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2024-08-31 17:12本頁面
【正文】 today it is difficult to provide a plete set of operational capabilities with required efficiency on a large scale it appears today that technological improvements in providing faster and more reliable hardware may answer the question positively.The hierarchical data model is based no a treelike structure made up of nodes and branches a node is a collection of data attributes describing the entity at that opint the highest node of the hierarchical tree structure is called a root the nodes at succeeding lower levels are called children.A hierarchical data model always starts with a root node every node consists of one or more attributes describing the entity at that node dependent nodes can follow the succeeding levels the mode in the receding level bees the parent node of the new dependent nodes a parent node can have one child node as a dependent or many children nodes the major advantage of the hierarchical data model is the existence of proven database management systems that use the hierarchical data model as the basic structure there is a reduction of data dependency but any child mode is accessible only in a clumsy way this often results in a redundancy in stored data.The network data model interconnects the entities of an enterprise into a network in the network data model a database.Consists of a number of areas an area contains records in turn a recode may consist of fields a set which is a grouping of records may reside in an area or span a number of areas a set type is based on the owner record type and the member record type the manytomany relationship which occurs quite frequently in rap fife can be implemented easily the network data model is very pel the application programmer must be familiar with the logical structure of the database.
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