Cross-platform service user experience: A field study and an initial framework

Abstract

Many web-based services utilize both desktop and mobile terminals in delivering content and functionality to their users. In terms of user experience (UX), the overall chain of interactions, including mobile and non-mobile settings, becomes a central design target. The aim of this study was to investigate, what are the key elements of user experience associated with these, cross-platform interactions. This paper presents the findings from a four week long field study with three web-based cross-platform services. During the study, participants used the services on both their PCs and mobile devices. Diaries and interviews were used for gathering users' experiences with the services. Based on our findings and reflection with related work, we argue that central elements of cross-platform service UX include fit for cross-contextual activities, flow of interactions and content, and perceived service coherence. We propose an initial conceptual framework of cross-platform user experience. The framework can be used to guide the design of cross-platform web services, as it draws attention to elements of user experience that are essentially influenced by the characteristics of cross-platform settings.

Full text

Cross-Platform Service User Experience:
A Field Study and an Initial Framework
Minna Wäljas1, Katarina Segerståhl2, Kaisa Väänänen-Vainio-Mattila1,3,Harri Oinas-Kukkonen2
1Tampere University of Technology,
P.O. Box 589, FI-33101,
Tampere, Finland
firstname.lastname@tut.fi
2University of Oulu,
P.O. Box 3000, FI-90014
Oulu, Finland
firstname.lastname@oulu.fi
3Nokia Research Center
P.O. Box 1000
00045 Nokia Group, Finland
kaisa.vaananen-vainio-
mattila@nokia.com
ABSTRACT
Many web-based services utilize both desktop and mobile
terminals in delivering content and functionality to their users. In
terms of user experience (UX), the overall chain of interactions,
including mobile and non-mobile settings, becomes a central
design target. The aim of this study was to investigate, what are
the key elements of user experience associated with these, cross-
platform interactions. This paper presents the findings from a four
week long field study with three web-based cross-platform
services. During the study, participants used the services on both
their PCs and mobile devices. Diaries and interviews were used
for gathering users’ experiences with the services. Based on our
findings and reflection with related work, we argue that central
elements of cross-platform service UX include fit for cross-
contextual activities, flow of interactions and content, and
perceived service coherence. We propose an initial conceptual
framework of cross-platform user experience. The framework can
be used to guide the design of cross-platform web services, as it
draws attention to elements of user experience that are essentially
influenced by the characteristics of cross-platform settings.
Categories and Subject Descriptors
H.3.5 Online Information Services, H.5.2 User Interfaces.
General Terms
Design, Human Factors
Keywords
User experience (UX), cross-platform web services, crossmedial
interactions, field study, conceptual framework
1. INTRODUCTION
The focus in computing and related domains has migrated from
the traditional desktop environment into a network of mobile and
non-mobile devices and use contexts [6][18]. Interactive systems
are not any more restricted to a single platform, such as a mobile
phone, a desktop computer, or the web. As the capabilities of
mobile phones, especially smart phones and mobile internet
devices have evolved, mobile devices are now a common choice
for accessing various applications and services.
Cross-platform services – web-based services that are used on two
or more distinct interaction devices – are an inherent part of multi-
device ecosystems. Issues regarding the reality of end-user
computing, however, often hinder the use of cross-platform
systems. By end-user computing we refer to the practices that
users need to establish for managing multiple devices, accessories,
and connectivity [15]. Sometimes establishing these practices is
perceived as too big of a trade-off between effort and benefit,
resulting into abandoning distinct platforms or limiting utilization.
For example, in a study by Oulasvirta & Sumari [14] extraneous
tasks, such as synchronization and setup overhead of devices,
often determined whether a device in a multi-device ecosystem
was used or not in a particular situation. Plenty of work has been
done to advance the usability of cross-platform configurations,
however, knowledge about the experiential side of their use is still
somewhat limited. The purpose of this study is to contribute to the
body of knowledge on cross-platform service user experience.
The concept of user experience (UX) is a debated one. A very
basic definition of the term refers to the user’s responses, which
result from the interaction with a system in particular contexts of
use [8]. A conventional perspective to user experience is often
appliance-based, e.g., mobile interaction (the mobile) [9], web
user experience (browsing in desktop-environment)[12], or user
experience of web browsing on mobile phones (browsing in
mobile environments) [17]. Recent studies, however, have
adopted a more holistic and processual view in terms of service
user experience, user experience life cycles and distributed or
crossmedial user experience [26][5][21][23]. A central notion in
the context of cross-platform interactions is that the use of a
distinct system component is significantly influenced by prior and
expected experiences with other components in the system [23].
We conducted an empirical study with three web services to
investigate the elements of user experience that are essentially
associated with their cross-platform characteristics. We conducted
the analysis focusing on three key themes identified with related
work including (a) composition: how devices and functionality are
organized (b) continuity: how transitions between platforms work
and (c) consistency: how consistency is leveraged through distinct
system components. This paper reports the findings of the study
and proposes an initial conceptual framework of cross-platform
user experience that was formed based on prior research and the
field investigation. In the next section we will introduce the
background of the study and the key conceptual themes –
composition, continuity and consistency – that we will contribute
to with this research. In section three we will describe the field
study. In section four we will present the findings and analysis
from the study. This analysis will ground an initial framework for
conceptualizing cross-platform user experience, which is
introduced in section five. In section six we will discuss our
findings and the implications of the framework and finally, we
will conclude the paper and point out future research.
Copyright is held by the authors.
MobileHCI'10, September 7-10, 2010, Lisboa, Portugal.
ACM 978-1-60558-835-3.
219

2. BACKGROUND
In this section we discuss prior research on cross-platform or
multi-device systems regarding their design and usability as well
as the emerging work on service user experience and crossmedial
user experience. As opposed to strictly focusing on usability
factors or system characteristics, the scope of user experience
studies also includes the investigation of experiential outcomes of
interactions.
