EW is used for attaching certain adverbs to question words:
+--EW-+
| |
about when did it happen ?
The EW link is used because none of the other adverbial
modifier links (EA, EE, EN, EZ, etc.) are appropriate for
this situation, and would allow too broad a range of possible
linkages. Although the QI
link could fit in this situation, it is meant for forming
indirect questions ("I wonder when it happened?"), and is not
appropriate for such direct questions.