← VCE Software Development U3O2

Gantt chart: task dependencies

A link between two tasks where one cannot start or finish until the other is complete. The first is the predecessor, the next is the successor. Shown on a Gantt chart by an arrow.

Part of: VCE Software Development - U3O2 - Analysis and Design — Module 17, VCE Data Analytics - U3O2 - Analysis and Design — Module 13

Understanding Gantt chart: task dependencies in VCE Software Development U3O2

What it does: The arrow points from the task that must be done first (Design screens) to the task that relies on it (Code interface). Testing cannot properly begin until the code exists, so Test program is the successor and Code program is its predecessor. The predecessor comes first. The successor depends on it, so it has to wait. Finish-to-start is the most common dependency. The predecessor must finish before the successor can start. Dependency arrows link task bars. A diamond is normally used to show a milestone. 'Build the database' has to wait for the design, so it is the successor. Dependencies set the sequence of tasks. Costs are a separate part of project planning.

Common mistakes: With a finish-to-start dependency, successor B cannot begin until predecessor A finishes on day 3. B must start on day 4 (day 4-7), not day 2. Testing can only happen once the code is written, so A (Write code) is the predecessor and B is the successor. The line should say B is the successor of A.

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This module's key terms are also in a printable crossword (Modules 12–24) and word search (Modules 2–24).

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Learning
Duo
In a dependency, which task must be finished first?
The predecessorThe successor
Matches
Code interface ──> Design screens (arrow points back to the earlier task)
↓
The arrow is drawn backwards. A dependency arrow should run from the predecessor (Design screens) to the successor (Code interface).
Applying
Meanings
Term
dependency
Meaning
A link between two tasks where one cannot start or finish until the other is complete. The first is the predecessor, the next is the successor. Shown on a Gantt chart by an arrow.
Practice
A: Write requirements (no predecessor)
Testing
Gaps
Design -> Code Link type:
Check Answer
Spots
1A Gather requirements: day 1-3
2B Design screens: day 2-5

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Quick Questions

1. In a dependency, which task must be finished first?
A. The predecessor ✓
B. The successor
The predecessor comes first. The successor depends on it, so it has to wait.
2. Which statement describes a finish-to-start dependency?
A. Task B cannot start until Task A finishes ✓
B. Task B cannot finish until Task A starts
Finish-to-start is the most common dependency. The predecessor must finish before the successor can start.
3. A Gantt chart shows a dependency between two tasks using:
A. A diamond at the end of a task bar
B. An arrow from one task bar to the other ✓
Dependency arrows link task bars. A diamond is normally used to show a milestone.
4. A team must finish 'Design the database' before they can start 'Build the database'. 'Build the database' is the:
A. Predecessor
B. Successor ✓
'Build the database' has to wait for the design, so it is the successor.
5. Which pair of tasks has a dependency?
A. Write the code, then test the code ✓
B. Draw the logo, then book a meeting room
You cannot test code that has not been written yet. The logo and the meeting room do not rely on each other.

Match the Pairs

Task B depends on Task A → Task A is the predecessor and Task B is the successor, so B cannot start or finish until A is complete.
Finish-to-start (FS) → The successor task cannot start until the predecessor task has finished.
A dependency arrow on a Gantt chart runs from the predecessor to the successor → Design screens ──> Code interface
A successor task is the task that has to wait for another task to be complete → Test program (successor of Code program)
Code interface ──> Design screens (arrow points back to the earlier task) → The arrow is drawn backwards. A dependency arrow should run from the predecessor (Design screens) to the successor (Code interface).
Write SRS (predecessor) and Draw context diagram (successor) run at the same time, with no link → If one task is a successor, it must be linked to its predecessor by a dependency, so it cannot run at the same time with no arrow.

Key Term

dependency
A link between two tasks where one cannot start or finish until the other is complete. The first is the predecessor, the next is the successor. Shown on a Gantt chart by an arrow.

Fill in the Blanks

1. Design -> Code Link type: finish-to-start
Hint: Type the dependency type where the predecessor must finish before the successor can begin.
2. Design -> Code Design is the predecessor task
Hint: Type the word for the task that must come first in a dependency.
3. Design -> Code Code is the successor task
Hint: Type the word for the task that comes after, and waits on, another task.
4. Task 2 depends on Task 1
Hint: Type the verb that describes a task needing another task to be complete first.
5. Dependency arrow: Design -> Code
Hint: Type the keyboard symbol that draws a line pointing from the predecessor to the successor.

Spot the Error

Question 1
A A Gather requirements: day 1-3
B B Design screens: day 2-5
C A -> B finish-to-start
Line B — With a finish-to-start dependency, successor B cannot begin until predecessor A finishes on day 3. B must start on day 4 (day 4-7), not day 2.
Question 2
A Task A: Write code
B Task B: Test code
C B is the predecessor of A
Line C — Testing can only happen once the code is written, so A (Write code) is the predecessor and B is the successor. The line should say B is the successor of A.
Question 3
A A: Create database
B B: Load test data
C A depends on B
D Arrow points from A to B
Line C — Test data cannot be loaded until the database exists, so B depends on A. The dependency is written backwards, and it should read B depends on A.
Question 4
A FS: B starts when A starts
B Task A: Code login screen
C Task B: Test login screen
Line A — Finish-to-start (FS) means the successor starts only after the predecessor finishes. Saying B starts when A starts describes a start-to-start link instead.
Question 5
A T1: Build login page
B T2: Test login page, after T3
C T3: Fix bugs, after T2
Line B — T3 already depends on T2, so making T2 depend on T3 creates a circular dependency. Neither task could ever start. T2 should come after T1.

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