Event

An occurrence in time ; something that happens, occurs, or takes place at a specific point or interval.

Semantic Identity

semantic_id: wsf:Event
preferred_name: Event
aliases: [Occurrence, Happening]
status: Normative
version: 1.0.0
classification: Tier 1 (Foundational)
parent: wsf:Entity
authority: WSF

Definition

An Event is an occurrence in time ; something that happens, occurs, or takes place at a specific point or interval. Events are the foundation for representing change, action, and happening in semantic systems.

An Event is NOT:

A persistent entity (use Entity for things that persist);
A tendency or potential (use Disposition);
A state of affairs (use State);
An activity type (use Activity : but events are specific occurrences).

An Event IS:

Located in time;
Specific (this particular occurrence);
Distinguished from other events by identity;
May change state or produce outcomes;
May have participants (Agents, Entities).

Why Event Is Foundational

Event is foundational because:

Change requires events : something happens at a time;
History requires events : past occurrences are events;
Causality involves events : causes produce effects (which are events);
Actions are events : agent actions are specific occurrences;
Processes are sequences of events : structured change;
Provenance refers to events : assertions are made at events (asserted-at).

Without Event, the architecture cannot model change, history, or occurrence.

Event Types

WSF distinguishes several kinds of events:

1. Atomic Events

Occurrences at a point in time.

Examples:

A specific payment is received
A specific order is placed
A specific message is sent

2. Composite Events

Events composed of multiple atomic events.

Examples:

Order fulfillment (composed of payment, picking, shipping, delivery)
Customer onboarding (composed of registration, verification, activation)

3. Instantaneous Events

Occur at a specific instant with no duration.

Examples:

Click of a button
Sending a message
Recording a measurement

4. Interval Events

Occur over a duration.

Examples:

A workflow execution
A manufacturing process
A training session

5. Internal Events

Occur within an entity.

Examples:

System state change
Heartbeat
Decision made

6. External Events

Occur in the world outside entities.

Examples:

Natural disaster
Market change
Customer action

7. Agent Events

Performed by an agent.

Examples:

Order placed by Kwesi
Payment made by OTCHERE Inc
Decision made by Architecture Team

Event Structure

An Event SHALL carry:

event:
  semantic_id: wsf-ex:<event-instance>
  type: wsf-type:<event-type>
  occurred_at: ISO timestamp
  duration: ISO duration (optional, for interval events)
  participants:
    agents: [<Entities that performed or were involved>]
    entities: [<Entities affected>]
  location: <spatial location>
  context: <context of occurrence>
  changes:
    - state_change: <state changed>
      from: <previous state>
      to: <new state>
  produces:
    - <outcome produced>
  causes:
    - <cause events>
  triggered_by:
    - <triggering events>
  evidence:
    - <evidence of occurrence>
  provenance:
    source: <where the event was recorded>
    asserted_by: <who recorded it>
    authority: <authority for the record>

Event vs State (Critical Distinction)

Aspect	Event	State
Nature	Occurrence	Condition
Time	Specific instant or interval	Persists over time
Example	Order #12345 was placed	Order #12345 is in Paid state
Change	Happens, then is past	Exists until changed
Identity	Each event has unique identity	States can recur

The crucial distinction: A state can hold for an interval; an event occurs at a point or during an interval.

Event:  [Placed]→[Paid]→[Shipped]→[Delivered]
            ↓      ↓       ↓         ↓
State:    Pending  Paid    Shipped   Delivered

Events cause state changes. States hold between events.

Event vs Activity (Critical Distinction)

Aspect	Event	Activity
Nature	Occurrence	Type of occurrence
Time	Specific	Generic
Example	Order #12345 was shipped (Aug 29)	Shipping an order (activity type)
Identity	This specific occurrence	The activity as a concept

Events are specific occurrences. Activities are types of occurrences. An Activity is specialized through instances that are Events.

Event Patterns

Event Causation

Event A ──causes──► Event B

Events cause other events. Causal relationships form chains.

Event Sequence

Event A ──before──► Event B ──before──► Event C

Events occur in sequences. Sequences can be linear or branching.

Event Composition

Event X = Event A + Event B + Event C

Composite events are made of simpler events.

Event Participation

Event ──has-participant──► Agent

Events have participants (agents, entities, systems).

Event in Semantic Assertions

- assertion:
  subject: wsf-ex:Order-12345
  relationship: wsf-rel:occurred-at
  object: wsf-time:2026-08-29T10:15:00Z
  context: <context>

- assertion:
  subject: wsf-ex:Order-12345
  relationship: wsf-rel:has-event
  object: wsf-ex:Event-Payment-Received-12345
  context: <context>

- event:
  semantic_id: wsf-ex:Event-Payment-Received-12345
  type: wsf-type:PaymentReceived
  occurred_at: 2026-08-29T10:15:00Z
  participants:
    entities: [wsf-ex:Order-12345, wsf-ex:OTCHERE-Inc]
  changes:
    - state_change: Order-12345 status
      from: Pending
      to: Paid
  evidence:
    - Payment gateway log
  provenance:
    source: OTCHERE Payment Gateway
    asserted_by: OTCHERE Payment Gateway
    authority: OTCHERE Inc IT

Event Time

Events are located in time:

event_time:
  occurred_at: <instant>
  # OR
  occurred_during: <interval>
  recorded_at: <instant>
  observed_at: <instant>

Per the Temporal investigation, events have:

Occurrence time: When the event actually happened.
Recording time: When the event was recorded.
Observation time: When the event was observed.

These can differ (event happened before being recorded, or before being observed).

Event Identity

Each event has its own identity, distinguishing it from other events:

event:
  semantic_id: wsf-ex:Event-2026-08-29-001
  # Specific identifier for this specific occurrence

Even if two events have the same type (e.g., "Payment Received"), they have distinct identities if they are different occurrences.

