Hierarchical Dependence Graphs for Dynamic JDF Workflows

The Hierarchical Dependence Graph (HDG) described in this paper extends the theory of directed acyclic graph (DAG) by allowing hierarchical representation of workflows. It can be used to explicitly express the dependences across JDF (process) nodes and resources derived from any JDF job description. It defines a flexible and semantic-rich model to represent JDF workflow as a set of DAGs at different abstractions: intent level, process group levels and process execution level. By explicitly representing JDF workflows in the HDG, not only it enables the separation of the workflow itself from MIS/or Controller implementations to support fully dynamic JDF workflows, but also it provides a theoretic basis for formal analysis of JDF workflows. Furthermore, we introduce the concept of Connectivity Matrix and its transformations to allow two views derived from a single model: process-centric view and resource-centric view. By exploiting the fact that each of these views is a DAG with a hierarchical structure, we then show how various analytical properties defined for DAG can be recursively applied to analyze JDF workflows, particularly in the following perspectives: (1) validating JDF workflows in terms of cyclic dependence, missing resources and dangling resources; (2) identifying the impacted JDF nodes or resources due to the resource availability and workflow status changes; (3) intelligently handling failures or exceptions by considering causal relations between resources and processes.