What is a "predicate based search"?

Question

I overheard this at a coffee table conversation and i wasnt able to fathom what this was about. A bit of googling didnt throwup anything useful...

Clarification: Thanks guys for the initial take on it... but it appeared that the conversation was about "searching" through databses / internet, etc....

Answer 1

In general, a predicate is a function that takes one or more arguments, and returns a boolean value, indicating whether some statement about the arguments is true or false.

Examples of natural-language predicates might be "is blue", "is longer than two metres", "is owned by MC Hammer", "is underground".

When executing a search on some system - eg a file system, a database table, a graph - it might be that the system itself provides certain built-in searches (a file system might have a built-in search by filename; a graph might have a built-in search by distance from a given node); or, for more flexibility, there might be a way to search by providing a custom predicate function.

Depending on details, this custom predicate function could be passed as an expression tree, or a pointer to some actual executable code, or a query expression to be parsed. All that is required is that the system has some way to invoke the predicate on each candidate item; and that the predicate returns true or false for each candidate item.

The results of the search are then precisely those items for which the custom predicate returns true.