In many software intensive systems traceability is used to support a variety of software engineering activities such as impact analysis, compliance verification, and requirements validation. However, in practice, traceability links are often created towards the end of the project specifically for approval or certification purposes. This practice can result in inaccurate and incomplete traces, and also means that traceability links are not available to support early development efforts. We address these problems by presenting a trace recommender system which pushes recommendations to project stakeholders as they create or modify traceable artifacts. We also introduce the novel concept of a trace obligation, which is used to track satisfaction relations between a target artifact and a set of source artifacts. We model traceability events and subsequent actions, including user recommendations, using the Business Process Modeling Notation (BPMN). We demonstrate and evaluate the efficacy of our approach through an illustrative example and a simulation conducted using the software engineering artifacts of a robotic system for supporting arm rehabilitation. Our results show that tracking trace obligations and generating trace recommendations throughout the active phases of a project can lead to early construction of traceability knowledge.