---
title: `nexyron.feature_serve`
url: https://nexyron.tech/docs/cypher/procedures/abstraction-platform/registry/nexyron-feature-serve
description: nexyron.feature serve serve one subject feature map from a snapshot contract, optionally reusing a matching materialized snapshot
---

# `nexyron.feature_serve`

## Generic Description

`nexyron.feature_serve` serve one subject feature map from a snapshot contract, optionally reusing a matching materialized snapshot

```cypher
CALL nexyron.procedures()
YIELD name, description, parameters, output_columns
WHERE name = 'nexyron.feature_serve'
RETURN name, description, parameters, output_columns
```

Abstraction-platform registry procedures create, list, read, and inspect named contracts such as abstractions, features, datasets, snapshots, models, policies, interventions, scenarios, and split policies.

## Consumer-Level Explanation

This procedure belongs to the model and feature-serving runtime. Use it when you need feature resolution, scoring, explanation, evaluation, or model-quality analysis from already registered abstraction contracts.

### Parameters

-   `snapshot`: Snapshot definition name Required.
-   `subject_id`: Requested subject identifier Required.
-   `at`: Optional as-of timestamp in epoch milliseconds for contextual query placeholders Optional.
-   `system_at`: Optional system-time cutoff in epoch milliseconds for dual-time contextual query placeholders Optional.
-   `prefer_materialized`: When true, reuse a matching materialized snapshot before computing on demand Optional.

### Output Columns

-   `subject_id`
-   `snapshot_ts`
-   `features`
-   `source`

## Example Contract Prerequisite

The executable Cypher blocks on this page query `nexyron.procedures()` so they work in an empty database and stay synchronized with the live procedure registry. A direct `CALL nexyron.feature_serve(...)` requires the named abstraction contracts, artifacts, features, snapshots, datasets, models, or policies referenced by that call to exist first; otherwise the runtime correctly fails with an unknown-contract error rather than inventing state.

## Conceptual Explanation

The important thing about `nexyron.feature_serve` is that it serves a snapshot-level feature map. Snapshot building now uses source-query-backed abstraction definitions to seed and validate subject rows when the snapshot declares `subject_abstraction`.

## More Detailed Explanation

In practical queries, start by deciding the row grain you want after the call: one row per node, one row per path, one row per registry object, one row per artifact, or one row per summary. Then keep that grain explicit with `YIELD` and named projections. That is the difference between a useful planner-facing example and a vague call that downstream tooling cannot safely compose. For contract-driven abstraction procedures, the executable examples on these pages intentionally inspect procedure metadata unless the required named artifacts are created in the same example.

## Advanced Example

```cypher
CALL nexyron.procedures()
YIELD name, parameters, output_columns
WHERE name = 'nexyron.feature_serve'
RETURN name,
       [p IN parameters | p.name] AS parameter_names,
       output_columns
ORDER BY name
```

## Real Use Cases

-   Register reusable member-retention contracts once, then let snapshots, datasets, models, and policies reference those names instead of duplicating raw Cypher in every workflow.
-   Keep admin and product teams aligned around one shared abstraction contract for members, households, facilities, interventions, and churn labels during quarterly retraining cycles.

## Real Limitations And Tradeoffs

-   This surface is contract-driven. If the registered feature, snapshot, dataset, model, or policy definition is weak, the procedure will faithfully execute that weak contract rather than silently repairing it.
-   Use `nexyron.feature_get` when you need one raw feature value. Use `nexyron.feature_serve` when you need the feature map defined by a snapshot.