ETL Testing - BRD Mapping

Understanding Business Requirements in ETL Testing

When working with ETL (Extract, Transform, Load) testing in a data warehouse project, the first and most important step is understanding the business requirements. Without clear requirements, ETL testing cannot be performed efficiently. This article explains what business requirements look like in ETL testing, their importance, and how they help in data validation.

What is a Business Requirement Document (BRD)?

A Business Requirement Document (BRD) is a formal document that outlines all the objectives and requirements of a project, program, or business solution. It explains why the project is being developed and what it aims to achieve. In ETL testing, the BRD helps ensure that data is extracted, transformed, and loaded correctly from source systems to the target data warehouse.

Other similar documents include:

• SRS (Software Requirement Specification): Defines software functionality requirements.

• PRD (Product Requirement Document): Outlines product-related requirements.

In data warehouse projects, the BRD also includes details about the business needs and expected outcomes as the project progresses.

Key Documents in ETL Testing

In ETL testing, two critical documents are used to ensure data correctness and consistency:

1. ETL Mapping Document (Mapping Sheet)

2. Database Schema Document (Source and Target Schema)

1. ETL Mapping Document

The ETL mapping document contains detailed information about data sources and their target destinations. It includes:

• Source table names and fields.

• Target table names and fields.

• Data transformation rules.

• Reference tables and lookup values.

For example, consider a banking project. The source table Account_SRC has columns such as Account Number, Customer ID, Branch Code, and Account Type. The target table DW_Account (data warehouse table) stores the transformed data. If an Account Number in the source table has 8 digits, but the target table requires 10 digits, the transformation rule will pad zeros in the beginning to make it 10 digits (e.g., 12345678 → 0012345678).

The mapping document helps testers verify that transformations are applied correctly before moving data to the data warehouse.

2. Database Schema Document

The schema document defines the structure of source and target tables, including:

• Column names.

• Data types.

• Any transformations applied.

For example, in the Customer Table, the source schema may contain:

• First Name

• Last Name

• Customer ID

In the target schema, the transformation may combine First Name and Last Name into a single Full Name column. This change should be documented in the schema so testers can validate it correctly.

Why Are These Documents Important?

These documents play a crucial role in ETL testing by:

• Ensuring data consistency and accuracy between the source and target systems.

• Defining transformation rules so testers can verify data changes.

• Helping in identifying errors, missing data, or incorrect transformations.

Conclusion

Business requirement documents (BRD), ETL mapping documents, and schema documents are essential in ETL testing. They help testers understand how data should be transformed and stored in the data warehouse. By using these documents, ETL testers can ensure that data is correctly extracted, transformed, and loaded, resulting in accurate and reliable business reports.