Towards Practical Graph-Based Verification for an Object-Oriented Concurrency Model

To harness the power of multi-core and distributed platforms, and to make the development of concurrent software more accessible to software engineers, different object-oriented concurrency models such as SCOOP have been proposed. Despite the practical importance of analysing SCOOP programs, there are currently no general verification approaches that operate directly on program code without additional annotations. One reason for this is the multitude of partially conflicting semantic formalisations for SCOOP (either in theory or by-implementation). Here, we propose a simple graph transformation system (GTS) based run-time semantics for SCOOP that grasps the most common features of all known semantics of the language. This run-time model is implemented in the state-of-the-art GTS tool GROOVE, which allows us to simulate, analyse, and verify a subset of SCOOP programs with respect to deadlocks and other behavioural properties. Besides proposing the first approach to verify SCOOP programs by automatic translation to GTS, we also highlight our experiences of applying GTS (and especially GROOVE) for specifying semantics in the form of a run-time model, which should be transferable to GTS models for other concurrent languages and libraries.Comment: In Proceedings GaM 2015, arXiv:1504.0244

Canonical Algebraic Generators in Automata Learning

Many methods for the verification of complex computer systems require the existence of a tractable mathematical abstraction of the system, often in the form of an automaton. In reality, however, such a model is hard to come up with, in particular manually. Automata learning is a technique that can automatically infer an automaton model from a system -- by observing its behaviour. The majority of automata learning algorithms is based on the so-called L* algorithm. The acceptor learned by L* has an important property: it is canonical, in the sense that, it is, up to isomorphism, the unique deterministic finite automaton of minimal size accepting a given regular language. Establishing a similar result for other classes of acceptors, often with side-effects, is of great practical importance. Non-deterministic finite automata, for instance, can be exponentially more succinct than deterministic ones, allowing verification to scale. Unfortunately, identifying a canonical size-minimal non-deterministic acceptor of a given regular language is in general not possible: it can happen that a regular language is accepted by two non-isomorphic non-deterministic finite automata of minimal size. In particular, it thus is unclear which one of the automata should be targeted by a learning algorithm. In this thesis, we further explore the issue and identify (sub-)classes of acceptors that admit canonical size-minimal representatives. In more detail, the contributions of this thesis are three-fold. First, we expand the automata (learning) theory of Guarded Kleene Algebra with Tests (GKAT), an efficiently decidable logic expressive enough to model simple imperative programs. In particular, we present GL*, an algorithm that learns the unique size-minimal GKAT automaton for a given deterministic language, and prove that GL* is more efficient than an existing variation of L*. We implement both algorithms in OCaml, and compare them on example programs. Second, we present a category-theoretical framework based on generators, bialgebras, and distributive laws, which identifies, for a wide class of automata with side-effects in a monad, canonical target models for automata learning. Apart from recovering examples from the literature, we discover a new canonical acceptor of regular languages, and present a unifying minimality result. Finally, we show that the construction underlying our framework is an instance of a more general theory. First, we see that deriving a minimal bialgebra from a minimal coalgebra can be realized by applying a monad on a category of subobjects with respect to an epi-mono factorisation system. Second, we explore the abstract theory of generators and bases for algebras over a monad: we discuss bases for bialgebras, the product of bases, generalise the representation theory of linear maps, and compare our ideas to a coalgebra-based approach

Distributed computing practice for large-scale science and engineering applications

It is generally accepted that the ability to develop large-scale distributed applications has lagged seriously behind other developments in cyberinfrastructure. In this paper, we provide insight into how such applications have been developed and an understanding of why developing applications for distributed infrastructure is hard. Our approach is unique in the sense that it is centered around half a dozen existing scientific applications; we posit that these scientific applications are representative of the characteristics, requirements, as well as the challenges of the bulk of current distributed applications on production cyberinfrastructure (such as the US TeraGrid). We provide a novel and comprehensive analysis of such distributed scientific applications. Specifically, we survey existing models and methods for large-scale distributed applications and identify commonalities, recurring structures, patterns and abstractions. We find that there are many ad hoc solutions employed to develop and execute distributed applications, which result in a lack of generality and the inability of distributed applications to be extensible and independent of infrastructure details. In our analysis, we introduce the notion of application vectors: a novel way of understanding the structure of distributed applications. Important contributions of this paper include identifying patterns that are derived from a wide range of real distributed applications, as well as an integrated approach to analyzing applications, programming systems and patterns, resulting in the ability to provide a critical assessment of the current practice of developing, deploying and executing distributed applications. Gaps and omissions in the state of the art are identified, and directions for future research are outlined

A Descriptive Analysis of Language and Cognition in Congenitally Blind Children Ages 3 Through 9

Purpose This study was designed as an investigation of the semantic and cognitive functioning of congenitally blind children within the age range of 3 through 9 years, to help fill the gap in the existing research concerning the early development of the visually handicapped. Delays in cognitive development among school age congenitally blind children have been attributed to the limitations imposed by blindness on mobility and interaction with objects and events in the environment. It has been assumed that blind children must rely on less efficient sensory perception and discrimination processes resulting in a conceptualization of the world which may be inconsistent, incomplete, or significantly different from that of sighted children. If the object concept differs for blind children, the meaning of words used to refer to those objects could be expected to differ from the meanings assigned by sighted children. Problems in word meaning and concept development—and hence, in communication—are an important consideration in mainstreaming efforts in the public schools. Consequently, the present study sought to explore linguistic and cognitive representation of common objects among blind children, along with their understanding and use of dimensional concepts in dealing with those objects. Procedure Ten totally and congenitally blind children and ten sighted children of matching age, sex, and socioeconomic status were interviewed individually following a prescribed format. By means of these structured interviews, information was gathered concerning the cognitive functioning of each child, and responses were secured to the lexical semantic tasks. These tasks focused on verbally and tactually derived attributions for selected objects defined as more tangible and less tangible, as well as measures of receptive and expressive use of comparative adjectives of dimension. Conclusions 1. This analysis suggested that the information gained through tactual means does not differ significantly from that gained through vision. The meaning of common words, and the underlying object concept reflected through the children\u27s attributions, did not appear to be significantly altered by the absence of vision. The younger blind children were found to have an accurate, albeit shallow conception of the less tangible objects, probably as a result of reduced opportunity for meaningful interaction/exploration with those objects. 2. The total number of attributions by the sighted children was not significantly larger than that of the blind children. Much similarity in the kind of attributes used was noted between vision groups. The number of visually oriented attributes mentioned by the blind children was extremely small compared to the total number of attributes used. It was concluded, therefore, that the language of the blind children was based on the object concept they had developed through tactual experience, rather than being a reflection of the language of sighted children. 3. Cognitive delay was evident among the older blind children, leading to the observation that the entire group was functioning at a preoperational level of cognitive development. The blind children\u27s attributions revealed a tactually based conceptualization of the world that was related to their personal experience, but which was not found to differ significantly from the visually based conceptualization of the sighted children. In fact, the mental image/object concepts for both vision groups appeared to draw heavily on egocentric and functional characteristics of the objects. 4. Communication between blind and sighted children regarding the objects used in this study did not appear to be seriously disrupted by the absence of vision. However, the importance of assisting blind children to develop effective and systematic methods for gathering and organizing information through tactual means was underscored. The results of this study emphasize the need for blind children to experience objects and events first hand