INST 311 Lecture Notes - Lecture 6: Candidate Key, Multivalue, Unique Key
30 Aug 2018
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Document Summary
Logical data is data about database, that is, it stores information about how data is managed inside. For example, a table (relation) stored in the database and all its constraints, applied on that relation. Logical data independence is a kind of mechanism, which liberalizes itself from actual data stored on the disk. If we do some changes on table format, it should not change the data residing on the disk. All the schemas are logical, and the actual data is stored in bit format on the disk. Physical data independence is the power to change the physical data without impacting the schema or logical data. For example, in case we want to change or upgrade the storage system itself suppose we want to replace hard-disks with ssd it should not have any impact on the logical data or schemas. The er model defines the conceptual view of a database. It works around real-world entities and the associations among them.
