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Used by web applications and adds an intermediate

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Used by Web applications and adds an intermediate layer between the clientand the database serverN-tier architecture -It is possible to divide the layers between the user and the stored data further intofiner components, thereby giving rise to n-tier architectures, where n may be four or five tiers. Besidesdistributing programming and data throughout a network, n-tier applications afford the advantage thatany one tier can run on an appropriate processor or operating system platform and can be handledindependently.
2.2Discuss the main categories of data models. What are the basic differences among the relationalmodel, the object model, and the XML model?
2.3What is the difference between a database schema and database state.
2.4Describe the three-schema architecture. Why do we need mappings among schema levels? Howdo different schema definition languages support this architecture?
External Level:includes a number of external schemas or user views. Each external schemadescribes the part of the database that a particular user group is interested in and hides the rest ofthe database from that user group. As in the previous level, each external schema is typicallyimplemented using a representational data model, possibly based on an external schema design in ahigh-level conceptual data modelMapping is needed because the conceptual internal mapping defines the communication betweenthe conceptual view and the stared database. It also specifies how conceptual records and fields arerepresented at the internal level.

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Term
Summer
Professor
Carlos Rodriguez
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