They describe the details of how data is stored in the computers
High level data models provide the concepts that are close to the way many users perceive data
Database provides necessary means to achieve this abstraction. By structure of a database we mean the data types, relations, and constraints that should hold on the data.
A view may be a subset of the database or it may contain virtual data that is derived from the database files but is not explicitly stored .
Can?t delete a row from primary table if there are related rows in secondary table.
LDI is the capacity to change the conceptual schema without having to change external schemas or application programs.
The no of entities participating in relation is called Degree of relationship
The relationship where both the participating entities belong to same entity type is called Recursive relationship
Both of them are relation ship constraints
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