| 1 | Back-End services |
| 2 | comprise Tier 3. |
| 3 | Distributed, object-based, |
| 4 | scalable, and reusable |
| 5 | Web server, Object broker |
| 6 | and Resource Manager |
| 7 | Middleware forms Tier 2 |
| 8 | Tier 1 is a high-level, browser-based Front End |
| 9 | for visual programming (including selection of applications, |
| 10 | generation of input data sets, specification of resources, |
| 11 | post-processing and visualizations) |