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Part 2: Modelling XML Data
Managing XML and Semistructured Data
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In this section…In this section…
More XML syntax [XML glossary – by Sun] [XML Tutorials]
XML DTD and XML Schema XML Query data model Comparison of XML with semistructured data
Papers:• XML, Java, and the future of the Web by Jon Bosak, Sun Microsystems. • W3C XML Query Data Model Mary Fernandez, Jonathan Robie. • Extracting Schema from Semi structured Data Nestorov, Abiteboul, Motwani.
SIGMOD 98• Data on the Web Abiteboul, Buneman, Suciu : Section 3.3
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More XML Syntax: AttributesMore XML Syntax: Attributes
<book price = “55” currency = “USD”>
<title> Foundations of Databases </title>
<author> Abiteboul </author>
…
<year> 1995 </year>
</book>
<book price = “55” currency = “USD”>
<title> Foundations of Databases </title>
<author> Abiteboul </author>
…
<year> 1995 </year>
</book>attributes are alternative ways to represent data (Single valued, unordered)
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More XML: Oids and More XML: Oids and ReferencesReferences
<person id=“o555”> <name> Jane </name> </person>
<person id=“o456”> <name> Mary </name>
<children idrefs=“o123 o555”/>
</person>
<person id=“o123” mother=“o456”><name>John</name>
</person>
<person id=“o555”> <name> Jane </name> </person>
<person id=“o456”> <name> Mary </name>
<children idrefs=“o123 o555”/>
</person>
<person id=“o123” mother=“o456”><name>John</name>
</person>oids and references in XML are just syntax (ID, IDREF) The value of IDREF attribute must match the value of some ID attribute in the document. The value of IDREFS attribute can contain several references to elements with ID
attribute separated with whitespaces.
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XML Semantics: a Tree !XML Semantics: a Tree !
<data>
<person id=“o555” >
<name> Mary </name>
<address>
<street> Maple </street>
<no> 345 </no>
<city> Seattle </city>
</address>
</person>
<person>
<name> John </name>
<address> Thailand </address>
<phone> 23456 </phone>
</person>
</data>
<data>
<person id=“o555” >
<name> Mary </name>
<address>
<street> Maple </street>
<no> 345 </no>
<city> Seattle </city>
</address>
</person>
<person>
<name> John </name>
<address> Thailand </address>
<phone> 23456 </phone>
</person>
</data>
data
Mary
person
person
name address
name address
street no city
Maple 345 Seattle
JohnThai
phone
23456
id
o555
Elementnode
Textnode
Attributenode
Order matters !!!
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More XML: CDATA SectionMore XML: CDATA Section
Syntax: <![CDATA[ .....any text here...]]>
Example:
<![CDATA[ <slide>..A sample slide..</slide> ]]> which displays as:
<slide>..A sample slide.. </slide><slide>..A sample slide.. </slide>
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More XML: Entity ReferencesMore XML: Entity References Entity references to replace illegal XML characters
(Escape characters) Syntax: &entityname; (a form of macros) Example: (what happens if we simply use <?)
<element> this is less than < </element> Some entities: < <
> >
& &
' ‘
" “
& Unicode char
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More XML: Processing InstructionsMore XML: Processing Instructions Syntax: <?target argument?> Example 1:
Example 2:
<product> <name> Alarm Clock </name> <?ringBell 20?> <price> 19.99 </price></product>
<product> <name> Alarm Clock </name> <?ringBell 20?> <price> 19.99 </price></product>
<?wilfred.lecture.Program QUERY="MSc,PhD,all"?> <slide type="all"> <title>COMP630H</title> </slide>
<?wilfred.lecture.Program QUERY="MSc,PhD,all"?> <slide type="all"> <title>COMP630H</title> </slide>
Target application Data for processing
Note: <?xml version = “1.0”?> is not PI
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More XML: CommentsMore XML: Comments
Syntax <!-- .... Comment text... -->
Yes, they are part of the data model !!!
