Combining type checking with model checking for system verification

Type checking is widely used in mainstream programming languages to detect programming errors at compile time. Model checking is gaining popularity as an automated technique for systematically analyzing behaviors of systems. My research focuses on combining these two software verification techniques synergically into one platform for the creation of correct models for software designs. This thesis describes two modeling languages ATS/PML and ATS/Veri that inherit the advanced type system from an existing programming language ATS, in which both dependent types of Dependent ML style and linear types are supported. A detailed discussion is given for the usage of advanced types to detect modeling errors at the stage of model construction. Going further, various modeling primitives with well-designed types are introduced into my modeling languages to facilitate a synergic combination of type checking with model checking. The semantics of ATS/PML is designed to be directly rooted in a well-known modeling language PROMELA. Rules for translation from ATS/PML to PROMELA are designed and a compiler is developed accordingly so that the SPIN model checker can be readily employed to perform checking on models constructed in ATS/PML. ATS/Veri is designed to be a modeling language, which allows a programmer to construct models for real-world multi-threaded software applications in the same way as writing a functional program with support for synchronization, communication, and scheduling among threads. Semantics of ATS/Veri is formally defined for the development of corresponding model checkers and a compiler is built to translate ATS/Veri into CSP# and exploit the state-of-the-art verification platform PAT for model checking ATS/Veri models. The correctness of such a transformational approach is illustrated based on the semantics of ATS/Veri and CSP#. In summary, the primary contribution of this thesis lies in the creation of a family of modeling languages with highly expressive types for modeling concurrent software systems as well as the related platform supporting verification via model checking. As such, we can combine type checking and model checking synergically to ensure software correctness with high confidence

Listening and Normative Entanglement: A Pragmatic Foundation for Conversational Ethics

People care very much about being listened to. In everyday talk, we make moral-sounding judgements of people as listeners: praising a doctor who listens well even if she does not have a ready solution, or blaming a boss who does not listen even if the employee manages to get her situation addressed. In this sense, listening is a normative behaviour: that is, we ought to be good listeners. Whilst several disciplines have addressed the normative importance of interpersonal listening—particularly in sociology, psychology, media and culture studies—analytic philosophy does not have a framework for dealing with listening as a normative interpersonal behaviour. Listening usually gets reduced mere speech-parsing (in philosophy of language), or into a matter of belief and trust in the testimony of credible knowers (in social epistemology). My preliminary task is to analyse why this reductive view is taken for granted in the discipline; to diagnose the problem behind the reduction and propose a more useful alternative approach. The central task of my work is to give an account of listening which captures its distinctively normative quality as an interpersonal way of relating to someone: one listens not because the speaker is an epistemic expert, but because the speaker is a person, worthy of recognition and care. I created a framework which accomplishes this by deploying the conceptual resources of conversation sociology and psycholinguistics, in counterpoint to the standing philosophical work on the ethics and politics of speech and silencing, to create a practical ethics of listening to people

The influence of instructional approach on the reading strategies of beginning readers

There are a number of models of reading development which propose that reading develops in a set sequence of stages (e.g. Frith 1985, Marsh et al 1981), and that each child must pass through one stage before it can move onto the next. It is been pointed out that these models very rarely take into account external factors such as the method of instruction that the children receive (Stuart and Coltheart 1988, Goswami and Bryant 1990) and what effect such factors would have on progression through the stages. This study investigated how the factor of instruction influenced how children read. Young children taught by two different methods were studied. Scottish five and six year olds taught by a phonics method, where they were shown the correspondences between letter segments and their sounds, were compared with New Zealand children of the same age taught by a language experience approach. Samples were matched for reading age, chronological age, time at school, vocabulary knowledge and digit span. Error analyses of responses to single words showed a marked divergence in reading strategies. The Scottish children were much more likely to attempt to read unfamiliar words, whereas the New Zealand children often failed to attempt to read items they did not know. The errors the Scottish children made were also qualitatively different to those of the New Zealand children. The Scottish children were better at pronouncing nonwords and were more advanced in spelling performance. The Scottish children were also superior at a test of simple phonological segmentation. They also produced a word length effect when reading words. The New Zealanders, however, were better at pronouncing irregular words and were faster readers, especially with familiar classroom words. They did not produce a word length effect even when words were distorted. Overall the Scottish children showed more evidence of a grapheme to phoneme conversion strategy, which in turn was correlated with good reading performance. The New Zealanders displayed signs of a more visual approach to reading. There was some overlap between the national groups particularly regarding the prevalence of errors incorporating beginning and end letters. The older children in each national group also showed a greater convergence of strategy use than the younger readers. This work therefore has implications for the efficacy models of reading, such as Frith's (1985). Matched groups of children should display the same reading strategies if reading skill is accomplished in universal stages, in this study they do not. Future models of reading development will need to take into consideration how the child is taught to read

