← VCE Software Development U3O2

SRS content: analytical tools depicting existing systems

An SRS includes context, data flow and use case diagrams to show how an existing system works, and these diagrams link to the requirements.

Part of: VCE Software Development - U3O2 - Analysis and Design — Module 55

Understanding SRS content: analytical tools depicting existing systems in VCE Software Development U3O2

What it does: A Level 1 data flow diagram breaks the system into processes, data stores and flows, giving detailed evidence of the existing system. Diagrams act as evidence of the current system. They help the reader understand it before the new solution is built. In the analysis stage, the SRS uses these tools to depict the existing system and show why the new solution is needed. Use cases show what users do with the current system, so each use case can be traced to a functional requirement in the SRS.

Common mistakes: A Level 0 context diagram shows the whole system as ONE process with its external entities. It does not show processes inside the system. That is the job of a Level 1 DFD. It should read 'Shows: one system, entities'. The data flow diagram that shows processes and data stores is Level 1. Level 0 is the context diagram. The line should say 'Data flow (Level 1)'.

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This module's key terms are also in a printable crossword (Modules 52–71) and word search (Modules 52–85).

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Learning
Duo
Which diagrams can an SRS include to depict an existing system?
Context, data flow and use case diagramsOnly a Gantt chart and a project log
Matches
SRS diagrams section: includes only a use case diagram, so the existing data flows are shown
↓
A use case diagram does not show data flows or data stores. A context diagram or DFD is needed to depict how data moves in the existing system.
Applying
Meanings
Term
SRS analytical tools
Meaning
An SRS includes context, data flow and use case diagrams to show how an existing system works, and these diagrams link to the requirements.
Practice
SRS Section 2: Existing system
Testing
Gaps
SRS diagram: diagram = Level 0
Check Answer
Spots
1Diagram: Context (Level 0)
2Shows: many processes inside

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Quick Questions

1. Which diagrams can an SRS include to depict an existing system?
A. Only a Gantt chart and a project log
B. Context, data flow and use case diagrams ✓
The SRS includes analytical tools such as context, data flow and use case diagrams to show how the current system works. A Gantt chart is a project management tool.
2. What role does a data flow diagram play in an SRS?
A. It is evidence of how data moves through the existing system ✓
B. It is the final program code for the new system
Diagrams act as evidence of the current system. They help the reader understand it before the new solution is built.
3. A context diagram in an SRS shows the existing system as:
A. One process with the external entities that exchange data with it ✓
B. A detailed set of every internal process and data store
A Level 0 context diagram shows the whole system as one process and its data flows with external entities. Internal detail belongs in a Level 1 data flow diagram.
4. Which diagram in an SRS shows who uses the existing system and what they can do?
A. Context diagram
B. Use case diagram ✓
A use case diagram shows actors and the use cases they take part in. A context diagram shows data flows between the system and its entities.
5. How should the diagrams in an SRS relate to the requirements?
A. Each diagram should help explain or support specific requirements ✓
B. Diagrams are separate and should not match the requirements
Linking diagrams to requirements shows where a need comes from. For example, a missing data flow in the diagram can lead to a functional requirement.

Match the Pairs

Context diagram (Level 0) → Shows the existing system as one process, with the external entities and the data flows between them, as evidence in the SRS
Use case diagram → Shows the actors who use the existing system and the tasks they perform, which can be linked to the functional requirements
An SRS includes a Level 1 DFD to show the processes and data stores of the existing system in detail → DFD Level 1: Process 2.0 Check Stock reads D1 Inventory
Linking a diagram to a requirement shows where the need came from, so the requirement is backed by evidence → FR4: The system must record returns (see DFD 1, process 3.0 Process Return)
SRS diagrams section: includes only a use case diagram, so the existing data flows are shown → A use case diagram does not show data flows or data stores. A context diagram or DFD is needed to depict how data moves in the existing system.
SRS lists context, DFD and use case diagrams with no link to any requirement → The diagrams are not linked to the requirements. Each diagram should be referenced by the requirements it supports, otherwise it is not evidence.

Key Term

SRS analytical tools
An SRS includes context, data flow and use case diagrams to show how an existing system works, and these diagrams link to the requirements.

Fill in the Blanks

1. SRS diagram: context diagram = Level 0
Hint: Type the diagram name that shows the whole system as one process with its external entities.
2. SRS diagram: data flow diagram = Level 1
Hint: Type the two-word diagram type that breaks the system into processes, data stores and flows.
3. SRS diagram: use case diagram = actors
Hint: Type the diagram type that shows actors and what they do with the system.
4. Req R4: Parents can book interviews Evidence: use case Book Interview -> R4
Hint: Type the requirement ID that the evidence line links back to.
5. Purpose: show how the existing system works
Hint: Type the word for a system that is already in use now, before the new solution is built.

Spot the Error

Question 1
A Diagram: Context (Level 0)
B Shows: many processes inside
C Evidence: how data flows now
D Links to: REQ-01, REQ-02
Line B — A Level 0 context diagram shows the whole system as ONE process with its external entities. It does not show processes inside the system. That is the job of a Level 1 DFD. It should read 'Shows: one system, entities'.
Question 2
A Diagram: Data flow (Level 0)
B Shows: processes and stores
C Evidence: current order steps
D Links to: REQ-03
Line A — The data flow diagram that shows processes and data stores is Level 1. Level 0 is the context diagram. The line should say 'Data flow (Level 1)'.
Question 3
A Diagram: Use case
B Actors: Student, Teacher
C Shows: where data is stored
D Links to: REQ-05
Line C — A use case diagram shows actors and what they can do with the system. Data stores belong on a data flow diagram. It should read 'Shows: what each actor can do'.
Question 4
A SRS section: Existing system
B Tools: context, DFD, use case
C Purpose: show the new system
D Each diagram links to a REQ ID
Line C — In this SRS section the diagrams depict the EXISTING system, so they show how it works now. They are not a design of the new system. It should read 'Purpose: show how it works now'.
Question 5
A REQ-06: Record each payment
B Evidence: none needed
C Shows how payments work now
Line B — Diagrams act as evidence for requirements. Each requirement should point to the diagram element that supports it, such as DFD process 2.0 Pay. Saying no evidence is needed is wrong.

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