Metrics Reference

Metrics are defined within the <Functions> element and represent data-reading functions the automaton uses to observe the state of other automata or monitored objects.

Metric element

<Metric Id="checkPickingConfirmation" Type="object" MinWait="0">
  <System
    Name="checkPickingConfirmation"
    Class="wms.WaterFallConnector"
    Path="/wms/src/WaterFallConnector.java"/>
  <Query>
    SELECT GLOBALSTATE_STATUS
    FROM Scenario_Follower_Manager
    WHERE groupLabel = 'this.GROUPLABEL'
  </Query>
  <Input>
    <Parameter LocalVariable="wmsPickingListId" TargetVariable="pickingListId"/>
  </Input>
  <Output>
    <Parameter LocalVariable="confirmedQuantities" TargetVariable="confirmedQuantities"/>
  </Output>
  <Enumeration>
    <Const Value="confirmed"/>
    <Const Value="pending"/>
    <Const Value="error"/>
  </Enumeration>
</Metric>

Attributes

Attribute	Required	Description
`Id`	Yes	Unique identifier within `<Functions>`. Referenced by state `IdMetric` attributes.
`Type`	No	Execution context: `object` for metrics tied to monitored objects, `automaton` for metrics reading other automaton instances directly.
`MinWait`	No	Minimum interval in milliseconds between successive evaluations of this metric.

Child elements

`<System>`

Specifies the runtime implementation.

Attribute	Description
`Name`	The method name to invoke
`Class`	The fully qualified class name
`Path`	The implementation file path

`<Query>`

A SQL-like expression that reads the target automaton's or object's state. See Query Syntax for the full specification.

`<Input>`

Maps global state variables into the metric's input parameters.

`<Output>`

Maps the metric's return values back into the automaton's global state. The MetricSymbol attribute on <Output> can optionally specify the variable name used to expose the metric value externally.

`<Enumeration>`

Defines the set of values the metric can return. Each <Const Value="..."/> declares one possible return value.

<Enumeration>
  <Const Value="confirmed"/>
  <Const Value="pending"/>
  <Const Value="error"/>
</Enumeration>

Enumeration values are used as MetricValue conditions on outgoing transitions from states associated with this metric. Only transitions whose MetricValue matches a declared constant will fire.

Metric vs Action

Both metrics and actions use <System>, <Input>, and <Output>. The key difference is their purpose:

A metric reads state and returns a value from the enumeration, driving transitions.
An action performs an operation and may update global state variables, but does not return an enumeration value that drives transitions directly.

In the XAL Designer, metrics are configured in the Metric section of the state panel, and actions in the Action section.