XMLSchema, RelaxNG

T. Pitner, L. Bártek, A. Rambousek. L Grolig FI MU Brno 2020

XMLSchema - Motivation
Stronger tool for XML data model specification than DTD, it allows: ● Separate type (e.g. element type) from its occurrence (i.e. element with particular name) ● More primitive data types. ● Allows to use namespaces. ● Allows to specify content model (elements) more accurate way. ● Allows new type inheritance. ● Allows modular schema design and schema reuse. ● XML Schema has an XML syntax.

XMLSchema
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> <!-- here the schema definition goes --> </xs:schema>

XMLSchema - Element type
<xs:element name="element_name"> <!-- here comes the type definition -placed either right here (so called "local") or as a referenced one (so called "global") --> </xs:element>

XMLSchema - Element type (short)
<xs:element name="element_name" type="element_type"/>

XMLSchema - Simple type
<xs:simpleType name="TypeName"> <xs:restriction base="BaseTypeName"> ... </xs:restriction> </xs:simpleType> e.g. <xs:simpleType name="MyString32"> <xs:restriction base="xs:string"> <xs:maxLength value="32"/> </xs:restriction> </xs:simpleType>

XMLSchema - Union
<xs:simpleType name="isbnType"> Union of two simple types - string <xs:union> restricted by regular expression <xs:simpleType> <xs:restriction base="xs:string"> and enumeration <xs:pattern value="[0-9]{10}"/> </xs:restriction> </xs:simpleType> <xs:simpleType> <xs:restriction base="xs:NMTOKEN"> <xs:enumeration value="TBD"/> <xs:enumeration value="NA"/> </xs:restriction> </xs:simpleType> </xs:union> </xs:simpleType>

XMLSchema - inheritance
<xs:simpleType name="isbnTypes"> <xs:list itemType="isbnType"/> isbnTypes - basic type, </xs:simpleType> isbnTypes10 - derived type <xs:simpleType name="isbnTypes10"> restriction <xs:restriction base="isbnTypes"> <xs:minLength value="1"/> <xs:maxLength value="10"/> </xs:restriction> </xs:simpleType>

with

XMLSchema - Complex type
<xs:complexType name="TypeName"> complex type <xs:sequence> <xs:element ...> ... typically defines <xs:attribute ...> elements </xs:element> </xs:sequence> </xs:complexType>

applies to elements sequence of child

XMLSchema - Group of elements
<xs:group name="GroupName"> <xs:sequence> <xs:element ... /> ... </xs:sequence> </xs:group>

group type - reusable sequence of child elements

<xs:choice> and <xs:all>

choice or all type - may be used instead of sequence

XMLSchema - Attribute group
<xs:attributeGroup name="AttributesGroupName"> <xs:attribute ... use="required"/> ... </xs:attributeGroup>

attribute group - reusable set of attributes

XMLSchema - Namespaces
<xs:schema targetNamespace="http://example.org/ns/books/" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:bk="http://example.org/ns/books/" elementFormDefault="qualified" attributeFormDefault="unqualified"> .../... </xs:schema>

XMLSchema - reference
<book isbn="0836217462" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="file:library.xsd"> or <book isbn="0836217462" xmlns="http://example.org/ns/books/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="file:library.xsd">

RelaxNG - Alternative to Schema
<addressBook> <card> <name>John Smith</name> <email>js@example.com</email> </card> <card> <name>Fred Bloggs</name> <email>fb@example.net</email> </card> </addressBook>

RelaxNG vs DTD
<!DOCTYPE <!ELEMENT <!ELEMENT <!ELEMENT <!ELEMENT ]> addressBook [ addressBook (card*)> card (name, email)> name (#PCDATA)> email (#PCDATA)>

Do you like this or that? element addressBook { element card { element name { text }, element email { text } }* }

RelaxNG - Cardinality indication
element addressBook { element card { element name { text }, element email { text } }* }

could be + or ? or * or nothing

RelaxNG - Options
element addressBook { element card { # here is the option (element name { text } | (element givenName { text }, element familyName { text })), element email { text }, element note { text }? }* }

RelaxNG - Options with attributes
element addressBook { element card { (element name { text } | attribute name { text }), (element email { text } | attribute email { text }) }* }

RelaxNG - Grammar
grammar { start = AddressBook AddressBook = element Card = element card { Name = element name { Email = element email } addressBook { Card* } Name, Email } text } { text }

RelaxNG - Enumerations
element card attribute attribute attribute } { name { text }, email { text }, preferredFormat { "html" | "text" }

element card { element name { text }, element email { text }, element preferredFormat { "html" | "text" } }