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This paper builds on a technical report written by Carl Hewitt and Henry Baker called "Actors and Continuous Functionals". What is called a "goal-oriented activity" in that paper will be referred to in this paper as a "transaction". The word "transaction" brings to mind an object closer in function to what we wish to present than does the word "activity". This memo, therefore, presents the definitions of a reply and a transaction as given in Hewitt and Baker's paper and points out some discrepancies in their definitions. That is, that the properties of transactions and replies as they were defined did not correspond with our intuitions, and thus the definitions should be changed. The issues of what should constitute a transaction are discussed, and a new definition is presented which eliminates the discrepancies caused by the original definitions. Some properties of the newly defined transactions are discussed, and it is shown that the results of Hewitt and Baker's paper still hold given the new definitions.

The demand for performance and resources that is placed on the system is dictated by the application alone in non-interactive environments, and by a combination of application and user interactions in interactive environments. Understanding user interaction can provide valuable information about which resources will be needed ahead of time. This leads to performance optimizations such as better resource allocations for applications that can utilize a given resource more productively, and transitioning devices to a more appropriate energy performance state before the demand arrives. The challenge is to provide a performance/energy schedule that best matches the task at hand, since keeping the device in one performance level is not energy efficient due to the continually changing demand placed on the device. This dissertation addresses the challenge of designing energy efficient systems by examining the role of user interaction in energy consumption and in providing an energy-performance schedule that adequately accommodates user demand. It is shown that system performance can be tailored to a user's pattern of interaction and it's energy-performance schedule optimized.First, a detailed design of context capture systems in Linux's X-Window System is presented with an evaluation of the associated storage and computation overheads. Due to the overall low complexity of the application window representations, the overheads of computing interaction identifiers and storing a secondary representation of the application interface within the context capture system are likewise low. Additionally, a Microsoft Windows-based context capture system leveraging the Active Accessibility framework is discussed and applied to improving the navigation of cascading pull-down menus.Secondly, this dissertation addresses the application of interaction capture in energy and delay management of Wireless Network Interface Controllers/Cards (WNICs) and hard drives. The Interaction Aware Prediction (IAP) system for WNICs is evaluated showing that the available power modes can be effectively managed to provide energy efficiency while maintaining performance. Similarly, the Interaction Aware Spin-up Prediction (IASP) uses interaction awareness to reduce or eliminate the interactive delays associated with aggressive hard disk energy management.

Faceted browsing (also called faceted search or faceted navigation) is an exploratory search model where facets assist in the interactive navigation of search results. Facets are attributes that have been assigned to describe resources being explored; a faceted taxonomy is a collection of facets provided by the interface and is often organized as sets, hierarchies, or graphs. Faceted browsing has become ubiquitous with modern digital libraries and online search engines, yet the process is still difficult to abstractly model in a manner that supports the development of interoperable and reusable interfaces. We propose category theory as a theoretical foundation for faceted browsing and demonstrate how the interactive process can be mathematically abstracted in order to support the development of reusable and interoperable faceted systems. Existing efforts in facet modeling are based upon set theory, formal concept analysis, and light-weight ontologies, but in many regards they are implementations of faceted browsing rather than a specification of the basic, underlying structures and interactions. We will demonstrate that category theory allows us to specify faceted objects and study the relationships and interactions within a faceted browsing system. Resulting implementations can then be constructed through a category-theoretic lens using these models, allowing abstract comparison and communication that naturally support interoperability and reuse. In this context, reuse and interoperability are at two levels: between discrete systems and within a single system. Our model works at both levels by leveraging category theory as a common language for representation and computation. We will establish facets and faceted taxonomies as categories and will demonstrate how the computational elements of category theory, including products, merges, pushouts, and pullbacks, extend the usefulness of our model. More specifically, we demonstrate that categorical constructions such as the pullback and pushout operations can help organize and reorganize facets; these operations in particular can produce faceted views containing relationships not found in the original source taxonomy. We show how our category-theoretic model of facets relates to database schemas and discuss how this relationship assists in implementing the abstractions presented. We give examples of interactive interfaces from the biomedical domain to help illustrate how our abstractions relate to real-world requirements while enabling systematic reuse and interoperability. We introduce DELVE (Document ExpLoration and Visualization Engine), our framework for developing interactive visualizations as modular Web-applications in order to assist researchers with exploratory literature search. We show how facets relate to and control visualizations; we give three examples of text visualizations that either contain or interact with facets. We show how each of these visualizations can be represented with our model and demonstrate how our model directly informs implementation. With our general framework for communicating consistently about facets at a high level of abstraction, we enable the construction of interoperable interfaces and enable the intelligent reuse of both existing and future efforts.

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We are primarily concerned with interactive systems whose behaviour is highly reliant on end user activity. A framework for describing and synthesising such systems is developed. This consists of a functional description of the capabilities of a system together with a means of expressing its desired 'usability'. Previous work in this area has concentrated on capturing 'usability properties' in discrete mathematical models. We propose notations for describing systems in a 'requirements' style and a 'specification' style. The requirements style is based on a simple temporal logic and the specification style is based on Lamport's Temporal Logic of Actions (TLA) [74]. System functionality is specified as a collection of 'reactions', the temporal composition of which define the behaviour of the system. By observing and analysing interactions it is possible to determine how 'well' a user performs a given task. We argue that a 'usable' system is one that encourages users to perform their tasks efficiently (i.e. to consistently perform their tasks well) hence a system in which users perform their tasks well in a consistent manner is likely to be a usable system. The use of a given functionality linked with different user interfaces then gives a means by which interfaces (and other aspects) can be compared and suggests how they might be harnessed to bias system use so as to encourage the desired user behaviour. Normalising across different users anq different tasks moves us away from the discrete nature of reactions and hence to comfortably describe the use of a system we employ probabilistic rather than discrete mathematics. We illustrate that framework with worked examples and propose an agenda for further work.

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