Parameter Passing Reference

Parameters allow automata to exchange data — between a parent and a child at spawn time, and between an automaton and its metric or action functions.

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Parameter element

<Parameter LocalVariable="orderId" TargetVariable="orderId"/>

Attribute	Required	Description
LocalVariable	Yes	The name of the variable in the current automaton's global state
TargetVariable	Yes	The name of the variable in the target context (child automaton or function)
Position	No	Used in some function types to specify the positional argument index

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Input parameters

<Input> blocks pass values into a function or child automaton.

In a metric or action, input parameters provide context to the implementation:

<Action Id="getOrder" Type="object">
  <System Name="getOrderFromShopify" Class="ecommerce.ShopifyConnector" Path="/src/ShopifyConnector.java"/>
  <Input>
    <Parameter LocalVariable="shopifyApiEndpoint" TargetVariable="apiEndpoint"/>
    <Parameter LocalVariable="orderId" TargetVariable="orderId"/>
  </Input>
</Action>

In a TransitionNew, input parameters pass values from the parent's global state to the child's global state at instantiation:

<TransitionNew IdInputState="newOrder" IdOutputState="instantiatedOperator"
  Path="ecommerce_backoffice.xal" Type="Operator">
  <Input>
    <Parameter LocalVariable="shopifyApiEndpoint" TargetVariable="shopifyApiEndpoint"/>
    <Parameter LocalVariable="shopifyCredentials" TargetVariable="shopifyCredentials"/>
  </Input>
</TransitionNew>

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Output parameters

<o> blocks capture values returned by a metric or action and write them into the automaton's global state:

<Metric Id="checkPickingConfirmation" Type="object">
  <System Name="checkPickingConfirmation" Class="wms.WaterFallConnector" Path="/src/WaterFallConnector.java"/>
  <o>
    <Parameter LocalVariable="confirmedQuantities" TargetVariable="confirmedQuantities"/>
  </o>
</Metric>

After the metric executes, the value of TargetVariable returned by the function is written into the LocalVariable in the automaton's global state.

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Loop input parameters

<LoopInput> is used exclusively in TransitionNewMulti. It contains a single <Parameter> pointing to a list variable in the parent's global state. The transition iterates over the list and spawns one child instance per item:

<TransitionNewMulti IdInputState="Start" IdOutputState="Cycle"
  Path="patcher.xal" Type="RecycleAppPools" MinWait="300">
  <LoopInput>
    <Parameter LocalVariable="AppPools" TargetVariable="AppPool"/>
  </LoopInput>
</TransitionNewMulti>

Each spawned child receives one element from the AppPools list as the value of its AppPool variable.

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Variable resolution

When the designer writes parameter values to XAL, variables that match a global state variable name are automatically prefixed with this.GLOBALSTATE_. This prefix is resolved by the platform runtime and is invisible in the designer interface.

For example, if the automaton has a global state variable named DbHostName, a parameter referencing it will appear in the XAL as:

<Parameter LocalVariable="DbHostName" TargetVariable="DbHostName"/>

But may be stored internally as this.GLOBALSTATE_DbHostName depending on the context.