5. Conclusion

The Security functionality provided by the protocols is almost equivalent. While the FTAM and RDA authentication and authorisation mechanisms are a mere mapping to those of the accessed file system or database, DFR defines own mechanisms. No sound statements on efficiency and reliability issues of the protocols can be made right now. These have to be derived from experiences with trial implementations. According to the discussion in section 4, we can conclude that FTAM provides too few support for data access in integrated engineering environments. It is well suited for file transfer between heterogeneous application systems but if the flexibility information stores has to be supported, the need for retrieval operations arises. The idea to press a complete database into a file of the VFS and then access the single FADUs inside by FTAM services makes only sense for very simple structured databases. DFR may be used for data access in well defined and not bound to change applications and environments. With the fixed structure of the document store and the limited set of operations, the protocol is well suited for the access to e.g., mechanical parts databases or CAD archives, whose structure is defined once and keeps stable afterwards. If we want to store heterogeneous documents on a coarse grained level and put descriptive data into the attributes, then DFR is appropriate (it was designed with this application in mind). A potential drawback for such an application is the lacking genericity of the standard that may limit the adoption capabilities to different engineering environments. If complete flexibility is desired and data on the fine grained level shall be managed, then RDA is the most appropriate protocol. On the other hand on its current standardisation status (only SQL specialisation defined) users are limited to databases with SQL access or they have to define their own database language specialisation. Furthermore RDA is a quite complex protocol. For well defined applications, like the ones described in the context of DFR, it provides more functionality than needed. Taking a look at the standardisation and implementation status of the protocols, we can state, that while FTAM is a mature (1988) and DFR is a young (1991) international standard, RDA still has draft standard status. Accordingly, there are several FTAM products available, but no DFR or DRA products are known to the author. According to [5] several SQL vendors are planning to have RDA products …