Adding a Simple Index to the Sequence Set
Each of the blocks we created for our Sequence Set contains a range of records that might contain the record we are seeking.
We can construct a simple single-level index for these blocks.
The combination of this kind of index with the sequence set of blocks provides complete indexed sequential access. This method works well as long as the entire index can be held in memory.
If the entire index cannot be held in memory, then we can use a B+ Tree which is a B-Tree index plus a sequence set that holds the records.