Why no sue for using linked list?

Question

I found a patent with active status apparently claimed the linked-list data structure.

A computerized list that may be traversed in at least two sequences comprising: a first sequence of items that comprise said list; and a primary pointer and an auxiliary pointer for each of said items of said list, said primary pointer being adapted to direct a computer program to a first following item and defining a first sequence to traverse said list, said auxiliary pointer being adapted to direct said computer program to a second following item and defining a second sequence to traverse said list.

I wonder even though the data structure is patented, how on earth almost every system is using this data structure without being sued by the assignee? If the assignee wants can he/she sue for using the claimed data structure?

What am I missing?

Note: Post corrected as pointed out by Eric S

Answer 1

The cited document was a patent application, not yet a patent. Patent claims often narrow between the application stage and the eventual patent. The application was granted as patent US 7028023B2. The first claim of the patent is:

1. A computerized list that may be traversed in at least two sequences comprising:

   a plurality of items that are contained in said computerized list; and

   a primary pointer and an auxiliary pointer for each of said items of said computerized list such that each of said items has an associated primary pointer and an associated auxiliary pointer, said primary pointer functioning as a primary linked list to direct a computer program to a first following item and defining a first sequence to traverse said computerized list, said auxiliary pointer functioning as an auxiliary linked list to direct said computer program to a second following item and defining a second sequence to traverse said computerized list.

This isn't really my field, but I note that this is not covering all linked lists, but implements a primary and auxiliary pointer to traverse the lists. I don't believe standard linked lists work this way, but I'm not really qualified to state so with authority. I will point out that the patent cites 13 patents as prior art. I'd have to read the file history in PAIR to learn more of what the examiner considered.

As to your question, the assignee could sue anyone utilizing the invention as specified by the claims. With software, this isn't always easy as programs get compiled and you likely don't have access to the source code. I point out that the assignee who owns the patent would do the suing. It is often not the inventor.