| Back-End services |
| comprise Tier 3. |
| Distributed, object-based, |
| scalable, and reusable |
| Web server, Object broker |
| and Resource Manager |
| Middleware forms Tier 2 |
| Tier 1 is a high-level, browser-based Front End |
| for visual programming (including selection of applications, |
| generation of input data sets, specification of resources, |
| post-processing and visualizations) |