fix deploy action

Author: dimitri-yatsenko

.github/workflows/main.yml

@@ -45,9 +45,11 @@ jobs:
           myst build --html
 
       - name: Upload artifact for deployment
+        if: github.ref == 'refs/heads/main'
         uses: actions/upload-pages-artifact@v3 
         with:
           path: './book/_build/html'
+          name: github-pages
           retention-days: 1  # save storage 
 
   deploy:

book/30-schema-design/060-diagrams.ipynb

@@ -560,80 +560,7 @@
     "     ↓                  ↓\n",
     "        AuthorBook\n",
     "```\n",
-    "\n",
-    "In code:\n",
-    "```python\n",
-    "@schema\n",
-    "class Author(dj.Manual):\n",
-    "    definition = \"\"\"\n",
-    "    author_id : int\n",
-    "    ---\n",
-    "    name : varchar(100)\n",
-    "    \"\"\"\n",
-    "\n",
-    "@schema\n",
-    "class Book(dj.Manual):\n",
-    "    definition = \"\"\"\n",
-    "    isbn : varchar(13)\n",
-    "    ---\n",
-    "    title : varchar(200)\n",
-    "    \"\"\"\n",
-    "\n",
-    "@schema\n",
-    "class AuthorBook(dj.Manual):\n",
-    "    definition = \"\"\"\n",
-    "    -> Author\n",
-    "    -> Book\n",
-    "    ---\n",
-    "    author_order : tinyint\n",
-    "    \"\"\"\n",
-    "```\n",
-    "\n",
-    "**Features**:\n",
-    "- No special notation for association table—looks like any other table\n",
-    "- Thin solid lines indicate foreign keys are in primary key (cascading identity)\n",
-    "- Top-to-bottom layout shows you can populate Author and Book first, then AuthorBook\n",
-    "- Underlined names show Author and Book are independent dimensions\n",
-    "\n",
-    "### Key Observations\n",
-    "\n",
-    "1. **Cyclic vs. Acyclic**:\n",
-    "   - Traditional notations allow: `Employee ←→ Department ←→ Manager ←→ Employee` (cycle)\n",
-    "   - DataJoint requires: `Employee` → `Department` → `DepartmentManager` (acyclic)\n",
-    "\n",
-    "2. **Information Density**:\n",
-    "   - Crow's Foot shows more detail (nullable, optional)\n",
-    "   - DataJoint emphasizes structure and flow\n",
-    "   - Both require hovering/inspection for complete details\n",
-    "\n",
-    "3. **Semantic Meaning**:\n",
-    "   - Traditional: Focus on cardinality (how many)\n",
-    "   - DataJoint: Focus on identity cascade (how entities relate conceptually)\n",
-    "\n",
-    "4. **Reading Strategy**:\n",
-    "   - Crow's Foot: Examine each endpoint's symbols\n",
-    "   - DataJoint: Follow the line styles and direction\n",
-    "\n",
-    "### When Each Notation Excels\n",
-    "\n",
-    "**Use Chen's ER when**:\n",
-    "- Doing initial conceptual modeling\n",
-    "- Working with business stakeholders\n",
-    "- Need to explicitly name relationships\n",
-    "- Database implementation is secondary\n",
-    "\n",
-    "**Use Crow's Foot when**:\n",
-    "- Documenting existing databases\n",
-    "- Cardinality and optionality are critical\n",
-    "- Working with DBAs familiar with this standard\n",
-    "- Need to show all relationship details\n",
-    "\n",
-    "**Use DataJoint when**:\n",
-    "- Designing scientific workflows\n",
-    "- Primary key cascade matters for your queries\n",
-    "- Working with hierarchical or time-series data\n",
-    "- The DAG structure matches your domain (no cycles)\n",
-    "- You want diagrams to be executable (code generates diagrams)"
+    "\n"
    ]
   },
   {