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XML NamespacesXML Namespaces
http://www.w3.org/TR/REC-xml-names (1/99)
name ::= [prefix:]localpart
<book xmlns:isbn=“www.isbn-org.org/def”>
<title> … </title>
<number> 15 </number>
<isbn:number> …. </isbn:number>
</book>
<book xmlns:isbn=“www.isbn-org.org/def”>
<title> … </title>
<number> 15 </number>
<isbn:number> …. </isbn:number>
</book>
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<tag xmlns:mystyle = “http://…”>
…
<mystyle:title> … </mystyle:title>
<mystyle:number> …
</tag>
<tag xmlns:mystyle = “http://…”>
…
<mystyle:title> … </mystyle:title>
<mystyle:number> …
</tag>
XML NamespacesXML Namespaces syntactic: <number> , <isbn:number> semantic: provide URL for schema namespace declaration apply within the content of the specified element multiple namespace prefixes can be declared
Belong to this namespace
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XML Data ModelsXML Data Models
Several competing models: Document Object Model (DOM):
• http://www.w3.org/TR/2001/WD-DOM-Level-3-CMLS-20010209/ (2/2001)
• class hierarchy (node, element, attribute,…)• objects have behavior• defines API to inspect/modify the document
XPath data model XML Query data model Infoset (a set of information items of an XML document)
• PSV (post schema validation)• http://www.w3.org/TR/xml-infoset/
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XML Data v.s. E/R, ODL, XML Data v.s. E/R, ODL, RelationalRelational
Q: is XML better or worse ? A: serves different purposes
• E/R, ODL, Relational models: For centralized processing, when we control the data
• XML: Data sharing between different systems we do not have control over the entire data on the Web Data centric Vs Document centric documents
Do NOT use XML to model your data ! Use E/R, ODL, or relational instead. Use XML to exchange data instead.
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XLinkXLink Generalizes HTML’s href Many types: simple, extended, locator, ...
• Discuss only simple links, which is a link that associates exactly two resources, one local and one remote, with an arc going from the former to the latter. Thus, a simple link is always an outbound link.
<person xmlns:xlink=“http:///.w3.org/1999/xlink” xlink:type=“simple” xlink:href=“http://a.b.c/myhomepage.html” xlink:title=“The Homepage” xlink:show=“replace” xlink:actuate=“onRequest”> .....
</person>
<person xmlns:xlink=“http:///.w3.org/1999/xlink” xlink:type=“simple” xlink:href=“http://a.b.c/myhomepage.html” xlink:title=“The Homepage” xlink:show=“replace” xlink:actuate=“onRequest”> .....
</person>
required attributes
optional attributes
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XLinkXLink show attribute (specify desired presentation) can be
• “new” (new window)• ”replace” (same window)• ”embed”• ”other”
actuate attribute (specify desired timing of traversal) can be• “onLoad” (immediate loading)• ”onRequest” (post-loading, event triggered)• ”other”• ”none”
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XLinkXLink
href attribute:• a URI or• an XPointer (next)
More about XLink can be found in: [http://www.w3.org/TR/xlink/]
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XPointerXPointer
An extension of XPath (next week) Usage:
• href=“www.a.b.c/document.xml#xpointerExpr”
An XPointer expression points to:• A point• A range
Reference [http://www.w3.org/TR/2001/CR-xptr-20010911/]
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XPointerXPointer
Pointing to a point (=XML element or character)• Full form: e.g. #xpointer(id(“3652”))
• Bar name: e.g. #3652
• Child sequence: e.g. #xpointer( /1/3/2/5), #xpointer( /bib/book[3])
Pointing to a range: e.g. #xpointer(id(3652 to 44)) Most interesting examples use XPath
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XML v.s. Semistructured DataXML v.s. Semistructured Data SSD integrates of heterogeneous sources
with non-rigid structure, eg biological data, Web data{lecture: {title: “XML”,
date: “1-Jan-2005”, instructor: { name: “Wilfred”,
department: “CS”} }
} both described best by a graph both are schema-less, self-describing
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Similarities and DifferencesSimilarities and Differences
