The OT using Apache ANT as pipeline infrastructure. Thats OK in general, but there are several shortcomings once you have to integrate or extend the OT implementation for enterprise use cases (see e.g. discussion "Pipeline refactoring", "Diving Into Performance Improvements").
Because DITA-OT is "only" a reference implementation there might be other implementation out there already using a better approach because they started development once the limitation of the OT implementation already known?
Yes there are two available I'm aware of with different key aspects:
- XMLmind DITA Converter (see http://www.xmlmind.com/ditac/what_is_ditac.html)
Key Aspects: Easier use, integration and improved output.
Reality: Bad and monolithic design with hard coded java based pipeline and a small user community. No real advantage compared to existing DITA-OT.
- DITA XProc Pipelines (see https://community.emc.com/docs/DOC-8740)
Key Aspects: greater flexibility, extensibility, portability, performance.
Implementation based on XProc (XML Pipeline Language). The design is one step in the right direction and shows the much higher scalability (functional and non functional) of this design, e.g. in case you want to use a extended semantics for validation you can add ISO-Schematron based rules for validation using existing "ISO Schematron schema for DITA" stylesheet and build-in "p:validate-with-schematron" step in XProc and add it into the existing pipeline.
This implementation isn't perfect, it mainly use XProc markup for the implementation which makes the code long and hard to read / maintain. The usage of the right language for each step which is one advantage of XML pipelining isn't consequent implemented in this implementation. Based on currently available XProc Engines (http://tests.xproc.org/results/) this implementation is not yet ready for enterprise but this will change in the near future the more real world examples are available and used in production.