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System Context Diagram: Description & Examples

System Context Diagram: Description & Examples
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  • 0:00 What Is a System…
  • 0:53 The Context Bubble
  • 1:56 External Entities
  • 3:01 Data Flows
  • 5:19 Lesson Summary
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Lesson Transcript
Instructor: Gregory Fouquet

Greg has developed and taught classroom and virtual project management workshops for Fortune 500 companies in the US and Europe and has a MBA.

In this lesson, you will learn the three key elements of a system context diagram. In addition, this lesson will describe how you can use this powerful diagramming tool to help identify the scope of a system.

What Is a System Context Diagram?

Imagine for a moment that you need a general understanding of an automated ordering system. Wouldn't it be helpful if you could develop a high-level view of that system without getting bogged down with all of its processing details? Well, that's what a system context diagram can do for you.

It's a picture worth a thousand words. . . or even ten thousand words if it's a really big system. You can think of a system context diagram as a high-level map of a system and its surrounding environment. Drawing a context diagram helps you to understand how a system interacts with other systems, business units, and key personnel. In addition, you can use it to help define the scope of a system's operations. System context diagrams are drawn using only three diagramming elements, which are the context bubble, external entities, and data flows.

Billing System Context Diagram
Example Billing System Context Diagram

The Context Bubble

The first diagramming element we'll discuss is the context bubble. It's drawn as a circle in the center of the diagram and identifies a conceptual boundary that encloses a group of related processes or activities. For example, you could show all of the internal manual and automated processing associated with an ordering system as a single context bubble.

Since a context diagram is a high-level view of a system, the specific details associated with its internal operations are not shown. Masking the internal structure of a system's operations is referred to as information hiding. This concept enables you to focus on identifying and understanding the behaviors and data interactions of a system without being distracted by the complexity of its internal processing.

When a context diagram is used as a tool for setting scope, you simply declare which operations or processes are in or out of scope. If they are in scope, you include them within the context bubble. If you decide they're out of scope, then you place them on the outside of the context bubble.

External Entities

The out of scope items constitute the second diagramming element of a context diagram: the external entities. They are drawn as boxes, pictures, or stick figures surrounding the context bubble and are adjacent systems, business units, people, governmental agencies, or other things located outside the context boundary. Because external entities are outside the scope of the system, their internal processing is not defined. The key reason you show them on a context diagram is because external entities interact with the system.

Consider the following example. You, a customer (an external entity) order a book (the interaction) from a book store website (the ordering system). In addition, you pay for the purchase (another interaction) with your credit card, which is authorized and approved (more interactions) by your credit card company (another external entity).

Interactions with external entities represent either inputs to the system or outputs from the system. Therefore, external entities are the sources and/or sinks of the data processed by the system.

Data Flows

The last diagramming element of a context diagram is the data flows, which are drawn as labeled arrows and represent exchanges of information between the system and its associated external entities. The direction of the arrow indicates whether the flow is an input or an output. Each external entity must have at least one data flow to or from the context bubble. Data flows identify the data content of real objects, such as transactions, messages, records, documents, emails, screen displays, and reports.

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