ETL Concepts

ETL Concepts

Extraction, transformation, and loading. ETL refers to the methods involved in accessing and manipulating source data and loading it into target database.

The first step in ETL process is mapping the data between source systems and target database(data warehouse or data mart). The second step is cleansing of source data in staging area. The third step is transforming cleansed source data and then loading into the target system.

Note that ETT (extraction, transformation, transportation) and ETM (extraction, transformation, move) are sometimes used instead of ETL.

Glossary of ETL

Source System

A database, application, file, or other storage facility from which the data in a data warehouse is derived.

Mapping

The definition of the relationship and data flow between source and target objects.

Metadata

Data that describes data and other structures, such as objects, business rules, and processes. For example, the schema design of a data warehouse is typically stored in a repository as metadata, which is used to generate scripts used to build and populate the data warehouse. A repository contains metadata.

Staging Area

A place where data is processed before entering the warehouse.

Cleansing

The process of resolving inconsistencies and fixing the anomalies in source data, typically as part of the ETL process.

Transformation

The process of manipulating data. Any manipulation beyond copying is a transformation. Examples include cleansing, aggregating, and integrating data from multiple sources.

Transportation

The process of moving copied or transformed data from a source to a data warehouse.

Target System

A database, application, file, or other storage facility to which the "transformed source data" is loaded in a data warehouse.

Figure 1.12 : Sample ETL Process Flow