LIN CHIACHENG
  1. Work
  2. NEXUS

01 / 07INDEPENDENT BUSINESS SYSTEM PROJECT

NEXUS

Customers, quotes, projects and billing in one workflow.

NEXUS chairman workspace, with schedules, operating indicators and active projects.
Concept design — chairman view.

An ongoing business system I proposed after noticing friction in my previous work, built step by step with the technology I am learning and AI support.

ROLE
PRODUCT / DEVELOPMENT
STACK
React · Spring Boot · PostgreSQL · Docker
STATUS
IN DEVELOPMENT · 2026

GitHub (Private)

01

Learning to build, starting with familiar work.

Where it started

At my previous workplace, paper records, spreadsheets, and customer information were separated across different places, so the same details had to be checked repeatedly and decisions were harder to keep in one view. After coming to Japan to study development, I contacted former colleagues and proposed bringing the customer, estimate, project, and billing flow into one system. NEXUS grew from those conversations and is still being built and verified. The aim is to turn repeated daily checks into a clearer workflow that can be used continuously.

The central idea

Not adding features, but reconnecting the workflow itself into one.

NEXUS / 01
  • Customer
  • Quotation
  • Project
  • Finance

NEXUSOne operating base

A concept for connected work

Four stages of the concept

  1. 01EXPERIENCE

    Experience

  2. 02OBSERVE

    Observe

  3. 03REFRAME

    Reframe

  4. 04BUILD

    Build

Organizing principles

  1. 01

    Organize

    Make scattered information findable.

  2. 02

    Connect

    Join flows that were separated.

  3. 03

    Simplify

    Reduce unnecessary actions.

02

Connect the work before adding features.

BEFORE

  • Customer listExcel
  • EstimatesExcel / Word
  • Project trackingSpreadsheet
  • BillingSeparate system
NEXUSConnected as one.

OUTCOME

  1. 01

    Build the main flow first

    Because requirements keep changing, build the main flow first and add the rest gradually.

  2. 02

    Keep operation simple

    Many functions are fine; complicated operation is not.

  3. 03

    Keep the final judgment human

    AI widens the perspective; the final judgment stays human.

Why does one job require looking in so many places? I started with the relationship between customers, quotes, projects and billing, then worked out the screens.

When customer records, estimates, projects and billing sit in separate places, finding the needed information takes longer and judgment slows down.

What was prioritised was not the number of features but a flow that can be used without hesitation.

CHAPTER NOTE

The problem was not a shortage of features, but a business flow that had been split apart.

NEXUS / 02 · NOTE

03

A business system you can actually use.

Turning the direction and decisions into usable screens and flows.

Customer records and project progress come together in one place for everyday work.

NEXUS starts from the customer inquiry and carries estimates, projects and billing on one operating base.

Workspace — the entry to daily work.
Workspace — the entry to daily work.

Core modules

  1. 01

    CUSTOMERCustomer management

    Customer records and related context in one place.

  2. 02

    QUOTATIONQuotation

    Inquiry through quotation, handled in one flow.

  3. 03

    PROJECTProject management

    The project record continues after quotation.

  4. 04

    OPERATIONSBilling, payment and operations

    Billing, payment and management on the same foundation.

Working screens

These screens come from the quotation prototype and integration stage. The rewrite is a separate development stage.

Project management — projects and their status.
Project management — projects and their status.
Quotation items — the input screen for AI-assisted item creation.
Quotation items — the input screen for AI-assisted item creation.

Website redesign

Home, services and project listing, shown as the website redesign alongside the business system.

Website redesign — home.
Website redesign — home.
Website redesign — services.
Website redesign — services.
Website redesign — project listing.
Website redesign — project listing.

An early rewrite record

This supplied screen records the contact foundation. The PR was unmerged at the time of the record; this is not evidence of a delivered complete business system.

Contact foundation — the supplied early screen.
Contact foundation — the supplied early screen.

Concept design

Concept screens exploring administrator and operations views, shown separately from implemented features and real operating figures.

