the big idea

what was wrong with early databases (network and hierarchical)

• the user’s operations were coded directly in terms of data structures
• these data structures closely mirrored the way the data was actually stored
• when developer changed the data structures for performance,the queries had to be rewritten

the solution

• have an abstract data model
• queries and insertions all expressed in terms of abstract model
• hide the details of the actual data structures from the user

in other words…

• data abstraction!

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