide range of possible presentation resolutions and output the outputs from the system. As such, no action is required by
modalities require that the module make adaptive decisions Rodger to disconnect as he leaves. The loss of Bluetooth
based on the context of the interaction to exclude some part of connection automatically causes the system to purge his
the result tree from the actual output if necessary. This becomes records from the pools.
especially necessary when device constraints such as memory
C. Service Model
or bandwidth make the make of sending the entire dataset
literally impossible. The link module may also carry out The system supports the concept of local versus remote, and
semantic transformations on the data, ie, linearizing text for a simple versus complex services. We define local services as
brail display, or converting text to speech for an audio device, services that act on information, objects, and entities within the
and cache the information for the duration of an interaction. general locality of the object itself (possibly even on the same
These properties are exploited in providing speech output to the object), while remote services act upon objects outside that
headset in our scenario, while stripping out hyperlinks and domain. For example, in our scenario local services provide
images in the result set. identifying information about the book, and capabilities such as
As Kindberg [8] points out, it is generally good practice purchasing, while remote services such as the review search are
within fault-tolerant systems to presume that devices will fail accessed from the appropriate sites as needed. Likewise,
on a regular basis, and that is the approach taken by our design. complex services act upon the output of simple services, while
Input and output devices are held in separate pools, allowing simple services act upon local information. For example,
for both overlaps and multiple entries for the same physical transforming acceleration data to gesture identifiers is a simple
device. Input devices are added to the pool when they make service, while retrieving the reviews is a complex service that
contact, and are removed after a timeout period. This prevents must inspect profile information (possibly a remote complex
the pool from becoming stagnant (ie, containing logical devices service itself) to make a decision, and then fetch the appropriate
that are no longer communicating). Output devices are likewise information from a remote service to output. The primary
added to their own pool on first contact. However, output reason for the existence of this distinction is speed of access.
devices are only discarded if the link or connector module Local and simple services help to make an environment “smart”
notifies the pool of a failure, or if an associated composite by allowing the various parts of the environment to act in
physical device is discarded from either pool due to failure in concert. At the same time, most of the decisions made expected
communication. The connector or link module may to be fast, resource-frugal, and fairly simplistic. As such, the
additionally force the device to reconnect with some fixed system can call of these services constantly and push their
period in order to “clean” the pool. In all cases, output devices results to output devices without user intervention. The remote
are contractually bound to reconnect on loss of connection, or complex services, on the other hand, are “heavyweight” by
Sajid H. Sadi and Pattie Maes 40
comparison, and thus their use is limited to on-request accesses. information, or requiring additional authentication if the
Since the remote services are only accessed on request, the information is especially sensitive. Due to the low resolution
discovery procedure is reduced to the services notifying a nature of the most common devices, this is expected to be the
centrally accessible directory service of their existence. Such exceptional case, and therefore security policies are themselves
announcements must of course be accompanied by a list of implemented as a service which other services may query.
service and tuple-set dependencies, so that the system can filter Like the cell phone or the public terminal, certain devices
out non-relevant services. All local services operate under the may have the ability to request additional services by virtue of
prevue of the context management system, thus obviating being composite input-output devices. As a natural side effect
discovery. As stated previously, the scope of this project allows of the architecture, a device may easily direct the results of its
us to assume that the system has been specialized to the request (via a command to the system) to a different device.
environment it is embedded in. As such, the local service set Therefore, the wristband can easily have its output sent to the
can be chosen to match the supported devices, and any remote headset or even to a stationary display designated for that
services requiring constant invocation can be proxied by a local purpose. As long as the device can find out about the target
forwarding service. device in some way, or the target device can be selected by the
user to be the output device of choice, the output, being
D. System Operation
naturally device-agnostic, can be routed to it. This allows the
Being geared towards use in ubiquitous interfaces and smart system to fulfill the goal of Ubicomp of providing a seamless
objects, the system in general “pushes” data to target devices. end-to-end experience to the user without device lock-in during
Incoming tuple-sets are automatically processed by the local an interaction [11].
simple services and made available to link modules for output.
