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Advanced Database Technology and Design phần 6

Một DB suy D là D ba = (F, DR, IC), trong đó F là một tập hợp hữu hạn các sự kiện mặt đất, DR một tập hợp hữu hạn các quy tắc suy, và IC một tập hợp hữu hạn các ràng buộc toàn vẹn. F tập hợp các sự kiện được gọi là một phần extensional của DB (EDB), và DR bộ và IC với nhau tạo thành một phần cái gọi là intensional (IDB). | Multimedia Database Management Systems 263 We also have to illustrate the events arising from the temporal state changes of an actor that is when object A starts its presentation then the A temporal event is raised. Special attention should be paid to the event generated when the actor finishes its execution naturally when there are no more data to be presented and to distinguish this event from the TAC operator . Therefore t_event We define now temporal composition representation. Let A B be two actors. Then the expression A t_event t_interval TAC_operator B represents all the temporal relationships between the two actors where t_interval corresponds to the length of a vacant temporal interval. Therefore temporal_composition 0 object temp_rel object temp_rel t_event t_interval TAC_operator For instance the expression 0 0 A 4 B 0 C conveys this message zero seconds after the start of the application start A 4 seconds after the start of A stop B 0 seconds after the end of B start C. Finally we define the duration dA of a multimedia object A as the temporal interval between the temporal events A and A . Another aspect of object composition in IMDs is related to the spatial layout of the application that is the spatial arrangement and relationships of the participating objects. The spatial composition aims at representing three aspects The topological relationships between the objects disjoint meet overlap etc. The directional relationships between the objects left right above above-left etc. The distance characteristics between the objects outside 5 cm inside 2 cm etc. . Spatiotemporal Composition Model An IMD scenario presents media objects composed in spatial and temporal domains. A model that captures those requirements is presented here. For uniformity reasons we exploit the spatiotemporal origin of the image 0 that corresponds to the spatial and temporal start of the application i.e. Team-Fly 264 Advanced Database Technology and Design upper left corner of the .