EI is when you take existing large systems and you make them work together, and its really hard because the systems aren't designed to work together, and made harder because bigco internal teams aren't exactly known for the quality of their infrastructure.
Relevance is one famous company that staffs world-class engineers and does EI[0]. They also write databases[1]. and languages[2].
As a soon-to-graduate who knows both Lisp and Haskell, I'm curious what exactly this means.