<person id=“o123”>
<name> Alan </name>
<age> 42 </age>
<email> ab@com </email>
</person>
<person id=“o123”>
<name> Alan </name>
<age> 42 </age>
<email> ab@com </email>
</person>
{ person: &o123
{ name: “Alan”,
age: 42,
email: “ab@com” }
}
{ person: &o123
{ name: “Alan”,
age: 42,
email: “ab@com” }
}
person
name age email
Alan 42 ab@com
person
name age email
Alan 42 ab@com
father father
<person father=“o123”> …</person>
{ person: { father: &o123 …}}
similar on trees, different on graphs
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More DifferencesMore Differences XML is ordered, SSD is not XML can mix text and elements:
<talk> Teaching XML is horrible
<speaker> Wilfred Ng </speaker>
</talk>
XML has lots of other stuff: entities, processing instructions, comments
! these differences make XML data management harder
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Document Type DefinitionsDocument Type DefinitionsDTDDTD
part of the original XML specification an XML document may have a DTD XML document:
well-formed = if tags are correctly closed
Valid = if it has a DTD and conforms to it
validation is useful in data exchange
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Very Simple DTDVery Simple DTD
<!DOCTYPE company [ <!ELEMENT company ((person|product)*)> <!ELEMENT person (ssn, name, office, phone?)> <!ELEMENT ssn (#PCDATA)> <!ELEMENT name (#PCDATA)> <!ELEMENT office (#PCDATA)> <!ELEMENT phone (#PCDATA)> <!ELEMENT product (pid, name, description?)> <!ELEMENT pid (#PCDATA)> <!ELEMENT description (#PCDATA)>]>
<!DOCTYPE company [ <!ELEMENT company ((person|product)*)> <!ELEMENT person (ssn, name, office, phone?)> <!ELEMENT ssn (#PCDATA)> <!ELEMENT name (#PCDATA)> <!ELEMENT office (#PCDATA)> <!ELEMENT phone (#PCDATA)> <!ELEMENT product (pid, name, description?)> <!ELEMENT pid (#PCDATA)> <!ELEMENT description (#PCDATA)>]>
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Very Simple DTDVery Simple DTD
<company> <person> <ssn> 123456789 </ssn> <name> John </name> <office> B432 </office> <phone> 1234 </phone> </person> <person> <ssn> 987654321 </ssn> <name> Jim </name> <office> B123 </office> </person> <product> ... </product> ...</company>
<company> <person> <ssn> 123456789 </ssn> <name> John </name> <office> B432 </office> <phone> 1234 </phone> </person> <person> <ssn> 987654321 </ssn> <name> Jim </name> <office> B123 </office> </person> <product> ... </product> ...</company>
Example of valid XML document:
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DTD: The Content ModelDTD: The Content Model
Content model:• Complex = a regular expression over other elements
• Text-only = #PCDATA
• Empty = EMPTY
• Any = ANY
• Mixed content = (#PCDATA | A | B | C)*
<!ELEMENT tag (CONTENT)><!ELEMENT tag (CONTENT)>
contentmodel
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DTD: Regular ExpressionsDTD: Regular Expressions
<!ELEMENT name (firstName, lastName))
<!ELEMENT name (firstName, lastName))
<name> <firstName> . . . . . </firstName> <lastName> . . . . . </lastName></name>
<name> <firstName> . . . . . </firstName> <lastName> . . . . . </lastName></name>
<!ELEMENT name (firstName?, lastName))<!ELEMENT name (firstName?, lastName))
DTD XML
<!ELEMENT person (name, phone*))<!ELEMENT person (name, phone*))
sequence
optional
<!ELEMENT person (name, (phone|email)))<!ELEMENT person (name, (phone|email)))
Kleene star
alternation
<person> <name> . . . . . </name> <phone> . . . . . </phone> <phone> . . . . . </phone> <phone> . . . . . </phone> . . . . . .</person>
<person> <name> . . . . . </name> <phone> . . . . . </phone> <phone> . . . . . </phone> <phone> . . . . . </phone> . . . . . .</person>
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Attributes in DTDsAttributes in DTDs
<!ELEMENT person (ssn, name, office, phone?)><!ATTLIS person age CDATA #REQUIRED>
<!ELEMENT person (ssn, name, office, phone?)><!ATTLIS person age CDATA #REQUIRED>
<person age=“25”> <name> ....</name> ...</person>
<person age=“25”> <name> ....</name> ...</person>
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Attributes in DTDsAttributes in DTDs
<!ELEMENT person (ssn, name, office, phone?)><!ATTLIS person age CDATA #REQUIRED
