39386761
Reasoning about Interference in an Object-Based Design Method
The property of a (formal) development method which gives the development process the potential for productivity is compositionality, compositional development methods for concurrent systems are elusive because of interference. A companion paper shows how object-based concepts can be used to provide a designer with control over interference and proposes a transformational style of development in which concurrency is introduced only in the final stages of design. That approach relies on restrictions to the object graphs which can arise and works for systems which involve limited interference. The current paper discusses the problems of interference and shows how a suitable logic can be used to reason — during design — about those systems where interference plays an essential role. Here again, concepts are used in the design notation which are taken from object-oriented languages since they offer control of granularity and ways of pinpointing interference. A further paper is in preparation which discusses the semantics of the object-based design notation.
15308825
Scientific Decisions which Characterize VDM
The formal description and development method known as VDM has been used extensively, its specification language is now an ISO standard, and it has influenced other specification languages. The origins of VDM are normally placed in language description or semantics but it is probably best known in the wider arena of formal methods for (general) program specification and design. This paper sets out a personal view of some of the key technical decisions which characterize the Vienna Development Method.
2399941
Operational semantics: Concepts and their expression
6772552
Fixing the semantics of some concurrent object-oriented concepts
Abstract Concurrent object-oriented languages provide a suitable target for a compositional design process that copes with the interference inherent with concurrency. Fixing the semantics of an object-based design language has been undertaken using structured operational semantics and by a mapping to the pi-calculus. These two approaches are outlined and contrasted. In particular, the difficulties in the two approaches of justifying the proof rules of the proposed design method are explained.
9236653
The Early Search for Tractable Ways of Reasoning about Programs
This article traces the history - up to around 1990 - of research on reasoning about programs. The main focus is on sequential imperative programs but some comments are made on concurrency. The main thesis is that the idea of reasoning about programs has been around since they were first written; the search has been to find tractable methods.
45828501
Formal Definition in Program Development
The intent of the current paper is to show how a large problem like compiler development can be divided in a way which provides a structure for arguments of correctness. Although mechanically checked proofs are not envisaged, the use of formal notation is recommended so that the basis for correctness arguments exists.
42189866
Episodes in Space: Qualitative Representation and Reasoning Over Spatio-Temporal Objects
There is growing interest in many application domains for the temporal treatment and manipulation of spatially referenced objects. Handling the time dimension in spatial databases can greatly enhance and extend their functionality and usability by offering means of understanding the spatial behaviour in time. Few works, to date, have been directed towards the development of formalisms for representation and reasoning in this domain. In this paper, a new approach is presented for the representation and reasoning over spatio-temporal relationships. The approach is simple and aims to satisfy the requirements of coherency, expressiveness and reasoning power. Consistent behaviours of spatial objects in time are denoted episodes. The topology of the domain is defined by decomposing episodes into representative components and relationships are defined between those components. Spatio-temporal reasoning is achieved by composing the relationships between the object components using constraint networks. New composition tables between simple spatio-temporal regions and between regions and volumes are also derived and used in the reasoning process.
7423994
Computational Perspectives on Map Generalization
33896540
A Triangulated Spatial Model for Cartographic Generalisation of Areal Objects
Cartographic generalisation involves interaction between individual operators concerned with processes such as object elimination, detail reductions amalgamation, typification and displacement. Effective automation of these processes requires a means of maintaining knowledge of the spatial relationships between map objects in order to ensure that constraints of topology and of proximity are obeyed in the course of the individual generalisation transformations. Triangulated spatial models, based on the constrained Delaunay triangulation, have proven to be of particular value in representing the proximal and topological relations between map objects and hence in performing many of the essential tasks of fully automated cartographic generalisation. These include the identification of nearby objects; determination of the structure of space between nearby objects; execution of boundary simplification, merge and collapse operations; and the detection and resolution, by displacement, of topological inconsistencies arising from individual operators. In this paper we focus on the use of a triangulated model for operations specific to execution of merge operations between areal objects. The model is exploited to identify the regions of space between nearby objects and to execute merge operations in which the triangulation is used variously to adopt intervening space and to move adjacent rectangular objects to touch each other. Methods for updating the triangulation are described.
14219539
Characterisation and generalisation of cartographic lines using Delaunay triangulation
A method is presented for generalising cartographic lines using an approach based on determination of their structure. Constrained Delaunay triangulation is used to construct a skeleton of the space surrounding the lines and hence represent line features in terms of skeleton branches. Several statistical measures are used to characterise the triangulation branches. The measures enable selective generalisation of different types of line feature, leading to the possibility of user-specification of the style of generalisation. In our implementation of the approach, the triangulation is updated dynamically to allow both sides of multiple lines to be processed, while guaranteeing topological consistency between the resulting generalised lines.
13190855
Conflict resolution in cartographic name placement
Abstract The increasing application of computer cartography in geographical information systems and in professional map production has highlighted the requirement for automatic positioning of cartographic text in a manner that ensures legibility. An important aspect of the implementation of automated name placement is the avoidance of conflict, in particular due to overlap between names, and between names and map features. This paper reviews the automated strategies that have been adopted for conflict resolution. The majority of these may be classified as either iterative or graph-search procedures. In general the problem may be seen as one in which initially trial positions are generated for each of a selected set of names. These trial positions should obey rules relating to text characteristics and to the relationships between names and other map features. Conflict resolution then consists in finding, for each name, a trial position that obeys the cartographic rules governing the relationships between names.