Welcome to this issue of the Proceedings of the ACM on Human-Computer Interaction, bringing together contributions from the community on Engineering Interactive Computing Systems (EICS). The EICS track of the PACM-HCI is the primary venue for research contributions at the intersection of Human-Computer Interaction (HCI) and Software Engineering.

Current design approaches mainly focus on co-design activities for creating (novel) digital artefacts. Less attention is paid on implications of new technologies on people and their experiences. This paper proposes a conceptual framework aimed at describing and supporting systematic and sustained critical co-reflection on artefact use. It employs and expands ideas from design research and user-oriented design approaches to describe sources and nature of critical co-reflection and to discuss appropriate analytical lenses. Experience spaces are introduced as a complementary concept to design spaces. An experience space is a conceptual space emerging from the collaborative creation, manipulation, merging and discarding of experience-related descriptions of technology appropriation. From a critical reflective perspective, designers not only care about rich design spaces with diverse design proposals but also about rich experience spaces displaying diverse appropriation processes and a broad spectrum of users' perspectives on effects of artefact use. The paper suggests that artefact ecologies constitute the elements of experience spaces.

Task models have been used for decades in interactive system design and there are several mature modelling approaches with corresponding tool support. However, in our own work, we have also experienced their limitations, especially in situations where task models are partial ancillary models and not primary artifacts. This was one of the motivations for this paper, which presents a systematic examination of literature to better understand the current place of task models in the continual evolution of user-centred software development practices. While overview work in this domain typically focuses on the analysis of representative task modelling notations and/or tools and relies on foundation papers, we apply a mixed top-down and bottom-up approach to identify relevant themes and trends in the use of task models over the last twenty-years. The paper identifies and discusses dominant patterns of use as well as gaps. It provides a comprehensive framing of both past and present trends in task modelling and supports those who want to incorporate task modelling in their own work. From this we identify areas of research that should receive greater attention in order to address future considerations.

Within the domain of interactive system development and design, particularly for safety-critical systems, there is an inherent tension between formalisms used for software engineering methodologies and the creative aspects of design. In this paper we consider how we might better unify these by way of a framework for design spaces and design artefacts. We present formal definitions for simple and complex design spaces and then describe how they are incorporated into traces. We then discuss how these can be used to reason about considerations such as preservation of requirements and iterative changes throughout the design process and provide some small examples of this.

The persona approach is often treated as a single user-centered design method, but there are variations and adaptations for different design contexts which go beyond local customization. The paper discusses a set of dimensions and success criteria for describing the different persona uses, presenting a new framework. It then specifically investigates personas in the context of end-user development. Professional designers need to consider the design space for potential end-user tools. In addition they need to understand that their users are often designers themselves (they are designer-users), requiring that they also consider the design spaces of their users. Two-level personas are introduced to make professional designers more aware of such nested design spaces. A two-level persona consists of one first-level persona and a set of second-level personas to additionally represent complex designer-user relationships. The effectiveness of the approach is investigated in an exploratory empirical study. The results suggest that two-level personas add value when designing end-user design tools.

This paper introduces higher-order processes as a means to describe complex human-computer interaction systems by integrating different HCI theories. A higher-order process consists of components, which are (sub-)processes themselves. The behaviour of a process results from the behaviour of its components and their interaction. While processes at the lowest level describe the essential units of a system, higher-level processes focus on the way their components interact and produce a new kind of behaviour. Such a behaviour can roughly be characterized as 'more planned'. We further propose a convenient specification formalism for higher-order processes based on partial equations.