The flow of a web application is characterized by the systematic organization of web pages, page data, page actions, and mappings to logic and the interconnection of these components.
Data flow diagrams are used to graphically represent the flow of data in a business information system.
A use case is a description of how a person who actually uses that process or system will accomplish a goal.
An Entity Relationship Diagram (ERD) is a visual representation of different entities within a system and how they relate to each other.