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2024-12-13 11:34本頁面
【正文】 atabases are integratedcircuit and electronicdevice layouts. Geographic databases are spatial databases used to store geographic information, such as maps. Geographic databases are often called geographic information systems. Geographic data are spatial in nature, but differ from design data in certain ways. Maps and satellite images are typical examples of geographic data. Maps may provide not only location information such as boundaries, rivers and roadsbut also much more detailed information associated with locations, such as elevation, soil type, land usage, and annual rainfall. Geographic data can be categorized into two types: raster data (such data consist a bit maps or pixel maps, in two or more dimensions.), vector data (vector data are constructed from basic geographic objects). Map data are often represented in vector format. Third. Multimedia Databases Recently, there has been much interest in databases that store multimedia data, such as images, audio, and video. Today multimedia data typically are stored outside the database, in files systems. When the number of multimedia objects is relatively small, features provided by databases are usually not important. Database functionality bees important when the number of multimedia objects stored is large. Issues such as transactional updates, querying facilities, and indexing then bee important. Multimedia objects often have descriptive attributes, such as those indicating when they were created, who created them, and to what category they belong. One approach to building a database for such multimedia objects is to use database for storing the descriptive attributes, and for keeping track of the files in which the multimedia objects are stored. However, storing multimedia outside the database makes it harder to provide database functionality, such as indexing on the basis of actual multimedia data content. It can also lead to inconsistencies, such a file that is noted in the database, but whose contents are missing, or vice versa. It is therefore desirable to
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