ところで
By the way (changing the topic)machine translation
FormationAt the start of a sentence: ところで、…
ところで is used to TURN to a new topic in conversation, equivalent to Vietnamese "à mà" or "nhân tiện" ("by the way"): ところで、夏休みの予定は? (by the way, what are your plans for summer vacation?). The new topic is usually unrelated, or only distantly related, to what was being discussed.
Its position is fixed at the start of the sentence, followed by a comma. This is a word of polite SPOKEN language — fine in conversation and casual email; rarely seen in formal essays.
Two words to keep separate: ところが means "however" (a result contrary to expectation) — completely different despite being only one character off. And ついでに also translates as "nhân tiện" ("while at it"), but it refers to an ACTION done alongside another (while out shopping, also picking up medicine), whereas ところで only changes the TOPIC of conversation, with no accompanying action.
Examples
ところで、夏休みの予定はもう決めましたか。
By the way, have you decided on your summer vacation plans yet?
ところで、この近くにおいしいラーメン屋はありますか。
By the way, is there a good ramen place near here?
仕事の話はこれで終わりです。ところで、最近田中さんに会いましたか。
That's it for work talk. By the way, have you seen Mr. Tanaka lately?