<control> Element

The <control> element defines a control block that is available for this component. A control block is a sequence of steps that can be performed after the component has been installed. For example, a component for a database application might include control blocks to start or shut down the database. A <call> step can invoke a control block by name, which causes the control block steps to be executed in order.

The <control> element children consist of an optional <paramList> element followed by a body, which consists of an optional local <varList> element followed by zero or more “shared” steps. See Shared Steps. The body is not included if the control block is declared abstract.

By default, a derived component inherits all accessible control blocks of its base component. Semantics for overriding a control block are the same as those for overriding an install block.

Attributes for the <control> Element

The <control> element has the following attributes:

• access – An optional attribute of type accessEnum, which specifies the accessibility of the control block. These are the possible values:

  • PUBLIC – Access is unrestricted, which is the default value.

  • PROTECTED – Access is limited to derived components and entities that are in the same path.

  • PATH – Access is limited to entities that are in the same path.

  • PRIVATE – Access is limited to this component.

  Only PUBLIC blocks can be run directly from the component.

• modifier – An optional attribute of type modifierEnum, which specifies the override requirements for the control block. These are the possible values:

  • ABSTRACT – The block cannot include a body. Instead, the body must be specified by nonabstract derived components. A control block can only be declared abstract if the component is also declared abstract. An abstract block cannot be private. Nonabstract blocks must declare a body.

  • FINAL – The control block cannot be overridden by derived components.

  If this attribute is omitted, derived components can choose whether to override the block.

• name – A required attribute of type entityName, which is the name of the control block. This is referenced from a <call> step to execute the control.

• description – An optional attribute that is a string that describes the control block.