In particular, the fact that most users are only now beginning to experience the ubicomp vision and integrate this new, unique class of technology into their work practices suggests that another change in focus may be on the horizon: “[T]he shift from user-centered design to context-based design corresponds with recent developments in pervasive, ubiquitous computing networks and in the appliances that connect with them, which are radically changing our relationships with personal computing devices” (Gay & Hembrooke, 2003)

Activities also span place; that is, it is common for work to take place outside of the immediate office environment. However, current office technologies sometimes present a very different view of information across different physical and virtual settings.

The idea that activities may exist at different levels of granularity is not a new one. Boer, van Baalen & Kumar (2002) provide a model explaining how an activity at one level of analysis may be modeled as an action—a component of an activity—at another. This holds true for individual users, as in the example provided above, but is even more pronounced when a single activity is viewed from multiple participants’ perspectives.

Additionally, activities need to be represented in such a way that their contents can be shared, with the caveats that individual participants in an activity may have very different perceptions of the activity, they may bring different resources to play over the course of the activity, and, particularly for large activities in which many individual users participate, users themselves may come and go over the life of the activity.

Recognizing the mediating role of the digital work environment in enabling users to meaningfully collaborate is a critical step to ensuring the success of these systems.

User studies and intuition both suggest that the activities that a knowledge worker engages in change—sometimes dramatically—over time. Projects and milestones come and go, and the tools and information resources used within an activity often change over time as well. Furthermore, activities completed in the past and their outcomes often impact activities in the present, and ongoing activities will, in turn, affect activities that will be undertaken in the future. Capturing activity over the course of time has long been a problem for desktop computing.

Supporting the multifaceted aspects of activity in a ubicomp environment becomes a much more complex proposition. If activity is to be used as a unifying organizational structure across a wide variety of devices such as traditional desktop and laptop computers, PDAs, mobile telephones, personal-server style devices (Want et al., 2002), shared public displays, etc., then those devices must all be able to share a common set of activity representations and use those representations as the organizational cornerstone for the user experience they provide. Additionally, the activity representations must be versatile enough to encompass the kinds of work for which each of these kinds of devices are used

The challenges exist due in large part to the inherent complexity of human activity, the technical affordances of the computing tools used in work practice, and the nature of (and culture surrounding) knowledge work.

We describe five challenges for matching computation to activity. These are: •Activities are multifaceted, involving a heterogeneous collection of work artifacts; •Activities are dynamic, emphasizing the continuation and evolution of work artifacts in contrast to closure and archiving; •Activities are collaborative, in the creation, communication, and dissemination of work artifacts; •Activities exist at different levels of granularity, due to varying durations, complexity and ownership; and •Activities exist across places, including physical boundaries, virtual boundaries of information security and access, and fixed and mobile settings.