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I've seen some conflicting examples for these, so I want to make sure I understand the differences.

Excel 2018 は後方互換性をもつ (is backward compatible) if it can open a file made in Excel 2017
Excel 2017 は前方互換性をもつ (is forward compatible) if it can open a file made in Excel 2018

Excel 2018 ver 2.00 は上位互換性をもつ (is backward compatible) if it can open a file created in Excel 2018 ver 1.00
Excel 2018 ver 1.00 は下位互換性をもつ (is forward compatible) if it can open a file created in Excel 2018 ver 2.00

is this right?

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That is right. 後方交換性 and 上位交換性 means “backward compatible”, while 前方交換性 and 下位交換性 means “forward compatible”

For 前方 and 後方, it takes the meaning of "Forward" and "Backward", but not "Before" and "After". You can think that the software "moves forward" by releasing new versions. Then it will makes sense (at least to me).

For 上位 and 下位, you can think that the software “moves upward” and “reach higher levels” by releasing new versions. 上位 has a meaning of “high rank”. So when we saying a software is backward compatible, that is the newer version (the version of a “higher level”) is compatible with the older ones, we use the word 上位交換性. The thing that you are describing is on the upper level, so 上位. I am not sure if this makes sense to you or not, but this is how I remember the words.

  • I can see why people get confused..「後」and「前」usually means "after" and "before" in a temporal sense, which is usually what software version numbering implies.「後方」and「前方」are usually confined to spatial (rather than temporal) descriptions of "back" and "front". – droooze Apr 19 '18 at 6:48

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