Install Compatibility

A component can be install compatible with another component. The first component must be call compatible with the other component. Uses of the other component must also be able to be replaced safely with uses of the first component in these cases:

• When making a call to an install block of the other component

• When a component extends from the other component

• When a component contains a reference to the other component

Install compatibility is the same as structural compatibility.

The constraints imposed by install compatibility mean that any existing installed component can be safely replaced by another install-compatible component. You do not have to modify the data structures that describe how the original was installed. Call compatibility is a much weaker statement, because the call-compatible component might need to be reinstalled to properly update the data structures.

For install compatibility to hold, both components must belong to the same version tree. They cannot be components from two distinct version trees.

The provisioning software only enforces install compatibility for components that serve as types, which are called component types. When a component type is updated to refer to a new version of a component, the new version is install compatible with the original version. Thus, you can make install-compatible updates to component types without rebuilding and reinstalling all of the existing components that have been derived from that type. A change made to a component type that is not install compatible must be encoded as a new, distinct component version tree with its own type name. In such cases, the new component type can maintain call compatibility with the original by extending from the original component type. To easily identify the relationship between types, use a versioning system to encode component type names. For example, the component names EJB-1.0 and EJB-1.1 are an easy way to indicate that EJB-1.1 is a later version of the EJB-1.0 component type.

Install compatible implies call compatible, but the reverse is not true. Also, if components are not call compatible, they are not install compatible.