The usefulness of design patterns in forward engineering is already well-known and several tools provide support for their application in the development of software systems. While the role of design patterns in reverse engineering is still argued primarily due to their informal definition which leads to various possible implementations of each pattern. One of the most discussed aspects related to design patterns is about the need of their formalization according to the drawbacks this can represent. Formalization leads to the identification of the so-called sub-patterns, which are the recurring fundamental elements design patterns are composed of. In this paper we analyze the role sub-patterns play in two reverse engineering tools: FUJABA and SPQR. Attention is focused on how sub-patterns are exploited to define and to detect design patterns. To emphasize the similarities and differences between the two approaches, the Composite Design Pattern is considered as example.