Documenting database schemas

Posted on:October 8, 2023 at 10:33 PM

Effective database documentation plays a crucial role in maintaining data accessibility, comprehensibility, and security. In this article, we’ll look at how to document database objects, provide practical strategies for describing a database schema, and explore diverse approaches to crafting comprehensive schema documentation.

Table of contents

Open Table of contents

Understanding databases and schemas

Before we dive into the details, let’s clarify some fundamental concepts:

Tables are the primary database objects that store data in a tabular format. Each row in a table represents a single record or entity, while each column denotes an attribute or field of that record. In any given database, multiple schemas can provide different organizational methods for its components.

Key Aspects of database documentation

Adequate documentation is the cornerstone of a well-managed database. Here are vital aspects to consider:

1. Comments and descriptions

Most modern relational database management systems (RDBMS) allow you to add comments or descriptions to various database objects, providing context, explanations, and usage notes.

2. Data dictionary tables

Some databases have dedicated tables or schemas where metadata and documentation about the database’s structure are stored, including metadata for tables, columns, indexes, constraints, and more information.

3. Naming conventions

Clearly defined naming conventions for database objects ensure consistency, meaning, and understanding among users.

4. Data flow diagrams

For complex databases, data flow diagrams visually represent how data moves within the system, showing relationships between tables, views, and procedures.

5. Entity-relationship diagrams (ERDs)

ERDs provide graphical representations of the database schema, helping users visualize the structure and relationships between entities.

6. User guides

Detailed user guides or manuals instruct users on interacting with the database, executing queries, and utilizing stored procedures or views.

7. Data dictionary views

System views or catalog tables in some databases offer valuable metadata about database objects to include in the documentation.

8. Change logs

Maintaining change logs or version histories informs users about the database’s evolution, documenting modifications and updates.

9. Access control and security guidelines

Incorporating information about user roles, permissions, and security guidelines ensures the secure and controlled use of the database.

10. Sample Queries and use cases

Providing sample SQL queries and use cases illustrates practical data retrieval and manipulation.

Effectively describing a database schema

Let’s explore adequate database schema documentation through an example:

Example: Device management schema

Here’s an example of external database schema documentation. This documentation effectively conveys vital points such as data meaning, relationships, business processes, user roles, usage, constraints, example values, data source, data evolution, and significant views.

The following key points make this schema documentation effective:

Data Meaning

This schema manages data related to various electronic devices, particularly IoT devices, and records their operational events. It serves as a central repository for critical information about device events, performance, and health.

Relationships

The schema establishes relationships primarily between the device_event and device_procedures tables. These relationships enable correlations between device events and maintenance procedures, aiding in troubleshooting and performance analysis.

Business Process

The data within this schema directly supports the management of electronic devices, particularly IoT devices, by capturing and analyzing their operational events. It is integral to optimizing device performance and ensuring their efficient operation.

User Roles

This schema is relevant to various user roles within an organization, including device administrators, maintenance teams, and technical staff responsible for managing electronic devices and maintaining their health.

Data Usage

The data within this schema serves multiple purposes, including:

Constraints and Validation

Constraints are applied to ensure data integrity and maintain referential integrity for table relationships. This ensures that the data remains accurate and consistent throughout its use.

Example Values

Sample data values for event_id, device_id, event_timestamp, event_type, and event_details could be added to illustrate typical event log entries and their relevance. For instance:

Data Source

The data source for this schema includes electronic devices, particularly IoT devices, within the organization’s infrastructure. It captures event logs generated by these devices.

Data Evolution

Over time, the schema accumulates records of electronic device events and maintenance procedures, providing historical insights into device behavior, performance trends, and maintenance history.

Views

Two key views are available in this schema:’

Ways to Document Schemas

Now, let’s discuss how to document database schemas effectively:

Option 1: Annotate within the database

You can add comments or descriptions directly to database objects using SQL commands. This approach is suitable when only database designers or developers contribute to documentation.

For example, in PostgreSQL, you can add comments using the COMMENT command:

COMMENT ON SCHEMA public IS 'Main schema for application';
COMMENT ON TABLE customers IS 'Stores customer information';
COMMENT ON COLUMN customers.customer_id IS 'Unique identifier for customers';

Option 2: Store metadata separately

Create tables within the database to store metadata and documentation about schemas, tables, and columns, allowing technical writers to maintain documentation independently.

Here’s a simplified example in PostgreSQL:

CREATE TABLE metadata (
    table_name VARCHAR(255),
    column_name VARCHAR(255),
    description TEXT
);

Option 3: Document externally

This method involves maintaining documentation outside the database, often in structured formats. While it provides flexibility, it can lead to inconsistencies if not synchronized with schema changes.

Here are the critical steps for external documentation:

  1. Choose a documentation format: Select a format that suits your team’s needs, such as plain text, Markdown, PDF, HTML, or specialized documentation tools.

  2. Structure the documentation: Organize content logically, covering schema overview, tables, views, procedures, relationships, data dictionary, usage, security, and change history.

  3. Describe schema objects: Provide comprehensive descriptions for each object, including purpose, columns, relationships, usage, constraints, and examples.

  4. Highlight key points: Include a section summarizing critical aspects like data meaning, user roles, data source, and views.

  5. Include visuals (optional): Visual representations like entity-relationship diagrams can enhance understanding.

Extra Credit: View documentation using SchemaCrawler

If you choose to document database objects within the database, tools like SchemaCrawler can help retrieve metadata and generate documentation.

To learn more about SchemaCrawler’s capabilities as a database schema discovery tool, check out their website (https://www.schemacrawler.com/) as well as their excellent interactive tutorials on Killacoda at (https://killercoda.com/schemacrawler).

Wrapping up

In conclusion, adequate database documentation ensures clarity, efficiency, and security. Whether you annotate within the database, store metadata separately, or document externally, the goal is to empower your team with the knowledge needed to manage and utilize the database effectively.

Start documenting today to guide your database journey and make it a valuable asset for your organization.