Runtime Values and Expressions¶

Runtime values let SchemAlign resolve dynamic values while a pipeline runs.

Named values¶

Named values are explicit.

academic_period={{current_term}}
file_name=graduates_{{current_term}}_{{yyyymmdd}}.csv

current_term should be defined as a named runtime value, not inferred from a generic artifact.

Value sources¶

Named values may come from:

Source	Example
System value	`{{run_id}}`
Date value	`{{yyyymmdd}}`
SQL scalar value	`current_term = select current_term from academic_period`
Upstream node-published value	`next_page_token = response.body.nextPageToken`

Resolution timing¶

Expressions should resolve immediately before the node that uses them executes.

1. Node becomes ready.
2. SchemAlign loads the node config.
3. Expression-enabled fields are resolved.
4. The node receives prepared config.
5. The node executes.

A node runner should receive a resolved value:

{
  "url": "https://example.edu/report?academic_period=202640"
}

not the unresolved expression:

{
  "url": "https://example.edu/report?academic_period={{current_term}}"
}

Field-level expression support¶

Not every field should support expressions.

Good candidates:

URLs
query parameters
headers
SQL text
file names
file paths
email subject
email body
output artifact names

Fields that usually should stay literal:

node type
organization ID
project ID
credential selector
runtime selector
unsafe custom node runtime settings
most boolean toggles