!" DTDs rely on a mechanism based on the use of. !" It is intended to specify cross references" !" Reference to a figure, chapter, section, etc.!

Transcription

1 MULTIMEDIA DOCUMENTS! XML Schema (Part 2)"!" DTDs rely on a mechanism based on the use of attributes (ID et IDREF) to specify links into documents"!" It is intended to specify cross references"!" Reference to a figure, chapter, section, etc.! <!ELEMENT Chapitre (TitreChapitre, Parag+) > <!ATTLIST Chapitre id ID #REQUIRED > <!ELEMENT Reference (#PCDATA) > <!ATTLIST Reference Destination IDREF #REQUIRED > Christine Vanoirbeek" EPFL IC CGC" Bâtiment BC (Station 14)" 1015 LAUSANNE" christine.vanoirbeek@epfl.ch" <Reference Destination= Chap1 > Voir chapitre 1 </Reference>... <Chapitre id=chap1>... </chapitre>! Multimedia documents - XML schema (part 2) ! (2)!!" XML schema implements a more general method, inspired from the «#key#» concept (as used in databases)" Preliminary remark: the XPath language"!" The XPath langage (a W3C recommandation) aims at addressing parts of an XML documents (element, attribute and text)"!" It proposes a non-xml syntax for the specification of expressions allowing to address a (set of) node(s) in a well defined context"!" Examples"!". : the current node!!" e : the element <e>!" * : any element!!" f/e : an element of type <e> child of <f>!" f//e : an element of type <e> descendant from : the value of attribute a! Multimedia documents - XML schema (part 2) ! (3)! Multimedia documents - XML schema (part 2) ! (4)!

2 !" Each question has a number (specified via an attribute)" <xs:element name="question"> <xs:simplecontent> <xs:extension base="xs:string"> <xs:attribute name="questionid" type="xs:string" use="required"/> </xs:extension> </xs:simplecontent>!" Each answer refers to a question number! (via the attribute NoQuestion)" <xs:element name="answer" maxoccurs="unbounded"> <xs:simplecontent> <xs:extension base="xs:string"> <xs:attribute name="noquestion" type="xs:string" use="required"/> </xs:extension> </xs:simplecontent> Multimedia documents - XML schema (part 2) ! (5)! Multimedia documents - XML schema (part 2) ! (6)!!" Definition of a key associated to «#Questionnaire#»" <xs:element name="questionnaire"> <xs:sequence minoccurs="0" maxoccurs="unbounded"> <xs:element name="question"> </xs: element> </xs:sequence> <xs:key name="questionkey"> <xs:selector xpath="./question"/> <xs:field xpath="@questionid"/> </xs:key> Utilisation de xpath Chemin d accès Spécification d un élément ou attribut Multimedia documents - XML schema (part 2) ! (7)!!" Definition of a reference to a key (keyref) associated to «#Sondage#»" <xs:element name= Sondage > <xs:keyref name="questionref" refer="questionkey"> <xs:selector xpath=".//answer"/> <xs:field xpath="@noquestion"/> </xs:keyref> Multimedia documents - XML schema (part 2) ! (8)!

3 Definition of links (summary)"!" Unicity of the key is related to the level where it is defined "!" In our example: questionnaire!!" An XML parser checks"!" The unicity of the key!!" The fact that existing keys are indeed refereed!!" The specification of keys and key references are based on the use XPath"!" xpath is a W3C standard language allowing to address parts of an XML documents (element, attributes or text)!!" xpath is based on a non-xml syntax! Unicity constraint"!" Definition of a unicity constraint related to a catalog" <xs:unique name="bookid"> <xs:selector xpath=".//book"/> <xs:field xpath="isbn"/> </xs:unique>!" «#keyref#» may refer «#key#» or «#unique#»" Multimedia documents - XML schema (part 2) ! (9)! Multimedia documents - XML schema (part 2) ! (10)! Summary"!" It has been explained how to"!" Use/define simple content models (elements and attributes)! #" Use of predefined types #" Derivation (restriction, list, union)!" Define complex content models! #" Constructors (sequence, choice, all) #" Occurrences indicators (MinOccurs, MaxOccurs) Simple vs complex content models"!" Simple content models correspond to leaves in a hierarchy of elements"!" Text content (with no attributes)!!" Derivation may be used to constraint the definition (restriction, list ou union)!!" Complex content models correspond to structured elements"!" Define mixed content, empty ou any types of elements!!" restriction and extension may be used for refining their definition!!" Define links! #" ID, IDREF (document oriented) #" UNIQUE, KEY et KEYREF (databases oriented) Multimedia documents - XML schema (part 2) ! (11)! Multimedia documents - XML schema (part 2) ! (12)!

