Restore Classic Sales ER diagram in Diagramming chapter

Add the MySQL tutorial ER diagram image to the Real-World Example section
and include a comparison table highlighting differences between traditional
Crow's Foot notation and DataJoint's workflow-centric diagram notation.
Also add cross-reference to the Classic Sales example.

Author: claude

book/30-design/060-diagrams.ipynb

@@ -411,11 +411,7 @@
   {
    "cell_type": "markdown",
    "metadata": {},
-   "source": [
-    "## Real-World Example: Classic Sales Database\n",
-    "\n",
-    "Let's examine a real database—the [MySQL tutorial sample database](https://www.mysqltutorial.org/getting-started-with-mysql/mysql-sample-database/):"
-   ]
+   "source": "## Real-World Example: Classic Sales Database\n\nLet's examine a real database—the [MySQL tutorial sample database](https://www.mysqltutorial.org/getting-started-with-mysql/mysql-sample-database/).\n\n### Traditional ER Diagram\n\nHere is the classic Entity-Relationship diagram from the MySQL tutorial:\n\n![Classic Sales ER Diagram](../images/mysql-classic-sales-ERD.png)\n\nThis diagram uses Crow's Foot notation, where:\n- Lines with crow's feet indicate \"many\" relationships\n- Single lines indicate \"one\" relationships\n- The diagram shows cardinality but not the semantic nature of relationships\n\n### DataJoint Diagram\n\nNow let's see how the same database appears in DataJoint notation:"
   },
   {
    "cell_type": "code",
@@ -432,15 +428,7 @@
   {
    "cell_type": "markdown",
    "metadata": {},
-   "source": [
-    "**Reading this diagram**:\n",
-    "1. **Independent entities at top**: `Productline`, `Office`, `Customer` (underlined)\n",
-    "2. **Follow solid lines down**: Track how primary keys cascade through the hierarchy\n",
-    "3. **Identify association tables**: Look for converging lines (e.g., `Orderdetail` links `Order` and `Product`)\n",
-    "4. **Dashed lines**: Reference relationships that don't cascade identity\n",
-    "\n",
-    "The vertical layout reveals the workflow: create products and customers first, then orders, then order details."
-   ]
+   "source": "### Comparing the Two Diagrams\n\n**Reading the DataJoint diagram**:\n1. **Independent entities at top**: `Productline`, `Office`, `Customer` (underlined)\n2. **Follow solid lines down**: Track how primary keys cascade through the hierarchy\n3. **Identify association tables**: Look for converging lines (e.g., `Orderdetail` links `Order` and `Product`)\n4. **Dashed lines**: Reference relationships that don't cascade identity\n\n**Key differences from the ER diagram**:\n\n| Aspect | Traditional ER (Crow's Foot) | DataJoint |\n|--------|------------------------------|-----------|\n| **Layout** | Arbitrary arrangement | Top-to-bottom workflow order |\n| **Line meaning** | Cardinality only (one vs. many) | Semantic relationship type |\n| **Primary key cascade** | Not visible | Solid lines show direct join paths |\n| **Workflow sequence** | Must read documentation | Clear from vertical structure |\n\nThe vertical layout reveals the workflow: create product lines and offices first, then products and employees, then customers and orders, and finally order details and payments.\n\n:::{seealso}\nFor the complete schema with data and example queries, see the [Classic Sales](../80-examples/010-classic-sales.ipynb) example.\n:::"
   },
   {
    "cell_type": "markdown",
@@ -619,4 +607,4 @@
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+}