Event Lifecycle

Events follow the lifecycle:

Occurrence → Recording → Observation → Assertion → Validation → Historical Record

Each stage may have its own timestamp and provenance.

Event Sources

Events may originate from:

System events: Generated by systems (e.g., application logs).
Agent actions: Performed by agents.
Observations: Recorded by observation.
Inferences: Derived from other events.
External sources: Reported by external systems.

Each source has its own provenance requirements.

Event Examples

Order Placed

event:
  semantic_id: wsf-ex:Order-12345-Placed
  type: wsf-type:OrderPlaced
  occurred_at: 2026-08-29T09:00:00Z
  duration: PT0S (instantaneous)
  participants:
    agents: [wsf-ex:Kwesi]
    entities: [wsf-ex:Order-12345]
  context: wsf-ctx:OTCHERE-CustomerPortal
  changes:
    - state_change: Order-12345 status
      from: null
      to: Pending
  produces:
    - wsf-ex:Order-12345 (new entity)
  evidence:
    - Order placement log
    - Customer portal session
  provenance:
    source: OTCHERE Order Service
    asserted_by: OTCHERE Order Service
    authority: OTCHERE Inc

Payment Received

event:
  semantic_id: wsf-ex:Payment-12345-Received
  type: wsf-type:PaymentReceived
  occurred_at: 2026-08-29T10:15:00Z
  duration: PT0S
  participants:
    entities: [wsf-ex:Order-12345, wsf-ex:OTCHERE-Inc, wsf-ex:PaymentGateway]
  context: wsf-ctx:OTCHERE-PaymentProcessing
  changes:
    - state_change: Order-12345 status
      from: Pending
      to: Paid
    - state_change: OTCHERE-Inc balance
      from: <previous>
      to: <new>
  evidence:
    - Payment gateway log
    - Bank statement
  provenance:
    source: OTCHERE Payment Gateway
    asserted_by: OTCHERE Payment Gateway
    authority: OTCHERE Inc Finance

Order Shipped

event:
  semantic_id: wsf-ex:Order-12345-Shipped
  type: wsf-type:ItemsShipped
  occurred_at: 2026-08-29T14:30:00Z
  duration: PT15M (loading time)
  participants:
    entities: [wsf-ex:Order-12345, wsf-ex:OTCHERE-Warehouse]
  context: wsf-ctx:OTCHERE-Warehouse
  changes:
    - state_change: Order-12345 status
      from: Paid
      to: Shipped
  produces:
    - wsf-ex:Shipment-TRK-2026-08-29-001
  evidence:
    - Warehouse fulfillment log
    - Shipping confirmation
    - Tracking number assignment
  provenance:
    source: OTCHERE Warehouse System
    asserted_by: OTCHERE Warehouse System
    authority: OTCHERE Inc Operations

Event Validation

Events SHALL be validated for:

Time validity: Occurred_at is consistent with related events.
Participant existence: All referenced participants exist.
Causal consistency: Causes occurred before effects.
State change validity: State transitions are valid.
Evidence presence: At least one evidence item.
Provenance presence: Source, asserted_by, authority recorded.

Event in Digital Twin Pattern

Events are central to the Digital Twin pattern (per CR-WSF-17 Rev.1 §16):

Entity Instance (OTCHERE DC-01)
   ├── Identity
   ├── State (current)
   ├── Events (history)
   ├── Relationships
   ├── Capabilities
   ├── Context
   ├── Time
   └── Space

The event history provides the operational record of the digital twin.

Event in Simulation Pattern

Events drive simulation (per CR-WSF-17 Rev.1 §17):

Initial State → Event/Action → Transition → Resulting State → Next Event

Each transition is an event; each state is between events.

Related Concepts

Entity : Things that participate in events
State : Conditions held between events
Disposition : Tendencies that manifest in events
Capability : Dispositions realized through events
Time : Events occur in time
Space : Events occur in space

Related ADRs

ADR-WSF-09 : Foundational Concept Taxonomy
ADR-WSF-12 : Semantic Assertion Model (events in assertions)
ADR-WSF-16 : Semantic Evolution & Versioning (event records)
ADR-WSF-19 : Semantic Relationship Model (event relationships)

Cross-Repository References

Canonical semantic asset: wsf/concepts/event.md

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Event

Semantic Identity

Definition

Why Event Is Foundational

Event Types

1. Atomic Events

2. Composite Events

3. Instantaneous Events

4. Interval Events

5. Internal Events

6. External Events

7. Agent Events

Event Structure

Event vs State (Critical Distinction)

Event vs Activity (Critical Distinction)

Event Patterns

Event Causation

Event Sequence

Event Composition

Event Participation

Event in Semantic Assertions

Event Time

Event Identity

Event Lifecycle

Event Sources

Event Examples

Order Placed

Payment Received

Order Shipped

Event Validation

Event in Digital Twin Pattern

Event in Simulation Pattern

Related Concepts

Related ADRs

Cross-Repository References

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Event

Semantic Identity

Definition

Why Event Is Foundational

Event Types

1. Atomic Events

2. Composite Events

3. Instantaneous Events

4. Interval Events

5. Internal Events

6. External Events

7. Agent Events

Event Structure

Event vs State (Critical Distinction)

Event vs Activity (Critical Distinction)

Event Patterns

Event Causation

Event Sequence

Event Composition

Event Participation

Event in Semantic Assertions

Event Time

Event Identity

Event Lifecycle

Event Sources

Event Examples

Order Placed

Payment Received

Order Shipped

Event Validation

Event in Digital Twin Pattern

Event in Simulation Pattern

Related Concepts

Related ADRs

Cross-Repository References