id ID #REQUIRED
manager IDREF #REQUIRED
manages IDREFS #REQUIRED>
<!ELEMENT person (ssn, name, office, phone?)><!ATTLIS person age CDATA #REQUIRED
id ID #REQUIRED
manager IDREF #REQUIRED
manages IDREFS #REQUIRED>
<person age=“25” id=“p29432” manager=“p48293” manages=“p34982 p423234”> <name> ....</name> ...</person>
<person age=“25” id=“p29432” manager=“p48293” manages=“p34982 p423234”> <name> ....</name> ...</person>
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Attributes in DTDsAttributes in DTDsTypes: CDATA = string ID = key IDREF = foreign key IDREFS = foreign keys separated by space (Monday | Wednesday | Friday) = enumeration NMTOKEN = must be a valid XML name NMTOKENS = multiple valid XML names ENTITY = you don’t want to know thisKind: #REQUIRED #IMPLIED = optional value = default value value #FIXED = the only value allowed
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Using DTDsUsing DTDs
Must include in the XML document Either include the entire DTD:
• <!DOCTYPE rootElement [ ....... ]> Or include a reference to it:
• <!DOCTYPE rootElement SYSTEM “http://www.mydtd.org”>
Or mix the two... (e.g. to override the external definition)
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DTDs as GrammarsDTDs as Grammars<!DOCTYPE paper [ <!ELEMENT paper (section*)> <!ELEMENT section ((title,section*) | text)> <!ELEMENT title (#PCDATA)> <!ELEMENT text (#PCDATA)>]>
<!DOCTYPE paper [ <!ELEMENT paper (section*)> <!ELEMENT section ((title,section*) | text)> <!ELEMENT title (#PCDATA)> <!ELEMENT text (#PCDATA)>]>
<paper> <section> <text> </text> </section> <section> <title> </title> <section> … </section> <section> … </section> </section></paper> A DTD = a grammar
A valid XML document = a parse tree for that grammar
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DTDs as SchemasDTDs as Schemas
Not so well suited: impose unwanted constraints on order
<!ELEMENT person (name,phone)>
references cannot be constrained can be too vague:
<!ELEMENT person ((name|phone|email)*)>
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XML SchemasXML Schemas generalizes DTDs uses XML syntax two documents: structure and datatypes
• www.w3.org/TR/2001/REC-xmlschema-1-20010502• www.w3.org/TR/2001/REC-xmlschema-2-20010502
XML Schemas• Elements v. Types• Regular expressions• Expressive power
XML-Schema is very complex• often criticized• some alternative proposals
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XML SchemasXML Schemas<xs:element name=“paper” type=“papertype”/>
<xs:complexType name=“papertype”>
<xs:sequence>
<xs:element name=“title” type=“xs:string”/>
<xs:element name=“author” minOccurs=“0”/>
<xs:element name=“year”/>
<xs: choice> < xs:element name=“journal”/>
<xs:element name=“conference”/>
</xs:choice>
</xs:sequence>
</xs:element>
<xs:element name=“paper” type=“papertype”/>
<xs:complexType name=“papertype”>
<xs:sequence>
<xs:element name=“title” type=“xs:string”/>
<xs:element name=“author” minOccurs=“0”/>
<xs:element name=“year”/>
<xs: choice> < xs:element name=“journal”/>
<xs:element name=“conference”/>
</xs:choice>
</xs:sequence>
</xs:element>DTD: <!ELEMENT paper (title,author*,year, (journal|conference))>
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Elements v.s. Types in Elements v.s. Types in XML SchemaXML Schema
<xs:element name=“person”> <xs:complexType> <xs:sequence> <xs:element name=“name” type=“xs:string”/> <xs:element name=“address” type=“xs:string”/> </xs:sequence> </xs:complexType></xs:element>
<xs:element name=“person”> <xs:complexType> <xs:sequence> <xs:element name=“name” type=“xs:string”/> <xs:element name=“address” type=“xs:string”/> </xs:sequence> </xs:complexType></xs:element>
<xs:element name=“person” type=“ttt”><xs:complexType name=“ttt”> <xs:sequence> <xs:element name=“name” type=“xs:string”/> <xs:element name=“address” type=“xs:string”/> </xs:sequence></xs:complexType>
<xs:element name=“person” type=“ttt”><xs:complexType name=“ttt”> <xs:sequence> <xs:element name=“name” type=“xs:string”/> <xs:element name=“address” type=“xs:string”/> </xs:sequence></xs:complexType>
DTD: <!ELEMENT person (name,address)>
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Types:• Simple types (integers, strings, ...)
