This thesis is concerned with the problems that novices have in learning to program: in particular it is concerned with the difficulties experienced by novices learning at a distance, using instructional materials which have been designed especially for novices. One of the major problems for novices is how to link the new information which they encounter with their existing knowledge. Du Boulay, O'Shea and Monk (1981) suggest helping novices to bridge the gap between their existing knowledge and new information by teaching via a conceptual model, which serves to explain the new information in familiar terms. In this thesis the difficulties which novices have when learning to program with the help of a conceptual model were investigated. The curricula and conceptual models of four different programming languages are examined, all of which were designed to teach novices. Du Boulay, O'Shea and Monk (1981) have suggested criteria for analysing conceptual models. It is argued that these criteria, however, do not address the presentation of the conceptual model, and so are insufficient to evaluate them. An additional form of analysis was proposed and used, in addition to the criteria offered by Du Boulay et al. This is a way of describing the conceptual model which distinguishes three views of the conceptual model: state, procedure and function, and which highlights the different aspects which are important for the novice learner by identifying the different kinds of knowledge which are necessary to understand the conceptual model. This analysis of the conceptual models showed that the environments are not as exemplary as the du Boulay et al's criteria suggest, and indicated that three of the environments, SOLO, PT501 and DESMOND, lack a functional representation, and that the fourth, Open Logo, has other different problems. An empirical study was carried out to study the transfer effects of learning two of the languages, a high level and a low level language, sequentially. There was no evidence for such transfer effects. The difficulties novices have in learning the four different languages were also investigated. These studies show that even though the novices were studying environments designed for novices learning at a distance, they did not develop good levels of competence, and the problems they had fall into two main categories: programming and pedagogical. Although the different languages had different aims and curricula, novices had some problems which were common to all or most of the languages. These included understanding flow of control, developing and using programming plans, developing accurate mental models, and in the high level languages, understanding recursion. It is argued that some of these problems are related to the conceptual models. In particular, the difficulties novices had in developing and using plan knowledge, which is one of their main problems, can be explained by the lack of an appropriate functional description in the languages. The subjects' pedagogical problems arose from the relationship between the style and structure of the curriculum, its content, and the subjects themselves. In all the four texts the teaching material is very carefully structured and it is suggested that this may encourage the learner to adopt an over-dependent attitude towards the text, and in some cases, to work at an inappropriate syntactic level. The relationship between the distance learning situation and the novice programmer is discussed, and recommendations are made for improving the curricula used for teaching novices programming.

Indexical programming means programming languages and/or computational models based on indexical logic and possible world semantics. Indexical languages can be considered as the result of enriching conventional languages by allowing constructs to vary according to an implicit context or index. Programs written in an indexical language define the way in which objects vary from context to context, using context switching or indexical operators to combine meanings of objects from different contexts. Based on indexical semantics, in indexical programs, context parallelism means that computations of objects at different contexts can be performed in parallel, and indexical communication means that parallel computation tasks at different contexts communicate with each other through indexical operators provided by the indexical language. The dissertation defines the indexical functional language mLucid--a multidimensional extension of the programming language Lucid proposed by Ashcroft and Wadge. The language enriches the functional language ISWIM by incorporating functional semantics with indexical semantics. The indexical semantics of mLucid is based on the context space consisting of points in an arbitrary n-dimensional integer space. The meanings of objects, called intensions, in mLucid are functions from these contexts to data values. The language provides five primitive indexical operators, origin, next, prev, fby and before to switch context along a designated dimension. The dimensionality of an intension in the indexical semantics of mLucid is defined as the set of dimensions that determines the range of the context space in which the tension varies. An abstract interpretation are defined that maps mLucid expressions to approximations of dimensionalities. Context parallelism and indexical communication in mLucid programs are defined by a semantics-based dependency relation between the values of variables at different contexts. In parallel programming, the context space of mLucid is divided into a time dimension and space dimensions. The time dimension can be used to specify time steps in synchronous computations, or to specify indices of data streams in asynchronous computations. The space dimensions can be used to specify process-to-processor mappings. The dissertation shows that mLucid supports several parallel programming models, including systolic programming, multidimensional dataflow programming, and data parallel programming. / Graduate

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Intermittent computer users, generally unable to program, often need more flexibility than current applications can offer them. A first step to providing such flexibility is to consider the psychological issues underlying the users' needs and the communication of these needs. This thesis does this by exploring the possibility of "Automatic Programming" where users communicate their requirements and the computer generates programs to meet them.

A necklace is a representative of an equivalence class of k-ary strings under rotation. Efficient algorithms for generating (i.e., listing) necklaces have been known for some time. Many applications, however, require a restricted class of necklaces for which no efficient generation algorithm previously existed. This dissertation addresses this problem by developing fast algorithms to generate the following restricted classes of necklaces: (a) unlabeled necklaces, (b) fixed density necklaces, (c) necklaces where the number of each alphabet symbol is fixed, (d) chord diagrams, (e) necklaces which avoid a particular Lyndon substring, and (f) bracelets. An analysis for each algorithm (a), (b), (e), and (f) shows that the amount of computation is proportional to the number of strings produced. Experimental results give a strong indication that the algorithms for (c) and (d) also achieve this time bound. In addition, a new derivation of the known formula for counting chord diagrams is presented, along with a linear time algorithm to generate a basis for the n-th homogeneous component of the free Lie algebra. / Graduate

In an ever faster changing environment, software developers not only need agile methods, but also agile programming paradigms and tools. A paradigm shift towards declarative programming has begun; a clear indication of this is Microsoft's substantial investment in functional programming. Moreover, several attempts have been made to enable visual programming. We believe that software development is ready for a new paradigm which goes beyond any existing declarative paradigm: visual compositional-relational programming. Compositional-relational programming (CRP) is a purely declarative paradigm -- making it suitable for a visual representation. All procedural aspects -- including the increasingly important issue of parallelization -- are removed from the programmer's consideration and handled in the underlying implementation. The foundation for CRP is a theory of higher-order combinatory logic programming developed by Hamfelt and Nilsson in the 1990's. This thesis proposes a model for visualizing compositional-relational programming. We show that the diagrams are isomorphic with the programs represented in textual form. Furthermore, we show that the model can be used to automatically generate code from diagrams, thus paving the way for a visual integrated development environment for CRP, where programming is performed by combining visual objects in a drag-and-drop fashion. At present, we implement CRP using Prolog. However, in future we foresee an implementation directly on one of the major object-oriented frameworks, e.g. the .NET platform, with the aim to finally launch relational programming into large-scale systems development.

The work in this thesis covers mainly the design and analysis of many important Non-Numerical Parallel Algorithms that run on MIMD type Parallel Computer Systems (PCSs), in particular the NEPTUNE and the SEQUENT BALANCE 8000 PCSs available at Loughborough University of Technology.