1. A method comprising: receiving, by at least one computing device, a request for one or more advertisements, each advertisement comprising content that is to be served for display in an initial web page; selecting, by the at least one computing device, one or more keyword candidates from the initial web page; performing, by the at least one computing device, a first query of a network for a first set of web pages containing a first keyword candidate from the one or more keyword candidates, the first query being performed using the first keyword candidate; identifying, by the at least one computing device, a contextual relevancy of the first keyword candidate to the initial web page by analyzing one or more of the web pages of the first set of web pages returned by the first query performed using the first keyword candidate; selecting, by the at least one computing device, one or more representative keywords from the one or more keyword candidates using the contextual relevancy of the first keyword candidate to the initial web page; selecting, by the at least one computing device in response to the request, the one or more advertisements using the one or more representative keywords selected using the identified contextual relevancy of the first keyword candidate to the initial web page; and transmitting, by the at least one computing device, the selected advertisement such that the selected advertisement is served for display with the initial web page.
1. A method comprising: receiving, by at least one computing device, a request for one or more advertisements, each advertisement comprising content that is to be served for display in an initial web page; selecting, by the at least one computing device, one or more keyword candidates from the initial web page; performing, by the at least one computing device, a first query of a network for a first set of web pages containing a first keyword candidate from the one or more keyword candidates, the first query being performed using the first keyword candidate; identifying, by the at least one computing device, a contextual relevancy of the first keyword candidate to the initial web page by analyzing one or more of the web pages of the first set of web pages returned by the first query performed using the first keyword candidate; selecting, by the at least one computing device, one or more representative keywords from the one or more keyword candidates using the contextual relevancy of the first keyword candidate to the initial web page; selecting, by the at least one computing device in response to the request, the one or more advertisements using the one or more representative keywords selected using the identified contextual relevancy of the first keyword candidate to the initial web page; and transmitting, by the at least one computing device, the selected advertisement such that the selected advertisement is served for display with the initial web page. 8. The method of claim 1 wherein analyzing the one or more keyword candidates comprises: generating, by the at least one computing device, a first sum of presence scores; and ordering, by the at least one computing device, the one or more keyword candidates in terms of the first sum of presence scores.