Expression 
Object of the Business Rule Framework that returns a result.
The following data is processed in an expression on the basis of a freely definable regulation (such as a calculation rule):
Data of the application
Data of the objects associated with the application (such as business partner data)
Once the system has processed the data, the expression returns a result of a certain type (for information about the permitted result types, see below in the 'Structure' section).
You can nest expressions, in other words expressions can access results of other expressions. This means that you can link expressions with one another without restriction.
As a result, there are expressions that access other expressions, and expressions (final expressions) that cannot access any other expressions.
At present, the following result types are supported in the calculation of an expression:
B for Boolean
C for character (maximum length 50)
D for date
F for floating point number
I for integer (maximum four bytes)
M for currency amount incl. currency key
N for numerical character string
P for packed decimal number
T for time
R for reference to a structure or internal table
S for string
You use the expression type to determine how an expression is actually calculated. The expression type itself is determined by the implementing class.
'Implementing class' is a technical term. It is used synonymously for expression type in the sense of 'implementing class of an expression'.
To maintain an expression, the following fields are usually available:
The first two sections Administrative Data and Result Typing are very similar in all expression types.
Administrative Data section
Short Text
Group
Version
Import Status
Created By
Created On/At
Application Class
Language
Expression Type
Result Typing section
In the Result Typing section the following fields are displayed, depending on the expression type:
Result Type
Field/Structure Length
Output Length
Decimal Places
Positive and negative formulation of a Boolean fact
The other sections and fields of the other sections vary according to the expression type.