What Does XML Schema Mean?
An XML schema is the structural layout of an XML document, expressed in terms of constraints and contents of the document. Constraints are expressed using a combination of the following:
- Grammatical rules governing the order of elements
- Data types governing an element and content attribute
- Boolean predicates that the content has to satisfy
- Specialized rules including uniqueness and referential integrity constraints
Techopedia Explains XML Schema
XML schemas are expressed using Document Type Definition (DTD) language, which is native to the XML specification but with a fairly limited capability. An XML document can be associated with a schema language, either by markup in the XML document or through some external means.
The process of checking whether an XML document adheres to a schema is called validation. XML documents are valid if they satisfy schema requirements with which they are associated, including constraints such as:
- Structure as specified by a regular expression syntax
- Requirements for interpretation of character data
- Elements and attributes to be included along with their allowed structure