The dynamicity and variability of context

Abstract—In this paper we report about our experience in
using mobile computing middleware in context of health-care.
The dynamicity and variability of context and conditions make
this environment very suitable for the use of mobile and
wearable computing techniques. The use of small and portable
devices can be very beneficial in terms of efficiency and vital
support to patients. However, the many challenges that this
environment presents need to be addressed, possibly by a general
mobile computing framework that could be used in different
mobile settings. We will discuss these issues in the paper along
with the description of the prototype we have developed.
1 Introduction
Small and portable devices, such as mobile phones, PDAs
and the like, have recently been pushed on the marked and
have allowed for complex cooperation and communication
patterns that were not foreseeable some time ago. The ability
to carry these devices, share the content using communication
networks, possibly wireless, and synchronize their content
with more standard devices have been seen as essential
features. However, these technologies still come with some
limitations and differences with respect to the standard
computing platforms we have used for years. Resources (such
as battery, bandwidth, memory) are by orders of magnitude
smaller, and patterns of use change depending on the network
availability and on the location of users.
Applications have begun to be developed for these devices
in order to allow data synchronization, Internet browsing, and
cooperation. The most targeted domains have been Mobile
Commerce and E-shopping, however it is becoming clear that
the use of mobile technologies will become quite pervasive in
our lives and that we need to support development of
applications in different areas.
In particular, we have recently been involved in the use of
mobile computing in health care setting. The healthcare
environment is quite unique in that it brings with it several
constraints and requirements that any deployable application
would have to adhere to. The most obvious issues are those of
patient confidentiality and doctor- patient relationship. It is
vital that medical data is kept confidential via the use of
potentially several vertical layers of security.
Healthcare data is mission critical and errors introduced by an
application can have potentially fatal consequences. For
example, in the case of a medical prescribing tool, a
miscalculation or misprint in the dosage of any particular drug
to be administered could have serious consequences for the
patient. Hence, it is important that some kind of data integrity
assurance is supported by the application.
The clinical health-care working environment is ‘highly
mobile’, with clinicians constantly moving around from
patient to patient while performing their duties. This
constrains the shape and performance of computing devices
that can be used in such an environment. Many organizations
have attempted to implement computing solutions to aid
clinicians with their every day duties using a networked
desktop environment. In practice, such solutions have failed to
reach their target users, and instead simply served as
administration systems. The reason behind this is the fact that
in such a highly mobile environment, clinicians make
decisions at the ‘point of care’ i.e., the patients bedside, and
they do not have the time to leave and potentially queue up to
refer to a desktop based application. Hence, the ideal platform
for use in such an environment is the PDA or tablet PC
platform, which the clinician can carry around and use
wherever necessary.
In this paper we will introduce the platform we have
developed for use in health-care scenarios and show the
general principles that have driven our design decisions. We
will show how the platform is planned to be used, and how it
can improve the efficiency of patient care.
The paper is structured as follows: Section 2 describes the
mobile computing environment and the challenges it presents.
Section 3 introduces our case study, looks at the motivation
and describes our adopted architecture. Section 4 describes the
implementation in details. Section 5 discusses the interesting
outcomes of our work and shares some of the experience
gained from working in a mobile computing environment.
Finally, Section 6 concludes the paper and outlines our
planned future work.
2 Mobile Computing
Point of care delivery is vital for the success of any
application in the clinical healthcare environment. Hence, the
use of a PDA platform utilizing wearable technology is ideal
and is adopted by the work described in this paper. Wearable
and mobile technologies introduce considerations and
constraints that have to be dealt with when developing
software. This section highlights some of these and explains
how they impact upon development.
Exploiting Mobile Computing in Health-care
Usman Arshad*$, Cecilia Mascolo*
and Marcus Mellor$
*
Dept. of Computer Science, University College London, Gower St, WC1E 6BT London UK
$
Capula Elan, Palmerston Court, Palmerston Way, London, SW8 4AJ London UK
2.1 Network Model
Mobile networks can be roughly classified into two types,
ad-hoc or nomadic. An ad-hoc network is one that is formed
by two or more mobile enabled devices that are in reach of
each other and can form a compatible network. This model is
suited to a peer-to-peer scenario there is no guarantee of any
device remaining available or indeed being available at all. It
provides no guarantee of resources or services, and has to deal
with changing conditions such as disconnections, and resource
availability.
