Namespace-Time: Unifying the SOAP/WS-* and REST Models

I have always believed that the SOAP/WS-* and REST models were duals, and I have a model to explain the seeming dichotomy. I wrote about it earlier.

Now here's the picture to provide the kiloword equivalent.

Namespace-Time: Why REST and SOAP Composition Models are so Different

There's a mini-controversy going on over the importance of hyperlinks, and whether they're only usable by humans. Jonathan Marsh seems to think that hyperlinks are less useful for machine-to-machine interaction. The REST viewpoint seems to be that services without hyperlinks "dead-end" the Web, hence the absence of solid support for links in SOAP is a further argument against its usefulness.

I have (as usual) a different viewpoint on this altogether. I think SOAP and REST are duals. They both model the Universe of Discourse, but in different ways. With apologies to Einstein, I think the universe being modelled exists in a Namespace-Time continuum. REST lies on the Namespace axis where hyperlinks play (URIs form a namespace). SOAP lies on the Time axis, which is not surprising considering its verb-orientation. That also explains why there is much more emphasis on process orchestration in the SOAP/WS-* world ("Do this, then do that" is time-sequenced). Even within the SOAP/WS-* world, while services are verb-oriented, metadata on services is noun-oriented. No wonder many recent registries for SOAP-based services are based on RESTful APIs (WSO2 Registry and Mule Galaxy).

It would be silly to disparage REST for being silent on "process", just as it would be silly to accuse SOAP of "dead-ending" services from a namespace perspective.

REST resources are composable in Namespace (to form content). SOAP services are composable in Time (to form process). Decide how you want to model your Universe, then take your pick.