Dr. Matthew Koll in 1999 at a presentation entitled "Major Trends and Issues in the Information Industry" has used the interesting metaphor of Needle in a Haystack for searching the Web. He has grouped different search scenarios into 12 categories as follows: a known needle in a known haystack, a known needle in an unknown haystack, an unknown needle in an unknown haystack, any needle in a haystack, the sharpest needle in a haystack, most of the sharpest needles in a haystack
All the needles in a haystack, affirmation of no needles in the haystack, things like needles in any haystack, let me know whenever a new needle shows up, where are the haystacks? and finally needles, haystacks -- whatever. I'd like this metaphor and I think we can map different search scenarios into it very easily which can be helpful to develop efficient search strategies.