A nomadic network is one that includes a fixed network
infrastructure of base stations. Mobile devices are able to rely
on the resources made available on the fixed infrastructure as
long as they remain within reach of network coverage. This
model is suited to a client-server approach where client would
be the mobile device and the server would be available via the
fixed infrastructure. This model still has the problem of
disconnections to the network when mobile devices go out or
range. The work described in this paper is based on a nomadic
model using a client server approach, although the application
we are developing has extensions of use in emergency areas
where base stations are not in reach: we will speak more about
this extension in the future work section at the end of the
paper.
2.2 Mobile communications
Mobile communications are weak and prone to
disconnections. This means that traditional applications that
rely on network access will not work unless they use an
always-on technology, and even then, they could encounter
pockets of no coverage. In our view it is important for
applications to take temporary disconnections into account,
and adapt accordingly. This involves the use of reflection to
detect network availability and the ability of an offline mode
of operation when disconnected. This marks a move towards
thick client devices with embedded intelligence.
The situation is complicated further when potentially many
concurrent users have access to the same piece of data. In such
a situation if some people are working offline on locally
cached copies the data while others are working online,
inconsistencies can quickly develop. Hence, there is a clear
need to be able to identify such inconsistencies and deal with
them accordingly. With weak communications, data transfer
rates have to be taken into account. Application developers
need to consider the time it takes to download data to a device
or to upload from it and whether this time delay makes the
application unusable. Of course, data rates depend on the type
of mobile technology that is to be used, but is even more
significant in cases where a user is charged for connection to
network on a time basis.
2.3 Resources
Mobile devices such as PDA’s are extremely resourceconstrained in terms of memory, processing power, battery
lifetime and screen size. Applications for such devices need to
be resource conserving and lightweight enough to achieve a
level performance deemed usable. The application developer
also needs to take into account the strain put on these
resources during runtime, and there are often tradeoffs to be
made as to where to execute processes and store information,
whether it be locally on the mobile device or remotely on a
more powerful device. More details on these issues can be
found in [6] and [7].
The way we address these issues is discussed in Section 4.
The fact that PDAs have a very small screen and a different
means of navigation than traditional systems means that
careful consideration needs to go into the development of a
usable user interface.
In the next section we will describe our approach to the use
of mobile computing in health-care.
3 Our approach
3.1 Scenario
The motivation behind the work described in this paper is to
aid the clinician by empowering him/her with mission critical
information at the point of care. This is achieved by
developing a PDA based application that uses mobile
technology in a Client-Server Nomadic setting. The
application being developed combines an Electronic Patient
Record (EPR) system with an e-prescribing application. The
purpose of an EPR system, is to replace traditional paper
based methods of documenting patient records with electronic
records that are available to multiple users concurrently. The
records are dynamic in that they change on a regular basis,
and global consistency is important. One example of the
dynamic nature of patient records is current medication that is
prescribed to a patient. The e-prescribing application provides
the clinician with a database of drug information including the
complexities of drug interactions and contra-indications. The
clinician is able to prescribe drugs to his patients and the
application flags up potential problems caused by drug
interactions.
3.2 Architecture
Figure 1 shows the architecture we have adopted: a clientserver architecture separated by a mobile network. The server
connects to a central data-store, which contains data shared by
the client PDA devices. The communication between the
client and the server is via a packet based communication
protocol. A session is initiated by a clinician logging in to the
system via the client User Display. This initiates the
Downloader component to contact the server and retrieve
patient record data from the database. Once downloaded the
clinician is able to navigate the data via the application. If data
are modified by the clinician, the Updater component ensures
that the changes are reported to the server and that the datastore is updated accordingly. It also makes sure that the
change is communicated to all other clients logged onto the
system.
One of the key aspects of our approach is ability of the
client to work offline, i.e., if the client PDA is out of reach of
the network any changes made by the clinician are cached
locally until such a time at which the network is once again
available. To enable this the client needs to be network aware.
