Cross-platform service user experience: a field study and an initial ...

Cross-Platform Service User Experience: A Field Study and an Initial Framework Minna Wäljas1, Katarina Segerståhl2, Kaisa Väänänen-Vainio-Mattila1,3,Harri Oinas-Kukkonen2 1

Tampere University of Technology, P.O. Box 589, FI-33101, Tampere, Finland [email protected]

2

University of Oulu, P.O. Box 3000, FI-90014 Oulu, Finland [email protected]

3

Nokia Research Center P.O. Box 1000 00045 Nokia Group, Finland [email protected]

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.

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, crossplatform 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 crosscontextual 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.

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].

Categories and Subject Descriptors H.3.5 Online Information Services, H.5.2 User Interfaces.

General Terms Design, Human Factors

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.

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 multidevice 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, Copyright is held by the authors. MobileHCI'10, September 7-10, 2010, Lisboa, Portugal. ACM 978-1-60558-835-3.

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2.1.2 Service Delivery

2. BACKGROUND

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.

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.

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.

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.

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.

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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.

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.

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.

User experience that is formed upon interactions with crossplatform 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]

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 contextaware 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.

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.

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.

2.3.1 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.

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

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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].

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.)

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]

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.)

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. Figure 4: Desktop and mobile UIs of Dopplr

3.1 The Studied Services

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.

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.)

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.

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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.

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.

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.

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.

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

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”.

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:

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

“With the mobile you can do the important things and it has to be simple and fast.” (DP, U3)

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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.

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.

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.

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.

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.

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)

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.

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.

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.

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

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”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)

“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)

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.

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.

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.

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)

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.

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.

5. AN INITIAL FRAMEWORK OF CROSSPLATFORM 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.

“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.

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 crosscontextual activities, flow of interactions and content, and perceived service coherence.

5.1 Composition

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:

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.

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Figure 5: The overview of an initial framework for cross-platform service user experience configuration does not match actual user expectations. For this reason a certain degree of functional modularity should be considered.

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 crossplatform 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.

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.

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

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

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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 crossplatform systems are first used, the threshold to carry out crossplatform 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-ofbox experience, coherent system image and crossmedial referencing [21].

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.

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.

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.

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 crossplatform 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.

6. CONCLUSIONS AND FUTURE WORK

5.3.1 Designing for Consistency

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 crossplatform 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.

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.

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

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.

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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 multidevice 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.

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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).

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