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Hello,

1. An assertion is a predicate expressing a condition that we wish the database always to satisfy.

2. The where clause corresponds to the selection predicate of the relational algebra.

What is meaning of "predicate" here?
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Any group of words that designates a property or characteristic of something is a predicate.

Suppose you want to find every description in your database that contains the word "amount".
Here's the predicate you are interested in: contains the word "amount".
This group of words designates a certain property or characteristic that you are looking for in the database.

Suppose now that you want to find every total in your database that is greater than 100,000.
Here's the predicate you are interested in: is greater than 100,000.
This group of words designates a certain property or characteristic that you are looking for in the database.

Predicates make it possible for you to look for specific things in a database and select specific things out of the database. You look for and select the things that have the characteristics you designate in the predicates you specify.

I hope this helps.
CJ
Comments  
Hello,

Thanks Sir.(Mr. CJ)