Fully understanding object-oriented systems is difficult if one is limited to merely performing static analysis of the source code: Techniques based on dynamic analysis are needed. Several tools exist that implement techniques for analyzing traces of object interactions; however, due to lack of a common exchange format these tools do not interoperate. In this paper, we propose a graph-based format, called Compact Trace Format (CTF), for exchanging traces of object interactions. The design of CTF takes into account the size explosion problem that makes run-time information hard to manipulate. To achieve this, we start by presenting techniques for reducing the size of traces without affecting their content. Then, we show how the concept of transforming the tree representation of a trace into an acyclic compact graph can be used to define the core of CTF schema.