# Binding to Model
After creating the [input and output models](https://docs.decisionrules.io/doc/rules/common-rule-features/input-and-output), you need to bind these models to your Decision Table. The binding determines which data fields are used in your rule logic.
**Basic Binding:**
* **Input Model** → Bound to **condition columns**.
* **Output Model** → Bound to **result columns**.
## **Understanding Model Binding**
### **What Can Be Bound**
You can select any **leaf field** from the input/output model as a condition or result variable.
{% hint style="warning" %}
You cannot select a parent/root field that contains children as a condition/result variable. Only leaf fields (fields with no children) can be bound.
{% endhint %}
### **Use Case Example**
Consider the following model structure:
From this model structure, here's what can and cannot be bound to columns:
#### **Can be bound:**
**Input:**
* `delivery.distance.car`
* `delivery.distance.ship`
* `delivery.distance.plane`
* `delivery.tariff`
* `package.weight`
* `package.longestSide`
**Output:**
* `shippingCost`
* `deliveryMethod`
* `status`
#### **Cannot be bound:**
* `delivery` (has children: `distance`, `tariff`)
* `delivery.distance` (has children: `car`, `ship`, `plane`)
* `package` (has children: `weight`, `longestSide`)
### **Flexible Usage**
**You don't need to use every field as a column.** Model fields can be used in different ways:
* As column bindings (condition or result columns).
* In calculations and expressions without being bound to a column.
* Referenced multiple times in different columns or cells.
This flexibility applies to both input and output models.
## **How to Bind Models**
### **Binding Input Model to Condition Columns**
1. Navigate to the **Decision Table Model**.
2. Create new input field.
3. Navigate to the **Decision Table Designer**.
4. Create a new **condition column**.
5. In the column header dropdown, select the input field you want to bind.
### **Binding Calculation field to Condition Columns**
1. Navigate to the **Decision Table Designer**.
2. Create new **calculation column** (rename it for better readability)
3. Create a new **condition column**.
4. In the column header dropdown, select the calculation field you want to bind.
### **Binding Output Model to Condition Columns**
1. Navigate to the **Decision Table Model**.
2. Create new output field.
3. Navigate to the **Decision Table Designer**.
4. Create a new **result column**.
5. In the column header dropdown, select the output field you want to bind.
{% hint style="info" %}
Condition columns can also be bound to [Rule variables](https://docs.decisionrules.io/doc/rules/common-rule-features/rule-variables)
{% endhint %}
