XML schema part1 EN

MULTIMEDIA DOCUMENTS XML Schema (Part 1) : MULTIMEDIA DOCUMENTS XML Schema (Part 1) Christine Vanoirbeek EPFL – IC – CGC Bâtiment BC (Station 14) 1015 LAUSANNE christine.vanoirbeek@epfl.ch


About DTDs : About DTDs DTDs aim at defining document classes; they specify The type of authorized elements in a document instance, as well as potential attributes associated to those elements The organization rules of elements 2 constructors (sequence and choice) 3 occurrence indicators (optional element, optional element potentially repeated, mandatory element potentially repeated)


DTDs : DTDs An example


DTDs : DTDs Some comments Global structure of the recipe 2 structures are proposed for « item »; they take into consideration 2 frequent types of recipes [1] [2] Attributes (role, type, optional or mandatory, assignment of the value) Empty elements Links


Why XML schema? : Why XML schema? From publishing to document processing! Typed elements and attributes number date boolean … Hierarchy of types (similarly to programming languages)


Why XML schema? : Why XML schema? The DTDs only offer very basic possibilities for reusing definition of elements Such as,by example: address, references, etc. An object oriented approach supporting the specialization and extension of elements definition


Why XML schema? : Why XML schema? Using DTDs, 3 occurrence indicators are available ? * + Using XML schema, it is possible to mention explicitely the minimum and maximum number of occurrences Example: specification of a limited number of keywords in a paper


Why XML schema? : Why XML schema? DTDs make use of a specific syntax, it implies two major drawbacks Existing XML-based tools (validation, transformation, etc.) may not be used Namespaces are not supported The XML schema language is based on the XML syntax Objective: to propose a unified paradigm


Namespaces : Namespaces A simple XML schema


Namespaces : Namespaces How to deal with several languages inside an XML document? element complexType schema sequence http://www.w3.org/2001/XMLSchema string integer boolean Recipe Title Comment http://www.recipes.org The XML schema vocabulary allows a document class designer to specify its own vocabulary Item


Main components of an XML Schema : Main components of an XML Schema Prologue Schema root Definition of elements Complex elements (subdivided into sub-elements) Simple elements (potentially typed) Mixed elements (text + tagged elements) Empty elements Element of « any » type


Definition of structured elements : Definition of structured elements The name of an element is specified via the “name” attribute associated to the XML schema “element” The composition rule is specified via the child element “complexType”; it may include 3 constructors sequence choice all The number of occurrences are specified by the attributes “minOccurs” et “maxOccurs”


Sequence : Sequence


Choice : Choice


All : All


Definition of the content models : Definition of the content models Local definition


Definition of the content models : Definition of the content models Global definition …


Definition of the content models : Definition of the content models Use of an explicit type declaration …


Definition of the content models (summary) : Definition of the content models (summary) Local definitions Global definitions Benefit: definitions are factorized Use of an explicit type declaration Object-oriented mechanisms may be used Important remark: the use of one or another way to define the elements is not reflected in the document instance.


Definition of simple types : Definition of simple types Preliminary remark Lexical space Exemple: float (2.57 , +2.57 , .257E1) Value space


Hierarchy of predefined types : Hierarchy of predefined types Text Numbers Time related types


Type derivation : Type derivation Restriction Limits the value range of the base type; the semantic is not affected List Specify the content type of a simple element as a list of values of one type Union The value may be specified using alternate type candidates


Restriction : Restriction Use of facets


List : List 1 -25000 1000


Union : Union


Definition of attributes : Definition of attributes Example 1


Definition of attributes : Definition of attributes Example 2 ...


Definition of attributes : Definition of attributes Occurrences and default value ...


Group of attributes : Group of attributes xs:attributeGroup name="pictureFeatures">


Example of recipe (1) : Example of recipe (1)


Example of recipe (2) : Example of recipe (2)