Christof Lutteroth

Realistic load testing of Web applications

We present a new approach for performing load testing of Web applications by simulating realistic user behaviour with stochastic form-oriented analysis models. Realism in the simulation of user behaviour is necessary in order to achieve valid testing results. In contrast to many other user models, Web site navigation and time delay are modelled stochastically. The models can be constructed from sample data and can take into account effects of session history on user behaviour and the existence of different categories of users. The approach is implemented in an existing architecture modelling and performance evaluation tool and is integrated with existing methods for forward and reverse engineering

Domain Specific High-Level Constraints for User Interface Layout

We present the Auckland Layout Model (ALM), a constraint-based technique for specifying 2D layout as it is used for arranging the controls in a graphical user interface (GUI). Most GUI frameworks offer layout managers that are basically adjustable tables; often adjacent table cells can be merged. In the ALM, the focus switches from the table cells to vertical and horizontal tabulators between the cells. On the lowest level of abstraction, the model applies linear constraints, and an optimal layout is calculated using linear programming. However, bare linear programming makes layout specification cumbersome and unintuitive, especially for GUI domain experts who are often not used to such mathematical formalisms. In order to improve the usability of the model, ALM offers several other layers of abstraction that make it possible to define common GUI layout more easily. In the domain of user interfaces it is important that specifications are not over-constrained, therefore ALM introduces soft constraints, which are automatically translated to appropriate hard linear constraints and terms in the objective function. GUIs are usually composed of rectangular areas containing controls, therefore ALM offers an abstraction for such areas. Dynamic resizing behavior is very important for GUIs, hence areas have domain-specific parameters specifying their minimum, maximum and preferred sizes. From such definitions, hard and soft constraints are automatically derived. A third level of abstraction allows designers to arrange GUIs in a tabular fashion, using abstractions for columns and rows, which offer additional parameters for ordering and alignment. Row and column definitions are used to automatically generate definitions from lower levels of abstraction, such as hard and soft constraints and areas. Specifications from all levels of abstraction can be consistently combined, offering GUI developers a rich set of tools that is much closer to their needs than pure linear constraints. Incremental computation of solutions makes constraint solving fast enough for near real-time use.

A source code independent reverse engineering tool for dynamic Web sites

This paper describes a tool for black box reverse engineering of Web applications that reconstructs analysis models based on the concepts of form-oriented analysis. Recovering such models is motivated by requirements engineering and load testing. In particular, the paper addresses the problem of screen classification and discusses its conceptual underpinnings.

A quantitative quality model for gesture based user interfaces

The technological advancement of computers and cameras over the past few years has given us the ability to control objects without touching them. There have already been a number of attempts at producing gesture based applications, but many of them have usability issues. This paper proposes a model that reflects the usability of a gesture based interface, in order to evaluate and improve a gesture-controlled system. The model defines four levels of abstraction, with the higher levels based on the lower ones. The levels of the model allow us to propose quantitative notions for 1) the parameters affecting the quality of individual gestures, 2) the overall quality of a gesture, 3) the quality of particular functionalities, or use cases, in a system, and 4) the overall quality of a system. The model was evaluated using an existing gesture-based interface for a popular media center application.

A type system for reflective program generators

In this paper we describe a type system for a generative mechanism that generalizes the concept of generic types by combining it with a controlled form of reflection. This mechanism makes many code generation tasks possible for which generic types alone would be insufficient. The power of code generation features are carefully balanced with their safety, so that we are able to perform static type checks on generator code. This leads to a generalized notion of type safety for generators.

Framework for Healthcare4Life : a ubiquitous patient-centric telehealth system

Health care systems in many developed countries are rapidly approaching a crisis point. The reasons are an aging population, a shrinking number of workers, health care costs increasing faster than the economy, expensive new treatment options, poor public finances, and the reducing pool of health care professionals. The problem is compounded by the fact that elderly are more often affected by chronic diseases which require ongoing, often expensive, treatment. Telehealth and telecare applications are rapidly gaining in popularity because of their promise to use existing health care resources more effectively and hence to lower costs. However, usage is limited by a design often centered around the requirements of the clinical user, healthcare provider, and the equipment vendor. Many existing systems suffer from high initial costs, cannot be extended by third parties, require extra costs to add new functionalities, and are designed to create a continuing revenue source for the vendor. Furthermore the systems are usually designed to manage diseases rather than prevent them, and do not address the social and psychological needs of the patient. In this paper we critically analyse existing consumer health informatics systems and propose a framework for overcoming the identified shortcomings. The proposed system is ubiquitous, extendable by third parties, contains social aspects, and puts the user in control. Evidence from related research suggests that the design will increase motivation and participation, encourage family and social support, and improve the recording of health parameters by reducing user resistance.

