Repository reports are established by metadata reporter. There is no need of SQL or other transformation since it is a web app.
It is a medium of filtering rows in a mapping. Data needs to be transformed through filter transformation and then filter condition is applied. Filter transformation contains all ports of input/output, and the rows which meet the condition can only pass through that filter.
Reusable transformation is used numerous times in mapping. It is different from other mappings which use the transformation since it is stored as a metadata. The transformations will be nullified in the mappings whenever any change in the reusable transformation is made.