This is achieved by the server Presence Broadcaster regularly
broadcasting one-way messages on the network, which are
picked up by the Presence Receiver on the client. As long as
the client receives these messages, it assumes it is still
connected to the network. This information is fed into the
updater, which makes the decision as to whether to cache the
changes or send them to the server.
While offline, a client may miss updates made by other
clients. A process to receive these missed updates once the
client is again online is put in place. Further to this, while
offline, the clinician may make updates that conflict with
updates made by other clients. The Conflict Dectector and
Resolver component and the Logging component take care of
this. Further details are provided in Section 4.5.
4 Implementation
We now describe the details of the platform we have
developed. The server is a Java application that provides
access to an Oracle database. The client device is also a Java
application. The server retrieves data via an API that returns
the data in the form of an XML document. Similarly changes
to the data are committed to the database by passing the API
an XML document representing the changed data. The reasons
for choosing XML are discussed in Section 4.4. The Server
exists as part of a fixed network infrastructure that is extended
to the mobile clients using an 802.11b wireless LAN.
4.1 Presence Information
In order to be network aware, the platform needs a
mechanism to gain presence information. The clients use two
approaches to gain this information
1) Active approach – The clients are responsible for
checking if the network is accessible to them. The client
would send something similar to a ping command to the
server expecting a response to indicate accessibility. This
approach is efficient, as minimal messages have to be sent
over the network. However the client has to do more
work.
2) Passive approach – In this approach the Server is the
active component and continually broadcast a message
over the network attempting to reach clients. The clients
simply listen for this message continually and as long as it
is received on a regular basis, they assume the network is
available. This approach has the disadvantage of putting
extra load on the network
We use the passive approach in our scenario at the expense
of the increased network load. This method is preferred as it
requires minimal work on the part of the client, and given the
scarce resources available on the client it is preferable to push
work onto the server end. Further to this, it is expected that
the client is likely to require a lot of access to the network,
hence increasing the number of times the ping-like message
would have to be sent.
4.2 Working offline
Applications for mobile devices can fall into three main
categories, when dealing with disconnections.
1) Always-on Applications – These are dependent on
network availability and require constant interaction with
other networked machines, for example web based
applications. These applications would fail completely if
the network was unavailable, and hence are only
deployed with always on communications such as GSM,
or are limited to the afforded boundary of coverage.
2) Hot Sync Applications – These are commonplace on PDA
platforms. In hot sync, it is not critical that the network is
constantly available, and the user can continue to use the
application when disconnected. When the user reconnects
to the network, a synchronisation process takes place to
filter across relevant information generated as a result of
being disconnected to the network. The synchronisation
process often occurs as a result of the user taking
affirmative action to execute the process. A typical sync
application could be a synchronization of an email inbox
between a laptop and a PDA.
3) Auto update applications – These applications fall in
between the other two approaches. Being connected to the
network is important in such applications, however the
user is able to work offline when the network is not
available. Once back in reach of the network an
automatic synchronisation process can take place. These
applications appear similar to hot sync applications, but
there are distinct differences. As mentioned, Sync
applications often perform synchronisation as a result of
an affirmative action on the part of the user, whereas in
auto update applications, synchronisation remains
transparent to the user. Further to this auto update
applications often involve data that is shared by multiple
users, hence synchronisation on a regular basis is
important so modifications made to the shared data is
filtered throughout the system, whereas hot sync
applications usually involve synchronisation between a
small number of devices (usually two) often belonging to
a single user.
Our application follows the auto update model, which
exploits transparency as far as possible, including the
implementation of an automatic conflict resolution component
(see Section 4.7). Transparency makes the application more
usable, as the target users will not want to worry about
whether they are working online or offline.
Figure 1. Architecture
Central
Datastore
Server
Application
Updater Downloader
Datastore Connectivity Component
Conflict
detector and
resolver
Logging
component
Packet based communicator
Presence
Broadcaster
Downloader
Packet based communicator
Updater
PDA based Client Application
Mobile Network
Presence
Reciever
User Display
At the time of writing, many applications particularly those
that depend on network availability, have tended to treat
PDAs as thin clients, i.e., where the PDA is nothing more than
a basic IO device. However our approach employs the PDA as
a thick client with the embedded intelligence to store
information locally when it is disconnected from the network.
