Traceability enables the developer to keep track of changes in software development artifacts. Compared to that of single product development, traceability management in software product line development is much more complicated as it has to deal with traceability of individual products through the commonality and variability of the families of products. However, the existing traceability research treated traceability for families of products in an ad-hoc way and did not adequately address the relationship between traceability of domain engineering artifacts and that of application engineering artifacts. In this paper, we develop a formal representation that represents traceability between features and requirements at platform level. Also we present a procedure for constructing platform traceability from the trace abilities of a family of products. The proposed traceability representation and construction can be used as a basis for automated management of software product line trace abilities and for traceability representation and construction between artifacts of other stages of software product line.