Re: [xml-dev] Is the set of languages expressible using XML asuperset of the set of languages expressible using JSON?
I would say JSON is clearly more expressive from the POV of how many types of data and structures can be represented directly (i.e. without some extra schema layer) with the available delimiters. XML only has data content and attribute values, and all are strings. JSON has numbers and arrays etc, extra to XML.
I would say XML is more expressive from the POV of the purpose-roles of data that can be represented directly with the available delimiters. JSON has no distinctions here. XML has content, attribute values, comments and PIs (and declarations, if you count DTDs). Each role is a pre-classification of the data to allow a separation of concerns. (SGML had even more lifecycle roles, being able to mark sections as temporary or to be ignored.)
XML is also more expressive from the POV of what constraints can be enforced: because of DTDs which are part of XML. (Again, XSD is irrelevent to the question of the expressiveness of XML on its own.)
Rick
