Modeling Physical Architecture Instead of Logical Data Flow

One of the most frequent missteps I’ve seen in data flow modeling isn’t about notation or structure—it’s about perspective.

When a DFD shows microservices, servers, or network hops, it’s no longer a logical model. It’s a physical architecture sketch, masquerading as a data flow diagram.

That distinction isn’t academic. A logical DFD captures the what happens to the data, not where it runs. A physical DFD, by contrast, defines where the logic lives—something that belongs in a different kind of diagram.

My experience has taught me that teams who conflate the two end up with models that confuse stakeholders and mislead developers. The data flow becomes entangled with deployment decisions, making it hard to reason about transformations and risks.

This chapter shows you how to untangle logic from infrastructure. You’ll learn when to use each view, how to keep them separate, and why mixing them destroys clarity. I’ll also share how Visual Paradigm supports both views without blurring the lines.

Understanding the Core Difference

What Is a Logical DFD?

A logical DFD focuses on business processes, their inputs, outputs, and transformations—without regard to technical implementation.

It answers: What’s being done to the data?

Examples: “Verify customer identity,” “Calculate tax,” “Generate invoice.”

These are abstract actions that could be performed in any system, regardless of technology.

What Is a Physical DFD?

A physical DFD maps processes to real-world components: servers, databases, queues, or services.

It answers: Where is this logic actually running?

Examples: “Customer service microservice,” “AWS Lambda function,” “SQL Server database.”

This is architecture-level detail—crucial for deployment, monitoring, or performance tuning.

Why Mixing Them Is a Critical Error

When you draw a server in your logical DFD, you’re forcing the model to carry technical baggage. The process “Generate Invoice” now becomes “Invoice Generator Service (Node.js, hosted on AWS),” which distracts from the core transformation.

Business stakeholders can’t engage with this. Developers get trapped in implementation details too early.

Worse, these diagrams become fragile. A change in deployment architecture—like moving from a monolith to a microservices setup—breaks the model, even if the logic hasn’t changed.

When to Use Each View

Use Logical DFDs When:

• Building a requirements model with business analysts
• Designing workflows independent of technology
• Onboarding stakeholders unfamiliar with infrastructure
• Documenting high-level business processes

Use Physical DFDs When:

• Planning deployment architecture
• Designing system integration or API boundaries
• Validating performance, scalability, or security constraints
• Preparing technical documentation for DevOps or SRE teams

They serve different purposes. One is for logic. The other is for infrastructure.

How to Keep Them Separate

Step 1: Start with the Logical View

Begin every DFD project with a purely logical model. Focus on:

• Business processes (verb + object, e.g., “Process Order”)
• Data flows that reflect business events (e.g., “Order Details”)
• Data stores that represent business records (e.g., “Customer Database”)
• External entities as real-world roles (e.g., “Customer,” “Payment Gateway”)

Do not name processes “Service A” or “Microservice B.”

Step 2: Add Physical Implementation Later

Once the logical flow is validated, you can create a physical DFD from the same model.

Each logical process becomes a physical component:

• “Generate Invoice” → “Invoice Service (Node.js, Docker)”
• “Verify Payment” → “Payment Validator (Python, AWS Lambda)”

This way, you preserve the original intent while adding deployment context.

Step 3: Use Visual Paradigm to Maintain Both Views

Visual Paradigm lets you model both views in the same project without mixing them.

Here’s how:

• Create a Logical DFD in a dedicated workspace.
• Create a Physical DFD in a separate view.
• Use model links to connect logical processes to physical components.
• Apply view filters to show only logical or physical elements.
• Use diagram templates to standardize symbol sets and labeling.

This keeps your models clean, traceable, and reusable.

Common Mistakes to Avoid

Mistake 1: Calling a Physical Diagram a “Process”

“Customer Service Queue” is a physical structure. In a logical DFD, it should be “Process Customer Requests.”

Change the label. Strip out infrastructure.

Mistake 2: Drawing Network Paths in the DFD

Lines should represent data movement, not network hops.

If a line crosses a firewall or traverses a cluster, that’s a deployment diagram issue—*not* a flow diagram one.

Mistake 3: Using Microservice Names as Process Names

“OrderService v2.1” is not a process. “Process Order” is.

Keep the name business-meaningful, even if the implementation changes.

Practical Guidelines

Use this checklist when reviewing a DFD:

• Are all process names verbs that reflect business actions?
• Do any process names include server names, frameworks, or deployment platforms?
• Are data stores named after databases or services?
• Do any data flows include technical terms like “API,” “REST,” or “Kafka”?
• Could a non-technical stakeholder understand this model?

If more than one answer is “yes,” you’re likely modeling physically instead of logically.

Comparison: Logical vs Physical DFD

Aspect	Logical DFD	Physical DFD
Focus	Business processes & data transformations	Technical implementation & deployment
Process Examples	Verify Identity, Calculate Tax	Auth Service (Java, Tomcat)
Data Flow Names	Customer Data, Order Summary	Order JSON (via REST API)
Use Case	Requirements analysis, stakeholder alignment	Deployment planning, system integration
Change Resistance	High – logic remains stable	Low – infrastructure changes often

Final Advice: Let the Model Reflect the Purpose

I’ve seen teams spend hours refining a DFD that shows Kubernetes pods, only to realize it was supposed to capture business logic. The time lost is not just in rework—it’s in miscommunication.

Always ask: Who is this diagram for?

If it’s for business decision-makers, keep it logical. If it’s for engineers, you can build a physical counterpart.

Never assume that a DFD must include infrastructure. Separate the what from the where.

When you do, your data flow becomes a true reflection of logic—not a shadow of deployment.

Frequently Asked Questions

What’s the main difference between logical and physical DFD?

Logical DFDs focus on what happens to data—abstract business processes and transformations. Physical DFDs show where those processes run, including infrastructure components like servers, services, and databases.

Can I use the same DFD for both business and technical teams?

No. A single DFD cannot serve both audiences well. Use a logical DFD for business stakeholders and a separate physical DFD for technical teams. Keep them aligned but distinct.

Should I draw microservices in my logical DFD?

No. Microservices are deployment artifacts. In a logical DFD, they should be represented as abstract processes like “Process Payment” or “Validate User.”

How do I convert a logical DFD to a physical one?

Map each logical process to one or more physical components. Use model links in tools like Visual Paradigm to associate them. Update process names to include technical details, and replace abstract data stores with real databases or queues.

Why not just model everything in one diagram for complete traceability?

Because it sacrifices clarity. Mixing logic and implementation creates confusion, especially during changes. Keep views separate—traceability can be handled via model links, not by merging views.

When should I use a physical DFD instead of a logical one?

Use a physical DFD when designing system deployment, defining API boundaries, or explaining integration points. Use logical DFDs during requirements gathering, process modeling, or system design discussions.