Data structure used for implementing spreadsheets

Question

What is the data structure used by spreadsheets program like ms-excel?

Answer 1

I got this question in an interview today.

The answer they were looking for (because I asked the interviewer at the end) was to implement a class structure that used multiple objects; formulas, references, and numerics.

Not much more detail to offer but suffice it to say that programs like google docs are much more interesting (to code) than they seem.