streamlined UUID and primary key sections

Author: dimitri-yatsenko

book/30-database-design/012-integrity.md

@@ -84,17 +84,19 @@ Completeness prevents missing values that could invalidate analyses:
 ---
 
 ## 3. Entity Integrity
-**Each entity has a unique, reliable identifier.**
+**Each real-world entity corresponds to exactly one database record, and each database record corresponds to exactly one real-world entity.**
 
-Entity integrity ensures one-to-one mapping between database records and real-world entities:
-- **Primary keys** uniquely identify each row
-- **Uniqueness constraints** prevent duplicates
-- **Identification strategies** (auto-increment, UUIDs, natural keys)
+Entity integrity ensures a **one-to-one correspondence** between real-world entities and their digital representations in the database. This is not simply about having unique identifiers—it's about establishing a reliable, bidirectional mapping where:
+- Each real-world entity must be represented by exactly one unique record in the database
+- Each database record must correspond to a single, distinct real-world entity
+- **Primary keys** uniquely identify each row and enable this correspondence
+- **Uniqueness constraints** prevent duplicate records for the same entity
+- **Identification strategies** (auto-increment, UUIDs, natural keys) support reliable entity matching
 
-**Example:** Each mouse has exactly one unique ID.
+**Example:** Each mouse in the lab has exactly one unique ID, and that ID refers to exactly one mouse—never two different mice sharing the same ID, and never one mouse having multiple IDs.
 
 **Covered in:**
-- [Primary Keys](025-primary-key.md) — Identification strategies
+- [Primary Keys](020-primary-key.md) — Entity integrity and the 1:1 correspondence guarantee (elaborated in detail)
 - [UUID](030-uuid.ipynb) — Universally unique identifiers
 
 ---

book/30-database-design/015-table2.ipynb renamed to book/30-database-design/015-table.ipynb

@@ -294,7 +294,7 @@ Surrogate keys are especially useful for entities that exist only in digital for
 
 ## Universally Unique Identifiers (UUIDs)
 
-**UUIDs** (Universally Unique Identifiers) are 128-bit identifiers that are designed to be globally unique across time and space. They are standardized by RFC 4122 and provide a reliable way to generate surrogate keys without coordination between different systems.
+**UUIDs** (Universally Unique Identifiers) are 128-bit identifiers that are designed to be globally unique across time and space. They are standardized by [RFC 9562](https://www.rfc-editor.org/rfc/rfc9562.html) (which obsoletes RFC 4122) and provide a reliable way to generate surrogate keys without coordination between different systems.
 
 ### UUID Format
 
@@ -387,6 +387,10 @@ print(uuid3_value)  # Different from UUID5 but also deterministic
 
 ### Practical UUID Examples
 
+For detailed examples of using UUIDs in DataJoint tables, including table definitions, insertion code, and working with UUIDs in foreign key relationships, see [UUIDs in DataJoint](025-uuid.ipynb).
+
+Here are some conceptual examples showing UUIDs as primary keys:
+
 #### Example 1: Social Media Posts
 (DataJoint)
 ```python
@@ -497,32 +501,7 @@ Different databases handle UUIDs differently:
 - **SQLite**: TEXT or BLOB
 - **SQL Server**: UNIQUEIDENTIFIER type
 
-(DataJoint)
-```python
-@schema
-class User(dj.Manual):
-    definition = """
-    user_id : uuid
-    ---
-    username : varchar(50)
-    """
-```
-
-(Equivalent SQL)
-```sql
--- MySQL
-CREATE TABLE user (
-    user_id BINARY(16),
-    username VARCHAR(50) NOT NULL,
-    PRIMARY KEY (user_id)
-);
-
--- PostgreSQL
-CREATE TABLE user (
-    user_id UUID NOT NULL PRIMARY KEY DEFAULT gen_random_uuid(),
-    username VARCHAR(50) NOT NULL
-);
-```
+In DataJoint, UUIDs are automatically stored as `BINARY(16)` in MySQL for efficient storage. See [UUIDs in DataJoint](025-uuid.ipynb) for practical implementation examples.
 
 
 # Practical Examples of Ensuring Entity Integrity