ILFs can contain business data, control data and rules based data. The type of data contained in an ILF is the same type of data an EI to contains and maintains.

It is common for control data to have only one occurrence within an ILF. For example control data file may only contain parameter settings, or a status setting. For example, part of the on board automobile system only contains current information, oil pressure, engine temperature, so on and so forth. This particular process of the on board system does not care about historical data – only the current instance. When the status changes the file is updated with current information and there is no historical information. The on board system may keep track of historical changes in diagnostics files, but this would be a totally separate process. This process is not used to keep the car running, but to help a mechanic understand what has been going on with the engine.

Real Time and Embedded Systems: For example, Telephone Switching is made of all three types, Business Data, Rule Data and Control Data. Business Data is the actual call, Rule Data is how the call should be routed through the network, and Control Data is how the switches communicate with each other. Like control files it is common real time systems will have only one occurrence in an internal logical file.

Business Applications: An example of Business data is customer names, addresses, phone number, so on and so forth. An example of Rules Data is a table entry that tells how many days a customer can be late before they are turned over for collection.