Jazz improvisatory procedures may be divided into two broad and sometimes overlapping categories: paraphrase and chorus improvisation. The former consists mostly of an embellishment or ornamentation technique, while the latter suggests that the soloist has departed completely from a given theme or melody and is improvising freely on nothing but a chord structure.
Most improvisation in the modern jazz era belongs to the second category, and Rollins’s recording is a landmark for maintaining thematic and structural unity in this type of playing.
This according to “Sonny Rollins and the challenge of thematic improvisation” by Gunther Schuller; this foundational work of jazz analysis from 1958 is reprinted in Keeping time: Readings in jazz history (New York: Oxford University Press 2015 193–202; RILM Abstracts of Music Literature 2015-155).
Today is Rollins’s 90th birthday! Above, the artist around the time of the recording; below, the recording itself.