Enterprise Resource Planning (ERP): Sales & Supply Chain Engine

Integrated Business Process Management Solution

A robust enterprise system connecting Order-to-Cash (O2C) and Procure-to-Pay (P2P) workflows.
Engineered to handle complex document lifecycles, temporal pricing logic, and strictly consistent inventory auditing.

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System Overview

This application serves as the central nervous system for a trading enterprise. It bridges the gap between the Sales Department (Commercial) and the Warehouse (Logistics), ensuring that financial documents perfectly match physical inventory reality.

The core engineering challenge was to implement strict Business Rules that prevent data inconsistency during concurrent user operations (e.g., creating invoices while stock is moving).

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Domain Model & Database Schema

The system relies on a Highly Normalized Relational Model. The architecture explicitly defines relationships between Articles, Warehouses, and their dynamic states via Stock Cards.

erDiagram
    WAREHOUSE ||--|{ STOCK_CARD : maintains
    ARTICLE ||--|{ STOCK_CARD : tracked_by
    STOCK_CARD ||--|{ TRANSACTION_ITEM : records_movement
    TRANSACTION_DOC ||--|{ TRANSACTION_ITEM : contains
    TRANSACTION_DOC }|--|| WAREHOUSE : originates_from
    CUSTOMER ||--|{ ORDER : places
    ORDER ||--o| INVOICE : generates

    ARTICLE {
        string SKU
        string Name
        string UnitOfMeasure
    }
    STOCK_CARD {
        decimal Quantity_Physical
        decimal Quantity_Reserved
        decimal Total_Value
        decimal Average_Price
    }
    TRANSACTION_DOC {
        string DocNumber
        date Date
        enum Type "Receipt | Delivery | Transfer"
        enum Status "Draft | Posted | Reversed"
    }

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Module 1: Sales Subsystem (Commercial)

Designed for the Sales Representative persona, this module handles the commercial lifecycle with a focus on flexibility and financial accuracy.

🔹 Workflow Flexibility

• Order-to-Invoice: Sales Reps can input a Customer Order (Narudžbenica). Upon approval, the system can auto-generate a generic Invoice inheriting all line items.
• Direct Invoicing: Supports ad-hoc sales where no prior order exists (Direct Entry).

🔹 Financial Computation Engine

• Temporal Pricing Logic: The system manages Price Lists (Cenovnici). When creating an invoice, the engine resolves the Item Price and VAT Rate based on the Invoice Date (not necessarily the current date), ensuring historical accuracy.
• Granular Calculation:
  • Calculates VAT (PDV) and Base Amount per Line Item.
  • Aggregates totals at the Document Header level.

🔹 Output & Reporting

• Customer Invoice: Generates a professional PDF with all line items for external distribution.
• Sales Ledger (KIF - Knjiga izlaznih faktura): A mandatory fiscal report aggregating all issued invoices within a user-defined date range.

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Module 2: Warehouse Management (WMS)

Designed for the Warehouse Manager, acting as the "Source of Truth" for physical goods.

🔹 Transaction Management

The system supports full lifecycle management for three distinct document types:

1. Goods Receipt (Primka): Increases stock value/quantity.
2. Delivery Note (Otpremnica): Decreases stock value/quantity.
3. Inter-Warehouse Transfer (Međumagacinski promet): Atomically moves stock between locations (Credit Origin / Debit Destination).

🔹 Lifecycle & State Machine

• Draft: Editable state. No impact on the ledger.
• Posted (Knjižen): Finalized state. Updates the Stock Card permanently.
• Reversed (Stornirano): Corrective mechanism. Instead of deleting records (which destroys audit trails), the system creates a "Storno" effect to nullify the financial impact while keeping the history.

🔹 Initialization

• Opening Balance (Početno Stanje): Specialized functionality to initialize Stock Cards at the beginning of a fiscal year.

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Module 3: Cross-Module Integration (The "Glue")

This is the most technically complex part of the system, ensuring synchronization between Sales and Warehouse.

The Reservation Protocol (Crucial Logic)

To prevent "Overselling," the system enforces strict checks during the Invoice creation process:

1. Real-Time Availability Check:

   • When a Sales Rep enters an item, the system queries the specific Stock Card (Article + Warehouse combo).
   • Logic: If Requested > (Physical - Reserved), the system warns the user and blocks the line item.

2. Dynamic Reservation Updates (CUD Hooks):

   • The attribute ReservedQuantity on the Stock Card is automatically updated via event listeners on:
     • Create: Adding an item increments reservation.
     • Update: Changing quantity adjusts the reservation delta.
     • Delete: Removing an item releases the reservation.

3. Automated Document Chaining:

   • Once an Invoice is finalized, the system can automatically generate a corresponding Delivery Note (Otpremnica), carrying over all data to the warehouse team.

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Analytics & Reporting Intelligence

The system provides deep insights into inventory health and financial standing.

Report Type	Description	Technical Implementation
Stock List (Lager Lista)	Shows current Quantity and Total Value for all items in a warehouse.	Aggregates data from active Stock Cards.
Stock Card Analytics (Magacinska Kartica)	A detailed chronological ledger of every movement.	Reconstructs history: Opening + Inputs - Outputs = Balance.

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Tech Stack

• Platform: Mendix Studio Pro (Model-Driven Engineering)
• Database: Relational SQL Schema (3NF)
• Logic: Event-driven Microflows for reservation handling.
• Reporting: OQL (Object Query Language) for complex datasets.

Compliance Note

The system is designed to uphold ACID (Atomicity, Consistency, Isolation, Durability) properties. Critical financial data is protected against partial updates, ensuring the ledger is always balanced.