3rd party integration: How to get XML Schema (.xsd) for a custom entity, to use with a mapper

Question

Is there an easy way to get the xml schema/DTD for a custom entity, specifically an .XSD file for that entity (which will then be used to create a map to be able to transform the fields of the entity to a 3rd-party message format)?
So have a custom entity with lots and lots of fields. Each of the fields will map to a differently named field to match the schema of the 3rd party entity. A very common situation. Looking to use a tool like the Biztalk mapper or Altova's MapForce to generate
an .xslt file to transform the downloaded entity (service.Retrieve with all columns) to the new format. (Will implement a typical VETR pattern.)
Apparently with CRM 4 there was a call that provided this, but from 2011 has not been available. Working with a crm 2015 system.

Answer 1

That will give a descriptor of the table and allow creation of an .XSD file, but it's really complex in terms of types, and the there's type conversion. It might be an easy way to get a schema, with the downside being it's hard to use that schema. 
It seems easier to do a fetch of the record with all fields filled in using service.Retrieve, and then converting this to xml, using Microsoft's guidance leads to using https://msdn.microsoft.com/en-us/library/hh675409.aspx which will serialize the entity
into XML with all the fields converted to type string, and with complex fields likewise converted to strings with additional information about the type. 
Using this it's possible using an number of tools to create an easier to use .XSD file.
However, it would seem most integrations of this type are using 3rd party CRM connectors. Perhaps this is why Microsoft hasn't provided anything direct (and took away what they did have in crm4.0 due to it generating a hard to use .XSD or due to letting
their partners continue income streams from selling connectors").
But without using 3rd party connectors, or following the still tedious method of generating .XSD (a useable .xsd), have not yet come up with an easy, automatic way to get an .XSD or to easily integrate with 3rd party message format.