When completed, APT will provide all the functionality of RPS2 and much more. Nonetheless, even after the transition, there will be needs for the old RPS2 file format, at least for a few years. However, it is our intention to reduce reliance on RPS2 format as quickly as possible. RPS2 format is a difficult-to-parse, irregular language. The freedom its format allows is very expensive in terms of the cost of maintaining the parser. We are still finding cases where the parser is incapable of catching some errors in the RPS2 format. The reasons for allowing a path to support importing RPS2 files into the APT are given below. But over time, they will be mitigated and the new APT format, based on XML, will serve all the purposes of the RPS2 file. Even better than that will be the use of the APT persistent state files for maintaining state between sessions (see section 4.4). These files will include many computed objects that will not be part of the XML proposal description and will be even more useful to PIs than RPS2 files ever were.
Figure 4 summarizes the standard dataflow through the system. A Phase 1 proposal file is converted to a Phase 2 format XML file for starting proposal development with the APT. Results can be saved as XML files, which can be subsequently be shared with other users. In addition, results will be saved automatically in a persistent state mentioned. After developing the proposal, the user will submit it to STScI through APT. For reasons discussed in section 4.2.3, this submission file will be an RPS2 file in the near future.