Event Diagrams, System Data Flow Diagram and Physical ERD

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Event Diagrams

A data flow diagram for a single event handler and the agents and data stores that provide inputs or receive outputs. An event diagram is a context diagram for a single event. It shows the inputs, outputs, and data store interactions for the event. By drawing an event diagram for each process, users do not become overwhelmed by the overall size of the system. They can examine each use case as its own context diagram.Before drawing any event diagrams, you may find it helpful to have a list of all the data stores available.The simplicity of event diagramming makes the technique a powerful communication tool between users and technical professionals.Here is an example of an Event diagram.

Most event diagrams contain a single process - the same process that was named to handle the event on the decomposition diagram. For each event, illustrate the following:

• The inputs and their sources. Sources are depicted as external agents. The data structure for each input should be recorded in the repository.
• The outputs and their destinations. Destinations are depicted as external agents. The data structure for each output should be recorded in the repository.
• Any data stores from which records must be "read" should be added to the event diagram. Data flows should be added and named to reflect what data is read by the process.
• Any data stores in which records must be created, deleted, or updated should be included in the event diagram. Data flows to the data stores should be named to reflect the nature of the update.

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System Data Flow Diagrams

System data flow diagram illustrates how data is processed by a system in terms of inputs and outputs. As its name indicates its focus is on the flow of information, where data comes from, where it goes and how it gets stored.System data flow diagrams are easier to understand by technical and non-technical audiences. It can provide a high level system overview,complete with boundaries and connections to other systems and a detailed representation of system components.

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Logical and Physical ERD

Entity relationship diagram (ERD) represents a detailed picture of the entities needed for a business. In forward engineering, ERD will be transformed into a relational database eventually. There are two types of ERD - Logical and Physical. They are used in different stages of development, and are inter-related.Logical ERD models information gathered from business requirements. Entities and relationships modeled in such ERD are defined around the business's need. The need of satisfying the database design is not considered yet.
Physical ERD represents the actual design of database. It deals with conversion from logical design into a schema level design that will be transformed into relational database.Logical ERD is treated as base, refinement occurs by defining primary keys, foreign keys and constraints. Sometimes, relationships need to be resolved by introducing additional tables, like a Linked table for a many to many relationship.