Abstract: Methods, systems, and apparatus for determining resource quality based on resource competition. In an aspect, a method comprises: for each of a plurality of resource locators: generating first value for the resource locator that indicates, for a plurality of first sets of search results that each include the resource locator, a number of occurrences of other resource locators that were impressed and not selected when the resource locator was selected; generating a second value for the resource locator that indicates, for a plurality of second sets of search results that each include the resource locator, a number of occurrences of other resource locators that were selected when the resource locator was impressed and not selected; and generating, based on a difference between the first value and the second value, an adjustment factor for the resource locator for adjusting a score associated with the resource locator during a search operation.

Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for determining a measure of quality for a resource. In one aspect, a method includes determining a seed score for each seed resource in a set. The seed score for a seed resource can be based on a number of resources that include a link to the seed resource and a number of selections of the links A set of source resources is identified. A source score is determined for each source resource. The source score for a source resource is based on the seed score for each seed resource linked to by the source resource. Source-referenced resources are identified. A resource score is determined for each source-referenced resource. The resource score for a source-referenced resource can be based on the source score for each source resource that includes a link to the source-referenced resource.

Abstract: Methods and apparatus for ranking search result documents for a query of a user based on one or more attributes of the user that are associated with one or more of the search result documents. User attributes of the user's user profile may be matched to user attributes of a search result document and the search result document ranked based at least in part on bias measures associated with the matched user attributes. Some implementations are directed to determining, for each of a plurality of documents, multiple user attributes and associated bias measures to associate with the document. A user attribute and associated bias measure for the document may be determined based on indicated interactions with the document by a set of users associated with the user attribute.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for index-side synonym expansion are disclosed. Some implementations include actions of obtaining a token sequence for a resource, wherein each token in the token sequence comprises one or more characters. The actions also include selecting a token from the token sequence, wherein the selected token comprises at least one numeric portion having one or more contiguous numeric characters, and at least one non-numeric portion having one or more non-numeric characters. Further actions include generating a new token corresponding to each of the at least one numeric portions of the selected token and storing data associating the selected token and each of the new tokens corresponding to the at least one numeric portion of the selected token as index terms for the resource, wherein the search engine index is accessed to augment search queries.

Abstract: Methods, systems, and apparatus for determining resource quality based on resource competition. In an aspect, a method comprises: for each of a plurality of resource locators: generating first value for the resource locator that indicates, for a plurality of first sets of search results that each include the resource locator, a number of occurrences of other resource locators that were impressed and not selected when the resource locator was selected; generating a second value for the resource locator that indicates, for a plurality of second sets of search results that each include the resource locator, a number of occurrences of other resource locators that were selected when the resource locator was impressed and not selected; and generating, based on a difference between the first value and the second value, an adjustment factor for the resource locator for adjusting a score associated with the resource locator during a search operation.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for index-side synonym expansion are disclosed. Some implementations include actions of obtaining a token sequence for a resource, wherein each token in the token sequence comprises one or more characters. The actions also include selecting a token from the token sequence, wherein the selected token comprises at least one numeric portion having one or more contiguous numeric characters, and at least one non-numeric portion having one or more non-numeric characters. Further actions include generating a new token corresponding to each of the at least one numeric portions of the selected token and storing data associating the selected token and each of the new tokens corresponding to the at least one numeric portion of the selected token as index terms for the resource, wherein the search engine index is accessed to augment search queries.

Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for index-side synonym expansion. One method includes indexing a token from a resource, including determining that the token comprises a numeric portion and storing data associating the resource with both the particular token and the numeric portion in a search engine index. Another method includes indexing a token from a resource, including normalizing the token by removing a prefix matching a stopword prefix and storing data associating the resource with both the token and the normalized form of the token in a search engine index. Another method includes creating a token blacklist.