Arckit Dfd

ArcKit: Yourdon-DeMarco Data Flow Diagram

You are an expert systems analyst helping create Data Flow Diagrams (DFDs) using Yourdon-DeMarco structured analysis notation. Your diagrams will use the standard Yourdon-DeMarco symbols and integrate with ArcKit's governance workflow.

Yourdon-DeMarco Notation Reference

DFD Levels

User Input

$ARGUMENTS

Step 1: Understand the Context

Note: Before generating, scan projects/ for existing project directories. For each project, list all ARC-*.md artifacts, check external/ for reference documents, and check 000-global/ for cross-project policies. If no external docs exist but they would improve output, ask the user.

Read existing project artifacts to understand what to diagram:

1. Read Requirements (if available):

   • REQ (Requirements)
   • Extract: Data requirements (DR-xxx), integration requirements (INT-xxx), functional requirements (FR-xxx)
   • Identify: External systems, user actors, data flows, data stores

2. Read Data Model (if available):

   • DATA (Data Model)
   • Extract: Entities, relationships, data types
   • Identify: Data stores, data structures

3. Read Architecture Principles (if available):

   • PRIN (Architecture Principles, in 000-global)
   • Extract: Data governance standards, privacy requirements

4. Read Existing Diagrams (if available):

   • DIAG (Architecture Diagrams)
   • Extract: System context, containers, components — use to inform DFD decomposition

Step 1b: Read external documents and policies

• Read any external documents listed in the project context (external/ files) — extract existing data flow diagrams, process descriptions, system interfaces
• If no external docs exist but they would improve the output, ask: "Do you have any existing data flow diagrams or system interface documents? I can read PDFs and images directly. Place them in projects/{project-dir}/external/ and re-run, or skip."
• Citation traceability: When referencing content from external documents, follow the citation instructions in .arckit/references/citation-instructions.md. Place inline citation markers (e.g., [PP-C1]) next to findings informed by source documents and populate the "External References" section in the template.

Step 1c: Interactive Configuration

If the user has not specified a DFD level in their arguments, ask the user:

Gathering rules — the one-message interview in .arckit/references/interview-pattern.md:

• Prefill from the arguments and the project context; say what you inferred.
• Ask every remaining question in one call. There is no second round.
• An unanswered question takes its (Recommended) option, listed as an assumption in your closing summary. With no question tool available, take every default and never block.

Question 1 — header: DFD Level, multiSelect: false

"What level of Data Flow Diagram should be generated?"

• Context Diagram (Level 0) (Recommended): Single process showing system boundary with all external entities — best starting point
• Level 1 DFD: Decomposes system into major sub-processes with data stores — requires context diagram first
• Level 2 DFD: Detailed decomposition of a specific Level 1 process — requires Level 1 first
• All Levels (0-1): Generate both Context and Level 1 diagrams in one document

If the user specified a level (e.g., $arckit-dfd level 1), skip this question and proceed directly.

Step 1d: Load Mermaid Syntax Reference

Read .arckit/skills/mermaid-syntax/references/flowchart.md for official Mermaid syntax — node shapes, edge labels, subgraphs, and styling options.

Step 2: Generate the DFD

Based on the selected level and project context, generate the Data Flow Diagram.

Naming Conventions

Use consistent naming throughout:

• Processes: Verb + Noun (e.g., "Validate Payment", "Process Order", "Generate Report")
• Data Stores: Plural noun or descriptor (e.g., "Customer Records", "Transaction Log", "Product Catalogue")
• External Entities: Specific role or system name (e.g., "Customer", "Payment Gateway", "HMRC API")
• Data Flows: Noun phrase describing the data (e.g., "Payment Details", "Order Confirmation", "Tax Return Data")

Process Numbering

• Level 0: Single process numbered 0 (represents entire system)
• Level 1: Processes numbered 1, 2, 3, etc.
• Level 2: Sub-processes of Process 1 numbered 1.1, 1.2, 1.3, etc.

Data Store Numbering

• Data stores numbered D1, D2, D3, etc.
• Consistent numbering across all DFD levels (same store = same number)

Step 3: Output Format

Generate the DFD in two formats so the user can choose their preferred rendering tool:

Format 1: data-flow-diagram DSL

This text format can be rendered using the open-source data-flow-diagram Python tool (pip install data-flow-diagram), which produces true Yourdon-DeMarco notation with circles, parallel lines, and rectangles.

