A data function can be either an internal logical file (ILF) or an external interface file (EIF). Each type of data function is assessed to identify:

- data functions that change internally: DETs added, deleted or changed; and
- data functions that change type but do not change internally (that is, an EIF is changed into an ILF or vice versa).

Determine which data functions will change and how many function points each data function represents after the change, applying the standard FPA rules.

For data functions that change internally an impact factor is calculated from the percentage of DETs changed. The percentage change is defined as the ratio of DETs changed divided by the original number of DETs.

Percentage change = Number of DETs added/changed/deleted / Number of DETs in original data function * 100

The impact factor is taken from the table below using the percentage change in the number of DETs.

Percentage DETs | <= 33.3% | <= 66.6% | <= 100.0% | > 100.0% |
---|---|---|---|---|

Impact Factor | 0.25 | 0.50 | 0.75 | 1.00 |

If a data function changes type (for example, an external interface file becomes an internal logical file), a value of 0.40 is used for the impact factor. However, in case of a change of type one needs to check if there is also an internal change of the Logical File (change of DETs). If the number of DETs changes as well as the type, the impact factor due to the change in the number of DETs must be determined. The value of the impact factor due to the change in type is compared with that due to the change in the number of DETs and the higher value is used in the calculation of the enhancement function point size.

The number of enhancement function points for a single changed data function is determined as follows:

EFP
_{CHANGED}
= FP
_{CHANGED}
x I
_{CHANGED}

The number of enhancement function points arising from a change in data functions therefore depends on the extent of the change in the data function.

If an EIF or an ILF is split into two (or more) data functions, one deleted data function and two (or more) added data functions are counted.

If an EIF and an ILF are combined, two deleted data functions and one added data function are counted.