Introduction Data functions relate to logical data that is stored and made available for update and retrieval. Data functions may be identified as Internal Logical Files (ILFs) or External Interface Files (EIFs). ILFs and EIFs are user-identifiable groups of logically related data or control information. As such, they are logical groupings and not physical representations of those groupings of data. It is possible, but very unlikely, that the logical will match the physical. Consequently, ILFs and EIFs should be counted in an identical manner regardless of the physical database structure in an application, even if the delivery and maintenance requirements and the productivity rates are different because of the nonfunctional characteristics outside of function points. ILFs are maintained within the boundary of the application being measured, and EIFs are read or referenced only within the boundary of the application being measured but are maintained within a different application boundary. When function point counters size an application in function points, they typically experience the greatest degree of counting difficulty in identifying the data functions.