Index Entry Array

James D. Anderson and José Pérez-Carballo “Information Retrieval Design”:

When two or more entries have identical headings or subheadings, these duplicate headings are usually merged for display, resulting in “entry arrays” that might look something like this:

United States
>Armed Forces
>>Afro-Americans. Bibliography 25
>>>History 24-30, 339
>>California. History. 20th century 54
>>China. History. 20th century 332
>>>Military life. History 442
>Gays 74-80, 445-450
>>Government policy 76
>>History. 20th century 78-80
>>Legal status, laws, etc. 76-78