In data warehousing ETL processes, populating a fact table requires looking up business keys in dimension tables to retrieve their corresponding surrogate keys.

The 'Dimension lookup/update' step is the primary tool for this. It is specifically designed to manage slowly changing dimensions (SCDs) by looking up a business key, returning the technical (surrogate) key, and optionally updating the dimension if the key is not found or has changed.

The 'Combination lookup/update' step is used for a specific type of dimension, often called a "junk dimension." It looks up a combination of low-cardinality fields and returns a single surrogate key, creating a new dimension entry if the combination is new. Both steps accomplish the core task of retrieving surrogate keys from a dimension to be used in a fact table.

C. the 'Select values' step: This step alters the stream's metadata, such as renaming fields or changing data types. It does not perform database lookups to retrieve keys.

D. the 'Filter rows' step: This step routes rows to different outputs based on specified conditions. It is used for flow control, not for retrieving data from a dimension table.

1. Hitachi Vantara - Pentaho Documentation

Dimension lookup/update step: This official documentation describes the step's purpose: "This step allows you to implement slowly changing dimensions (SCDs). You can use this step to look up and update a dimension table... The step adds a new field to the stream containing the technical key from the dimension."

Source: Hitachi Vantara Pentaho 9.4 Documentation

"Dimension lookup/update".

2. Hitachi Vantara - Pentaho Documentation

Combination lookup/update step: This document explains the step's function for junk dimensions: "This step allows you to look up and update a junk dimension... The step returns a technical key for the combination of dimension fields."

Source: Hitachi Vantara Pentaho 9.4 Documentation

"Combination lookup/update".

3. Kimball

R.

& Ross

M. (2013). The Data Warehouse Toolkit: The Definitive Guide to Dimensional Modeling (3rd ed.). Wiley. While not specific to Hitachi Vantara software

this foundational academic text describes the underlying principles. Chapter 6

"Fact Table Core Concepts

" details the process of replacing natural keys with surrogate keys during the ETL load process

which is the exact function performed by the 'Dimension lookup/update' and 'Combination lookup/update' steps.

Source: Chapter 6

"Fact Table Core Concepts

" and Chapter 7

"Fact Table Systems

" pp. 165-170

201-205.