1. Primary disadvantage of index-sequential le organization is that performance degrades as the file grows. This can be remedied by costly reorganizations.

2. B+-tree file structure maintains its effciency despite frequent insertions and deletions. It imposes some acceptable update and space overheads.

3. A B+-tree index is a balanced tree in which every path from the root to a leaf is of the same length.

4. Each nonleaf node in the tree must have between [n/2] and n children, where n is fixed for a particular tree.