Explain The Deference Between External, Internal, And Conceptual Schemas?


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he internal schema describes how the data will  be physically stored and accessed, using the facilities provided by a  particular DBMS. For example, the data might be organized so that all  the insurance policies belonging to a given customer were stored close  together, allowing them all to be retrieved into the computer's memory  in a single operation.                The conceptual schema (sometimes called the  logical schema) describes the stored data in terms of the data model of  the DBMS. In a relational DBMS, the conceptual schema describes all  relations that are stored in the database                The external schemas specify views that enable  different users of the data to see it in different ways. As a simple  example, some users of policy data might not require details of the  commission paid. By providing them with a view that excludes the  Commission Rate column, we would not only shield them from unwanted (and  perhaps unauthorized) information, but also insulate them from changes  that might be made to the format of that data.

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