[M] added missing DOI

paper.bib

@@ -3,7 +3,8 @@
   author={Cranshaw, Justin and Schwartz, Raz and Hong, Jason I and Sadeh, Norman},
   booktitle={International AAAI Conference on Weblogs and Social Media},
   pages={58},
-  year={2012}
+  year={2012},
+  url = {https://ssrn.com/abstract=2168428}
 }
 
 @inproceedings{zhang2013hoodsquare,
@@ -12,7 +13,8 @@
   booktitle={2013 International Conference on Social Computing},
   pages={69--74},
   year={2013},
-  organization={IEEE}
+  organization={IEEE},
+  doi={10.1109/socialcom.2013.17}
 }
 
 @INPROCEEDINGS{data20,
@@ -23,4 +25,5 @@
   author = {Nelly Barret and Fabien Duchateau and Franck Favetta and Loïc Bonneval},
   booktitle = {International Conference on Data Management Technologies and Applications (DATA)},
   pages = {294-301},
+  doi={10.5220/0009885702940301}
 }
\ No newline at end of file