DTDs were the first standard mechanism for XML validation, and for all practical purposes still are.
They define the roles and structure of XML elements.
“Snowplow provides all of our event data in a data model which we own and can shape to our organisational needs.
The W3C XML specification states that a program should not continue to process an XML document if it finds a validation error.
The reason is that XML software should be easy to write and all XML documents should be compatible.
Check out their website to get details on supported standards, reference documentation, etc.
The XPath assertion applies a specified XPath expression to the received message and validates the resulting nodes against an expected value.
A person can verify if the documents adhere to a set conventions about how vehicle elements should be used.
For example, a person can tell that the this XML instance is invalid: We know that a motorcycle typically has two wheels and doesn't have a sunroof.
In this article I show how to do the latter and assume the reader is at least familiar with XML 1.0, DTDs, XSLT, and XPath.
XML schemas are necessary for communicating the structure of an XML document type to a machine. A person can easily interpret and understand both XML instances from the words used to describe their components.
With HTML, for example, it is possible to create documents with lots of errors (for instance, when you forget an end tag).