Discovery is a qualitative process. It identifies nouns (things) and verbs (actions, transformations, decisions, calculations).
Data Collection is a quantitative process. It identifies adjectives (colors, dimensions, rates, times, volumes, capacities, materials, properties).
Discovery comes first, so you know what data you need to collect.
Imagine you're going to simulate or automate the process. What values do you need? This is the information the implementation teams will need.
Elicitation is discovering the customer's needs. Discovery is about mapping the customer's existing process.
If there is no existing process, i.e., a new (greenfield) process is being built from scratch, then a form of discovery will occur during Requirements and Design.
Process Mapping is a big part of discovery. A picture is worth a thousand words. An animation is worth even more.
Processes may be mapped differently based on needs, industry standards, and the information to be represented.
I give specific names to modular components.
Discovery and Data Collection both make use of the Observation technique in the BABOK. Methods include:
Domain Knowledge Acquisition: https://rpchurchill.com/wordpress/posts/2018/05/21/domain-knowledge-acquisition/
This presentation and other information can be found at my website: