sequence diagram for point of sale terminal

This context-level DFD is next “exploded” to produce a Level 1 DFD that shows some of the detail of the system being modeled. The context diagram shows the entire system as a single process and gives no clues as to its internal organization. The system’s interactions with the outside world are modelled purely in terms of data flows across the system boundary. This helps to create an accurate drawing in the context diagram. It is common practice to draw the context-level data flow diagram first, which shows the interaction between the system and external agents that act as data sources and data sinks. Thus, the identification of entities and relationships offers a comprehensive view of the structure of the database of the current or proposed system and assists in both system analysis and design phases of the SDLC. A relationship, illustrated with a diamond, refers to the connection of two entities, such as a sale to a customer generating a sales invoice. In an ERD, an entity represented by a rectangle is an external or internal element or a transaction of an organization, for example, a customer or a sale. Chen in 1976, are a conceptual modeling technique emphasizing data entities of an organization and their relationships, complementing, thus, DFD. Entity–relationship diagrams (ERD), proposed by P. Entity–Relationships DiagramsĭFD, despite its name, is a logical modeling tool focusing mainly on processes without emphasizing data relationships and flows.

Stefanou, in Encyclopedia of Information Systems, 2003 IV.A.3.

Sequence diagram for point of sale terminal