Explain how materialization evaluation works with example?

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 Materialization

It is easiest to understand intuitively how to evaluate an expression by looking at a pictorial representation of the expression in an operator tree.


In this method, the given expression evaluates one relational operation at a time. Also, each operation is evaluated in an appropriate sequence or order. After evaluating all the operations, the outputs are materialized in a temporary relation for their subsequent uses. The example of figure 3.6 is computed as following:



By repeating the process, we will eventually evaluate the operation at the root of the tree, giving the final result of the expression. In our example, we get the final result by executing the projection operation at the root of the tree, using as input the temporary relation created by the join.

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