Layer Compression in Decision Diagrams

A number of compact representation forms that are investigated in the knowledge compilation community are utilized in interactive product configuration and other forms of decision support. Multi-valued decision diagrams (MDDs) are particularly well suited for interactive configuration. However, for large variable domains MDDs can be unnecessarily large if many values are repeating on different edges. In this paper we suggest exploiting the repetitive occurrences of values through the introduction of pseudo-nodes. The technique can be easily applied over MDDs as well as their more succinct counterpart, interval decision diagrams (IDDs). The compactness of the resulting representations, layer-compressed MDDs (lcMDDs) and layer-compressed IDDs (lcIDDs), is demonstrated empirically on artificial and real-world instances.