• Complex types (regular expressions, like in DTDs)
Element-type-element alternation:• Root element has a complex type
• That type is a regular expression of elements
• Those elements have their complex types...
• ...
• On the leaf nodes we have simple types
Elements v.s. Types in Elements v.s. Types in XML SchemaXML Schema
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Simple TypesSimple Types
String Token Byte unsignedByte Integer positiveInteger Int (larger than integer) unsignedInt Long Short ...
Time dateTime Duration Date ID IDREF IDREFS
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Facets of Simple TypesFacets of Simple Types
Examples length minLength maxLength pattern enumeration whiteSpace
maxInclusive maxExclusive minInclusive minExclusive totalDigits fractionDigits
•Facets = additional properties restricting a simple type
•15 facets defined by XML Schema
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Facets of Simple TypesFacets of Simple Types
Can further restrict a simple type by changing some facets
Restriction = subset
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Not so Simple TypesNot so Simple Types
List types:
Union types Restriction types
<xs:simpleType name="listOfMyIntType">
<xs:list itemType="myInteger"/>
</xs:simpleType>
<xs:simpleType name="listOfMyIntType">
<xs:list itemType="myInteger"/>
</xs:simpleType>
<listOfMyInt>20003 15037 95977 95945</listOfMyInt>
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Local and Global Types in Local and Global Types in XML SchemaXML Schema
Local type: <xs:element name=“person”>
[define locally the person’s type] </xs:element>
Global type: <xs:element name=“person” type=“ttt”/>
<xs:complexType name=“ttt”> [define here the type ttt] </xs:complexType>
Global types: can be reused in other elements
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Local v.s. Global Elements inLocal v.s. Global Elements inXML SchemaXML Schema
Local element: <xs:complexType name=“ttt”>
<xs:sequence> <xs:element name=“address” type=“...”/>... </xs:sequence> </xs:complexType>
Global element: <xs:element name=“address” type=“ttt”/>
<xs:complexType name=“ttt”> <xs:sequence> <xs:element ref=“address”/> ... </xs:sequence> </xs:complexType>
Global elements: like in DTDs
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Regular Expressions in Regular Expressions in XML SchemaXML Schema
Recall the element-type-element alternation: <xs:complexType name=“....”>
[regular expression on elements] </xs:complexType>
Regular expressions: <xs:sequence> A B C </...> = A B C <xs:choice> A B C </...> = A | B | C <xs:group> A B C </...> = (A B C) <xs:... minOccurs=“0” maxOccurs=“unbounded”> ..</...> = (...)* <xs:... minOccurs=“0” maxOccurs=“1”> ..</...> = (...)?
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Local Names in XML-SchemaLocal Names in XML-Schema<xs:element name=“person”> <xs:complexType> . . . . . <xs:element name=“name”> <xs:complexType> <xs:sequence> <xs:element name=“firstname” type=“xs:string”/> <xs:element name=“lastname” type=“xs:string”/> </xs:sequence> </xs:element> . . . . </xs:complexType></xs:element>
<xs:element name=“product”> <xs:complexType> . . . . . <xs:element name=“name” type=“xs:string”/>
</xs:complexType></xs:element>
<xs:element name=“person”> <xs:complexType> . . . . . <xs:element name=“name”> <xs:complexType> <xs:sequence> <xs:element name=“firstname” type=“xs:string”/> <xs:element name=“lastname” type=“xs:string”/> </xs:sequence> </xs:element> . . . . </xs:complexType></xs:element>
<xs:element name=“product”> <xs:complexType> . . . . . <xs:element name=“name” type=“xs:string”/>
</xs:complexType></xs:element>
name hasdifferent meaningsin person andin product
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Subtle Use of Local NamesSubtle Use of Local Names<xs:element name=“A” type=“oneB”/>
<xs:complexType name=“onlyAs”> <xs:choice> <xs:sequence> <xs:element name=“A” type=“onlyAs”/> <xs:element name=“A” type=“onlyAs”/> </xs:sequence> <xs:element name=“A” type=“xs:string”/> </xs:choice></xs:complexType>
<xs:element name=“A” type=“oneB”/>
<xs:complexType name=“onlyAs”> <xs:choice> <xs:sequence> <xs:element name=“A” type=“onlyAs”/> <xs:element name=“A” type=“onlyAs”/> </xs:sequence> <xs:element name=“A” type=“xs:string”/> </xs:choice></xs:complexType>
<xs:complexType name=“oneB”> <xs:choice> <xs:element name=“B” type=“xs:string”/> <xs:sequence> <xs:element name=“A” type=“onlyAs”/> <xs:element name=“A” type=“oneB”/> </xs:sequence> <xs:sequence> <xs:element name=“A” type=“oneB”/> <xs:element name=“A” type=“onlyAs”/> </xs:sequence> </xs:choice></xs:complexType>
<xs:complexType name=“oneB”> <xs:choice> <xs:element name=“B” type=“xs:string”/> <xs:sequence> <xs:element name=“A” type=“onlyAs”/> <xs:element name=“A” type=“oneB”/> </xs:sequence> <xs:sequence> <xs:element name=“A” type=“oneB”/> <xs:element name=“A” type=“onlyAs”/> </xs:sequence> </xs:choice></xs:complexType>
Arbitrary deep binary tree with A elements, and a single B element
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Attributes in XML SchemaAttributes in XML Schema
<xs:element name=“paper” type=“papertype”/>
<xs:complexType name=“papertype”>
<xs:sequence>
<xs:element name=“title” type=“xs:string”/>
. . . . . .
