What do "patterns, which separately match parts of a page" and "interactions between patterns" mean? Database System Concepts by Abraham Silberschatz, Henry F. Korth and S. Sudarshan says


  Information extraction using simple patterns, which  separately
  match parts of a page, is relatively error prone. Machine-learning techniques
  can perform much more sophisticated analysis, based on interactions between
  patterns, to minimize errors in the information extracted, while maximizing the
  amount of information extracted. 


What do "patterns, which  separately match parts of a page" and "interactions between patterns" mean respectively?
Simple patterns could mean regular expressions or extended regular expressions, each of which can be used to match parts of a page without considering the impact of other matches. 

Interactions between patterns could mean the conditional probabilities among all findings, either the matched patterns or the unmatched patterns. Additionally, they could mean more complicated probabilistic or logical rules.

We could dive a lot deeper and wider into the subject of information extraction. However, the understanding as basic as the above should be suffice for a first-time reading.