36993113
A Collaborative Schema Integration System
Conceptual modelling as applied to database development can be described as a two stage process: schema modelling followed by schema integration. Schema modelling is the process of transforming individual user requirements into a conceptual schema: an implementation-independent map of data requirements. Schema integration is the process of combining individual conceptual schemas into a single, unified schema. Single-user tools for schema modelling have enjoyed much success partly because the process of schema modelling has become relatively well formalised. Although a number of formal approaches to conducting schema integration have been proposed, it appears that schema integration tools have not enjoyed the same level of success. This we attribute not so much to the problem of formalisation but to the inherent collaborative nature of schema integration work. This paper first discusses the importance of collaboration to schema integration work. It then describes SISIBIS, a demonstrator system employing the IBIS (Issue Based Information System) scheme to support collaborative database design.
6465500
Proximity Search with a Triangulated Spatial Model
The proximity relations inherent in triangulations of geometric data can be exploited in the implementation of nearest-neighbour search procedures. This is relevant to applications such as terrain analysis, cartography and robotics, in which triangulations may be used to model the spatial data. Here we describe neighbourhood search procedures within constrained Delaunay triangulations of the vertices of linear objects, for the queries of nearest object to an object and the nearest object to an arbitrary point. The procedures search locally from object edges, or from a query point, to build triangulated regions that extend from the source edge or point by a distance at least equal to that to its nearest neighbouring feature. Several geographical datasets have been used to evaluate the procedures experimentally. Average numbers of edge‐edge distance calculations to find the nearest line feature edge disjoint to another line feature edge ranged between 15 and 39 for the different datasets examined, while the average numbers of point‐edge distance calculations to determine the nearest edge to an arbitrary point ranged between 7 and 35.
12540236
Map generalization in the Web age
Geographic information represents our understanding of the association of phenomena with their location on and near the Earth’s surface. When presented in map form, an essential aspect of that information is that it may be adapted in semantic abstraction and level of geometric detail according to the purpose of the map and the extent of the Earth that is being considered at any one time. Representations of small areas in detail result in so-called large-scale maps, while representations of large regions in lesser detail are referred to as small-scale maps. Traditionally, cartographers have performed the task of adapting the content and the level of detail of a map to suit its scale and purpose, and this process is called map generalization. The widespread use of geographic information in computers in the context of geographical information systems (GIS) has brought with it the demand for automation of map generalization. Ideally, when accessing geographic information in a GIS, it would be possible to be able to modify the level of generalization of the available geo-data entirely automatically. At present, no such automatic facilities are readily available in commercial GIS. Some commercial GIS do provide mapgeneralization tools that the user may apply in a somewhat ad hoc manner to selected geometric data. These tools appear, however, to be targeted at cartographic specialists wanting to derive a generalized dataset from a more detailed one. There are some notable examples of the way in which automated map-generalization tools have been exploited for purposes of professional map production. For example, the Institut Géographique National of France have used GALBE (this issue) to generalize the entire French road network to produce 1 : 250 000 scale maps from their BDCarto database (approximately 1 :50 000). More recently, the demand for automated map generalization, which has been longstanding in the context of conventional GIS, has been reinforced by the prevalence of geographical information access on the Internet. There are several types of public access map-based Web sites that allow a user to zoom in and out of a particular region, but at present this is usually based on stepping between independent pre-generalized datasets which may differ markedly in their degree of generalization. It would be desirable to be able to change the level of detail on such systems in a smooth and progressive manner rather than the quantum-leap changes that often characterize the current approach. Hand-held computers and mobile phones with small screens can now support the display of small maps, but the size
205571678
A Prolog Rule-Based System for Cartographic Name Placement
Manual name placement is an extremely time consuming task and has been one of the most difficult aspects of the map production process to automate. It is complicated by the large number of rules required for the selection and placement of names. A hybrid Prolog/Fortrau rule-based system is described for placing names on a variety of map types. It uses a set of Prolog primitives for spatial search and name placement operations. The Ordnance Survey's 1:625000 scale digital dataset has been used to illustrate the application of rules for the selection of labels as well as for controlling their size and orientation. The application to other types of maps and diagrams is also briefly described.
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.
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.
22477823
A typed logic of partial functions reconstructed classically
This paper gives a comprehensive description of a typed version of the logic known as LPF. This logic is basic to formal specification and verified design in the software development method VDM. If appropriately extended to deal with recursively defined functions, the data types used in VDM, etc., it gives the VDM notation and its associated rules of reasoning. The paper provides an overview of the needed extensions and examines some of them in detail. It is shown how this nonclassical logic-and the extensions-can be reconstructed classically by embeddings into classical infinitary logic.
31900993
Geographical Interfaces to Museum Collections
7190198
Reasoning About Partial Functions in the Formal Development of Programs
Partial functions and operators are used extensively in the formal development of programs and thus development methods have to clarify how to reason about them. There are a number of approaches which cover up the fact that ''First Order Predicate Calculus'' does not handle undefined logical values. There is also at least one specific ''Logic of Partial Functions'' (LPF) which tackles the issue at its root by using a weaker logic. Recently, we have come to realise that LPF fits a particular way of developing programs. This paper explains why LPF is a suitable logic for ''posit and prove'' development and explores some problems that other approaches present.
33452389
Interference Revisited
28161210
Modularizing the Formal Description of a Database System
Specification languages have been proposed, and are being developed, which offer ways of splitting specifications into separate components or modules. It is important that such languages are able to cope with modularizations which are required by realistic specification tasks. This paper offers a challenge problem in modularization based on a description is of an existing database system. The chosen modularization is motivated by the need to separate coherent units about which useful properties can be deduced.