So far, we've examined the Extract, Transform, and Load processes as distinct steps in handling data. We learned how to get data out of sources (Extract), how to clean and reshape it (Transform), and how to place it into a target system (Load). But the real power comes when these stages are linked together into an automated sequence. This connected sequence is what we call an ETL pipeline.

Think of an ETL pipeline like an automated assembly line for your data. Raw materials (your initial data) enter at one end, move through various processing stations (Extraction, Transformation), and emerge as a finished product (clean, structured data ready for use) at the other end, where it's stored (Loading).

An ETL pipeline, therefore, is a set of data processing steps executed in a specific order:

Extract: Data is retrieved from one or more source systems.
Transform: The extracted data undergoes cleaning, validation, structuring, and enrichment based on predefined rules.
Load: The transformed data is written into a target system, such as a database, data warehouse, or data lake.

The defining characteristic of a pipeline is that these steps are connected and often automated. The output of the Extraction stage serves as the input for the Transformation stage, and the output of Transformation becomes the input for the Loading stage. This creates a continuous flow of data from source to destination.

Here is a simple diagram illustrating this flow:

A typical ETL pipeline showing the sequence from data source, through Extract, Transform, and Load stages, to the target system.

Pipelines are designed to be repeatable and reliable. Instead of manually running each step every time new data needs processing, you define the pipeline once, and it can then be executed automatically on a schedule (e.g., daily, hourly) or triggered by specific events (e.g., a new file arriving).

The primary goal of building an ETL pipeline is to create a consistent, automated, and manageable process for moving and preparing data. This ensures that data arrives in the target system in the correct format and quality, ready for analysis, reporting, or use in applications.

In the following sections of this chapter, we'll look more closely at how these pipelines are structured, the types of tools used to build and manage them, and how to handle aspects like scheduling and monitoring.