Tree transformations are common in applications such as program rewriting in compilers. Using a series of simple transformations to build a more complex system can make the resulting software easier to understand, maintain, and reason about. Fusion strategies for combining such successive tree transformations promote this modularity, whilst mitigating the performance impact from increased numbers of tree traversals. However, it is important to ensure that fused transformations still perform their intended tasks. Existing approaches to fusing tree transformations tend to take an informal approach to soundness, or be too restrictive to consider the kind of transformations needed in a compiler. We use postconditions to define a more useful formal notion of successful fusion, namely postcondition-preserving fusion. We also present criteria that are sufficient to ensure postcondition-preservation and facilitate modular reasoning about the success of fusion.

Data relating to university students' engagement is collected internationally via several large-scale student surveys such as the North American National Survey of Student Engagement. The instruments employed measure the extent to which students put their efforts into activities associated with effective learning. It is claimed that these process measures act as a reliable proxy for student attainment, and there appears to be some evidence to support this. So far, there has been little work done to investigate engagement instruments and the data they generate from a subject perspective. This paper brings together data relating to Computer Science (CS) across the range of major engagement surveys. The results of this meta-analysis appear to indicate that CS rates lower than average on many of the major engagement benchmarks and in some cases, considerably so. Particular benchmark areas giving cause for concern are identified prompting questions as to how these results should be interpreted and used in the context of a particular learning domain. We also critique aspects of the surveys themselves, suggesting that further research is needed to better understand their appropriateness for individual subjects or for groups of subjects with shared traits. The paper argues that more qualitative data is required and that other measures (such as student expectation and some subject-specific measures) are needed for a greater understanding of the CS student experience.

Many bacteria exhibit multicellular behaviour, with individuals within a colony coordinating their actions for communal benefit. One example of complex multicellular phenotypes is myxobacterial fruiting body formation, where thousands of cells aggregate into large three-dimensional structures, within which sporulation occurs. Here we describe a novel theoretical model, which uses Monte Carlo dynamics to simulate and explain multicellular development. The model captures multiple behaviours observed during fruiting, including the spontaneous formation of aggregation centres and the formation and dissolution of fruiting bodies. We show that a small number of physical properties in the model is sufficient to explain the most frequently documented population-level behaviours observed during development in Myxococcus xanthus.

This article describes an approach to program optimization based on transformations, where temporal logic is used to specify side conditions, and strategies are created which expand the repertoire of transformations and provide a suitable level of abstraction. We demonstrate the power of this approach by developing a set of optimizations using our transformation language and showing how the transformations can be converted into a form which makes it easier to apply them, while maintaining trust in the resulting optimizing steps. The approach is illustrated through a transformational case study where we apply several optimizations to a small program.

Message Sequence Charts (MSCs) are a graphical language for description of scenarios in terms of message exchanges between communicating components in a distributed environment. The language is popular in capturing system requirements in the design of reactive systems and communication protocols. In this paper, we review a design anomaly, called race conditions, in an MSC specification and present a few drawbacks with the current solution. We propose a new approach to correcting race conditions, and the limitation of this approach is also discussed.