Pentaho Reporting provides many functions and expressions that may be used during report creation. A function in Pentaho Reporting is used to calculate a computed value, while an expression in Pentaho Reporting is a function whose scope is limited to the current dataset row. A function may maintain state, having access to many rows of data.
Starting from the Report Designer user interface, functions and expressions live in two different places because their scope is different. Functions can be found in report explorer, in particular, in the Data tab under the Functions group. The following screenshot shows how the report explorer looks with two functions defined:
Expressions, being related to the dataset, live in a different place: in the element properties panel. In particular, expressions live on each property of the panel, in the fourth column of the table showing an icon. There are two possible icons: the green plus...