1.3Business modeling

Business modeling is not the work of "mechanically drawing a fixed diagram." Even when visualizing the same business, the notation to choose (DFD/E-R diagram/UML/BPMN) depends on whether you want to clarify the relationship between data flow and processing, the structure of the data, the interaction between users and the system, or the branching, concurrency, and division of roles across an entire business process. Choosing a notation that does not fit the purpose fails to visualize the information you want to convey, and alignment with stakeholders breaks down.

1.3.1DFD and the E-R diagram

• A DFD (data flow diagram) is a notation that diagrams the relationships among data flow, processing (processes), data stores, and input/output with the outside world in a business or system. It suits analysis of the current state and consideration of business improvement, with a focus on the flow of data—which data, passing through which process, gets stored or output where.
• An E-R diagram (Entity-Relationship Diagram) is a notation that diagrams the entities of data handled by the business and the relationships among those entities. It suits designing the data structure and laying the groundwork for database design—what data items exist and how they relate. Where a DFD focuses on "the flow of data," an E-R diagram differs by focusing on "the structure of data."

1.3.2UML (use case diagram) and BPMN

• The use case diagram in UML (Unified Modeling Language) diagrams the interaction between users (actors) and the functions the system provides (use cases). It suits building consensus on the functional scope of the system—to whom, and enabling what, the system should provide. It does not express the internal procedural detail of a business process (who does what, in what order).
• BPMN (Business Process Model and Notation) diagrams, along a timeline, the procedure, branching (conditional branches), concurrent processing, and division of roles among multiple parties (lanes) across an entire business process. It suits As-Is/To-Be contrast of the whole business process—where the current procedure is inefficient, and what the desired procedure should be. Where a DFD focuses on the flow of data, BPMN focuses on the procedure and control flow of processing.

Suppose you are the system architect at a logistics company, and, given the issue that "the business process from shipping instruction to delivery completion is inefficient, with frequent delays in coordination between departments," you are tasked with current-state analysis via business modeling. A colleague proposes, "let's first draw an E-R diagram and enumerate all the data items involved." But the essence of this issue is not a surplus or shortage of data items—it is in what order, under what conditional branches, and who is responsible for what as processing is handed off among multiple parties: the shipping-instruction department, the warehouse department, and the delivery department. An E-R diagram suits clarifying data structure (entities and relationships), but it does not suit the purpose of visualizing the procedure, branching, and concurrency of processing that spans multiple departments. The notation to choose in this scenario is BPMN. By placing the shipping-instruction, warehouse, and delivery departments as separate lanes and arranging each department's processing along a timeline, you can visualize where the As-Is is inefficient—for example, "delivery instructions are backing up waiting on the warehouse department's inventory check" or "a particular conditional branch (arranging a substitute when stock is short) bounces back and forth across departments and is the main cause of delay"—and this same diagram can then be used to design the To-Be (the improved business process). If, in a later phase, you move on to detailed design of the data this business handles (database design), that is when an E-R diagram becomes useful. Rather than "just drawing whichever diagram is standard," the core of business modeling is choosing the notation according to what you want to clarify—data flow, data structure, functional scope, or the procedure and role division of the whole business process.

1.3.3Section summary

• A DFD focuses on data flow, and an E-R diagram focuses on data structure (entities and relationships)
• A UML use case diagram suits agreeing functional scope; BPMN suits the procedure, branching, and role division of the whole business process
• The core skill is choosing the notation by working backward from what you want to clarify (data, structure, interaction, or the whole process)