Software cost evaluation: a method for estimating software scale by fast function point method

The quick function point method is based on international standards 《ISO/IEC 24570－2005 Software Engineering NESMA Functional scale measurement 2.1 Definition and counting guide for function point analysis application 》 A software scale measurement method is proposed .

This method is suitable for the early stage of software project 、 Mid - 、 Scale estimation or measurement in later stages .

The basic process or steps of scale estimation or measurement by fast function point method are as follows ：

 Determine the count type 
 Identify system boundaries 
 Identify function point count items 
 Calculate the number of unadjusted function points 
 Calculate the adjusted function points .

So let Xinxing analyze each step in detail for you ：

One 、 Determine the count type

Determine the count type according to the type of requirement or project .

There are three types of counting ： New development 、 Continuous development and existing system counting .

 For new development requirements or projects , Expected （ Or actual ） The functions put into operation are counted ;
 For continuing development requirements or projects , Expected （ Or actual ） newly added 、 The modified and deleted functions are counted ;
 For existing systems , Count the actual functions .

Two 、 Identify system boundaries

When identifying the system boundary, pay attention to ：

 From the user's perspective , Not affected by system implementation ;
 Mainly to distinguish internal logical files （ILF） And external interface files （EIF）;
 Transaction functions should cross identified system boundaries .

3、 ... and 、 Identify function point count items

The function point count items are divided into Data function and Trading function Two types of .

 Data function —— Include internal logic files （ILF）、 External interface file （EIF）;
 Trading function —— Include external inputs （EI）、 External output （EO）、 External query （EQ）.

• Data function ： The function provided by the system to users to meet the internal and external data requirements of the product , That is, the system manages or uses those business data （ The business object ）, Such as “ Customer information ”“ Account transactions ” etc. .

Internal logic file or external interface file refers to “ file ” Not a file in the sense of traditional data processing , It refers to a group of customers that can identify 、 Logically related data or control information . therefore , These files and physical data sets （ Such as database table ） There is no necessary correspondence .

• Trading function ： The data processing function provided by the system to the user , That is, how the system processes and uses those business data （ The business object ）, Such as “ Transfer accounts ”“ Modify blacklist generation rules ”“ Look up transactions ” etc. .

Transaction function is also called basic process , Is user recognizable , A set of atomic operations in business , It may consist of multiple processing logic . for example ,“ Add teller information ” This basic process may include “ Information verification ”“ Modification confirmation ”“ Modify the result feedback ” Wait for a series of processing logic .

Four 、 Calculate the number of unadjusted function points

1. Count with estimated function points , The calculation formula is as follows ：

FP＝35ILF+15EIF

——FP： Unadjusted function points , The unit is function point ; ——ILF： Number of internal logical files ; ——EIF： Number of external interface files .

2. Count with estimation function points , The calculation formula is as follows ：

FP＝10ILF+7EIF+4EI+5EO+4*EQ

——FP： Unadjusted function points , The unit is function point ; ——ILF： Number of internal logical files ; ——EIF： Number of external interface files ; ——EI： Number of external inputs ; ——EO： Number of external outputs ; ——EQ： Number of external queries .

5、 ... and 、 Calculate the adjusted function points

Calculate the stage according to different scale , We need to consider the impact of implied demand and demand change on scale , therefore , The scale needs to be adjusted according to the timing of scale counting .

Adjusted function points （AFP）, The calculation formula is as follows ：

AFP＝FP*CF

——AFP： Adjusted function points , The unit is function point ; ——FP： Unadjusted function points , The unit is function point ; ——CF： Scale change adjustment factor , According to industry data , Early project estimation （ Such as budget estimation stage ） Usually the value is 1.5; Mid term project estimation （ Such as bidding and bid evaluation 、 Project approval 、 Technical solution stage ） Usually the value is 1.26; Middle and later stages of project estimation （ Such as the completion of demand analysis and post evaluation ） Usually the value is 1.0.