Core Concepts: DOC vs INDEX

TELA's dual-contract system enables modular, updatable, secure on-chain applications.

The Two Contract Types

📄 DOC Contract (Code Storage)

What it is: A container for a single file in your TELA app

Think: Each DOC = One file (like index.html, app.js, etc.)

Key Feature: 🔒 Immutable - Once deployed, code cannot be changed (security!)

📋 INDEX Contract (Application Manifest)

What it is: The "table of contents" that references all your DOC contracts

Think: INDEX = package.json (tells Engram what files to load)

Key Feature: ✏️ Updateable - Can point to new DOC contracts (flexibility!)

How It Works (Simple Flowchart)

Deployment:

Developer writes code
  ↓
Deploy index.html    → DOC Contract A (immutable)
Deploy app.js        → DOC Contract B (immutable)  
Deploy style.css     → DOC Contract C (immutable)
  ↓
Create INDEX Contract → References A, B, C
  ↓
Give users INDEX SCID → They can access your app!

User Access:

User enters INDEX SCID into Engram
  ↓
Engram fetches INDEX from blockchain
  ↓
INDEX says: "Load DOC A, DOC B, DOC C"
  ↓
Engram fetches all DOCs from blockchain
  ↓
Verifies hashes (security check)
  ↓
Executes app locally

One SCID opens your entire app!

Headers and Metadata: The ART-NFA Standard

What is ART-NFA?

ART-NFA (Artificer Non-Fungible Assets) is a standardized header system for DERO smart contracts. TELA adopts this standard to ensure:

• Consistency - Same metadata format across all DERO applications
• Interoperability - Tools can parse any ART-NFA compliant contract
• Identification - Easy detection of TELA contracts on the blockchain
• Integration - Seamless compatibility within DERO ecosystem

TELA Header Structure

TELA contracts use these standard headers:

Core Headers (v1):

"nameHdr"        // Contract/file name
"descrHdr"       // Description
"iconURLHdr"     // Icon URL or SCID

Enhanced Headers (v2):

"var_header_name"         // Updatable name (with TELA-MOD-1)
"var_header_description"  // Updatable description  
"var_header_icon"         // Updatable icon

TELA-Specific Headers

Beyond ART-NFA, TELA adds specialized headers:

"dURL"           // TELA decentralized URL (e.g., "myapp.tela")
"docType"        // File type (TELA-HTML-1, TELA-JS-1, etc.)
"subDir"         // Subdirectory path
"mods"           // TELA-MOD-1 tags (e.g., "vsoo,txdwd")
"DOC1"           // First DOC SCID (INDEX contracts)
"DOC2"           // Second DOC SCID (if exists)
// DOC3, DOC4... as needed

Header Version Evolution

Why Two Header Versions?

Example:

// v1 Headers (immutable)
STORE("nameHdr", "My App")        // Cannot change after deployment
 
// v2 Headers (mutable with TELA-MOD-1)
STORE("var_header_name", "My App")  // Can update via SetVar

Best Practice: Use v2 headers if you want the ability to update metadata later!

Signature Headers

TELA-DOC contracts include cryptographic signatures for file verification:

"fileCheckC"     // C value from DERO signature
"fileCheckS"     // S value from DERO signature

These ensure the code in the DOC hasn't been tampered with.

Key Benefits

DOC vs INDEX Comparison

Real-World Example

Building a Simple Calculator App:

Users only need the final INDEX SCID (xyz999...) to access your complete calculator app!

Technical Constraints

Size Limits (Blockchain Constraints):

Best Practices:

• ✅ Split large files across multiple DOC contracts
• ✅ Organize with SubDir paths (e.g., /js/, /css/)
• ✅ Modular design - Break into logical components
• ✅ Reusable libraries - Share common DOCs across apps
• ✅ Version control - New features = new DOCs + INDEX update

Why This Design?

The genius of separating DOC and INDEX:

The Bottom Line

DOC + INDEX = Secure + Flexible

DOC Contracts (Immutable)
  ✅ Security through immutability
  ✅ Cryptographic verification
  ✅ Cannot be tampered with
  
INDEX Contracts (Updateable)
  ✅ Apps can evolve
  ✅ Point to new DOCs
  ✅ Maintain same SCID for users
  
Result: Best of both worlds!

TELA makes blockchain development accessible to web developers while maintaining the security and decentralization benefits of blockchain technology.

Related Pages

Understanding TELA:

• TELA Overview - Platform introduction
• TELA Security Model - How security works
• Content Rating System - Community moderation

Build with TELA:

• Quick Start Tutorial - Deploy your first app
• TELA-CLI Overview - Command-line tools
• Templates - Ready-to-use starting points

Technical Reference:

• API Reference - Complete API docs
• Data Types - DOC and INDEX specifications