23. A non-transitory computer readable storage medium having stored therein instructions, which when executed by a computer system cause the computer system to: receive one or more search keywords from a user; select a plurality of candidate document identifiers in accordance with the one or more search keywords, each candidate document identifier corresponding to a respective document at a respective data source; for a respective candidate document identifier of the plurality of candidate document identifiers: retrieve a document corresponding to the respective candidate document identifier from a data source, wherein the document has a structure type; convert the document into a node stream, wherein the document conversion is initiated immediately after retrieving a predefined portion of the document; generate a customized data model for the document using the node stream in accordance with the structure type of the document; identify one or more candidate chunks within the customized data model in accordance with a set of heuristic rules associated with the structure type; and select one or more chunks of the candidate chunks that satisfy the one or more search keywords; and provide at least one of the selected one or more chunks for display to the user.
23. A non-transitory computer readable storage medium having stored therein instructions, which when executed by a computer system cause the computer system to: receive one or more search keywords from a user; select a plurality of candidate document identifiers in accordance with the one or more search keywords, each candidate document identifier corresponding to a respective document at a respective data source; for a respective candidate document identifier of the plurality of candidate document identifiers: retrieve a document corresponding to the respective candidate document identifier from a data source, wherein the document has a structure type; convert the document into a node stream, wherein the document conversion is initiated immediately after retrieving a predefined portion of the document; generate a customized data model for the document using the node stream in accordance with the structure type of the document; identify one or more candidate chunks within the customized data model in accordance with a set of heuristic rules associated with the structure type; and select one or more chunks of the candidate chunks that satisfy the one or more search keywords; and provide at least one of the selected one or more chunks for display to the user. 26. The computer readable storage medium of claim 23 , wherein the data source is a web server.