dfd

Generate Yourdon-DeMarco Data Flow Diagrams with structured analysis notation

Data Flow Diagram (DFD) Generation

Generate Yourdon-DeMarco Data Flow Diagrams using structured analysis notation.

Command

arckit dfd "<system or process>"

Description

Creates Data Flow Diagrams (DFDs) using Yourdon-DeMarco structured analysis notation. Shows how data moves through your system with processes, data stores, and external entities.

Arguments

• System or process: Name of system or process to diagram (e.g., ‘user registration’, ‘claims processing’)

When to Use

• For data requirements analysis
• GDPR / UK GDPR compliance documentation
• PII handling and data residency analysis
• Data transformation pipelines
• System integration planning

Required Context

• Requirements (ARC--REQ-.md) - For DR, INT, FR
• Data Model (ARC--DATA-.md) - For entities and relationships
• Architecture Principles (PRIN) - For data governance
• Architecture Diagrams (DIAG) - For component context

Interactive Configuration

Prompts for DFD level:

1. Context Diagram (Level 0) (Recommended) - Single process, system boundary
2. Level 1 DFD - Decompose into major sub-processes
3. Level 2 DFD - Detailed process decomposition
4. All Levels (0-1) - Generate both Context and Level 1

Yourdon-DeMarco Notation

Symbol	Shape	Description
External Entity	Rectangle	Source/sink outside system
Process	Circle (bubble)	Transforms data
Data Store	Parallel lines	Data at rest
Data Flow	Named arrow	Data in motion

DFD Levels

Level 0 (Context Diagram)

Purpose: Show entire system as single process with external entities

Example:

Customer → Payment System → Bank
Merchant → Payment System → Merchant

Level 1

Purpose: Decompose system into major sub-processes with data stores

Processes numbered: 1, 2, 3, etc. Data stores numbered: D1, D2, D3, etc.

Level 2+

Purpose: Further decompose specific Level 1 processes

Processes numbered: 1.1, 1.2, 1.3 (for Process 1), etc.

Output Formats

Format 1: data-flow-diagram DSL

Text format for the data-flow-diagram Python tool:

title Level 0 - Payment System

entity CUST "Customer"
entity BANK "Bank System"
process P0 "Payment System"

CUST --> P0 "Payment Request"
P0 --> CUST "Confirmation"
P0 --> BANK "Transaction"
BANK --> P0 "Response"

Renders with: pip install data-flow-diagram && dfd < file.dfd

Format 2: Mermaid (Approximate)

Flowchart approximation for inline rendering:

Document Contents

Generated document includes:

1. DFD in both formats (DSL + Mermaid)
2. Process specifications table
3. Data store descriptions
4. Data dictionary (all data flows defined)
5. Requirements traceability

Process Specification Table

Process	Name	Inputs	Outputs	Logic	Requirements
1	Validate Payment	Payment Request, Customer Details	Validated Payment, Error	Validate card, verify customer	FR-001, DR-002

Data Store Table

Store	Name	Contents	Access	Retention	PII
D1	Transaction Log	Transaction ID, amount, status	R/W by P2, R by P3	7 years	No
D2	Customer Records	Name, email, card token	R by P1, W by P2	Account lifetime	Yes

Validation Rules

Yourdon-DeMarco compliance:

• ✅ Every process has at least one input AND one output
• ✅ No “black holes” (only inputs) or “miracles” (only outputs)
• ✅ Data stores have at least one read and one write
• ✅ All data flows are named
• ✅ External entities only connect to processes
• ✅ Process numbering is consistent across levels
• ✅ Level 1 decomposes from Level 0
• ✅ Data flows balance across levels

Output

Creates: projects/{project}/diagrams/ARC-{PROJECT_ID}-DFD-{NNN}-v1.0.md

Naming Conventions

• Processes: Verb + Noun (“Validate Payment”, “Process Order”)
• Data Stores: Plural noun (“Customer Records”, “Transaction Log”)
• External Entities: Specific role (“Customer”, “Payment Gateway”)
• Data Flows: Noun phrase (“Payment Details”, “Order Confirmation”)

Related Commands

• arckit diagram - Generate C4 or deployment diagrams
• arckit data-model - Create formal data model
• arckit requirements - Source data requirements

Next Steps

After creating DFD:

1. Render with data-flow-diagram CLI for true notation
2. Or view Mermaid version in GitHub/VS Code
3. Validate all flows are named
4. Check process balance (no black holes/miracles)
5. Create Level 2 for complex processes
6. Use for GDPR/data protection documentation