2.1 Configuration of Cross-Platform Services
There are several terms that have been used when describing
systems comprising multiple interaction devices, platforms or
applications. In HCI, the terms multiple-user interface (MUI) [4],
or multi-device system are frequently used. Also the terms
distributed UI [10][2][23], multichanneling (originating from
marketing) and crossmedia [21][22] have been associated with
cross-platform compilations. In this paper, cross-platform services
are defined as being often web-based and encompassing two or
more computational platforms for interacting with the service. In
the following subsections we will discuss two fundamental
aspects of cross-platform service configurations, the way devices
are organized and the way the service is delivered using these
devices.
2.1.1 Device Organization
Denis and Karsenty [4] have defined three degrees of device
redundancy that illustrate how the roles of devices may be
organized. These include redundant devices, complementary
devices and exclusive devices. Redundant devices provide access
to the same data and functions. Complementary devices share a
zone of data and functions, but one or more of the devices provide
access to data or functions that are not available on the other
device(s). Finally, in a system with exclusive devices, each device
provides access to distinct data and functions.
Depending largely on device redundancy, the degree of
synergistic specificity of a service is determined. Schilling [19]
has defined synergistic specificity as “the degree to which a
system achieves greater functionality by its components being
specific to one another” within a specific configuration. Systems
high in synergistic specificity may be able to support functionality
and user experiences that more modular systems cannot. There are
systems in which the main functionality relies on optimizing the
components’ ability to work with each other. In such systems,
detaching the components or using them in isolation would result
to a loss in performance or in the worst case paralyze the whole
system [25]. Segerståhl [22] refers to the Apple iPod product
family as an example demonstrating a relatively high degree of
synergistic specificity, as the mobile devices are dependent on the
desktop application as the source of power and content. Some
systems are more flexible due to a higher degree of functional
modularity, i.e., devices included in them can be used in different
combinations and operated independently. A more modular
system may also achieve synergy when it is used in such a way
that the benefits of its components are merged. However, this
requires establishing combinatorial use practices. Device
redundancy and synergistic specificity are important concepts
describing the composition of a cross-platform system and may
help in explaining conflicts that occur, when users try to use
devices in a system in ways that are not supported by its
configuration.
2.1.2 Service Delivery
In this study we focus on two types of services that are defined by
how they are delivered. Some cross-platform services are
multichanneled, i.e., their functionality and content is channeled
through multiple devices. In multichanneling the aim is to provide
computational means for responding to users’ need for ‘anytime
and anywhere’ access to information and functionality [24]. For
example designing a web service that supports multichanneling
would require applying scalable content and interaction
techniques that enable operating the functionality on interaction
devices other than the primary device [13][17]. These services
often employ redundant or complementary devices where a subset
of core functionality is extracted from, e.g., the desktop version to
the mobile instance of the service.
Other services may extend across a range of distinct devices and
applications forming crossmedia systems [22]. The main
motivation for these is in optimizing communication channels and
interaction resources for the different contextual settings that
occur throughout the activities they support [1]. Crossmedia
systems employ often complementary but sometimes also
exclusive devices. The key difference between multichanneled
and crossmedial services is in their degree of synergistic
specificity. A multichanneled service is often low in synergistic
specificity as it is usually primarily operated on one platform.
However, crossmedial services are more synergistic in that they
only become fully functional when their components are used in
combinations. Figure 1 illustrates this distinction.
Figure 1: The conceptual distinction between multichanneled
and crossmedial cross-platform services.
2.2 Multi-Device Usability
Studies on multi-device usability or horizontal usability namely
focus on transitions between devices and how tasks are picked up
after these transitions [13][4][20][16]. Denis and Karsenty [4]
have proposed a conceptual framework of inter-usability that
proposes design principles addressing inter-device consistency,
transparency and adaptability. They focus on knowledge and task
continuity and how these can be better supported through design.
Knowledge continuity means supporting a shared memory of the
user and the service, i.e., the service “follows” a user’s activity
across platforms and task continuity means the system’s ability to
recover the state of operation after a user’s transition from one
device to another.
2.2.1 Inter-Device Consistency
With inter-device consistency, Denis & Karsenty [4] refer to
perceptual, lexical, syntactical and semantic consistency.
Perceptual consistency refers to appearance and structure of
information, graphics and the order in which information is
presented. Lexical consistency addresses labels and user interface
objects. Syntactical consistency refers to the availability of the
same operations on each device to attain a given goal. Semantic
consistency covers partition of data and functionality, effects of
operations and recovery of state data and context on devices.
220

The problem is that services and devices cannot and should not be
entirely consistent in every case. Heterogeneity of functionality,
for example in the case of crossmedial services may bring added
value to their use [22]. Yet, in line with basic usability principles
[11] we agree that ‘look and feel’, terminology and symbols as
well as interaction logic (navigation and the way certain
operations are performed) should be as consistent as possible
across devices and platforms.
2.2.2 Transparency
When systems demonstrate different degrees of redundancy and
heterogeneity, it is important to explicate their structure to the
users. Denis and Karsenty [4] point out the role of help and
manuals in helping users understand the limitations and
capabilities of devices in the service delivery process. The
importance of this kind of transparency is dependent also on the
users familiarity with different types of technologies. For expert
users it is easier to understand the potential and limitations of
distinct technologies, whereas users less familiar with current
technology may be confused about why certain devices afford
different types of interactions and tasks than others.
Today laypersons are, more often than not, able to use the web
and different kinds of mobile devices sufficiently well. However,
knowledge about practices for combining them in useful ways or
combining them altogether is not as common [22]. This is why
transparency – instead of pointing out limitations and capabilities
of devices – should focus on explicating combinatorial use
practices that users can adopt and integrate into their primary
activities.
2.2.3 Adaptability
In Denis & Karsenty’s framework adaptability is a two-fold
principle. On the one hand it emphasizes the system’s role in
helping the user learn and utilize its various components in
different use situations. On the other hand it means the system’s
ability to adapt itself to the user’s local environment and to the
characteristics of the device. The overall objective is to provide
information relevant to the current situation. Adaptability as
defined in [4] is different from adaptability discussed in context-
aware computing [3]. Denis & Karsenty’s use of the term is more
closely associated with the configuration of the system. System
configuration acts as a basis for assuming use situations and
adapting content and functionality on each device.