Designing a web-based telehealth system for elderly people: An interview study in New Zealand

Designing healthcare systems for the elderly is a challenging endeavour. Telehealth systems are gaining popularity among elderly users, but such applications are mostly doctor-centric and are predominantly used for managing and/or treating diseases instead of preventing them. They do little to motivate patients to change their lifestyle and proactively manage their health. To address these shortcomings, we propose a web-based telehealth system, which uses Web 2.0 technologies in order to add social support and user defined content. In this study, we determine the functional and interface requirements of the system by conducting open individual semi-structured interviews with eight elderly people of age range 60 to 87. A paper prototype and three interfaces of existing Web 2.0 health applications were used to determine the optimum user interface design of the system. A qualitative content analysis was used to evaluate the responses. Overall, the respondents were positive about the idea of using the web to manage their healthcare from home and made several suggestions such as including applications to manage their diet, physiotherapy exercises to improve their health conditions and simple network games to reduce loneliness.

Mobile games for elderly healthcare

The past decade has seen much progress of computer-based tools for health care management. At the same time, mobile devices have become ubiquitous and offer new and interesting means of interaction. In this project we investigate the use of mobile games for home based elderly care. We concentrate on rehabilitation exercises involving the arms joints and muscles, employing accelerometers to measure and give feedback to players. We discuss the design and evaluation of two such games, Bowling and Penguin Toss. A pilot study suggests that the two games are an effective means for performing range of motion exercises, but that usability depends a lot on the fluency of the interaction during the game. A purely gesture based gameplay seems to be more natural and more enjoyable for the players.

Constraint solving for beautiful user interfaces: how solving strategies support layout aesthetics

Layout managers provide an automatic way to place controls in a graphical user interface (GUI). With the wide distribution of fully GUI-enabled smartphones, as well as very large or even multiple personal desktop monitors, the logical size of commonly used GUIs has become highly variable. A layout manager can cope with different size requirements and rearrange controls depending on the new layout size. However, there has been no research on how the distribution of additional or lacking space, to all controls in the layout, effects aesthetics. Much of the previous research focuses on discrete changes to layout. This includes changing the layout elements [15], or swapping around layout elements [7]. In this paper we focus strictly on the optimization of resizing of GUI components, and in this area we focus on rather subtle changes. This paper describes and compares strategies to distribute available space in a visual appealing way. All strategies are modeled with a constraint-based layout manager, since such a layout manager can be used to describe a wide range of layouts. Some aesthetic problems of constraint based layout managers have been identified and solutions have been provided. In a user evaluation three solving strategies, equal distribution, weighted distribution and a minimal deviation, have been compared. As a result, the minimal deviation approach seems to be a good strategy for large and small layout sizes. The minimal deviation and the equal distribution strategy is best at large layout sizes while the weighted distribution approach seems to perform better at small layout sizes. Furthermore, the evaluation shows that layouts with a high degree of symmetry are clearly preferred by the users.

The Auckland layout editor: an improved GUI layout specification process

Constraint-based layout managers are more powerful than the common grid, grid-bag, and group layout managers. However, they are also more complex and come with potential problems such as over-constrained specifications and overlap in a GUI. Current GUI builders have little support for layout constraints, and it is not clear how such constraints can be made easily accessible to GUI designers. We will demonstrate a GUI builder -- the Auckland Layout Editor (ALE) -- that addresses these challenges, by allowing GUI designers to specify constraint-based layouts using only simple mouse operations. ALE guarantees that all operations lead to sound specifications, making sure that the layout is solvable and non-overlapping. To achieve the latter, we propose an algorithm that automatically generates the missing constraints that are necessary to keep a layout non-overlapping. Todays applications need to run on multiple devices with different screen sizes. For this a layout must have a good appearance at different sizes. To aid the designer in creating a layout with good resizing behavior, we propose a novel automatic layout preview, which displays the layout at its minimal and at an enlarged size chosen to visualize layout problems directly.