Add Task/TODO shape (RFC 5545 iCalendar VTODO)

[jeswr]

Type of Change

* [x] New domain file
* [ ] Update existing domain file
* [ ] Documentation only

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Domain

Domain file:        shapes/task.ttl
Purpose of domain:  Validation shape for tasks / TODO items.
Intended use cases: Personal task managers, to-do list apps, and any
                    Solid app that needs to record actionable items
                    for a user with status, due date, and priority.

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Shape Details

Shape name(s):      task_shape:TaskShape
Target class/node:  cal:Vtodo
Files changed:      shapes/task.ttl (new)

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Shape Change

* [x] New shape
* [ ] New version of existing shape
* [ ] Non-breaking constraint addition
* [ ] Documentation update

Description:

Adds a SHACL shape for cal:Vtodo grounded in the
W3C iCalendar in RDF vocabulary,
which mirrors the iCalendar VTODO calendar component defined in
RFC 5545 §3.6.2.

This sits alongside the existing meeting.ttl and event.ttl
domain files (both targeting cal:Vevent) and reuses the
W3C iCalendar in RDF vocabulary they already use.

Constraints cover:

• cal:summary (xsd:string, max 1) – short title
• cal:description (xsd:string, max 1) – longer description
• cal:dtstart (xsd:date or xsd:dateTime, max 1)
• cal:due (xsd:date or xsd:dateTime, max 1)
• cal:status (xsd:string, max 1, enum
  NEEDS-ACTION / IN-PROCESS / COMPLETED / CANCELLED
  per RFC 5545 §3.8.1.11 for VTODO)
• cal:priority (xsd:integer 0-9 per RFC 5545 §3.8.1.9)
• cal:percentComplete (xsd:integer 0-100; cross-field
  semantics with cal:status are documented but not enforced)
• cal:categories (xsd:string, repeatable)

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Immutability Confirmation

* [x] Existing constraints were not modified
* [x] Previously valid data remains valid
* [x] If behaviour changed, a new shape/version was introduced

(New file – no existing shapes were touched.)

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Examples

Valid example

@prefix cal: <http://www.w3.org/2002/12/cal/ical#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

</tasks/buy-milk>
    a cal:Vtodo ;
    cal:summary "Buy milk" ;
    cal:description "Two litres, semi-skimmed." ;
    cal:due "2026-04-25"^^xsd:date ;
    cal:status "NEEDS-ACTION" ;
    cal:priority 5 ;
    cal:percentComplete 0 ;
    cal:categories "shopping" , "errands" .

Invalid example

@prefix cal: <http://www.w3.org/2002/12/cal/ical#> .

</tasks/bad>
    a cal:Vtodo ;
    cal:status "DONE" ;             # Not in {NEEDS-ACTION, IN-PROCESS, COMPLETED, CANCELLED}
    cal:priority 11 ;               # Out of 0-9 range
    cal:percentComplete 150 .       # Out of 0-100 range

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Compatibility

* [x] Fully backwards compatible
* [ ] May cause new validation failures
* [ ] Breaking change

New domain file. No existing shape touched. Reuses the same
cal: namespace as meeting.ttl and event.ttl for a different
target class (cal:Vtodo).

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Validation

* [x] SHACL validation run
* [x] Example data tested

Tools used: pyshacl, plus the repository's scripts/validate-shacl-shapes-file.py, scripts/check-metadata-and-immutability-file.py, and scripts/check-namespaces-and-names-file.py.

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Reviewer Checklist

* [ ] Immutability respected
* [ ] Targeting is correct
* [ ] Constraints justified
* [ ] Examples match expected behaviour

[Copilot]

Pull request overview

Adds a new SHACL domain shape for task/TODO resources (cal:Vtodo) using the W3C iCalendar-in-RDF vocabulary, aligned with RFC 5545’s VTODO component. This extends the repository’s existing calendar-related shapes (e.g., meeting.ttl, event.ttl) with a task-focused validation shape.

Changes:

• Introduces task_shape:TaskShape targeting cal:Vtodo.
• Adds SHACL property constraints for core VTODO fields (summary, description, dtstart, due, status enum, priority range, percentComplete range, repeatable categories).
• Includes standard shape metadata (dct:created, vs:term_status, provenance links, references, sh:codeIdentifier).

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