Concept design — administrator dashboard.
Concept design — administrator dashboard.
Concept design — operations workspace.
Concept design — operations workspace.

Business lifecycle

  1. 01

    INQUIRY

    Inquiry and intake

  2. 02

    QUOTE

    Quotation

  3. 03

    CONTRACT

    Contract and customer

  4. 04

    DELIVERY

    Delivery and project

  5. 05

    BILLING

    Billing and payment

CHAPTER NOTE

A direction and its decisions can only be verified once they become screens and flows that can actually be used.

NEXUS / 03 · NOTE

04

Learning and building with AI.

I am still gaining development experience. I break work into smaller tasks and use AI to help organise, implement and cross-check them. When something is unclear, I return to the code, tests and actual screens before moving on.

Use AI.

But do not hand off judgment.

AI-assisted workflow

  1. 01

    Define the task

    State the requirements and the problem first.

  2. 02

    Explore with AI

    Organize, compare, surface risk and options.

  3. 03

    Make the decision

    Judgment, trade-offs and validation stay with me.

  4. 04

    Build a small step

    Implement in small steps and stack working units.

  5. 05

    Check it works

    Confirm with tests and review.

Different tools for different work.

01

Clarify the idea

Organise requirements, break down problems and compare possible next steps.

Environments
ChatGPT
Models used
GPT-5.6 · GPT-6
02

Build and revise

Use different environments and models for UI implementation, debugging and refactoring.

Environments
Codex · Cursor · OpenCode · OMO
Models used
Composer 2.5 · GPT-5.6 · GPT-6 · DeepSeek V4.1 · Muse 1.3
03

Compare the actual screens

Inspect screenshots and compare implementation with design intent from different perspectives.

Models used
Gemini 3.8 Flash · Grok 4.7 · GPT-6 Astra

I verify the result and decide what to accept.

I compare suggestions and model results, then accept or reject them. I inspect the code and actual behaviour, revise from what can be checked, and request another review when needed.

  • Build / Typecheck
  • Tests
  • Browser / E2E / Smoke
  • Screenshot / Visual QA

An overview of tools used on this project. Detailed assignments and methods belong in the separate AI Workflow study.

07 / AI DEVELOPMENT WORKFLOW →

05

Give the interface, logic and data clear roles.

I use the React, Spring Boot and PostgreSQL I have learned to connect the interface, business logic and stored data. Keeping their roles clear helps me understand and check each part.

Core layers

Conceptual responsibilities
Cross-cutting considerationsAUTH / ROLEIdentity and role scope
  1. 01

    Interface operations

    The interface operations a user works with.

    Frontend · React / TypeScript

  2. 02

    Business processing

    Processing that follows the business flow.

    Backend API · Spring Boot

  3. 03

    Data storage

    Storing the data that the system handles.

    Database · PostgreSQL

Cross-cutting considerationsDOCKER / VMDevelopment and deployment

Verified Supporting Engineering

  • Docker

    Containerizing the runtime so the system runs from the same baseline.

  • Git

    Managing the source and its history as one version record.

  • Authentication

    Identifying the user.

  • Authorization

    Scoping actions per role.

  • Validation

    Values are checked before they are used.

  • Audit Log

    Operations leave a record.

CHAPTER NOTE

Each tier is verified on its own, then made consistent as a whole. The structure is what fixes that order.

NEXUS / 05 · NOTE

06

Taking shape, and still improving.

Development is ongoing. I am checking with users and adjusting the features and interactions. Next comes further checking of the core workflow: what helps in practice, and what still needs to change.

  1. IDEA
  2. PROTOTYPE
  3. CORE SYSTEM
  4. NOW
  5. NEXT

  1. 01

    WHAT EXISTS NOW

    A basic flow that spans customer, estimates and projects.

  2. 02

    WHAT I LEARNED

    Designing the flow of judgment and information matters more than adding features.

  3. 03

    WHAT COMES NEXT

    Verification, improvement and automation for real operation.

The statement

From what is thought to what can be used.

NEXUS / 06
NEXUS — LIN CHIACHENG