After the requirements have been documented, they should be verified.
The process of verification involves determining where are the sinks and the sources of information.

Source

A source can be determined by tracing back from the requirement (needs and constraints) to the one who initiated that action (which could be a person or organization or another action).

Sink

A sink is a consumer of the result produced by the system.
Example: A user requests a report to be generated by the system. When the user reviews the report, he becomes a sink of the system.

Sometimes, there is redundancy of data, then we have to ask ourselves if there is something missing or the data is really useless?
Example: We performed source analysis and now know all the inputs. But we do not know the outputs (or perhaps they don't) exist at all? That is why we delete the inputs as redundant. Now when the sink is analyzed, we realize there are outputs which weren't recorded before so those inputs which got deleted weren't really redundant.

Process Models

Domain Models

During requirement analysis, different models are developed, these are very similar and contain explanation to the diagrams.

Business Domain

A software engineer has to understand the business requirements.
He has to understand how the business problem can be solved.
He has to learn the vocabulary of the workers of the business.
He might have to deal with problems which aren't related to his specialization.

Logical System Models

System models are techniques which help software engineers to understand the user needs and model business processes.
System models include: 1. User business processes. 2. User activities to conduct those processes. 3. Processes that need to be automated. 4. Processes that do not need to be automated.

Business Process Model

This provides a higher level pictorial model of the system to provide the reader, a basic overview.