and Infrastructure for Mobile Multimedia Applications
EPSRC GR/L64140 & GR/L64157
Alan Dix, 21/2/2002
User Interface Work
Work on Separable Notification for Feedthrough and Pace Impedance
A major strand of the UI work has been work on separable notification services to provide feedthrough of one user's actions to other users. This is critical in collaborative advanced mobile applications both for task-oriented update of shared information and also for peripheral awareness that has been widely recognised as essential for collaborative activity.
The basic problem is quite simple. In a collaborative setting one user A makes a modification to some shared data, or performs some event (this may be as simple as moving a cursor, or as major as replacing a whole file). We call this user's computer/device the active client (AC). In the system as a whole we want some other user P to be aware (either peripherally or more explicitly) of the event or change. We call this user's computer/device the passive client (PC). How do we propagate the event information from the active client to the passive client in a manner that is timely and effective for the users and efficient in terms of network and computational resources? Note that there are typically several passive clients and that the roles of active and passive client alternate during interaction. Furthermore, the phrase "timely and effective for the users" is itself a dynamic issue depending not just on the current application, but also on the current context including device characteristics, the user's current task, focus and location.
Figure 1 : Client-data interaction with notification server
It is common for data to be stored centrally in a database or other form of resource server. A notification server is a similar centralised component whose job is to manage this transmission of events. At a broader level a notification service (c.f. server) is the general system of components that enable appropriate notification and may or may not involve a notification server. Notification services will use event or messaging services, and may sometimes be bundled with them, but satisfy a different requirement. Within the context of the project we have made several significant theoretical advances within this area.
A journal paper is in final preparation bringing together the work on separability and pace impedance and experience of their use within Getting-to-Know. Furthermore, a web version of GtK is due to be launched shortly, focused on lower pace interactions and http-based transactions including client polling of the server (the current version of GtK is a Java based server intended for largely synchronous interactions with permanent client-server connections).
Point-of-presence as a Location for Components in Shared Collaborative Applications
In mobile applications shared data and notification will typically need to be mediated by central servers and databases. This means that all feedthrough to users encounters the delays of potentially global network transmission and consumes correspondingly high network resources. For remote interactions between users this is acceptable as they will typically require a lower pace of feedthrough (potentially managed through pace impedance matching). However, as users come together, for example, at a face-to-face meeting, they perceive their mobile devices as 'close' in physical space, but they may still be interacting via very remote servers. A proposed solution is to migrate aspects of interface/data/notification services closer to collaborating mobile users. The analysis of the options and issues arising was reported in  and , but has not been incorporated into current versions of GtK as it requires extensive support within the network infrastructure. While this is not currently practical, emerging all-IP based solutions for wireless networks (as typified by the Cellular-IP proposals) may offer such support and we expect our results in this area to be applicable in such cases.
Issues of Location and Context Awareness and the Nature of Cyberspace
One of the important aspects of mobile applications is that they operate at changing physical locations and in changing physical contexts. Awareness of these contexts is growing due to technologies such as GPS, phone-cell identification, bluetooth and device specific sensors. An early analysis of these issues was reported in  and a more detailed analysis of the nature of context aware applications and specifically location awareness was reported in . This includes various levels of analysis: an informal taxonomic classification of context awareness and location aware characteristics; a formal model of space for location services; and a computational model implemented on top of Limbo, a Linda-based shared tuple space . Developments of this strand were also presented at various keynotes [10,11]. This work was highly praised by referees because the majority of work within ubiquitous computing and context-aware interfaces is very closely tied to specific systems. In contrast, our work takes a more analytic view, building a framework to understand these many disparate systems.
Other UI Issues of Mobile and Related Technologies
As a side-effect of the focused streams within the project, a number of more disparate UI aspects of mobile and related interfaces were studied leading to various keynotes [12,13], journal and other publications [14, 15]. In particular, the work with Liu and Sun (Staffordshire University) and Narasipuram (Hong Kong City), on Norm-based analysis of network agents formed a bridge between the more technical issues and the social and economic impact of a network-connected society. These issues were at the periphery of this project, but were the subject of various invited talks, keynotes and articles [11,16,17,18].