Modeling and understanding complex non-manifold shapes is a key issue in shape analysis and retrieval. The topological structure of a non-manifold shape can be analyzed through its decomposition into a collection of components with a simpler topology. Here, we consider a decomposition of a non-manifold shape into components which are almost manifolds, and we present a novel graph representation which highlights the non-manifold singularities shared by the components as well as their connectivity relations. We describe an algorithm for computing the decomposition and its associated graph representation. We present a new tool for visualizing the shape decomposition and its graph as an effective support to modeling, analyzing and understanding non-manifold shapes.