</xs:sequence>
<xs:attribute name=“language" type="xs:NMTOKEN" fixed=“English"/>
</xs:complexType>
<xs:element name=“paper” type=“papertype”/>
<xs:complexType name=“papertype”>
<xs:sequence>
<xs:element name=“title” type=“xs:string”/>
. . . . . .
</xs:sequence>
<xs:attribute name=“language" type="xs:NMTOKEN" fixed=“English"/>
</xs:complexType>
Attributes are associated to the type, not to the elementOnly to complex types; more trouble if we want to add attributesto simple types.
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““Mixed” Content, “Any” TypeMixed” Content, “Any” Type
Better than in DTDs: can still enforce the type, but now may have text between any elements
Means anything is permitted there
<xs:complexType mixed="true"> . . . .
<xs:complexType mixed="true"> . . . .
<xs:element name="anything" type="xs:anyType"/> . . . .
<xs:element name="anything" type="xs:anyType"/> . . . .
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““All” GroupAll” Group
A restricted form of & in SGML Restrictions:
• Only at top level• Has only elements• Each element occurs at most once
E.g. “comment” occurs 0 or 1 times
<xs:complexType name="PurchaseOrderType">
<xs:all> <xs:element name="shipTo" type="USAddress"/>
<xs:element name="billTo" type="USAddress"/>
<xs:element ref="comment" minOccurs="0"/>
<xs:element name="items" type="Items"/>
</xs:all>
<xs:attribute name="orderDate" type="xs:date"/>
</xs:complexType>
<xs:complexType name="PurchaseOrderType">
<xs:all> <xs:element name="shipTo" type="USAddress"/>
<xs:element name="billTo" type="USAddress"/>
<xs:element ref="comment" minOccurs="0"/>
<xs:element name="items" type="Items"/>
</xs:all>
<xs:attribute name="orderDate" type="xs:date"/>
</xs:complexType>
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Derived Types by ExtensionsDerived Types by Extensions <complexType name="Address">
<sequence> <element name="street" type="string"/>
<element name="city" type="string"/>
</sequence>
</complexType>
<complexType name="USAddress">
<complexContent>
<extension base="ipo:Address">
<sequence> <element name="state" type="ipo:USState"/>
<element name="zip" type="positiveInteger"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="Address">
<sequence> <element name="street" type="string"/>
<element name="city" type="string"/>
</sequence>
</complexType>
<complexType name="USAddress">
<complexContent>
<extension base="ipo:Address">
<sequence> <element name="state" type="ipo:USState"/>
<element name="zip" type="positiveInteger"/>
</sequence>
</extension>
</complexContent>
</complexType>
Corresponds to inheritance
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Derived Types by RestrictionsDerived Types by Restrictions
(*): may restrict cardinalities, e.g. (0,infty) to (1,1); may restrict choices; other restrictions…
<complexContent> <restriction base="ipo:Items“> … [rewrite the entire content, with restrictions]... </restriction> </complexContent>
<complexContent> <restriction base="ipo:Items“> … [rewrite the entire content, with restrictions]... </restriction> </complexContent>
Corresponds to set inclusion
