Hard Nuts (in XML Cardinality Estimation)


-  Integration with       - e.g. StatiX exploits it during construction;
   schema information       limited integration during estimation

-  Slow construction      - full document scan required and CPU inten-
                            sive, e.g. for 100 MB document: construction 
                            time 10 min

-  //A//B                 - Only Position Histogram and Graph Synopsis 
                            support descendent-or-self at arbitrary
                            positions in the XPath expression

-  //A[3]/B               - estimate might depend on requested position

-  /A/following-sibling::B 
                          - sibling axes not supported by any approach

-  //A/following::B       - following or preceeding axis not supported by
                            any approach