Example Use Case: Centralised Sales & Inventory System

Mental Model: Identify the "Nouns"

To figure out what forms you need, look at your business operations and identify the key nouns. A form typically represents a person, an organisation, an item or asset, a trackable activity, or a location.

• People and Organisations: Customers, Suppliers, Employees.
• Items and Assets: Products, Vehicles, Equipment.
• Activities and Transactions: Orders, Invoices, Deliveries.
• Location: Warehouses, Retail Outlets.

Mental Model: When to Use a Subform

If a piece of information cannot logically exist on its own and always belongs to a larger record, it should be created as a subform.

This establishes a parent-child relationship, where multiple child records belong to a single parent.

Common examples:

• Order (Parent) & Order Items (Child): Each item belongs to a specific order and cannot exist on its own.
• Supplier (Parent) & Contact Persons (Child): Each contact person, such as an account manager or logistics contact, belongs to a specific supplier.
• Customer (Parent) & Delivery Addresses (Child): A customer can have multiple delivery locations

Note: Subforms can also be nested within other subforms, allowing you to represent multiple levels of related information if needed.

Mental Model: The Clipboard Test

1. Brainstorming Details

To figure out what details you need in a form, imagine using a physical paper form to capture the details of a record in your system. For a Customer, it might include a 'Name', 'Email', and 'Phone Number'. For a Product, it might include a 'SKU' and 'Unit Price'.

These details represent the essential data you need to capture.

2. Setting The Rules

Once you know your details, the next step is to define how each one should behave. To do this, ask yourself these four questions for every detail:

• Type / Format: What kind of data is this? If it is for money, set the format to be Currency so values like "Twenty" cannot be entered.
• Compulsory: Is this detail critical? If you absolutely cannot process an order without a customer's email, make it Compulsory.
• Min / Max Limits: What is a realistic range? For example, quantities cannot be negative, so the minimum should be set to 0. Maximum limits can also help keep text fields within a reasonable length (e.g., 50 characters).
• Default Values: What is the most common value? If most new orders start in a "Pending" state, set the default to "Pending" to save your team from entering the value every single time.

Mental Model: The "Belongs To" Test & The Master Folder Concept

The "Belongs To" Test

To figure out where links are needed, ask yourself: "Does this record belong to another record, depend on it, or contain smaller items within it or nested inside a parent?"

• Does an Order belong to a specific Customer? Yes. Therefore, the Order form needs a link to the Customer.
• Does an Order Item represent a specific Product from inventory? Yes. Therefore, the Order Item needs a link to the Product.
• Does an Order Item belong to a specific Order? Yes. This is a parent-child relationship.

The Master Folder Concept

When tracking orders through spreadsheets or physical paperwork, customer details are often logged repeatedly for every new transaction. This means the exact same information is repeated multiple times, which can lead to inconsistencies if details are recorded differently or updated in only some places.

Instead, think of your Customer form as a master folder that stores each customer's details exactly once. Each order then links to the customer using a unique identifier 'Customer ID', rather than duplicating the customer details. This way, customer details are stored once and remain consistent across all orders.

Note: If you need to capture a detail that is specific to a single order (such as the delivery address), you should add 'Delivery Address' as a text detail in Step 2. This gives the order its own address detail, completely separate from the customer's primary address.