Schema

1
Schema

• Formal language describing the structure of the
  XML document.
• Problems with DTDs
• Because the syntax is different from the XML
  syntax, it can be difficult to read and write
  DTDs.
• All data contents are character data. DTD does
  not provide support for data types.
• All elements are global.
• Difficult to write and understand.

2
A better schema language?

• XML Schemas became a W3C recommendation in May
  2001.
• There were working schema implementations before
  the proposed recommendation
• XML Data XML Data Reduced (xdr)
• Document Content Description (DCD)
• Schema for OO XML (SOX)

3
XML Data schema

• Like DTD, XML-Data schema can be used to specify
  the schema, or structure, of a particular class
  of documents.
• Benefits of using XML-Data language to describe
  the document structure.
• XML-Data uses XML syntax.
• XML-Data provides support for data types. You can
  specify the type of data contained in an element.
  
• XML-data supports global and local element
  specifications.

4
XML-Data schema example

• ltSchema xmlns"urnschemas-microsoft-comxml-data"
  xmlnsdt"urnschemas-microsoft-comdatatypes
  "gt
• ltElementType name"author" model"closed"
• content"textOnly" dttype"string"/gt
• ltElementType name"book" model"closed"
• content"eltOnly" order"seq"gt
• ltAttributeType name"category" dttypestring"
  required"yes"/gt
• ltattribute type"category"/gt
• ltelement type"author" minOccurs"1"
  maxOccurs"1"/gt
• ltelement type"title" minOccurs"1"
  maxOccurs"1"/gt
• ltelement type"price" minOccurs"1"
  maxOccurs"1"/gt
• lt/ElementTypegt
• ...
• lt/Schemagt

5
Document schema
Book
Category
author
title
price
ltbook category"Programming"gt ltauthorgtDon
Boxlt/authorgt lttitlegtEssential
XMLlt/titlegt ltpricegt25.95lt/pricegt lt/bookgt
6
XML-Data Reduced (XDR)

• XML-Data Reduced (XDR) language is a subset of
  ideas described in the XML-Data specification.
  The schema implementation in Microsoft XML
  Parser (MSXML) is based on the XML-Data Reduced
  language specification.
• The XML Schema implementation in MSXML is based
  primarily on the XML Data Note posted by the W3C
  in January 1998, and the Document Content
  Description for XML.
• The XML Schema implementation provided in MSXML
  focuses on syntactic schemas, without support for
  inheritance or other object-oriented design
  features.

7
From DTDs to XDRs

• lt!ELEMENT Foo (PCDATA tag1)gt
• ltElementType nameFoo contentmixed
• ordermanygt
• ltelement typetag1/gt
• lt/ElementTypegt

8
From DTDs to XDRs

• lt!ELEMENT Foo (PCDATA tag1)gt
• lt!ELEMENT tag1 gt
• ltElementType nameFoo contentmixed
• ordermanygt
• ltelement typetag1/gt
• lt/ElementTypegt
• ltElementType nametag1 gt
• lt/ElementTypegt

9
From DTDs to XDRs

• lt!ELEMENT Person (First, M, Last)gt
• ltElementType namePerson
• contenteltOnly
• orderseqgt
• ltelement typeFirst/gt
• ltelement typeM/gt
• ltelement typeLast/gt
• lt/ElementTypegt

10
From DTDs to XDRs

• lt!ELEMENT Foo ((X Y) (A, B?, C))gt
• ltElementType nameFoo
• contenteltOnly
• orderonegt
• ltgroup orderonegt
• ltelement typeX/gt
• ltelement typeY/gt
• lt/groupgt
• ltgroup orderseqgt
• ltelement typeA/gt
• ltelement typeB minOccurs0/gt
• ltelement typeC/gt
• lt/groupgt
• lt/ElementTypegt

11
From DTDs to XDRs

• lt!ELEMENT Person (First, M, Last)gt
• lt!ATTLIST Person age CDATA REQUIREDgt
• ltAttributeType nameage
• dttypeint" requiredyes/gt
• ltElementType namePerson
• contenteltOnly
• orderseqgt
• ltattribute typeagegt
• ltelement typeFirst/gt
• ltelement typeM/gt
• ltelement typeLast/gt
• lt/ElementTypegt

12
From DTDs to XDRs

• lt!ELEMENT Person (First, M, Last)gt
• lt!ATTLIST Person age CDATA REQUIREDgt
• ltElementType namePerson
• contenteltOnly
• orderseqgt
• ltAttributeType nameage
• dttypeint" requiredyes/gt
• ltattribute typeagegt
• ltelement typeFirst/gt
• ltelement typeM/gt
• ltelement typeLast/gt
• lt/ElementTypegt