Access Modes and Modifiers

Access modes and modifiers control how a component attributes can be used and by whom or what. Access modes and modifiers can effect contained components, component variables, procedures, and source data.

There are basically four access modes, public, private, path, and protected. While some access mode apply to all of the attributes others do not. There are two modifiers final and abstract.

Both the concept of inheritance and the access modes and modifiers function like their Java language counterparts. To understand either of these more fully, please refer to the "Plan and Component Language Specification" as well as the any books that explain these concepts for Java.

Component Access Modes and Modifiers

The access attribute for a component controls how a component can be deployed. There are two modes, path and public. If access is set to path, then the component can only be referenced by other components in the same path and cannot be directly installed by the user. If access is set to public, then no such restrictions apply. A component can be referenced by any other component regardless of its path and it can be deployed directly by a user. The default access mode for a component is public.

The modifiers, abstract and final, for a component effect deployment options. If the modifier is set to abstract then the component may not be installed. It serves only as a base component for other components to extend. Only abstract components may declare abstract child elements. If the modifier is set to final then the component may not be extended by another component. If the modifier is omitted, then the component may be extended and installed.

Component Variable Access Modes and Modifiers

The access attribute for a component variable controls what can access the variable. There are four access modes, public, private, path, and protected. If the access mode is set to public, then access to the variable is not restricted in any way. If the access mode is set to protected, then access to the variable is restricted to derived components and entities in the same path. If the access mode is set to path, then access to the variable is restricted to entities in the same path. If the access mode is set to private, then access to the variable is restricted to the component containing the variable. The default access mode for a component is public.

The modifiers, abstract and final, for a component variable effect the default values and overrides for a component variable. If the modifier is set to abstract then the variable default attribute is omitted and must be specified by non-abstract derived components. Variables can only be declared abstract if the component is also declared abstract. Abstract variables may not be private. Non-abstract variables must declare a default value. If the modifier is set to final then the variable may not be overridden by derived components. If the modifier is omitted, then derived components can choose whether or not to override the variable.

Component Source Access Modes and Modifiers

The access attribute for a component source is not supported and therefore is implied to be public.

The modifiers, abstract and final, for a component source effect the overrides for the component source location. If the modifier is set to abstract then the source location is omitted and must be specified by non-abstract derived components. The source location for a component can only be declared abstract if the component is also declared abstract. If the source location is declared non-abstract then the source location must be specified. If the modifier is set to final then the source location may not be overridden by derived components. If the modifier is omitted, then derived components can choose whether or not to override the location for the source data.