The main goal in adaptability as considered in [4] is to promote
the use of devices within a system. However, a multi-device
configuration may also have other goals, contrary to maximizing
component usage. For example a heart rate monitoring system
comprising a mobile heart rate monitor and a web service is able
to provide support, not only for a wider range of tasks, but for a
wider range of users because it is distributed across the two
platforms [22]. Users who exercise casually are well off with the
mobile device and need not be burdened with excess features,
whereas more enthusiastic athletes are also able to benefit from
the system because they can combine the heart rate monitor with
the web service for more advanced tools to carry out long-term
follow-up and analysis [22]. This is an example of how a system
may adapt for different usages through its composition.
2.2.4 Usability and User Experience
Majority of prior work tackles how usability as a characteristic of
cross-platform services may be improved by incorporating certain
principles in design. Our focus is rather in what kinds of
characteristics in cross-platform systems influence user
experience, and what are the central elements of cross-platform
UX. The concept of user experience [8] extends the usability
perspective towards emotional aspects of system quality. Also,
more attention is paid to how user experiences are shaped with
respect to overall system use – not only a single platform or
device.
Usability is an integral part of designing for cross-platform
service user experience, however there are other aspects to
consider as well. With design choices, such as whether to
distribute functionality exclusively or redundantly across devices,
different types of user experiences can be evoked. For example,
the Apple ecosystem incorporates a relatively high degree of
synergistic specificity, i.e., coupling devices in such a way that
they cannot be used in isolation. This strategy on the one hand
allows for optimal consistency and continuity and reinforces
commitment to the brand – which may support an engaging and
positive user experience. However, on the other hand it restricts
the horizon of consumer choices through compatibility constraints
and may therefore reflect a negative user experience.
User experience that is formed upon interactions with cross-
platform systems and services may in some cases appear as
distributed or fractured. Distributed user experience [23] results
when (a) system components and configuration is not in line with
the users’ primary activity, (b) when linkages between media are
not fully supported, and (c) devices and service interfaces within a
system are fundamentally different in terms of presentation and
interaction style [21][23]. When user experience is coherent (as
opposed to distributed), appropriate combinatorial use of devices
and applications may be promoted which in turn may result to
more efficient utilization of and satisfaction with cross-platform
services. [24][21]
In this study on cross-platform user experience, we will focus on
system characteristics, that essentially influence, how users
position their interactions and experiences with the system. Thus,
we will slightly re-organize and clarify some of the common
themes from related work to support our analysis. The thematic
scheme used in this work is presented in the following section
with composition, continuity and consistency as the key themes.
2.3 Common Themes
In this paper we categorize system characteristics in such a way
that their identification and analysis supports designing for not
only usability but also user experience. We draw attention to three
main themes under which we will discuss and analyze our
findings. These include composition, continuity and consistency.
2.3.1 Composition
Composition determines, how platforms (applications and
devices) within a system or service relate to each other [22].
Requirements for composition differ depending on whether a
service is multi-channeled through different platforms or whether
it is distributed across them (crossmedia). In multichanneling
aspects such as tailoring the service for distinct devices is
important, whereas in the case of crossmedia, matching devices
and functionality with aspects of user’s primary activity is in
focus. For example when each device and its functionality in a
system is optimized for a specific use context or situation, the
service’s adaptability may be increased. In this study, adaptability,
as defined by Denis & Karsenty [4] is something that is achieved
when the composition of a system is appropriate. Composition is
one of the essential focal points in cross-platform design.
221

2.3.2 Continuity
Continuity supports interoperability, i.e., carrying out transitions
between platforms. Continuity is established through seamless
synchronization of data and content [4], but also by explicitly
supporting users in migrating their tasks across platforms
[16][21]. Continuity is supported by consistency in that it helps
users transfer their skills from one use situation to another [11].
Prior research has also demonstrated that continuity is not
sufficiently supported by consistency only, but requires active
interaction strategies that help users understand how devices can
be connected and used together [16][21]. This relates to the
transparency principle, but cannot be resolved only with user
manuals or help documentation. Bridging conceptual gaps
between devices and applications requires strategies that are
interweaved into the fabric of interactive situations, such as
crossmedial referencing which means that interactive situations on
one device propose linkages to other devices within the system.
These kinds of active techniques help affording distinct use
practices and suggest purposes for the different devices
[21][13][7].
2.3.3 Consistency
Consistency is one of the most highlighted principles in usability,
especially with multi-device systems. In our framework
consistency can be leveraged through a) perceptual (look n’ feel),
b) semantic (symbols and terminology) and c) syntactic
(interaction logic) consistency. Syntactic consistency refers to
what Denis and Karsenty tackle when discussing requirements for
the continuity principle. However, in this work these are
differentiated as continuity is referred to as something requiring
more active forms of interaction (see previous section). After
transitions from one device to another, consistency quite
understandably supports continuity, i.e., carrying on or “picking
up” the flow of interaction. [4]
In the following section we will introduce the field study that was
conducted to explore the experiential side of composition,
continuity and consistency in cross-platform settings.
3. THE FIELD STUDY
A field study with three cross-platform web services was carried
out in spring 2009. Qualitative data was collected with interviews
and diaries to gain an in-depth understanding of user experiences
associated with users’ interactions with the studied cross-platform
services. A questionnaire inquiring about the pre-defined themes
of cross-platform use (composition, continuity and consistency)
was also used to complement qualitative data. This section
describes the three selected services, as well as the research
procedure.
3.1 The Studied Services
We studied three web-based services with cross-platform
characteristics. These included facebook, Dopplr and Nokia
Sports Tracker.
Facebook (www.facebook.com) is a web service for social
networking. Users can, for example, join networks, add friends,
post status comments, create groups and send messages. There are
also thousands of applications created by service providers,
developers and users, which can be integrated to a facebook
account. The mobile user interface for facebook that was
investigated in this study, offers a subset of functionality found in
the PC version of the service. (See Figure 2.)
Figure 2: Desktop and mobile UIs of facebook
Nokia Sports Tracker (sportstracker.nokia.com) is a GPS-based
activity tracker. A mobile device is used to automatically store
workout data such as routes, speed, distance and time in user’s
training diary. Mobile images and audio annotations can be added
to locations. PC UI includes functionality for editing, viewing,
sharing and commenting workout information based on map
views. Users can also create and join groups. (See Figure 3.)