As explained in Section 4.1 the server continually
multicasts a presence message to the clients. In normal
(online) operation any modifications made to the data by
clients are immediately communicated back to the server,
which makes the appropriate modifications in the central data
store, logs the modification, and then multicasts the
modifications to filter them throughout the system. The offline
mode of operation is triggered when a presence message is not
received in a given period of time.
Once working offline, the middleware still accepts
modifications made to the data, but caches them locally. As
soon as the presence messages are again being received, the
client knows that it can once again enter into online mode,
however it is vitally important that the following three process
are carried out first:
• The client needs regain missed updates from the server to
maintain data consistency in the system.
• The client needs to commit the changes it has made
locally to the server
• A conflict check needs to be carried out to ensure that the
modifications made by the client while it was offline do
not conflict with modifications made by other clients.
These processes are achieved by the conflict resolution and
logging components (see Section 4.5).
4.3 Development on PDAs
One of the first things that became clear while prototyping
on the PDA platform was the limitation of memory, which
severely hinders the amount of data that can be downloaded to
a device. PDA applications have to work around this
limitation. In order to cope with it we decided to adopt a
‘session based download’ approach. For example, in the case
of the EPR application we decided that a doctor would log
into the system, and only the records of the patients assigned
to that doctor would be downloaded to the device, the session
being the use of the application by that doctor. We used this
approach as opposed to downloading all the patients on a
ward for example.
It is also important to consider memory usage at runtime,
as the size of data to be stored is not the only consideration.
Some runtime processes can also be memory intensive, for
example, depending on which parser is used, parsing XML
can consume a lot of memory. Further to this, XML parsing
itself can be a processor intensive process. Since our
application is centered on delivering data in XML, our choice
of parser would have to give us maximum performance.
Another important consideration for PDA like devices is
the extent of multithreading that is used. In our experience, the
use of too many concurrent threads on such a device can soon
make an application unusable. In fact, at time of writing, Palm
have only just added support for multitasking and
multithreading with the release of version 5 of their PDA
operating system PalmOS. Microsoft’s PocketPC operating
system has supported multithreading and multitasking since
release, however as the number of threads increases, memory
consumption is also increased and the application becomes
increasingly unusable.
Another constraining factor on the PDA platform is the
small screen size. This has considerable effect on the kind of
applications that can be deployed on such a device. The
biggest change is using a stylus as opposed to a keyboard or a
mouse. This change impacts the UI as many traditional UI
widgets or components are not usable via such an input
mechanism, hence the developer is restricted to simple
components such as buttons and dropdown lists. One of the
terms that is emerging to describe the desired features of a
PDA based user interface is ‘high poke ability’. This includes
using only simple widgets, but also encompasses usability
models such as ensuring that the user does not have to
frequently tap the screen to use the application to the extent
that it requires too much effort to get even a small amount of
work done. There is a shift from traditional desktop
applications, which strive to provide a complete and
comprehensive application that offers maximum functionality
and, to a system that is centred on the critical workflow of the
user and includes only the core and most important
functionality. In fact such restrictive and simple UIs make
PDAs intuitively easier to use and easier to learn than desktop
systems for non computer literate personnel.
Battery lifetime is another concern on PDA platforms, and
indeed battery technology is one area, which has not seen any
significant advancement and is not expected to in the near
future. Hence application developers will have to accept that
the workflow of their applications will have to conform to use
for short stints of time followed by a period of recharging the
device. Application sessions cannot be long lived such that
they exceed the battery lifetime. This problem is significantly
magnified with the introduction of wireless communication,
which can have significant drain on battery power.
Our application is being developed using the Java
programming language. Java is emerging as an important
language in the mobile device arena, and much of this is due
to its platform independent nature. With the market still
growing, a whole host of mobile devices have emerged
including mobile phones, PDAs, tablet PCs and laptop
computers each being ideal for use in some scenarios but not
others. Further to this many more such devices are likely to
emerge which are specifically designed for a certain
environment. Some companies such as Intermec already offer
specialised PDAs, which could for example be ruggedized for
use in an industrial setting. Another interesting trend at time
of writing is the way mobile phones are striving to become
more like PDAs, offering more complex applications, whereas
PDAs, are trying to become more like phones trying to offer
voice call capability. Such heterogeneity between different
hardware and operating systems means that platform
independence is highly desirable. With the realisation of this,
Sun Microsystems have already put considerable effort into
developing small lightweight java virtual machines and
standards such as Personal Java and J2ME to aid this. In our
application, the use of several of these devices as opposed to
just one may well be desirable. Hence we have made a point
of decoupling the UI from the core functionality in order to
make the application portable between these different devices
by accommodating an appropriate interface given the form
factor of the device.
