Function point

lastmod 2022-02-21created 2022-02-215 edits

A function point is a unit of measurement for expressing the amount of business functionality an information system (product) provides to users. Functional functions are used to calculate the functional size measurement (FSM) of software. The cost of a single unit (in dollars or hours) is calculated from past projects.

How to estimate FP (function points)

Estimate by referring to the FP documents provided by the National IT Industry Promotion Agency. Several things must be considered to prepare FP. First, take a look at the figure below from the National IT Industry Promotion Agency~

Calculation method:

These are the items to consider for FP. For now, you don't need to consider the complexity weights here or the adjustment factors to be considered next.

This is because most companies that require FP already have the format and the data to apply. In an FP spreadsheet written in Excel, you enter the function items and the basic data above, and the FP value is calculated for you.

Extract the function levels

The most important part of preparing FP is extracting the function items to which FP will be applied.

Usually they are organized into 3 levels, and each function's description is recorded in detail.

Distinguish internal logical files (ILF) and external interface files (EIF)

Most projects involve a DB or external integration.

So these items must be classified as ILF or EIF.

• DBs or files stored in the system being developed are counted as ILF,
• and items that must be fetched or updated through external integration are counted as EIF.

Write the external inputs (EI), external outputs (EO), and external queries (EQ)

First, external inputs (EI) are easy to understand if you think of C (create), U (update), and D (delete) in the commonly mentioned CRUD.

That is, count and write down the number of inputs, updates, and deletions for each function.

Next, you must clearly distinguish external outputs (EO) from external queries (EQ).

• An external output (EO) is an item where data is read, goes through a certain process, and is then output. In other words, think of it as content that is shown on screen after some internal processing.
• An external query (EQ), on the other hand, is a case where data is simply fetched from an internal logical file or external interface file and output as is.

Example

Size adjustment factor

Calculation method:

SW규모 = 0.4057 x (log e(기능점수) - 7.1978)^2 + 0.8878
   (단, 500FP 미만 1.28, 3,000FP 초과 1.153 적용)

Application complexity adjustment factor

Terminology

Data function types

Internal logical file (Internal Logical File; ILF)

Files maintained/managed by the system being estimated

External interface file (External Interface File; EIF)

Files referenced by the system being estimated

Transaction types

External input (External Input; EI)

Values input from outside

External output (External Output; EO)

Values output to the outside (involves data processing)

External query (External Query; EQ)

External input/output (no data processing)

Favorite site

• Wikipedia (en) Description of function points
• On how to write FP (Function Point)
• Function point definitions and cost estimation
• Function Point estimation and utilization
• Function point (simplified method) example
• Publication of the 2014 revised edition of the SW project cost estimation guide
  • End-KOSA_-_2014_SW_project_cost_estimating_guides_amendment_guidance.pdf ¹
  • KOSA_-SW_project_cost_estimate_Guide-_2014_edition.pdf ²
• Function Point estimation and utilization ³

References