Figure 3: Desktop and mobile UIs of Nokia Sports Tracker
Dopplr (www.dopplr.com) is a travel information service with an
online community feature. Dopplr allows users to share their trips,
experiences and travelling plans. It also offers information about
places that users have visited. Users can add reviews and
comments to the service. (See Figure 4.)
Figure 4: Desktop and mobile UIs of Dopplr
The mobile platform that was used in the field study was the
Nokia smart phone with Series 60 user interface (S60). Users used
various Nokia smart phone devices (their own ones), but the UI
was the same for all users to maintain the comparability of the
results.
According to the conceptual distinction between various types of
cross-platform services (as presented in Section 2.1), facebook
and Dopplr are defined as services conforming to the
multichanneled type whereas Nokia Sports Tracker is defined as a
crossmedial service.
222

3.2 Method and Approach
This study was a qualitative field study. The aim was to
understand and conceptualize cross-platform user experience and
system characteristics that influence cross-platform service user
experience.
3.2.1 Data Collection and Participants
Semi-structured diaries were used for collecting data about users’
interactions and experiences with the services in both desktop and
mobile situations. Interviews were conducted in order to gain a
more in-depth understanding of users’ experiences and to
elaborate on the diary data. In addition, a questionnaire tackling
cross-platform interactions was used for complementing
qualitative data.
Participants for the study were recruited through mailing lists
intended for user study recruitment. Participants could sign up for
the study with a preference for any of the three services. Based on
participants’ preferences, three groups were formed. 11
participants used facebook, 8 participants used the Nokia Sports
Tracker and 7 participants used the Dopplr service. Gender
distribution among facebook and Dopplr users was fairly even,
however majority (7/8) of Nokia Sports Tracker users were male.
Participants were between ages 22 and 34. Half of the participants
had technical education.
Participants used the services for four weeks in their everyday
lives. During this time, they documented their experiences in
diaries for the first and the last week of the study. The diaries
were structured as follows: After each use situation, users were
asked to write down qualitative statements about the contexts of
use, and their interactions and experiences with the service. They
were also asked to write down positive and negative issues
affecting their experience with the service in each specific
interaction situation. After each diary period, at the end of the first
and fourth week of the study, interviews were carried out with
each participant. Interview data was used for complementing and
clarifying diary statements. Participants were also asked to fill out
a questionnaire addressing the quality of cross-platform
interactions. The questionnaire was constructed based on a review
of prior work [27][28] and an expert evaluation that had been
carried out with the investigated services prior to the field study
[28]. The questionnaire was constructed of statements that were
categorized under the themes of composition, continuity and
consistency. Participants were asked to rate their degree of
agreement with each statement on a 7-point Likert scale with
values from completely disagree (1) to completely agree (7).
Statements addressed users’ perceptions of system characteristics
and experiences in interactive situations. For example,
composition was addressed with statements such as “Different
components in the service support my activity in different ways”,
or “The service provides holistic support through its components.”
Support for continuity was inquired with statements such as
“Switching between using the service with different devices is
easy.” and “Using the service with different devices is easy.”
Statements addressing consistency included such as “The way the
service works is consistent across its different components” and
“Terminology is being applied consistently across the service”.
3.2.2 Data Analysis
The qualitative data related to cross-platform UX was extracted as
individual statements from user diaries and interviews (total of
165 statements). Emerging UX themes were analyzed in two
phases: In the first phase qualitative data was analyzed through
open coding, which resulted in categories of users’ experiential
responses to cross-platform interactions. In the second phase these
categories were reviewed with tool constructs from the thematic
scheme presented in section three. This way we were able to
systematically map users’ experiences with cross-platform
characteristics. Questionnaire results were used as descriptive
indications and to complement qualitative data.
4. FINDINGS AND ANALYSIS
In this section we present the findings of our study and analyze
them with regard to the emerging themes from open coding as
well as the thematic framework. In the following user quotes, we
refer to the services as ST = Nokia Sports Tracker, FB = facebook
and DP = Dopplr. U refers to users’ identification numbers.
4.1 Appropriateness of Composition
In situations where there are multiple components to a
system/service, the inclusion of each component needs to be
justified. This means that if the composition, i.e., the collage of
applications and devices and the way they’re combined, is not in
line with the user’s activity or needs, it may essentially hinder the
resulting user experience. Our findings can be described under
three aspects associated with system composition: component role
allocation, distribution of functionality and functional modularity.
4.1.1 Component Role Allocation
Component role allocation refers to how the system defines and
explicates the purpose, or role, of each of its components. A clear
structure of roles may help users allocate tasks between platforms
and find synergistic use practices.
Most users of the Nokia Sports Tracker perceived the mobile
device primarily as a data recorder and the PC as a browsing and
analyzing tool. This kind of clear task allocation was initially
driven by the users’ primary activity (performing physical
exercise), but may also have been supported by the fact that
functionality was distributed across the different devices in a
complementary manner (as opposed to being replicated). As one
of the users stated:
“Data transfer between the mobile and PC is easy and
both of them have a distinct role” (ST, U14)
Compared to Sports Tracker, the roles of the mobile terminal and
the PC interface were differing from how they functioned with
facebook and Dopplr. For most users of facebook, the PC UI was
the primary UI. Facebook was used with the mobile for keeping
updated and to pass time when the PC was not available. One
participant reported how s/he used the mobile facebook when on
the move:
“I use the mobile for as a status report, to see if there
is anything [in the service] that I’d like to take a
closer look at later[when I get home or to the
office].”(FB, U8)
The mobile was mostly used for browsing content, but also to do
short status updates. Users of Dopplr reported that they might use
the mobile version of Dopplr on the road for passing time and
reading reviews. The following comment sums users’
expectations of the mobile version:
“With the mobile you can do the important things and
it has to be simple and fast.” (DP, U3)
223

Many users wished for more functionality in the mobile UI, such
as being able to chat. This implies that what users’ considered as
“important” is associated with the situation, i.e., passing time on
the road, not necessarily with what the service is primarily
designed for.
