> Many languages have libraries built in that do something reasonable with JSON. What about cross-language? In C# I define a class containing a `DateTime` fiel

> Many languages have libraries built in that do something reasonable with JSON. What about cross-language? In C# I define a class containing a `DateTime` field, export the schema with xsd, and generate classes for Java with xjc, and get back a field of (an equivalent of) `DateTime` type. Doing what you suggest with JSON, I'd get a "string". Thanks but no thanks. > If you're going to go through the effort of a compile step, you should probably just use a binary protocol, […] I see absolutely no reason to use XML these days as a data format, In our product we use a relational db (SQLServer) combined with XML. Each table has a structured part which is put into relational columns, plus an extensions part that is put into a "Data" XML column for semi-structured data. SQLServer supports XQuery so we can query the semi-structured data from SQL when needed. This wouldn't fly with a binary format. EDIT: yes, SQLServer also supports JSON, but has special optimizations for XML (e.g., it can understand schema types, it supports XML indexes which "shred" XML to a more efficient binary representation based on schema, etc.)