XML
When people create HTTP APIs, one of the common decisions is about what format to use, usually revolving around “JSON or XML?”
It’s become axiomatic in some circles — especially in WS-* land, as well as in many other uses of XML — that the preferred (or only) means of offering extensibility is through URI-based namespaces, along with a flag to tell consumers when an extension needs to be understood (a.k.a. mustUnderstand).
For some time, I’ve noticed that people defining XML formats spend an inordinate amount of time talking about the structure of the format. This is especially apparent in standards working groups, where hours — no, days — can be spent agonizing over whether to make something an attribute or an element.
I’m intrigued by the JSON effort. While many people (and vendors) have chosen XML for data interchange because it’s not platform- or vendor-specific, these folks have chosen the other path; by leveraging the serialisation of data structures in ECMAScript (nee JavaScript) — a nearly ubiquitous language, on every desktop that has a browser — they get an automatic installed base and at least one API for free.
I’ve been talking with a few people about my previous assertion that the Infoset is a bad abstraction for data modelling, and my subsequent post about the informational properties of the Infoset.
Recently, I’ve been thinking about the influences that using the Infoset has on the information you place in it.
Without pointing fingers, some people have a bee in their collective bonnet about the dangers of allowing binary content to be represented in XML, care of XOP. Others are up in arms about re-inventing HTTP in SOAP, courtesy of the Representation Header. Both of these are products of the XML Protocol WG, of which I’m a member, so I’d like to share my viewpoint (which is not that of either my employer nor the working group, etc., ad nauseam).
An interesting issue poked its head up at the W3C Technical Plenary last week. XML Protocol (known as SOAP to mere mortals) is defined in terms of XML Infosets — it describes how to move Infosets around and process them, as the basis of Web services.