There were three statements in the questionnaire investigating
component role allocation: “I use the different devices for doing
different things in the service”, “I use the different devices for
doing similar things in the service but in different situations”, and
“Different components in the service support my activity in
different ways”. The results show that most users of Dopplr and
facebook did not use different devices for doing different things in
the service. Instead, different devices were used for doing similar
things in the service but in different situations. Whereas the third
statement assessing crossmedial composition was mostly agreed
upon by the users of Nokia Sports Tracker. This demonstrates
how users comply with different types of service delivery,
multichanneled and crossmedial.
Based on our findings, we identified two ways of defining the
structure of roles: task-based and situation-based. With the Nokia
Sports Tracker, the organization of component roles was defined
as being task-based, meaning that users used the service
components for different tasks or purposes. Whereas with
facebook and Dopplr, organization of component roles was
situation-based, meaning that different components were used for
similar purposes, but in different situations.
4.1.2 Distribution of Functionality
Distribution of functionality means the way in which entire
system functionality is allocated between system components. In
multichanneling, the idea is to deliver instances of the service
through different platforms. However, due to the constraints of
distinct platforms, such as the mobile, functionality may need to
be prioritized or reduced.
In Dopplr and facebook, this adaptation has resulted in a solution
where a subset of service functionalities is available on the
mobile. With facebook this subset was considered well defined,
taking into account the mobile use situations and how users would
utilize the service in them. The mobile facebook included the
most central functionality of the service. Users perceived it as
being suitable for keeping up-to-date with what was going on in
the service and for passing time when a PC was not available.
“With the mobile you can see things quickly and use
basic functionality of the service. You can see if there
are any new messages, see status updates and update
your status.”(FB, U15)
The strongly reduced amount of functionality on the Doppler
mobile UI however was disappointing to many users. It was
considered as excessively simplified compared to its PC
counterpart. This seemed to be the reason why users commented
and used the mobile version of Dopplr very little during the study.
One reason for this may also be, not only oversimplification, but
also the fact that functions on the mobile were not well selected. It
is important to understand the use context associated with each
platform in order to optimize functionality for each.
With the Nokia Sports Tracker, the different functionalities of the
PC and mobile UIs were perceived as complementary
(crossmedial composition). Users’ responses indicate that in this
case exclusive distribution of functionality can be justified. The
mobile versions of facebook and Dopplr offered a subset of main
functionality (typical in multichanneling). In the facebook case
this worked out fine, as core functionality was well defined to fit
with the situations in which the mobile facebook was used.
However, with Dopplr the degradation was too extensive or
unfitting – leading to oversimplification and non-use of the
mobile platform.
In the questionnaire, two statements investigated distribution of
functionality: ”It is easy to understand the role of each component
in the service” and “I do not have to use all of the components in
order to utilize the system”. Both statements were agreed upon by
users for the most part. In general, both ways of structuring
functionality, multichanneled and crossmedial, were experienced
as being appropriate despite the fact that in the Dopplr case this
could have been done more fittingly.
4.1.3 Functional Modularity
Functional modularity refers to the system’s ability to support a
set of core tasks with each of its components. This way, users can
utilize most important system functionalities even when they only
have access to one of its supported platforms.
With the Nokia Sports Tracker only the PC part of the service
includes functionality for browsing data stored in the server. Some
users hoped to be able to browse training data with their mobile
device, as they wanted to keep updated while on the road. Some
users even tried to use a browser for this on their mobiles but the
PC UI of the service was perceived too heavy for mobile
browsing. This indicates a mismatch between users’ needs and
service composition that results from synergistic specificity of the
mobile and PC UIs of the Nokia Sports Tracker. Not all core tasks
are supported on the mobile UI, which is on the one hand justified
with complementary (exclusive) component role allocation that
reduces complexity on the mobile. However, on the other hand
this may in some cases be problematic in terms of functional
modularity, meaning that the user does not have access to required
or expected core functionality on all components. In this case the
mobile device is a mobile phone, which is used in many types of
mobile situations, not only during workouts. This is the primary
reason, why users would expect to be able to do other things with
the application besides recording. As a contrasting example, in the
case of a heart rate monitoring system [22], the actual mobile
device in itself is limited in terms of functionality and users
understand that it cannot really be used in other types of contexts.
Users’ expectations regarding the mobile device (the mobile
phone) as well as the variety of contexts that it can be used in
effect how system composition in this case is experienced.
According to the questionnaire results, the users of facebook and
Dopplr did not feel that they were able to do everything they
wanted on the mobile while the PC UIs were seen as to support
users’ tasks well - facebook even very well.
4.2 Fluency of Task and Content Migration
Another key element of cross-platform service UX relates to how
users carry out their activity using the different devices and how
actions and content are synchronized across platforms.
4.2.1 Support for Task Migration
Support for task migration refers to the system’s ability to support
users in carrying on with their tasks and activity after transferring
from one device to another. Fluent task migration is partially
supported through consistency, in particular, consistent interaction
logic. In this case this was demonstrated in that users placed a
high value on the clarity of the mobile UI.
224

“It’s been surprisingly easy to use the service with the
mobile. It was easier to find things that I wanted as
there was none of that unnecessary clutter [compared
to the PC version].” (FB, U1)
However, this was not necessarily a result of consistency between
the PC and mobile versions of the service, but a result of
distribution of functionality. The user had gotten used to the
”cluttered” PC interface including third-party banners etc., but
when using the service on the mobile, interactions were free of
this clutter, which was perceived as positive.
The following statement in the questionnaire investigated system
support for task migration: “Switching between using the service
with different devices is easy”. The answers from the users of
facebook and Dopplr were close to neutral whereas the users of
Nokia Sports Tracker considered switching between devices easy.
With the Nokia Sports Tracker this was also more important
because the devices were used in synergistic combination.
4.2.2 Cross-Platform Transitions
Several users brought up how the mobile component (device and
UI) works together with the rest of the service. They appreciated
data transfer between devices being easy and free of technical
problems.
