Codd's Twelve Rules - Rule 8 - Physical Data Independence
Rule 8
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Physical Data Independence
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Rule
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Changes
in the physical level must not lead to a change in the next higher level
called logical level.
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Description
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Any
change in the physical level (lowest level that talks about how data is
stored in a database, say for example, in arrays or linked lists etc.) must
not lead to a change in the logical level (tables, columns, rows etc.).
Applications
that are defined on the physical level should be able to continue to work
even when changes are made to the internal implementation of data storage and
access methods.
The
way the data stored physically must be independent of how its accessed
logically.
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Example
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For example, relations are stored as unordered files. If the change from
unordered files to some other representation would not require a change in the
table design, attribute types etc.
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Some DBMS that fulfills this property
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Almost all Relational DBMSs
support this property.
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