> XML Schema is grossly over-engineered for its purpose; being the subject of > requirements from not only the document markup field, but also databases and > object models, it's a twisted monstrosity that tries to do many things, and > fails at most. Agreed, and I would add that it is seriously lacking in flexibility. (I would like to have words with whoever thought the "unique particle attribution rule" was a good idea.) That said, there's a timing issue in play here. A variety of tools supporting other validation systems, e.g., RelaxNG or Schematron are available now, but a few years back alternatives to XML Schema were much more limited. Despite our dislike we've used XML Schema in a couple of places for precisely this reason. > Specifically, it's very common for people to try to use schema to inform > "binding" tools into specific languages. However, the underlying metamodel of > XML, the Infoset, is both complex and a poor fit for most languages, so > bindings take "shortcuts" and expose a profile of XML's range of expression, > encouraging some patterns of use, while discouraging (or disallowing) others. > Since the bindings often make different decisions (based upon the language of > use), interoperability is difficult (sometimes, impossible). It very much depends on what you're doing and how you're doing it. If what you want is for your data to manifest directly as a data structure, XML is a lousy fit for that for a bunch of different reasons. Json is the clear choice in such cases. But there are other uses where the more complex Infoset of XML can be an asset. Really, it's all about how you use the available tools. > Furthermore, designing a schema that is extensible is incredibly convoluted > in XML Schema 1.0. Schema 1.1 was designed to address this failure, but it > hasn't been broadly adopted; most people I know in the field consider it a > failure. Yes, XML Schema makes this a lot harder to do than it should be, but in a lot of designs I've seen it also has to do with how XML is actually used. A bad design is a bad design, regardless of what schema language you use. > What surprises me and many others is that people are still using it and > promoting it, when it's well-understood by almost EVERYONE who was involved in > using XML for protocols in the past ten years agrees that it's a mistake. See above. I certainly wouldn't use XML Schema for anything new, but there's a lot of legacy stuff out there. Ned