What is the difference between pipelining and materialization?

These are the two approaches to query processing. In the materialization approach we start from the lowest level operations in the expressions. The inputs to the lowest level operations are the relations in the database. We execute the lowest level operations on the input relations and store the results in the temporary relations.

In the pipelining approach, several relational operations are combined into pipeline of operations, in which the results on the one operation are passed along to the next operation the pipeline. This approach is useful since it eliminates the cost of reading and writing temporary relations.