Proper ETL/data transformation tools for RDF?

I'm looking for a tool that can deal with proper ETL/data transformation tasks with RDF data. The tool should be able to handle whole (complex) records/entities/resources/objects, i.e., one should be able to access/work on an RDF Molecule/Minimum Spanning Graph/URI Declaration/Concise Bounded Description/resource-description/associated description during the whole processing pipeline. A more generic, but line-based example is, e.g., Talend (another one might be Pentaho). SPARQLMotion may directs a bit into the direction. The processing pipelines/scripts/jobs should be able to run on a scalabe environment.

An example transformation: I would like to be able to define constraints on values that are deeper in the object structure and based on this, I would like to conditionally modify another value that is deeper in the hierarchy (object structure).

Full disclosure: I work for Ontology Systems.

Our Ontology 4 platform sounds like it might be what you’re after: it is the basis for products we make used in data migration and integration, where we are often an alternative to more “traditional” data transformation tools. It takes a pipelined approach using RDF.

Might be worth taking a quick look at

Pentaho has a pretty easy to use plugin architecture (though the documentation on it is poor). I've had success with writing RDF plugins for Pentaho in the past (I was actually doing an ETL pipeline taking data from Accumulo and transforming it into RDF).

If you have a specific tool in mind that has a plugin system then you can likely build your pipeline up yourself, some ETL tools are starting to add RDF support but they seem to be fairly sparse right now.