Traceability has been defined by Gotel et al, as "the ability to follow the life of a requirement in both a forward and backward direction". Each traceability link follows a basic life cycle.
Jarke et al identified four types of traceability that they referred to as (i) backwards from requirements, (ii) forwards to requirements, (iii) backwards to requirements, and (iv) forward from requirements .
1. Orlena Gotel, Anthony Finkelstein: Contribution structures (Requirements artifacts). RE 1995: 100-107.
2. Matthias Jarke: Requirements Tracing - Introduction. Commun. ACM 41(12): 32-36 (1998)