4.4 Use of XML
The last section discussed how platform independence is
desirable. XML gives us a mechanism to generically represent
data, which is instantly transferable between heterogeneous
platforms. Our application takes this one step further with the
use of XSLT to cater for different platforms. For example,
consider the difference between a PDA and a tablet PC.
Clearly the tablet PC is much more feature rich and has a
much larger screen hence can present a lot more information
visually. One way to achieve this would be to pass all the
information available from the server to the mobile device
whether it be a PDA or tablet. On receiving the information
the different user interfaces on the two devices could decide to
display all the information, or in the case of the PDA, just a
small portion of it. However this clearly violates the concept
of trying to conserve memory and keep processing to a
minimum. Hence our application uses XSLT at the point of
data retrieval to filter out the information that is not required
for the device to which the data is to be sent. This is facilitated
by simply specifying a different XSL style sheet to the
transformer.
XML also separates our application into a middleware
layer and an application layer. This is achieved as the
middleware only deals with XML data. The data is retrieved
by the middleware at the server end from the enterprise
database system via an API that returns the data as XML
document. This document is then sent to the client device,
and the middleware hands off to the application layer by
passing it the XML document. Following this, any subsequent
changes made by the client are communicated to the
middleware as XML. Again the middleware sends the XML to
the server, at which point it hands off to the application layer
by passing it the XML, and so on. The point is that the
middleware handles all data as a CLOB of XML only, and
does not care about the semantics of the XML.
4.5 Conflicts and conflict resolution
Allowing users to work offline in a system in which data is
concurrently shared between multiple users, introduces
several complexities into an application. For example, changes
have to be cached locally until the user is back online at which
point they need to be filtered throughout the system. Also
while the user is offline he/she may well miss data updates
made by other users who were online. As a result the offline
client then has an inconsistent view of the data, and may well
make updates that conflict with updates that have already been
made.
Our middleware deals with the complexities of working
offline by using a server administered logging process and a
user configurable conflict resolution process. The server
maintains a global version number, which is incremented with
each update to the data. The update, along with the version
number, is logged by the server. Each of the clients maintains
a local version number, which corresponds to the last update
they received from the server. Comparison of the version
numbers between the server and client reveals whether any
updates have been missed, and hence resent. The sequence
diagram in Figure 2 and description below depicts how this
works.
Figure 2. Missed updates
As the diagram shows, both client A and B are online to
begin with, and individually download data from the server.
At the point of download the server sends the global version
number, which is recorded by the client. Client A then goes
offline, and Client B then makes two successive updates. The
server updates its global version number accordingly and
multicasts the update along with the new version number to all
the clients. Since client A was offline, it does not receive the
updates, and hence its version number remains at 1. Client A
then goes online once more, and on doing so sends a message
to the server which includes its version number. The server is
able to compare this to its global number and thus knows that
client A missed two updates. The server is able to consult its
log and resend the updates to client A.
The conflict resolution process is carried out on a per
update basis, so each time an update is sent back to the server,
it is compared against entries in the log for potential conflicts.
If a conflict does occur the resolution process can then be
started. The definition of a conflict depends on application
logic, and hence the middleware needs to provide a way for
the application to specify rules to resolve conflicts. Our
middleware achieves this through the use of XML. When the
server receives an update, it takes the XML for that update
along with the XML for previous updates from the log and
passes them to the conflict resolution module. This module
then compares the two pieces of XML for conflicts according
to rules defined by the application. If a conflict occurs the
middleware first tries to automatically resolve them, otherwise
the user can be notified accordingly.
