clean up diagramming section

Author: dimitri-yatsenko

book/20-concepts/01-relational.md

@@ -244,6 +244,12 @@ erDiagram
 Entity-relationship diagram in Crow's Foot notation, including an explicit relationship set. 
 :::
 
+```{figure} ../images/employee-project-datajoint.svg
+:align: center
+
+DataJoint diagram for the same design
+```
+
 
 # The DataJoint Model
 DataJoint solves a major dilemma in how relational databases are taught today [@10.48550/arXiv.1807.11104]

book/30-schema-design/035-diagrams.ipynb

@@ -62,7 +62,20 @@
     "    definition = \"\"\"\n",
     "    project_code  : varchar(8)\n",
     "    ---\n",
-    "    \"\"\""
+    "    project_title : varchar(50)\n",
+    "    start_date : date\n",
+    "    end_date : date\n",
+    "    \"\"\"\n",
+    "\n",
+    "@schema\n",
+    "class Assignment(dj.Manual):\n",
+    "    definition = \"\"\"\n",
+    "    -> Employee\n",
+    "    -> Project\n",
+    "    ---\n",
+    "    percent_effort : decimal(4,1) unsigned\n",
+    "    \"\"\"\n",
+    "\n"
    ]
   },
   {