terminology: XML schema versus XML application

Question

From what I read, DocBook and DITA are applications of XML, and HTML is an application of SGML:

• http://www.peachpit.com/articles/article.aspx?p=31286&seqNum=17
• http://xml.silmaril.ie/differences.html
• http://cs.au.dk/~amoeller/XML/xml/applications.html
• https://en.wikipedia.org/wiki/Standard_Generalized_Markup_Language#Applications

However, I cannot understand whether there is any difference between "applications" and "schemas"? Are these the same thing?

Answer 1

An application of a technology or standard (e.g. XML) to a given area such as publishing (e.g. DocBook or DITA), lending (e.g. MISMO), business documents (e.g. UBL, XBRL), and so on, merely means that the tech/standard has been applied to that area. It is in this sense that some refer to DocBook and DITA etc as XML applications.

A schema is a particular design artifact that constrains the vocabulary and grammar of a data format. An XML Schema (XSD) is a W3C Recommendation for schemas for XML documents. Each of the above mentioned XML applications has developed XML schemas for the particular sets of XML document in their respective sectors.

There is another use of application that refers specifically to an executable program. In this sense, an XML application is simply a specific program that processes (often an sector-restricted set of) XML documents.