Efficiency plays a key role in ranked retrieval. What is the primary computational bottleneck when ranking documents, and how can it be mitigated?
1) (a) Computing scores. (b) Reducing ranking precision in favor of efficiency.
2) (a) Keeping the dictionary in main memory. (b) Using compression.
3) (a) Sorting scores. (b) Using a heap data structure instead of an array.
4) (a) Sorting scores. (b) Breaking posting lists down (high and low tiers).