The word ‘Logical’ in information technology is usually associated with logical data base layouts or logical data models. However, in many situations, some physical considerations creep in to even the most logical of data models. When the term ‘logical’ is used in function point counting, it refers to the ‘conceptual’ or ‘functional’ user requirements, and excludes physical implementation or design requirements. Logical user requirements are those requirements that an experienced user in the subject matter area would identify as requirements of the software. Logical or functional user requirements describe what the software must do and do not include how the software will do the functions. Function points measure the size of these functional user requirements, only. Design and quality considerations although important to the software construction, are not part of the logical size of the software, and, therefore, they are not counted in function points.
This is similar to the size of a house being measured as the number of square feet or square meters contained within a floor plan, and it is not changed by how the house will be constructed.
In functional size measurement, the function point count reflects only what the application must do, not how it will do it.
Confusion can arise when the word logical is used in conjunction with words that sound physical like screen or report. A ‘logical screen’ may consist of one or more connected physical data entry screens that support a single function. Everything in function points is counted from a logical user viewpoint, and novice counters need to think ‘logically’ when they are counting function points.