Activity theory has gained increasing popularity as a tool for the design of interactive systems. Its central idea is that user actions can only be fully understood when analyzed within the context of motive-driven activities. However, this context is currently only partially explicit in existing models; e.g. the well-known model by Engestrom promotes social aspects of context, but does not make the physical and technical environment --- relevant aspects for interactive systems design --- explicit. We present a model that incorporates the social, physical and technical context of activities. This model supports designers and developers in understanding users, their activities and the respective contexts, and allows deriving requirements for the design process directly from the model. We believe this will prove especially helpful when designing for novel devices and multi-user scenarios. We illustrate the practical use of our model with examples from two domains: composition of IT services and co-located collaborative modeling.

Employees are increasingly participating in business processes using mobile devices. Often, this is supported by a mobile web application, which accesses various web services in the back-end. The high latency of the mobile network (e.g., EDGE) is perceived by the user each time a web service is called, in addition to the time needed to invoke the service itself. This high latency may lead to low usability, low acceptance rate, and finally compromises the overall process quality. To reduce the latency perceived by the user, we present a caching architecture for web services and an adaptive prefetching algorithm. The key characteristics of our approach are the compatibility with major mobile browsers and the independence of the caching proxy from the front-end application and the back-end services. We evaluate our approach on realistic traces of web service calls in an IT service management scenario. The traces were generated from handling real incidents according to the ITIL (ISO 20000) processes. The results confirm that using our approach, the latency perceived by the user is reduced by 24%.

Network latency is one of the most critical factors for the usability of mobile SOA applications. This paper introduces prefetching and caching enhancements for an existing SOA framework for mobile applications to reduce the user perceived latency. Latency reduction is achieved by proactively sending data to the mobile device that could most likely be requested at a later time. This additional data is piggybacked onto responses to actual requests and injected into a client side cache, so that it can be used without an additional connection. The prefetching is done automatically using a sequence prediction algorithm. The benefit of prefetching and caching enhancements were evaluated for different network settings and a reduction of user perceived latency of up to 31% was found in a typical scenario. In contrast to other prefetching solutions, our piggybacking approach also allows to significantly increase battery lifetime of the mobile device.