diff --git a/Physical_modelling.bib b/Physical_modelling.bib
index 7ec292a..48d0b30 100755
--- a/Physical_modelling.bib
+++ b/Physical_modelling.bib
@@ -125,7 +125,6 @@
   number = {4},
   month = dec,
   doi = {doi:10.1145/4879.5392},
-  pdf = {B/Bato-DS-1985.pdf},
 }
 
 @BOOK{BeDa-P-2003,
@@ -159,7 +158,6 @@
   number = {6},
   month = jun,
   doi = {doi:10.1145/362384.362685},
-  pdf = {C/Codd-EF-1970.pdf},
 }
 
 @BOOK{Conn-TM-2002,
@@ -233,7 +231,6 @@
   pages = {65--68},
   number = {5},
   month = may,
-  pdf = {R/Roti-S-1996.pdf},
 }
 
 @BOOK{Silb-A-2002-4E,
@@ -280,3 +277,48 @@
   month = jun,
 }
 
+@INPROCEEDINGS{Ceri-S-1982-partition,
+  author = {Stefano Ceri and Mauro Negri and Giuseppe Pelagatti},
+  title = {Horizontal data partitioning in database design},
+  booktitle = {Proceedings of the 1982 ACM SIGMOD International Conference on Management of Data},
+  year = {1982},
+  editor = {Mario Schkolnick},
+  pages = {128--136},
+  address = {Orlando, Florida, USA},
+  month = jun # {~2--4},
+  publisher = {ACM Press},
+  doi = {doi:10.1145/582353.582376},
+}
+
+@ARTICLE{Pete-W-1957-hash,
+  author = {W. W. Peterson},
+  title = {Addresssing for random access storage},
+  journal = {IBM Journal of Research and Development},
+  year = {1957},
+  volume = {1},
+  pages = {130--146},
+  number = {2},
+}
+
+@INPROCEEDINGS{Onei-PE-1987-bitmap,
+  author = {Patrick E. O'Neil},
+  title = {Model 204: {A}rchitecture and performance},
+  booktitle = {High Performance Transaction Systems, Second International Workshop},
+  year = {1987},
+  editor = {Dieter Gawlick and Mark N. Haynie and Andreas Reuter},
+  volume = {359},
+  series = {Lecture Notes in Computer Science},
+  pages = {40--59},
+  address = {Pacific Grove, California, USA},
+  month = sep # {~28--30},
+  publisher = {Springer},
+}
+
+@BOOK{Shas-DE-2003-tuning,
+  title = {Database Tuning: Principles, Experiments, and Troubleshooting Techniques},
+  publisher = {Morgan Kaufmann},
+  year = {2003},
+  author = {Dennis E. Shasha and Philippe Bonnet},
+  address = {San Francisco, California, USA},
+  isbn = {1558607536},
+}