The storage and analysis of large amounts of time-varying spatial and aspatial data is becoming an important feature of many application domains. This has fuelled the need for spatio-temporal extensions to data models and their associated querying facilities. To date, much of this work has focused on the relational data model, with object data models receiving far less consideration. Where descriptions of such object models do exist, these models fail to fully integrate their spatial, aspatial and temporal dimensions into a uniform and coherent model. In addition, there is currently a lack of systems which build upon these models to produce database architectures that address the broad spectrum of issues related to the delivery of a fully functional spatio-temporal DBMS. This paper presents a foundation for the development of such a system, called Tripod, by describing a spatio-historical object model based on a specialized mechanism, called a history, for maintaining knowledge about entities that change over time. Key features of the resulting model include: (i) consistent representations of primitive spatial and timestamp types; (ii) a component-based design in which spatial, timestamp and historical extensions are formalized incrementally, for subsequent use together or separately; (iii) compatibility with mainstream query processing frameworks for object databases; and (iv) the integration of the spatio-temporal proposal with the ODMG object database standard. The paper presents a comprehensive formal characterization of the model and illustrates its capabilities in a crime data management application. It is also shown how the model can be programmed using an extension to the ODMG language bindings. The model and language bindings have been fully implemented.
At the National Primary Care Research and Development Centre (NPCRDC) we have constructed a national database for all primary care groups (PCGs) in England. At its core, the database links information about population socio-economic and demographic characteristics to generic health status and to the organisation, resourcing and activities of general practice. In this paper we describe and discuss the problems with linking these data, and with defining the boundaries and the local populations of PCGs, given that they have been established on the basis of administrative expediency rather than geographical coherence. We then consider the implications of these difficulties for needs assessment in primary care groups.
A STUDY of orally administered attenuated poliovirus vaccine was conducted in a small community in Minnesota in 1958. In that study (1), the feeding of virus to only half of the participating families during the first half of the study provided an opportunity to study the spread of these strains of poliovirus to par¬ ticipants who received placebos. Prior to this study, intrafamily (2-4) and intrainstitutional (5) spread of attenuated poliomyelitis vaccine viruses had been reported. This study presents quantitative data on the community spread of vaccine strains of polio¬ virus. The design of the study, the vaccine strains used, the characteristics of the study population, the illnesses observed during the study, and the method of surveillance used to detect such illnesses were described in the earlier report (1).
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