Document update generation

A non-transitory computer storage medium encoded with a computer program, the program comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations comprising:

• identifying pairs of document object model content nodes where a first content node in each pair is in a first hierarchical representation of a first document and a second content node in each pair is in a second hierarchical representation of a second document, in which the content nodes represent visible content and in which identifying comprises:
• selecting the first and second content nodes such that a cost based on structural differences between the first and second hierarchical representations and a content difference between the first and second content nodes is minimized, wherein the cost is based on, at least, a distance of a shortest path between the first and second content nodes given a common ancestor node in the document object model;
• associating rendered layout information related to the first content node with the second content node;
• and
• determining whether to generate a snippet for the content difference between the first and second content nodes based on the rendered layout information.

A system comprising:

• a computer-readable storage device including instructions;
• and
• one or more data processing apparatus operable to execute the instructions and perform operations comprising:
• identifying pairs of document object model content nodes where a first content node in each pair is in a first hierarchical representation of a first document and a second content node in each pair is in a second hierarchical representation of a second document, in which the content nodes represent visible content and in which identifying comprises:
• selecting the first and second content nodes such that a cost based on structural differences between the first and second hierarchical representations and a content difference between the first and second content nodes is minimized, wherein the cost is based on, at least, a distance of a shortest path between the first and second content nodes given a common ancestor node in the document object model;
• associating rendered layout information related to the first content node with the second content node;
• and
• determining whether to generate a snippet for the content difference between the first and second content nodes based on the rendered layout information.