Vocabulary: tasks

Term: id
	Concept Type: Big Serial (Type)
Term: actor
	Concept Type: Integer (Type)
Term: attempt count
	Concept Type: Integer (Type)
Term: attempt limit
	Concept Type: Integer (Type)
Term: cron expression
	Concept Type: Short Text (Type)
Term: error message
	Concept Type: Short Text (Type)
Term: handler
	Concept Type: Short Text (Type)
Term: key
	Concept Type: Short Text (Type)
Term: parameter set
	Concept Type: JSON (Type)
Term: status
	Concept Type: Short Text (Type)
Term: time
	Concept Type: Date Time (Type)

Term: task
Fact type: task has id
	Necessity: each task has exactly one id
Fact type: task has key
	Necessity: each task has at most one key
Fact type: task is created by actor
	Necessity: each task is created by exactly one actor
Fact type: task is executed by handler
	Synonymous Form: handler executes task
	Necessity: each task is executed by exactly one handler
Fact type: task is executed with parameter set
	Necessity: each task is executed with at most one parameter set
Fact type: task is scheduled with cron expression
	Necessity: each task is scheduled with at most one cron expression
Fact type: task is scheduled to execute on time
	Necessity: each task is scheduled to execute on at most one time
Fact type: task has status
	Necessity: each task has exactly one status
	Definition: "queued" or "cancelled" or "succeeded" or "failed"
Fact type: task started on time
	Necessity: each task started on at most one time
Fact type: task ended on time
	Necessity: each task ended on at most one time
Fact type: task has error message
	Necessity: each task has at most one error message
Fact type: task has attempt count
	Necessity: each task has exactly one attempt count
Fact type: task has attempt limit
	Necessity: each task has exactly one attempt limit
	Necessity: each task has an attempt limit that is greater than or equal to 1

Rule: It is necessary that each handler that executes a task that is scheduled with a cron expression and has a status that is equal to "queued", executes at most one task that is scheduled with a cron expression and has a status that is equal to "queued".