XML schema

schemaschemasschema languagesXML schema languages.xmldata-schemaschema languageschema systemsstructure specification languageXML
An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself.wikipedia
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RELAX NG

Two more expressive XML schema languages in widespread use are XML Schema (with a capital S) and RELAX NG.
In computing, RELAX NG (REgular LAnguage for XML Next Generation) is a schema language for XML - a RELAX NG schema specifies a pattern for the structure and content of an XML document.

XML

Extensible Markup LanguageExtensible Markup Language (XML).xml
An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself. The process of checking to see if a XML document conforms to a schema is called validation, which is separate from XML's core concept of syntactic well-formedness.
Several schema systems exist to aid in the definition of XML-based languages, while programmers have developed many application programming interfaces (APIs) to aid the processing of XML data.

Document type definition

DTDDTDsdocument type declaration
The document type definition (DTD) language, which is native to the XML specification, is a schema language that is of relatively limited capability, but that also has other uses in XML aside from the expression of schemas.
, newer XML namespace-aware schema languages (such as W3C XML Schema and ISO RELAX NG) have largely superseded DTDs.

Document Definition Markup Language

DDML
Document Definition Markup Language (DDML) is an XML schema language proposed in 1999 by various contributors from the xml-dev electronic mailing list.

Namespace-based Validation Dispatching Language

NVDL
Namespace-based Validation Dispatching Language
Namespace-based Validation Dispatching Language (NVDL) is an XML schema language for validating XML documents that integrate with multiple namespaces.

Document Structure Description

Document Structure Description
Document Structure Description, or DSD, is a schema language for XML, that is, a language for describing valid XML documents.

Schema for Object-Oriented XML

SOX
Schema for Object-Oriented XML, or SOX, is an XML schema language developed by Commerce One.

Namespace Routing Language

NRL
Namespace Routing Language
In its simplest form, a Namespace Routing Language (NRL) schema consists of a mapping from namespace URIs to schema URIs.

XDR Schema

XDRXML-Data Reduced
The XML Schema (W3C) effort in the World Wide Web Consortium (W3C) received several other proposals, and while the final result has some similarities to the XML-Data proposal, it is significantly different.

CLiX (markup)

CLiXConstraint Language in XML
CLiX
The goal of CLiX is to enable users and developers to express business properties and complex constraints that cannot be handled in traditional schema languages, and to automate checks that would otherwise have to be hard-coded.

List of types of XML schemas

standards bodies
List of XML schemas
This is a list of notable XML schemas in use on the Internet sorted by purpose.

XML Schema (W3C)

XML SchemaW3C XML SchemaXSD
Two more expressive XML schema languages in widespread use are XML Schema (with a capital S) and RELAX NG.
Like all XML schema languages, XSD can be used to express a set of rules to which an XML document must conform in order to be considered "valid" according to that schema.

Schematron

Schematron
XML Schema Language comparison - Comparison to other XML Schema languages.

Text Encoding Initiative

TEIODDText Encoding Initiative (TEI)
Various parts of the extensive and sophisticated Text Encoding Initiative schemas are also re-used in an extraordinary variety of other schemas.
One Document Does it all ("ODD") is a literate programming language for XML schemas.

Abstract Syntax Notation One

ASN.1ASN.1 notationPER
However, they are both cross-platform standards, and are broadly popular for communications protocols, particularly when combined with an XML schema or JSON schema.

XML Information Set

infosetinformation setXML infoset
XML Information Set
Infoset augmentation or infoset modification refers to the process of modifying the infoset during schema validation, for example by adding default attributes.

Schema

schemas
Schema (disambiguation) (for other uses of the term)
XML schema

Predicate (mathematical logic)

predicatepredicatespredication
These constraints are generally expressed using some combination of grammatical rules governing the order of elements, Boolean predicates that the content must satisfy, data types governing the content of elements and attributes, and more specialized rules such as uniqueness and referential integrity constraints.

Uniqueness quantification

uniqueuniquenessone and only one
These constraints are generally expressed using some combination of grammatical rules governing the order of elements, Boolean predicates that the content must satisfy, data types governing the content of elements and attributes, and more specialized rules such as uniqueness and referential integrity constraints.

Referential integrity

referential integrity constraintforeign-key candidatesinclusion dependencies
These constraints are generally expressed using some combination of grammatical rules governing the order of elements, Boolean predicates that the content must satisfy, data types governing the content of elements and attributes, and more specialized rules such as uniqueness and referential integrity constraints.

XML validation

validationvalidatingvalid XML document
The process of checking to see if a XML document conforms to a schema is called validation, which is separate from XML's core concept of syntactic well-formedness.

Parsing

parserparseparsed
DTD-validating parsers are most common, but some support XML Schema or RELAX NG as well.

Grammar

grammaticalgrammaticallyrules of language
A schema is analogous to a grammar for a language; a schema defines what the vocabulary for the language may be and what a valid "sentence" is.

Document Schema Definition Languages

DSDLISO 19757's endorsed languages
The main ones (see also the ISO 19757's endorsed languages) are described below.