data-modeling

# Data Modeling

## When to Use This Skill

Use this skill when:

- **Data Modeling tasks** - Working on data modeling with entity-relationship diagrams (erds), data dictionaries, and conceptual/logical/physical models. documents data structures, relationships, and attributes
- **Planning or design** - Need guidance on Data Modeling approaches
- **Best practices** - Want to follow established patterns and standards

## Overview

Create and document data structures using Entity-Relationship Diagrams (ERDs), data dictionaries, and structured data models. Supports conceptual, logical, and physical modeling levels for database design and data architecture.

## What is Data Modeling?

**Data modeling** creates visual and structured representations of data elements and their relationships. It documents:

- **Entities**: Things about which data is stored
- **Attributes**: Properties of entities
- **Relationships**: How entities connect
- **Constraints**: Rules governing data

## Modeling Levels

| Level | Purpose | Audience | Detail |
|-------|---------|----------|--------|
| **Conceptual** | Business concepts | Business users | Entities, high-level relationships |
| **Logical** | Data structure | Analysts, designers | Entities, attributes, all relationships |
| **Physical** | Implementation | Developers, DBAs | Tables, columns, types, indexes |

### Conceptual Model

High-level view of business concepts:

- Major entities only
- Key relationships
- No attributes (or minimal)
- No technical details

### Logical Model

Technology-independent data structure:

- All entities and attributes
- Primary and foreign keys
- All relationships with cardinality
- Normalization applied
- No physical implementation details

### Physical Model

Database-specific implementation:

- Table names (physical naming)
- Column names and data types
- Indexes and constraints
- Views and stored procedures
- Database-specific features

## ERD Notation

### Entity (Rectangle)

An entity represents a