4 Facets: a summary"!" 3 categories of facets may be used, acting"!" On the value space!!" On the lexical space (pattern)!!" On the way spaces are dealt with during the parsing!!" The following table summarizes the available facets and the categories of types they apply" The «#pattern#» facet"!" Use of regular expression" <xsd:simpletype name="type "> <xsd:restriction base="xsd:string"> <xsd:pattern value="(.)+@(.)+"/> Multimedia documents - XML schema (part 2) ! (13)! Multimedia documents - XML schema (part 2) ! (14)! Restriction of complex types " Extension of complex types " <xsd:complextype name="contactstype"> <xsd:element name="person" maxoccurs="unbounded" type= PersonType"/> <xsd:attributegroup ref= AdditionalInfo"/> </xsd:complextype> <xsd:complextype name= CoreContacts"> <xsd:complexcontent> <xsd:restriction base="contactstype"> <xsd:element name="person"maxoccurs="50" type="persontype"/> <xsd:attributegroup ref= AdditionalInfo"/> </xsd:complexcontent> </xsd:complextype> An example <xsd:complextype name= Reference"> <xsd:element name="title" type="xsd:string"> <xsd:element name="author" type="xsd:string maxoccurs="unbounded"/> <xsd:element name="date" type="xsd:gyear"/> </xsd:complextype > <xsd:complextype name= Reference"> <xsd:complexcontent> <xsd:extension base="publication"> <xsd:element name="isbn" type="xsd:string"/> <xsd:element name="publisher" type="xsd:string"/> </xsd:extension> </xsd:complexcontent> </xsd:complextype > ISBN Title Author(s) Date Publisher Multimedia documents - XML schema (part 2) ! (15)! Multimedia documents - XML schema (part 2) ! (16)!

5 Control of derivations"!" Example: fixing a value for a facet" Prohibiting derivations"!" It is possible to limit the type of allowed derivations" <xsd:simpletype name= "CourseRegistrations"> <xsd:restriction base="xsd:nonnegativeinteger"> <xsd:mininclusive value="10" fixed="true"/> <xsd:maxinclusive value="60"/> <xsd:complextype name= PatientRecord" final="#all" PatientRecord cannot be extended nor restricted <xsd:simpletype name= MD-Registrations"> <xsd:restriction base="classsize"> <xsd:mininclusive value="15"/> <xsd:maxinclusive value= 100"/> Error! It is not possible to modify the value of a fixed facet! <xsd:complextype name= PatientRecord" final="restriction" PatientRecord cannot be restricted <xsd:complextype name= PatientRecord" final="extension" PatientRecord cannot be extended Multimedia documents - XML schema (part 2) ! (17)! Multimedia documents - XML schema (part 2) ! (18)! Additional features"!" Annotations <xs:annotation> may be used for adding comments"!" «$human being$» oriented <xs: documentation>!!" Application oriented <xs:appinfo>!!" A modular approach may be adopted in the framework of complex applications; it relies on the use of import and inclusion mechanisms" Conclusion"!" Using XML schema is at the frontier between specification of «#documents#» and «#data#» information it also takes into account hypertext models (to be discussed later)"!" Modeling concepts may be criticized but the potential offered by the use of standardized tools (validation, transformation, etc) open interesting perspectives for the design and implementation of distributed information systems" Multimedia documents - XML schema (part 2) ! (19)! Multimedia documents - XML schema (part 2) ! (20)!