---
title: Event modeling · Pele
description: Show how commands, events, and views change a system over time.
---

```mermaid
eventmodeling

tf 01 ui CartUI
tf 02 cmd AddItem
tf 03 evt ItemAdded
```

```mermaid
eventmodeling

tf 01 ui CartUI
tf 02 cmd AddItem { description: string }
tf 03 evt ItemAdded { description: string }
```

```mermaid
eventmodeling

timeframe 01 ui CartUI
timeframe 02 command AddItem { description: string }
timeframe 03 event ItemAdded { description: string }
```

```mermaid
eventmodeling

tf 01 ui CartUI
tf 02 cmd AddItem [[AddItem01]]
tf 03 evt ItemAdded [[ItemAdded]]
tf 04 cmd AddItem [[AddItem02]]
tf 05 evt ItemAdded [[ItemAdded]]

data AddItem01 {
  description: 'john'
  image: 'avatar_john'
  price: 20.4
}

data AddItem02 {
  description: 'jack'
  image: 'avatar_jack'
  price: 12.5
}

data ItemAdded {
  description: string
  image: string
  price: number
}
```

```mermaid
eventmodeling

timeframe 01 ui CartUI
timeframe 02 command AddItem [[AddItem01]]
timeframe 03 event ItemAdded [[ItemAdded]]
timeframe 04 command AddItem [[AddItem02]]
timeframe 05 event ItemAdded [[ItemAdded]]

data AddItem01 {
  description: 'john'
  image: 'avatar_john'
  price: 20.4
}

data AddItem02 {
  description: 'jack'
  image: 'avatar_jack'
  price: 12.5
}

data ItemAdded {
  description: string
  image: string
  price: number
}
```

```mermaid
eventmodeling

tf 01 ui CartUI
tf 02 cmd AddItem
tf 03 evt ItemAdded

rf 04 evt External.InventoryChanged
tf 05 pcr InventoryProcessor
tf 06 cmd ChangeInventory
tf 07 evt Cart.InventoryChanged
```

```mermaid
eventmodeling

timeframe 01 ui CartUI
timeframe 02 command AddItem
timeframe 03 event ItemAdded

resetframe 04 event External.InventoryChanged
timeframe 05 processor InventoryProcessor
timeframe 06 command ChangeInventory
timeframe 07 event Cart.InventoryChanged
```

```mermaid
eventmodeling

tf 01 evt ItemAdded
tf 02 ui OtherUI
rf 03 rmo CartItems ->> 01
```

```mermaid
eventmodeling

rf 02 evt CartCreated
rf 03 evt ItemAdded
rf 04 evt ItemRemoved
rf 05 evt CartCleared
tf 01 rmo CartUI ->> 02 ->> 03 ->> 04 ->> 05
```

```mermaid
eventmodeling

tf 03 evt ItemAdded
tf 02 rmo CartItems
tf 04 ui CartUI
```

```mermaid
eventmodeling

tf 03 evt External.InventoryChanged
tf 02 pcr InventoryProcessor
tf 04 cmd ChangeInventory
tf 05 evt Cart.InventoryChanged
```

```mermaid
eventmodeling

rf 01 evt Inventory.InventoryChanged
rf 02 evt External.InventoryChanged
```