“…it is easy to send a workout (from mobile) to the
web service. It always makes me happy.” (ST, U14)
There were three statements in the questionnaire investigating
cross-platform transitions. According to the users of the Nokia
Sports Tracker, transferring data between service components is
easy as well as connecting service components and using service
components together. In this case the Nokia Sports Tracker was
the only service requiring these types of combinatorial tasks and
thus the questions could not be applied to the facebook and
Dopplr cases.
4.2.3 Synchronization of Actions and Content
When users transferred between interactions on the PC and the
mobile platform and vice versa, they expected to see the exact
same content on both platforms. Thus, when users had access to
only partial content, they felt dissatisfied. These kinds of
situations occurred for example with Dopplr.
“Browsing did not work. The information of some city
could not be found with the mobile although I had
seen it on PC.” (DP, U1)
Those users of Nokia Sports Tracker who considered the mobile
device as a “recorder”, as opposed to those, who considered it
from the mobile phone perspective (described in 4.1.3.) did not
report on these kinds of issues. This was because they were not
interested in accessing content on the mobile to begin with, but
used the PC for that. Users’ conception of service composition
possibly influenced users expectations of how the devices should
work, and in these cases was supportive of a neutral experience.
Users also pointed out that if they carry out an action on one of
the devices, it should automatically be reflected on the UIs of all
other devices in the system, for example:
”PC and mobile are not working too well together;
Even if you have read a message on PC it is shown as
unread on mobile.” (FB, U2)
Users’ demand for automatic synchronization of actions that have
an impact on the state of content, such as in the case of marking
unread messages in facebook. Users expect the system state (the
state of content and actions) to be up-to-date, in real time, on all
platforms.
4.3 Service Consistency
We were not able to detect spontaneous comments by users (from
diaries or interviews) that would have been addressing
consistency, as it is referred to in related work: uniformity of UI
terminology, interaction logic or other consistency issues on
different platforms. One reason for this may be that it is not
something that users explicitly evaluate or think about. Another
may be that the services were sufficiently consistent on all
platforms and inconsistency was not something that would have
significantly influenced users’ experiences. Consistency was,
however reflected as a secondary, or facilitating factor with other
themes. For example, if users learned to use the service on each
platform easily, consistency may have contributed to this as it
supports the transference of skills. We had four statements in the
questionnaire investigating aspects of consistency. The statements
related to interaction logic, visual expression, terminology and
overall impression of consistency.
According to the questionnaire results, users agreed the most with
the statement on consistency of the terminology on PC and
mobile. Especially the users of facebook and Dopplr agreed on
this statement. However, there was diversity in users’ responses
regarding visual consistency and overall impression. Interaction
logic of Dopplr and facebook was considered somewhat
inconsistent, however this did not appear as significant when
investigating experiences. The users of Nokia Sports Tracker
perceived interaction logic as more consistent. This may be due to
the clear conceptualizations of service composition that users had.
5. AN INITIAL FRAMEWORK OF CROSS-
PLATFORM USER EXPERIENCE
Based on prior work and the findings of the presented field study,
we have constructed an initial framework for cross-platform
service UX. The framework conceptualizes a structured set of
distinct, designable characteristics of cross-platform systems that
essentially influence UX, and the respective main elements of
cross-platform service user experience.
An overview of this framework is depicted in Figure 5. In the
following, the main themes presented above, i.e. composition,
continuity and consistency are broken down into aspects that can
be addressed in the design of cross-platform services. We have
labeled the respective main UX elements as fit for cross-
contextual activities, flow of interactions and content, and
perceived service coherence.
5.1 Composition
As the analysis in Section 4.1 indicated, composition can be
broken down to the following system characteristics: component
role allocation, distribution of functionality, and functional
modularity.
225

Figure 5: The overview of an initial framework for cross-platform service user experience
5.1.1 Designing for Appropriate Composition
Component role allocation defines how users perceive the
purpose of each system component. Further, this determines the
expectations that users may have for component functionality.
Roles can be allocated to devices by the designers of a cross-
platform service or by the users. Designers can, for instance,
choose to limit the functionality on distinct platforms and tailor
them for specific purposes or they can try to provide full
functionality on all platforms. Users allocate roles through their
use practices, depending on the extent to which a system affords
it. We have identified task-based and situation-based role
allocation. Task-based allocation means the use of distinct
platforms for distinct purposes or tasks, whereas situation-based
allocation means using distinct devices for the same tasks, but in
different situations. Users often carry out situation-based
allocation meaning that they selectively use different interaction
devices in different situations. Understanding how users allocate
roles between system components helps in limiting unnecessary
functionality on some devices and emphasizing the importance of
others. We have shown that component role allocation may have a
significant impact on users’ experiences with the service.
Understanding the situations that users use the service in and also
how users use the devices that are used for delivering service
functionality helps to optimize their roles.
By distributing functionality exclusively, complexity of an
individual device may be reduced. A task that is primarily carried
out on one platform does not necessarily need to be included or
brought up-front on another. This applies to content as well.
Designers should consider the possibilities for distributing
functionality across several platforms in a system. Functionality is
usually distributed based on platforms’ individual strengths or
based on assumed use situations. For example, if it is known that a
specific device is only used in certain kinds of situations, it may
be justified to limit its functionality to support only those
situations. One of the simplest ways to do this is by forming a
situation-based subset of core functionality as was done in the
case of facebook. However, when including functionality on some
platforms and limiting it on others, there is always a risk that the
configuration does not match actual user expectations. For this
reason a certain degree of functional modularity should be
considered.
The degree of functional modularity determines how each
platform adapts to use in different situations. If core
functionalities are only available on one platform, this limits the
use of the service in situations where the platform is not available.
It is suggested that some degree of functional modularity is
always maintained, even though devices within a system are
specialized [22]. Systematic ways and patterns of distributing
functionality in different cross-platform settings need to be
studied further.
5.1.2 Fit for Cross-Platform Tasks
In our analysis, we have demonstrated how composition of a
cross-platform service may influence user experience. Component
role allocation influences users’ expectations of how the different
components in a system should function. Therefore, appropriate
role allocation needs to be in line with distribution of
functionality. In order to smoothen potential conflicts when
designing synergistic systems, a certain degree of functional
modularity should be maintained.
