The Structure File Editor is a tabbed pane within the Data File Editor window that enables you to create and edit layouts within a structure file. The layouts within a structure file can then be applied to a data file so that the Data File Editor is able to display the records within it in a way that makes them easier to view and edit.
Using layouts also makes it easier to filter records in a data file, as you can apply field conditions to a filter, as opposed to only being able to apply reference conditions when a layout is not used; see Filtering a Data File for more information.
Layouts are derived from the Data Division (level-01 fields and below in the File Section, the Working Storage Section, and the Linkage Section) of a COBOL program that uses the data file, and are created using the .idy file from the compiled program.
Structure files are not mandatory, but when applied to a data file, the fields within a record can be displayed in a structured way, making them easier to view and edit. If a structure file is not applied, the records are displayed unformatted, as long continuous strings of text.