> For the complete documentation index, see [llms.txt](https://doc.duaer.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.duaer.com/courses/level-two/chapter-1.md).

# Understand how items flow in Duaer

In Duaer, this chapter explains what one input looks like and how a node runs with many items.
## The item data structure <a href="#data-structure-of-n8n" id="data-structure-of-n8n"></a>

Duaer passes a list of items between nodes. One item usually holds a json object and may hold binary data. The next node runs once per item by default. That is the same idea as [run per item](/flow-logic/looping.md#executing-nodes-once).

When you read an execution, separate “this item” from “all items”. Keeping an array as a field on one json object behaves differently from splitting that array into many items. Node notes that mention the data structure open this section.
## Questions

### What does Duaer level-two chapter one cover?

How items move between nodes: what one input looks like, and how a node runs when there are many items. When a node note mentions the data structure, it links to this section.