| 摘要 |
<p>Based on a request for an advertisement, a social networking system retrieves information about a user and identifies candidate advertisement ("ad") objects having targeting criteria satisfied by the information about the user. The social networking system selects a candidate ad object based on associated bid prices and sends a description of the selected candidate ad object to an external system. The external system selects an alternative advertisement based on bid prices of advertisements stored by the external system and the description. The external system communicates a description of the alternative advertisement, including an external clearing price, to the social networking system. Based on a clearing price for the selected candidate ad object and the external clearing price, the social networking system selects the selected candidate ad object or the alternative advertisement for presentation to the user.</p> |