The composition of the system, when in line with the user’s
primary activity may have a significant, positive impact on user
experience. Appropriate composition can also influence UX on
individual devices. When functionality is distributed across
devices, the complexity on individual devices may be reduced,
leading to increased simplicity.
5.2 Continuity
Continuity can be broken down to characteristics that determine
how well the system supports: cross-platform transitions, task
migration and synchronization.
5.2.1 Designing for Fluency
Cross-platform transitions include interactions where the user
switches from using one device to using another. For example, if
the user uses facebook on the PC and switches to the mobile when
leaving the house and taking public transport, this is considered as
226

a cross-platform transition. Another example, perhaps a more
problematic one, is associated with the technology adoption phase
and initial interactions with service components. When cross-
platform systems are first used, the threshold to carry out cross-
platform transitions may be significant [21]. Most problematic are
those situations, in which users do not have sufficient information
and support in how to transfer use from one device to another,
such as, how to download and initiate the mobile version of a
service or how to transfer content to the web from a mobile
device. Connections between devices and applications need to be
made explicit in order for users to be able to take use of them. It is
not enough that devices can be technically interconnected. Their
combinatorial use also needs to be supported through the out-of-
box experience, coherent system image and crossmedial
referencing [21].
Appropriate support for task migration is needed, when carrying
out an activity and switching devices “on the run”. How are
situations in which a user begins one task on a device and
continues the same task on another device, supported? The type of
support again depends on whether the system is multichanneled or
crossmedial. In multichanneling, supporting repetition of tasks is
in focus. The same content and functionality needs to be available
on all platforms that are used for carrying out the task. With
crossmedia systems, a logical chain of tasks needs to be
supported.
Synchronization of actions and content is critical to
multichanneled cross-platform web services. Users expect to see
the exact same content and state of actions when migrating their
tasks from one platform to another. In order to support cross-
platform transitions and task migration, both content and actions
need to be synchronized across platforms. In the case of
multichanneling, this may not be as crucial if the system is high in
synergistic specificity. This is because the tasks that are carried
out on one device may tackle distinct content and utilize different
functionality than in the preceding situation.
5.2.2 Flow of Interactions and Content
The impact of continuity for user experience stems from users’
need to carry out activities fluently with or across various
platforms. The tasks need to be migrated or carried on smoothly
from one platform to another, and interactions continued without
needing to explicitly think about the device at hand. From the
content perspective, the service should be up-to-date
(synchronized) on all platforms, or otherwise the user may
experience the service as discontinuous set of subsystems, or even
technically unreliable.
5.3 Consistency
Consistency is emphasized in related work and conforms to basic
usability principles. In this case, it is applied in a horizontal sense,
across platforms and devices. The challenges regarding
consistency lie in the heterogeneity and constraints of different
technologies. Consistency can be leveraged on different levels to
promote a coherent system image.
5.3.1 Designing for Consistency
Implementing a similar look and feel across different service
platforms can support perceptual consistency. Semantic
consistency is achieved by using the same terminology and
symbols across devices. Incorporating a similar navigation
scheme on all devices may support consistency of interaction
logic.
In this study, users did not explicitly report consistency problems.
Consistency may not be something that is as such explicated in
users’ experiences, however it may rather be a background factor
that influences how users perceive connections between devices
and how quickly they learn the use of the service on different
platforms. Consistency also influences users’ perceptions of
continuity. If data or system state is not consistent on one platform
with what it was on the platform preceding that situation, users’
interpret this as a problem with continuity. For example, when
users reported that messages they had read on the PC UI were still
marked as unread on the mobile UI, they experienced this as being
inconsistent. However, as they also understood that the problem
had to do with insufficient synchronization and not for example
look n’ feel or navigation, this problem was associated with the
continuity theme. If, however, the system just (for some reason or
another) presented read messages in two different ways on
different platforms, then it would be a design flaw associated with
consistency.
5.3.2 Perceived System Coherence
When services are operated on different platforms and devices,
users perceive system coherence through a variety of aspects.
Coherence is influenced by composition, flow of interactions and
content as well as continuity. System coherence in a way
summarizes the experience of interacting with a service through
multiple devices. Coherent user experience, as discussed in related
work [21][22] is the ultimate target of cross-platform service
design. It is also a major design challenge due to the complex and
diverse nature of cross-platform services.
6. CONCLUSIONS AND FUTURE WORK
In this study we have demonstrated how characteristics distinct to
cross-platform environments may influence service user
experience. Based on our findings, service composition, i.e., how
devices and functionality are organized within the system and
continuity, and how tasks and actions are migrated across
platforms, turned out to be to most significant aspects influencing
user experience. We also found that users may not be at all that
sensitive to consistency issues between platforms, which is
perhaps overemphasized in a lot of related work. Quite
understandably consistency influences continuity and perceptions
of system composition. However, users are sufficiently good at
reasoning about the connections between service instances as long
as the idea, that this is the way the service is composed and should
work on different platforms, is there. By matching system
composition with users’ primary activity or with the situational
requirements that are associated to usage contexts or devices,
users’ experiences of services may be improved. The main
outcome from an appropriate composition is a better fit with the
users’ cross-contextual activities. The ultimate purpose of our
work is to draw more attention to how service composition and
continuity of interactions influence user experience of cross-
platform web services. We suggest that techniques for identifying
an appropriate structure of roles of service components for distinct
activity types as well as techniques for distributing functionality
accordingly are addressed in future design cases.
The presented framework contributes to HCI design by
explicating system characteristics that have an essential impact on
user experience in cross-platform settings. Becoming aware of
these elements will help in taking the central UX issues into
account when designing web services. Further guidelines and
checklists can be developed based on this framework that will
227

provide concrete support for cross-platform design. The
framework wraps together prior work and will be refined and
applied in future studies of different cross-platform service
configurations. As the complexity and heterogeneity of multi-
device ecosystems increases, user experiences become diversified.
However, understanding the basic dynamics of cross-platform
interactions and how they guide user experiences, this
heterogeneity may be turned into an asset. By promoting
combinatorial use practices, and supporting cross-platform user
experience through considerate design guidelines, new
opportunities for utilizing both existing and new technologies
become available.