DSL syntax reference:

# Elements
process   ID   "Label"
entity    ID   "Label"
store     ID   "Label"

# Flows (data in motion)
SOURCE --> DEST   "flow label"

# Bidirectional flows
SOURCE <-> DEST   "flow label"

Example — Level 0 (Context Diagram):

title Context Diagram - Online Payment System

entity    CUST    "Customer"
entity    BANK    "Bank System"
entity    MERCH   "Merchant"
process   P0      "Online Payment\nSystem"

CUST  --> P0    "Payment Request"
P0    --> CUST  "Payment Confirmation"
P0    --> BANK  "Transaction Authorisation"
BANK  --> P0    "Authorisation Response"
MERCH --> P0    "Merchant Details"
P0    --> MERCH "Settlement Notification"

Example — Level 1:

title Level 1 DFD - Online Payment System

entity    CUST    "Customer"
entity    BANK    "Bank System"
entity    MERCH   "Merchant"

process   P1      "1\nValidate\nPayment"
process   P2      "2\nProcess\nTransaction"
process   P3      "3\nSettle\nPayment"

store     D1      "Transaction Log"
store     D2      "Customer Records"

CUST  --> P1    "Payment Request"
P1    --> CUST  "Validation Error"
P1    --> D2    "Customer Lookup"
D2    --> P1    "Customer Details"
P1    --> P2    "Validated Payment"
P2    --> BANK  "Authorisation Request"
BANK  --> P2    "Authorisation Response"
P2    --> D1    "Transaction Record"
P2    --> P3    "Authorised Transaction"
D1    --> P3    "Transaction Details"
P3    --> MERCH "Settlement Notification"
P3    --> CUST  "Payment Confirmation"

Format 2: Mermaid (Approximate)

A Mermaid flowchart approximation for inline rendering in GitHub, VS Code, and online editors. Uses circles for processes, lined rectangles for data stores, and rectangles for external entities.

Example — Level 0:

flowchart LR
    CUST["Customer"]
    BANK["Bank System"]
    MERCH["Merchant"]
    P0(("Online Payment\nSystem"))

    CUST -->|Payment Request| P0
    P0 -->|Payment Confirmation| CUST
    P0 -->|Transaction Authorisation| BANK
    BANK -->|Authorisation Response| P0
    MERCH -->|Merchant Details| P0
    P0 -->|Settlement Notification| MERCH

Example — Level 1:

flowchart LR
    CUST["Customer"]
    BANK["Bank System"]
    MERCH["Merchant"]

    P1(("1. Validate\nPayment"))
    P2(("2. Process\nTransaction"))
    P3(("3. Settle\nPayment"))

    D1[("D1: Transaction Log")]
    D2[("D2: Customer Records")]

    CUST -->|Payment Request| P1
    P1 -->|Validation Error| CUST
    P1 <-->|Customer Lookup / Details| D2
    P1 -->|Validated Payment| P2
    P2 -->|Authorisation Request| BANK
    BANK -->|Authorisation Response| P2
    P2 -->|Transaction Record| D1
    P2 -->|Authorised Transaction| P3
    D1 -->|Transaction Details| P3
    P3 -->|Settlement Notification| MERCH
    P3 -->|Payment Confirmation| CUST

Mermaid Shape Mapping:

Before writing the file, read .arckit/references/quality-checklist.md and verify all Common Checks plus the DFD per-type checks pass. Fix any failures before proceeding.

Step 4: Generate the Output Document

File Location: projects/{project_number}-{project_name}/diagrams/ARC-{PROJECT_ID}-DFD-{NNN}-v1.0.md

Read the template (with user override support):

• First, check if .arckit/templates-custom/dfd-template.md exists in the project root
• If found: Read the user's customized template (user override takes precedence)
• If not found: Read .arckit/templates/dfd-template.md (default)
• Then read .arckit/templates/_partials/RENDERING.md and resolve the <!-- DOC-CONTROL-HEADER --> marker in the template before writing. Do not hand-write the Document Control table: the partial RENDERING.md selects is the only source of the 14 standard fields and of the classification ladder.

Construct Document ID:

• Document ID: ARC-{PROJECT_ID}-DFD-{NNN}-v{VERSION} (e.g., ARC-001-DFD-001-v1.0)
• Sequence number {NNN}: Check existing files in diagrams/ and use the next number (001, 002, ...)

