How is the structure of the haiku and the tanka similar?

Haiku - 17 syllables, three lines of 5/7/5, no rhyme scheme. Tanka - 31 syllables and traditionally one straight line but can be split into 5/7/5/7/7. Oldest form of japanese poetry. Used to evoke a moment or end an occasion. Structurally there is little similarity other than being short fixed verse but their purpose in focusing the reader and sharpening their attention through considered word choices are.