Dependency Graph Pattern

The Dependency Graph pattern handles the recursive dependency of resources by introducing dependency descriptions, which model a resources’ dependencies on other resources. Before a resource is acquired, its dependencies and recursively the dependencies of required resources are evaluated by a resource manager to set up a graph of recursively dependent resources. 1 Example Using one resource often means using many resources, because the initial resource depends on other resources. This dependency often continues recursively (Figure 1). A resource can be anything that is required for a user service or application, for example, a runtime software or hardware component, or a shared library. For example, in a pipes-and-filter architecture for image processing there is a processing chain with an image source, possibly filters, a feature detector, and a feature comparator. The result is given to a consumer such as a feature tracker which calculates a position from the feature positions in the image. The use of the tracker resource requires the use of a whole chain of other resources. Traditionally, it is left to the developers of the individual resources to find and use required resources, either by binding them directly through libraries or by asking a resource life cycle manager as described by Kircher and Jain [3]. a:Resource b:Resource