1. A computer-implemented method to determine a robust wrapper representing a data item of a plurality of data items in a document represented by a markup language, comprising: based on archival data representative of a temporal history of the document, developing a model indicative of the temporal history; based on the developed model, determining robustness characteristics for a plurality of different wrappers representing associated paths to the data item in a representation of the document, the robustness characteristics for each wrapper representing a likelihood that the corresponding wrapper will continue to be effective for extracting the data item when the document changes; and based on a result of the determining operation, providing, as a result wrapper, one of the plurality of wrappers that has a desired robustness characteristic; wherein the representation of the document relates to a tree having a plurality of nodes; wherein the temporal history of the document relates at least to an original tree and a plurality of changed trees indicative of trees that appeared during the temporal history of the document that are different from the original tree; wherein the developing operation includes: obtaining a plurality of pairs, each one of the plurality of pairs including a first element (T) and a second element (T′), wherein T is the original tree and T′ is a different one of the plurality of changed trees; determining a plurality of different change operations indicative of changes made to change T into T′ for each one of the plurality of pairs; and associating each one of the plurality of different change operations with a probability value indicative of a probability that the associated change operation is applied to the document.
1. A computer-implemented method to determine a robust wrapper representing a data item of a plurality of data items in a document represented by a markup language, comprising: based on archival data representative of a temporal history of the document, developing a model indicative of the temporal history; based on the developed model, determining robustness characteristics for a plurality of different wrappers representing associated paths to the data item in a representation of the document, the robustness characteristics for each wrapper representing a likelihood that the corresponding wrapper will continue to be effective for extracting the data item when the document changes; and based on a result of the determining operation, providing, as a result wrapper, one of the plurality of wrappers that has a desired robustness characteristic; wherein the representation of the document relates to a tree having a plurality of nodes; wherein the temporal history of the document relates at least to an original tree and a plurality of changed trees indicative of trees that appeared during the temporal history of the document that are different from the original tree; wherein the developing operation includes: obtaining a plurality of pairs, each one of the plurality of pairs including a first element (T) and a second element (T′), wherein T is the original tree and T′ is a different one of the plurality of changed trees; determining a plurality of different change operations indicative of changes made to change T into T′ for each one of the plurality of pairs; and associating each one of the plurality of different change operations with a probability value indicative of a probability that the associated change operation is applied to the document. 5. The method of claim 1 , wherein the determining operation comprises: evaluating the plurality of wrappers to determine whether the path associated with each wrapper leads to the data item in the document when the document is changed in accordance with the plurality of different change operations; based on a result from the evaluating operation and the probability values associated with the plurality of different change operations, determining a success/failure probability for each one of the wrappers.