[1] Interactive searches became possible in the 1980s with the advent of faster databases and smart terminals.
[2] Based on Boolean algebra, these types of searches utilize logical operations using binary or dyadic processes.
[3] The AND and NOT expressions are known as implied Boolean operators as they require or disallow a word or a phrase.
When using multiple Keywords this serves as an AND function requiring that all words with a + sign be in a search result.
[4] Some search engines, such as google, utilize systems with an implied AND operation.
This means that the search engine will automatically apply the AND function inbetween keywords without having to enter a symbol for the AND operation.