13. The system of claim 12 , wherein the method further comprises identifying the advertising word or phrase based on a retrieval operation or synthesis operation performed on the knowledge representation.
12. A system comprising: at least one processor; and at least one storage medium storing processor-executable instructions that, when executed by the at least one processor, perform a method for purchasing an advertisement opportunity based on a knowledge representation, the method comprising: obtaining purchaser-context information associated with at least one purchaser; computing a value, specific to the at least one purchaser, of an advertisement opportunity associated with at least one advertising word or phrase, the computing comprising: identifying, in a knowledge representation encoded as a data structure, a first concept representing at least a portion of the purchaser-context information, identifying, in the knowledge representation, a second concept with which the at least one advertising word or phrase shares at least one label, determining a semantic relevance between the first concept and the second concept based at least in part on the first and second concepts' relative positions in a topology of the knowledge representation, and computing the value of the advertisement opportunity as a function of the determined semantic relevance between the first and second concepts; comparing the computed value to a purchase price of the advertisement opportunity; and purchasing the advertisement opportunity in response to determining that the computed value exceeds the purchase price.