Internal Logical Files (ILF) - a user identifiable group of logically related data that resides entirely within the application boundary and is maintained through External Inputs. An internal logical file has the inherent meaning it is internally maintained, it has some logical structure and it is stored in a file.
Even though it is not a rule, an ILF should have at least one external output and/or external inquiry. That is, at least one external output and/or external inquiry should include the ILF as an FTR. Simply put, information is stored in an ILF, so it can be used later. The EO or EQ could be from another application. It is worth noting that it is possible that a specific ILF is not referenced by EO or EQ, but it is used by an EI (other than the EI that maintains it).
Again, even though it is not a rule, an ILF should have at least one external input.