5 Discussion
Performance is an important consideration for applications on
resource-constrained devices. Given the fact that XML is text
based, and the application will deal with transferring
reasonable amounts of the data over the mobile network,
means that there may well be a considerable delay while the
transfer is being downloaded. Hence, it was decided to
Examine
log
log
Version 1
PDA A Server PDA B
Download
Version 1
online
online
online
offline
Download
Version 1
Update
Version 2
Version 2
unreachable
log
Update
Version 3
Version 3
unreachable
Online
Version 1
Version 3
employ compression before sending the data over the
network.
The disadvantage to this is that we are now imposing on the
processing power of the mobile device during the
decompression process. However, the advantage gained was
far more significant. Using simple zip format, a compression
advantage in transmission time of the order of ten was seen.
This varies according to the content of the XML, however
given the data is similar to that of the English language other
compression techniques that exploit the entropy of this type of
data could show even more improvement.
The other potential overhead with using XML is the parsing
of the data. Many of the fully featured parsers in existence
would simply put too much drain on the memory and
processing power. However there are several ‘small footprint’
parsers that are available that offer basic parsing functionality.
We opted for NanoXML [3], but other similar parsers exist
such as TinyXML[4] and MinML[5].
One of the notable consequences of working in the mobile
environment is the different tradeoffs that have to be made.
For example consider the location where data should be
stored. It could be stored locally on the client device giving
the advantage of fast access. However, clearly this is going to
impact on the limited memory available on mobile devices.
Alternatively the data could be store remotely at the server
and downloaded as required, however this would incur a time
overhead as the data is downloaded to the device. Thus there
is a trade-off here between memory consumption and
communication overhead, and the decision depends on the
semantics of the data in relation to the application. For
example data that requires frequent accesses would be better
stored on the client then the server.
Another trade-off comes as a result of the weak processing
power on the mobile device. It would often be advantageous
to migrate processes to a more powerful machine such as the
server in our application. This would save time in executing
the process, although it would introduce a communication
overhead. It would also ease the processing load on the client
device. So again we have a trade-off between the
communication overhead and the load on the device.
The healthcare community is showing a strong trend in the
adoption of mobile technology, particularly in the use of
mobile device such as PDAs [1,2]. Hence there are a vast
amount of applications being developed for such devices.
Most of the established applications are stand alone with the
mobile devices such as drug databases and patient monitoring
tools. However there is currently a lot of work being done into
looking at systems that utilize mobile technology especially in
the area of EPR. These include the systems described by [8],
[9] and [10]. However current systems depend on the
availability of the wireless network and do not address the
issue of disconnections. Other work includes location aware
ad-hoc applications such as connecting a PDA to a remote
monitor at a patient’s bedside to explain diagnosis.
6 Conclusions and Future Work
In this paper we have identified the complexities
introduced when working in a mobile environment. In
particular we have looked at resource constrained mobile
devices such as PDAs, and shared our experience with
developing on this platform. Our case study has shown one
example of how small portable devices can be employed to
bring significant benefits over traditional workstation based
systems. Introducing mobile communications to the devices
opens the door to a whole range of novel application.
We found that in a PDA based development environment
the application programmer has to be more aware of the
implications of mobile computing and often adapt the usage
model of the application to accommodate these. Our case
study has presented a generic architecture that for data sharing
client server applications that could be employed in many
scenarios. In particular we have emphasized the ability of our
application to work in an offline mode of operation, and
having a mechanism to detect and resolve conflicting changes
to data using application specific rules.
The future direction of our work is looking to extend the
principals learned, into an ad-hoc peer to peer setting. This is
a more dynamic environment in which the mobile devices
cannot rely on resource availability at all. Further to this in an
ad-hoc setting, all devices may be potentially resource
constrained. The natural extension of our case study into an
ad-hoc environment is in the use of ambulatory care. For
example data may be recorded in an ambulance on the way to
the hospital and on reaching the destination transferred to a
clinicians PDA or automatically integrated into the hospital
system.
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http://www.sun.com/mobility/enterprise/feature_story.html
[9] D. K. Vawdrey, E. S. Hall, C. D. Knutson, A self-adapting, transportaware mobile patient healthcare insfrastructure.
http://www.poketdoktor.com/PoketDoktorArchitecture.pdf
[10] Sybase, Mobile computing in healtcare,
http://was.sybase.com/mec/2959healthcare.pdf


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