The use of rules-engines spans multiple computational and biomedical domains. Within the NCIs caBIG program, the orchestration of grid-based computational workflow has used the BPEL standard. However, recent strategic planning within caBIG has raised questions about the applicability of BPEL for other rule definition and execution scenarios. In response, we have reviewed the current state of rules-engine technologies, and have formulated an architectural model for the integration of heterogeneous rules-engines with caGrid.