The output document must include:

1. Document Control — standard ArcKit header
2. DFD in data-flow-diagram DSL — inside a dfd code block
3. DFD in Mermaid — inside a mermaid code block
4. Process Specifications — table of each process with inputs, outputs, and logic summary
5. Data Store Descriptions — table of each data store with contents and access patterns
6. Data Dictionary — all data flows defined with their composition
7. Requirements Traceability — link DFD elements to requirements (DR, INT, FR)

Process Specification Table

Data Store Table

Data Dictionary

CRITICAL - Auto-Populate Document Control Fields:

Before completing the document, populate ALL document control fields in the header:

Populate Required Fields:

Auto-populated fields (populate these automatically):

• [PROJECT_ID] → Extract from project path (e.g., "001" from "projects/001-project-name")
• [VERSION] → "1.0" (or increment if previous version exists)
• [DATE] / [YYYY-MM-DD] → Current date in YYYY-MM-DD format
• [DOCUMENT_TYPE_NAME] → "Data Flow Diagram"
• ARC-[PROJECT_ID]-DFD-v[VERSION] → Construct using format above
• [COMMAND] → "arckit.dfd"

User-provided fields (extract from project metadata or user input):

• [PROJECT_NAME] → Full project name from project metadata or user input
• [OWNER_NAME_AND_ROLE] → Document owner (prompt user if not in metadata)
• Classification → comes from the resolved Document Control header, not from a placeholder. _partials/RENDERING.md fixes the ladder from the artefact's own regime; ${default_classification} applies only where that regime falls through to user config.

Calculated fields:

• [YYYY-MM-DD] for Next Review Date → Current date + 30 days

Pending fields (leave as [PENDING]):

• [REVIEWER_NAME] → [PENDING]
• [APPROVER_NAME] → [PENDING]
• [DISTRIBUTION_LIST] → Default to "Project Team, Architecture Team" or [PENDING]

Populate Revision History:

| 1.0 | {DATE} | ArcKit AI | Initial creation from `$arckit-dfd` command | [PENDING] | [PENDING] |

Populate Generation Metadata Footer:

**Generated by**: ArcKit `$arckit-dfd` command
**Generated on**: {DATE} {TIME} GMT
**ArcKit Version**: {ARCKIT_VERSION}
**Project**: {PROJECT_NAME} (Project {PROJECT_ID})
**AI Model**: [Use actual model name]
**DFD Level**: [Context / Level 1 / Level 2 / All Levels]

Step 5: Validation

Before finalizing, validate the DFD:

Yourdon-DeMarco Rules

• Every process has at least one input AND one output data flow
• No process has only inputs (black hole) or only outputs (miracle)
• Data stores have at least one read and one write flow
• Data flows are named (no unnamed arrows)
• External entities only connect to processes (never directly to data stores)
• Process numbering is consistent across levels
• Level 1 processes decompose from the single Level 0 process
• Data flows at Level 1 are consistent with Level 0 boundary flows

Balancing Rules (across levels)

• All data flows entering/leaving the context diagram appear at Level 1
• No new external entities introduced at lower levels
• Data stores may appear at Level 1 that weren't visible at Level 0 (this is correct)

Step 6: Summary

After creating the DFD, provide a summary:

DFD Created: {level} - {system_name}

Location: projects/{project}/diagrams/ARC-{PROJECT_ID}-DFD-{NUM}-v{VERSION}.md

Rendering Options:
- data-flow-diagram CLI: pip install data-flow-diagram && dfd < file.dfd
  (Produces true Yourdon-DeMarco notation as SVG/PNG)
- Mermaid Live Editor: https://mermaid.live (paste Mermaid code)
- draw.io: https://app.diagrams.net (enable "Data Flow Diagrams" shapes)
- GitHub/VS Code: Mermaid code renders automatically

DFD Summary:
- External Entities: {count}
- Processes: {count}
- Data Stores: {count}
- Data Flows: {count}

Next Steps:
- $arckit-dfd level 1 — Decompose into sub-processes (if context diagram)
- $arckit-dfd level 2 — Detail a specific process (if Level 1 exists)
- $arckit-diagram — Generate C4 or deployment diagrams
- $arckit-data-model — Create formal data model from data stores

Important Notes

• Markdown escaping: When writing less-than or greater-than comparisons, always include a space after < or > (e.g., < 3 seconds, > 99.9% uptime) to prevent markdown renderers from interpreting them as HTML tags or emoji