DBMS Notes Personal

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 DATA VS INFORMATION

Data :  a series of numbers like 9086526829.

Information : This is Rita's ph no


Problem with File Systems : 

1. 



2. no queries, so write a code for each functionality for each case/storyline

3.     


DBMS follows "Abstraction" priciple.

different departments can see different part of data, but not all data. this is called as database view.






1. physical level/blueprint




3. view level - what end user sees







T1 - everything in our local system




app server - filter for currupt queries -  it identifies harmful query and restrict its execution



ER MODEL




every entity has one unique id - primary key

entity set -  list of students




Why ER diagram?
- To help design the database and create table, it is a blueprint


one customer can have multiple ph nos

derived attribute :
- age based on DOB




strong entity :  it has its own pk andidentifiable

weak entity : depends on other, if no loan, no payment will be there, even the payment no can be start from 1 again if load id changes

manager itself is an Employee








Extended ER features  : 

specialization :  big entity to specialized entity [top-down approach]




Generalization :  bottom-up, reverse of specialization

both are same in ER diagram, just based on our thinking pattern, name differs



instead of managing each entity individually, it will manage a single combined entity




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