fix link in normalization

Author: dimitri-yatsenko

book/30-schema-design/055-normalization.ipynb

@@ -45,7 +45,7 @@
         "\n",
         "**Attributes are subject to functional dependencies:** some attributes determine the values of others. Normalization ensures well-designed relations avoid storing data with tangled functional dependencies.\n",
         "\n",
-        "Mathematical normalization is founded on the Closed World Assumption (CWA) [@10.1145/320107.32010]. The CWA is the assumption that the only facts that are true are those that are explicitly stated in the database. Facts that are not stated in the database are assumed to be false: If a student enrollment is missing from the database, we assume that the student is not enrolled in that course. This is a simplifying assumption that allows us to reason about the data in the database in a more precise way.\n",
+        "Mathematical normalization is founded on the Closed World Assumption (CWA) [@10.1145/320107.320109]. The CWA is the assumption that the only facts that are true are those that are explicitly stated in the database. Facts that are not stated in the database are assumed to be false: If a student enrollment is missing from the database, we assume that the student is not enrolled in that course. This is a simplifying assumption that allows us to reason about the data in the database in a more precise way.\n",
         "\n",
         "This is an abstract, mathematical approach that requires reasoning about attribute-level dependencies independent of real-world entities.\n",
         "\n",