In a personal injury case, what is the difference between an examination for discovery and an interrogatory?

In Roitman v. Chan reflex, (1994), 99 B.C.L.R. (2d) 182 the court said at para. 11: “...the law should encourage the selection of the tool which is likely to achieve the best result for the least effort and cost.” Then at para. 12 the court noted: ...Generally speaking, issues involving extensive research, such as precise chronologies or exhaustive lists, would seem to be more appropriate for the more expansive time-frame permitted by interrogatories than for a more confrontational, time-pressured examination for discovery. Conversely, questions requiring a narrative answer are much more likely to remain in focus at an examination for discovery, where counsel can expand on and limit the witness's answers as appropriate.