As illustrated in the sections above, the occurrence of anomalous mechanical or thermal properties in framework materials is widely considered to be higher than in "traditional" dense inorganic materials. A bibliographic search of the literature to date reveals more than one thousand papers about negative thermal expansion (NTE) on MOFs alone, while negative linear compressibility (NLC) in framework materials accounts for several hundreds of papers, and negative Poisson's ratio appears in a few hundreds. However, despite these many reports on the properties of specific materials, one question remains mostly open: how can we identify systematically frameworks with anomalous behavior, and what is their prevalence in the chemical space of interest?