System context diagram

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A System Context Diagram (SCD) is the highest level view of a system, similar to Block Diagram, showing a (normally software-based) system as a whole and its inputs and outputs from/to external factors. SCDs are a type of Data Flow Diagram, and they should always be produced as DFDs. Context Diagrams show the interactions between a system and other actors with which the system is designed to face. SCD is very helpful in understanding the context in which the system will be part of software engineering.

Context diagrams are typically drawn using labeled boxes to represent each of the external entities and another labeled box to represent the system being developed. The relationship is drawn as a line between the entities and the system being developed. The relationships are labeled with a subject-verb-object format. For example, "customer places order." Context diagrams can also use many different drawing types to represent external entities. They can use ovals, stick figures, pictures, clip art or any other representation to convey meaning. Decision trees and data storage are represented in system flow diagrams.

Context diagrams are used early in a project to get agreement on the scope under investigation. Context diagrams are typically included in a requirements document. These diagrams must be read by all project stakeholders and thus should be written in plain language so the stakeholders can understand items within the document.

An alternative would be a use case diagram since it also represents the scope of the project at a similar level of abstraction.

The best System Context Diagrams are used to display how system inter operates at a very high level or how systems operate and interact logically. The system context diagram is a necessary tool in developing a baseline interaction between systems and actors; actors and system or systems and systems.