---
id: DATA-4
family: RT-DATA
level: core
profiles: [runtime]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/rt-data/data-4
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# DATA-4 — When a node is ready to run

*RT-DATA (Part II) · level: core · profiles: runtime · added in 1.0*

Readiness is the whole of a workflow's scheduling contract: it decides what runs, in what order, and what a node is guaranteed to have in hand when it does.

## The rule

> **Normative.** This is the rule.
>
> 1. A node runs once its incoming edges are satisfied.
>
> 2. A node with at least one incoming trigger edge is ready as soon as any one of those trigger edges is satisfied, and its data ports are not evaluated at all; such a node may legitimately run with an unfilled data port.
>
> 3. Otherwise its incoming data edges are grouped by the input port they target; a group is satisfied by at least one source that has completed, is on an active branch, and is not a round behind the consumer on a loop the two share; and every group must be satisfied.
>
> 4. That is an OR within a port and an AND across ports.

## Related rules

- Names: DATA-1, DATA-5, SG-19, SG-20
- Referenced by: BR-6, DATA-5, SG-19, SG-20

---

Rule identifiers are permanent and are never renumbered. This specification carries
no implementation status: each implementation publishes its own standing against
these rules. Licensed CC BY 4.0.