Construction incrémentale de spécifications de systèmes critiques intégrant des procédures de vérification

Cette thèse porte sur l'aide à la construction de machines d'états UML de systèmes réactifs. Elle vise à définir un cadre théorique et pragmatique pour mettre en œuvre une approche incrémentale caractérisée par une succession de phases de construction, évaluation et correction de modèles. Ce cadre offre des moyens de vérifier si un nouveau modèle est conforme à ceux définis durant les étapes précédentes sans avoir à demander une description explicite des propriétés à vérifier. Afin de pouvoir analyser les machines d'états, nous leur associons une sémantique LTS ce qui nous a conduit à définir une procédure de transformation automatique de machines d'états en LTS. Dans un premier temps, nous avons défini et implanté des techniques de vérification de relations de conformité de LTS (red, ext, conf, et confrestr). Dans un second temps, nous nous sommes intéressés à la définition d'un cadre de construction incrémentale dans lequel plusieurs stratégies de développement peuvent être mises en œuvre en s'assurant que le modèle final élaboré sera une implantation conforme à la spécification initiale. Ces stratégies reposent sur des combinaisons de raffinements qui peuvent être de deux types : le raffinement vertical pour éliminer l'indéterminisme et ajouter des détails ; le raffinement horizontal pour ajouter de nouvelles fonctionnalités sans ajouter d'indéterminisme. Enfin, nous transposons la problématique de construction incrémentale d'une machine d'états à la construction d'architectures dont les composants sont des machines d'états. Des conditions sont définies pour assurer la conformité entre des architectures dans le cas de la substitution de composants.This thesis focuses on supporting construction of UML state machines of reactive systems. It aims at developing a theoretic and pragmatic framework to implement an incremental approach characterized by a succession of construction, evaluation and correction of models. This framework provides the means to verify whether a new model is consistent with those defined in the previous steps without requiring an explicit description of the properties to be verified. To analyze the state machines, we associated with them a LTS semantics which led us to define a procedure for automatic transformation of state machines in LTS. Initially, we have defined and implemented verification technique of conformance relations on LTS (red, ext, conf and confrestr). In a second step, we have defined a framework for incremental construction in which several development strategies can be implemented ensuring that the final developed model will be an implementation consistent with the initial specification. These strategies are based on combination of refinements that may be of two types: vertical refinement to eliminate nondeterminism and add details, and the horizontal refinement to add new features without adding nondeterminism. Finally, we transpose the problem of incremental construction of state machines to the construction of architectures whose components are state machines. Conditions are defined to ensure conformance between architectures in the case of substitution of components

Doctor of Philosophy

dissertationEvents are one important type of information throughout text. Event extraction is an information extraction (IE) task that involves identifying entities and objects (mainly noun phrases) that represent important roles in events of a particular type. However, the extraction performance of current event extraction systems is limited because they mainly consider local context (mostly isolated sentences) when making each extraction decision. My research aims to improve both coverage and accuracy of event extraction performance by explicitly identifying event contexts before extracting individual facts. First, I introduce new event extraction architectures that incorporate discourse information across a document to seek out and validate pieces of event descriptions within the document. TIER is a multilayered event extraction architecture that performs text analysis at multiple granularities to progressively \zoom in" on relevant event information. LINKER is a unied discourse-guided approach that includes a structured sentence classier to sequentially read a story and determine which sentences contain event information based on both the local and preceding contexts. Experimental results on two distinct event domains show that compared to previous event extraction systems, TIER can nd more event information while maintaining a good extraction accuracy, and LINKER can further improve extraction accuracy. Finding documents that describe a specic type of event is also highly challenging because of the wide variety and ambiguity of event expressions. In this dissertation, I present the multifaceted event recognition approach that uses event dening characteristics (facets), in addition to event expressions, to eectively resolve the complexity of event descriptions. I also present a novel bootstrapping algorithm to automatically learn event expressions as well as facets of events, which requires minimal human supervision. Experimental results show that the multifaceted event recognition approach can eectively identify documents that describe a particular type of event and make event extraction systems more precise