7. ACKNOWLEDGMENTS
We thank Jarno Ojala for his valuable contribution in carrying out
parts of the field study. We thank the Graduate School on
Software Systems and Engineering the RichWeb project and the
Tauno Tönning Foundation for funding parts of this research.
This study has also been partly funded by Ministry of Education
of Finland (PALTI project 2007-2009).
8. REFERENCES
[1] Banavar, G. and Bernstein, A. 2002. Software Infrastructure
and Design Challenges for Ubiquitous Computing
Applications. Communications of the ACM 45(12), 92-96.
[2] Bång, M. Larsson, A. Berglund, E. Eriksson, H. 2005.
Distributed user interfaces for clinical ubiquitous computing
applications. International Journal of Medical Informatics,
Volume 74, Issue 7, Pages 545-551.
[3] Chen, G., and Kotz, D. 2000. A Survey of Context-Aware
Mobile Computing Research. Technical Report TR2000-381,
Department of Computer Science, Dartmouth College,
November 2000.
[4] Denis C. and Karsenty L. 2004. Inter-usability of multi-
device systems – a conc eptual framework. In Seffah A. and
Javahery H. (eds.) Multiple User Interfaces: Cross-Platform
Applications and Context-Aware Interfaces. Wiley & Sons.
[5] Dubberly, H. and Evenson, S. 2008. The Experience Cycle.
Interactions. 15(3). March and April 2008. ACM, New York.
[6] Feiner, S.K. 2000. Environment Management for Hybrid
User Interfaces. IEEE Personal Communications Oct. 50-53.
[7] Florins, M. and Vanderdonckt J. 2004. Graceful Degradation
of User Interfaces as a Design Method for Multiplaform
Systems. Proceedings of the IUI’04, Madeira, Portugal.
[8] Hassenzahl, M. 2004. The thing and I: Understanding the
relationship between user and product. In Funology, from
Usability to Enjoyment, pp.31-42.
[9] Jones, M., Marsden, G. 2006. Mobile Interaction Design.
Wiley, West Sussex, UK.
[10] Luyten, K.; Coninx, K. 2005. Distributed user interface
elements to support smart interaction spaces. Proc. 7th IEEE
International Symposium on Multimedia. 12-14 Dec. 2005.
[11] Nielsen, J. 1989. Coordinating User Interfaces for
Consistency. Neuauflage 2002 edn. The Morgan Kaufmann
Series in Interactive Technologies. San Francisco, CA, USA
[12] Nielsen, J. Designing Web Usability. 1999. Peachpitt Press,
USA.
[13] Oliveira, R., Rocha, H. V. 2005. Towards an Approach for
Multi-Device Interface Design. Proc. the Eleventh Brazilian
Symposium on Multimedia and the Web (WebMedia'05),
Pocos de Caldas - Minas Gerais, Brazil, December 5-7, 2005.
[14] Oulasvirta, A. and Sumari, L. 2007. Mobile kits and laptop
trays: Managing multiple devices in mobile information
work. Proc. of CHI 2007, ACM Press, NY, pp. 1127-1136.
[15] Oulasvirta, A. 2008. When Users “Do” the Ubicomp.
Interactions. 15(2). March and April 2008. ACM, New York.
[16] Pyla, S., Tungare, M., Holman, J., Pérez-Quiñones, M. 2009.
Continuous User Interfaces for Seamless Task Migration in
Human-Computer Interaction. Ambient, Ubiquitous and
Intelligent Interaction. In proc. HCI International 2009,
Springer Berlin, Heidelberg.
[17] Roto, V. 2006. Web Browsing on Mobile Phones –
Characteristics of User Experience. Doctoral Dissertation.
TKK Dissertations 49. Helsinki University of Technology.
[18] Savidis, A. & Stephanidis, C. 2005. Distributed Interface
Bits: Dynamic Dialogue Composition from Ambient
Computing Resources. Personal and Ubiquitous Computing
9(3), pp. 142-168.
[19] Schilling, M.A. 2000. Towards a general modular systems
theory and its application to inter-firm product modularity.
Academy of Management Review, Vol 25, pp. 312-334.
[20] Seffah, A. and Javahery, H. 2005. Multiple user interfaces:
cross-platform applications and context-aware interfaces.
John Wiley & Sons, Ltd.
[21] Segerståhl, K. 2008. Utilization of Pervasive IT
Compromised? Understanding the Adoption and Use of a
Cross Media System. Proc. MUM’08, ACM, 168-175.
[22] Segerståhl, K. 2009. Crossmedia Systems Constructed
around Human Activities: A Field Study and Implications for
Design. In Proc. INTERACT 2009.
[23] Segerståhl, K. & Oinas-Kukkonen, H.: Distributed User
Experience in Persuasive Technology Environments. In: Y.
de Kort et al. (Eds.), LNCS 4744, Persuasive 2007, Springer-
Verlag, Berlin Heidelberg, Germany (2007)
[24] Segerståhl K. & Oinas-Kukkonen, H. 2008. Mobile Web and
the Conceptual Grounds of Extended Information Services.
Social Mobile Media Workshop, Stanford University,
Stanford, CA, US, August 1, 2008.
[25] Simon, H. 1962. The Architecture of Complexity. Proc. of
the American Philosophical Society, vol 106, pp. 467-782.
[26] Väänänen-Vainio-Mattila, K., Väätäjä, H., Vainio, T. 2008.
Opportunities and Challenges of Designing the Service User
eXperience (SUX) in Web 2.0.In Saariluoma, P. and
Isomäki, H. (Eds.), Future Interaction Design II, Springer.
[27] Väänänen-Vainio-Mattila, K., Segerståhl, K. 2009. A Tool
for Evaluating Service User eXperience (ServUX):
Development of a Modular Questionnaire. User Experience
Evaluation Methods, UXEM'09 Workshop at Interact'09,
Uppsala, Sweden, August 25th, 2009.
[28] Väänänen-Vainio-Mattila, K., Wäljas, M. 2009. Developing
an Expert Evaluation Method for User eXperience of Cross-
Platform Web Services. Proceedings of Mindtrek’09, ACM.
228