Active Update On Distributed Spatial Databases

A mechanism of active update on distributed spatial databases is proposed in this thesis in order to improve the efficiency and security of the geo-informatics, and make spatial data better server for economics construction and social development. By constructing the structure of distributed active spatial databases, spatial data are managed and updated by active mechanism in order to actively keep the data consistency. Based on the techniques of . NET Remoting, a new model is further given, designed and implemented. The contributions of this paper may include four parts, the field-based slice of spatial data, the structure of distributed active spatial databases, the active update mechanism of spatial data,and the maintenance of spatial data consistency.First, the motivations of this thesis are studied. The developments of the mechanism of active update on distributed spatial databases are briefly overviewed internationally. Based on this overview, the scheme of the project is determined, and the structure of the paper is planned.Second, spatial databases are studied via the technologies on describing spatial objects, organizing the data,sharing the data and mutually operating data. Then, the distributed spatial databases are discussed in the aspects of characteristics, subsection principles and subsection types. Under this umbrella,spatial data relationships are operated subsection by subsection when the data in the distributed spatial databases are partitioned and amalgamated. It is suitable to both relational database, and object-relationships database, which mathecs the data model of Open GIS (Geographical Information Systems).Third, the characteristics of distributed spatial databases are firstly presented, e.g. hierarchical control, data independences, data redundance, and completeness. The distributed spatial databases improve the efficiencies of storage and retrieval by using a complicated physical structure. Then, the principles, types and methods of data partition are given in the context of the distributed spatial databases. This kind of dataIIIpartition is determined by the distributing characteristics of spatial objects in the field. With the suitable mechanism of data allocation and update, spatial data may be shared inside hierarchies.Fourth, the strategies are proposed to implement the active mechanism of the distributed spatial databases. The relation model of databases is extended to be with the active mechanism. In details, some important techniques of the active mechanism are put forwarded, e, g., the rule bases of cases, the realization mechanisms of case triggers, the implementing patterns of case triggers, and the strategies of implementing the active mechanism.Fifth, the data consistency may be mainly divided into strong consistency and weak consistency. The data consistency of distributed spatial databases is updated via the operation rules consistency in the context of redundant data consistency. And the strategies are also given to update the data consistency. The update of distributed spatial databases is synchronistic, asynchronous or multi-stations. The strong consistency is carried out by the protocols of submission with two phases. And the weak consistency is carried out by using the techniques of data replication. Based on the abovementioned, a novel model is proposed to actively keep the consistency of redundant data under the techniques of .NET Remoting.Finally, the mechanisms of the active update on distributed data are designed and implemented with the proposed model in a case study. The model depicts the written manipulations of redundant data via XML (extensible Markup Language). On each data node, two information queues are maintained, receiving queue and sending queue. And the web nodes are communicated by visiting the remote objects under the umbrella of .NET Remoting.