Dependency Graph

Definition

A dependency graph represents dependency relationships between nodes.

One node depends on another if it needs it first.

Example convention:

A -> B

means:

B depends on A

or:

A must come before B

Dependency graph = graph of required support or order.

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Direction Convention

Dependency graphs require a clear direction convention.

This chapter uses:

prerequisite -> dependent

Example:

Install packages -> Build app

This means the build depends on installed packages.

Some systems draw the arrow the other way, so the convention must be stated.

The arrow meaning must be explicit.

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Simple Example

Suppose:

A must happen before B
B must happen before C

Graph:

A -> B -> C

This shows the order constraint.

C depends on B.

B depends on A.

Dependency graphs make prerequisite structure visible.

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Shared Dependency

One node can support multiple later nodes.

Example:

A -> B
A -> C
B -> D
C -> D

Here D depends on both B and C.

Both B and C depend on A.

Dependency graphs can branch and merge.

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Circular Dependency

A circular dependency happens when dependencies loop back.

Example:

A -> B
B -> C
C -> A

This says:

A must come before B
B must come before C
C must come before A

The structure cannot find a clean starting point.

Circular dependencies often indicate a design problem.

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Final Summary

• A dependency graph represents what depends on what.
• Arrow direction must be defined clearly.
• This chapter uses prerequisite -> dependent.
• Dependency graphs show ordering constraints.
• They can branch, merge, or contain circular dependency.