For example, incoming RFID data is automatically
disambiguated but the identification service, and the output is V. DISCUSSION AND FUTURE WORK
routed to all local services by the xLink core for processing. The design intentions that guided the xLink project were
Any output is made available to output link modules for display. geared towards providing a highly adaptive, seamlessly
The link modules have control over whether the data is actually expressive data flow management system that is general
sent, while the services retain control of whether it is purpose in its architecture, but intended to be customized to
appropriate to produce output given a certain scenario. This support the specific requirements of the applications it serves.
allows the output devices to exhibit per-device and per-family As a result, we envision xLink as an embedded device, perhaps
“do-not-disturb” behavior, such as disabling notification to the embedded into a wall of a room enabled for ubiquitous
headset, while allowing services to operate in a context computing. As a part of the room, it can then be tuned to the
sensitive way. It is generally understood [2, 8, 7, 11] that purpose and interactions that the room is meant to support. As
ubiquitous interfaces must be proactive in anticipating needs, with any design tradeoff, this decision has both its strengths and
while at the same time working as a spatial and contextual filter weaknesses. It is highly adaptive, and capable of hosting a
for information so that the user is not inundated by requests for variety of connector and link modules that allow fine grained,
attention. At the same time, ubiquitous interfaces must allow low level control of the communication and data translation
the user control over the interface [1]. The chosen distribution capabilities offered by an instance of xLink. As a result, it is
of responsibility for inhibiting input is therefore balanced so also less capable of self-configuration and management. The
that object and devices continue to act like objects (ie, remain highly fault-tolerant design of the system allows for minimal
under the user’s control), but the overall environment can still maintenance, but the initial setup cost is not essentially
retain proactive agency. mitigated by this. Additionally, the tuple-set and device pool
While we have not discussed user sessions explicitly to this based internal architecture become limiting factors as the data
point, ownership of devices and sessions is a natural extension that must be represented becomes more complex and dependent
of the system. We define a session simply as the set of all on factors outside the direct prevue of xLink.
information available about a user through all available devices Nonetheless, we believe that xLink serves to fill an important
and services. When a device is aware of its ownership, it can niche between medium-scale context management solutions
inform the system of the ownership via a command tuple, such as EventHeap [7] and the devices themselves. By
which in turn propagates this information to other devices providing a common architecture for the housing and
connected to the session. For example, the cellular phone can maintenance of driver-like structures that connect devices to
identify the other devices that a person is carrying that are each other and to services, xLink abstracts away the low level
available for input or output in our scenario. However, complexity of such information management without impeding
ownership is a fluid property within the system, and can change the capabilities of the system, much as an operating system
easily. This fluidity is in some sense contrary to the privacy that hides the complexity of the devices that make up a computer
context management systems must support [1]. Within xLink, system while presenting software with the ability to access and
this factor is mitigated by having devices with known manipulate those devices. At the same time, xLink provides an
ownership, such as the cellular phone in our example. Services alternative and parallel for heavier protocol-based systems such
have the option to check for such devices before sending as InConcert [2], in that it allows commodity sensors with
ubiPCMM 2005 41
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investigation, especially in a highly localized system such as ** This paper is currently not available publicly. We would be glad to share a
xLink. As this work progresses, we hope to engage some of copy if there is interest.
these issues in the design space that is addressed by xLink.
ACKNOWLEDGMENT Sajid H. Sadi is currently a first year graduate student at the MIT Media Lab in
We would like to acknowledge the tireless help, critique, and Cambridge, MA, USA. Prior to joining the Media Lab, he received his BS in
computer science from Columbia University in New York, NY, USA in 2003.
encouragement of Assaf Feldman and the Ambient Intelligence He is interested in systems design, visualization, interactive design, and
Group, as well as the industrial liaisons of the MIT Media Lab techniques for integrating the physical reality with digital metadata.
for fostering the growth of this project. We also extend our Pattie Maes is an associate professor in MIT's Program in Media Arts and
Sciences. She founded and directs the Media Lab's Ambient Intelligence
appreciation to Aaron Zinman for the critique, review, and research group. Previously, she founded and ran the Software Agents group.
inspiration he provided for this paper. Prior to joining the Media Lab, Maes was a visiting professor and a research
scientist at the MIT Artificial Intelligence Lab. She holds bachelor's and PhD
degrees in computer science from the Vrije Universiteit Brussel in Belgium.
Her areas of expertise are human-computer interaction, artificial life, artificial
intelligence, collective intelligence, and intelligence augmentation. Maes is the
editor of three books, and is an editorial board member and reviewer for
numerous professional journals and conferences. She has received several
awards: Newsweek magazine named her one of the “100 Americans to watch
for” in the year 2000; TIME Digital selected her as a member of the Cyber-Elite,
the top 50 technological pioneers of the high-tech world; the World Economic
Forum honored her with the title “Global Leader for Tomorrow”; Ars
Electronica awarded her the 1995 World Wide Web category prize; and in 2000
she was recognized with the “Lifetime Achievement Award” by the
Massachusetts Interactive Media Council.