Symbol tables are used to store key-value pairs. In common arrays, we just take keys as the order index from 0 to n, and we save value.
Symbol tables used for searching by their keys not their values, so their keys needs to be comparable.
There are two kinds of data structures, the first kind is sequential table, implemented by list; the second kind is tree structure, which aims to meet demand for both binary search and insertion speed.
We usually use hash tables in application in order for convenience rather than BBST.