---
id: DATA-2
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-2
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# DATA-2 — Several sources on one port resolve to a single latest value

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

A merge point in a workflow is not a collector. A port fed by three edges is still one port, and what a node reads there is one value.

## The rule

> **Normative.** This is the rule.
>
> 1. A port fed by several edges receives exactly one value, never a list of them.
>
> 2. The value is the one produced by the most recent execution among the sources: a source carrying a later execution order wins; a source carrying an execution order wins over one carrying none; and where neither carries one, the source node identifier decides, lexicographically.
>
> 3. A collision between sources on one port is reported as a warning and never fails the run.


## What it means

A port fed by several edges never accumulates a list; it resolves to exactly
one value, and the resolution has a strict order of preference. A source that
completed later wins over one that completed earlier. Only when neither
source recorded a completion order at all does the tie-break fall to the
source node's own identifier — and that fallback is a genuine lexicographic
sort, not the order the edges happen to be drawn in a workflow: which edge
was drawn first has no bearing on which source wins.

## Example

Two sources, `node_early` and `node_late`, both wire into the same port. Each
completes with its own execution order recorded.

```json title="Resolved by completion order" verdict="resolved"
{"data": "second"}
```

The same port, fed by `node_a` and `node_b`, neither of which recorded a
completion order — and the edge from `node_b` is drawn first in the
workflow, ahead of `node_a`'s:

```json title="Resolved by source node identifier" verdict="resolved"
{"data": "from_a"}
```

`node_a` wins on the alphabetical sort even though its edge was declared
second.

## Related rules

- Names: SG-8
- Referenced by: SG-8

---

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.