The large number and heterogeneity of documents generated during the development of product line systems may cause difficulties to identify common and variable aspects among applications, and reuse of core assets available under the product line architecture. In this paper, we advocate the use of traceability relations to support product line engineering. We present a rulebased approach to allow for automatic generation of traceability relations between feature-based objectoriented documents. The rules are represented in an extension of XQuery and the documents are translated into XML. We present a traceability reference model with the different types of traceability relations and documents identified in our work, and describe our approach for automatic generation of traceability relations. A prototype tool has been developed to demonstrate and evaluate the approach.