1. Managing XML and Semistructured Data
Part 2: Modelling XML Data

2. 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

3. More XML Syntax: Attributes
<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)

4. More XML: Oids and References
<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>
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.

5. XML Semantics: a Tree ! Order matters !!! data person person id
Element node
Text node
Attribute node
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> </phone>
</data>
person
person id
address
name
address
name
phone
o555
street no
city
Mary
Thai
John
23456
Maple
345
Seattle
Order matters !!!

6. More XML: CDATA Section
Syntax: <![CDATA[ .....any text here...]]>
Example:
<![CDATA[ <slide>..A sample slide..</slide> ]]> which displays as:
<slide>..A sample slide.. </slide>

7. More 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:
<
>
&
&
&apos; ‘
" “
&
Unicode char

8. More XML: Processing Instructions
Syntax: <?target argument?>
Example 1:
Example 2:
<product> <name> Alarm Clock </name> <?ringBell 20?> <price> </price> </product>
Data for processing
Target application
<?wilfred.lecture.Program QUERY="MSc,PhD,all"?>
<slide type="all"> <title>COMP630H</title> </slide>
Note: <?xml version = “1.0”?> is not PI

9. More XML: Comments Syntax <!-- .... Comment text... -->
Yes, they are part of the data model !!!

10. XML Namespaces http://www.w3.org/TR/REC-xml-names (1/99)
name ::= [prefix:]localpart
<book xmlns:isbn=“
<title> … </title>
<number> 15 </number>
<isbn:number> …. </isbn:number>
</book>

11. Belong to this namespace
XML 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
<tag xmlns:mystyle = “ …
<mystyle:title> … </mystyle:title>
<mystyle:number> …
</tag>
Belong to this namespace

12. XML Data Models Several competing models: Document Object Model (DOM):
(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)

13. XML Data v.s. E/R, ODL, Relational
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.

14. XLink 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=“ xlink:type=“simple” xlink:href=“ xlink:title=“The Homepage” xlink:show=“replace” xlink:actuate=“onRequest”>
</person>
required attributes
optional attributes

15. XLink 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)
”none”

16. XLink href attribute: More about XLink can be found in:
a URI or
an XPointer (next)
More about XLink can be found in: [

17. XPointer An extension of XPath (next week) Usage:
href=“
An XPointer expression points to:
A point
A range
Reference [

18. XPointer 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

19. XML 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

20. Similarities and Differences
{ person: &o123
{ name: “Alan”,
age: 42, } }
<person id=“o123”>
<name> Alan </name>
<age> 42 </age>
< > </ >
</person>
<person father=“o123”> …
</person>
{ person: { father: &o123 …} }
person
name
age
Alan 42
father
similar on trees, different on graphs

21. More 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

22. Document Type Definitions DTD
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

23. Very 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)>
]>

24. Very Simple DTD Example of valid XML document: <company>
<person> <ssn> </ssn>
<name> John </name> <office> B432 </office>
<phone> 1234 </phone>
</person>
<person> <ssn> </ssn>
<name> Jim </name> <office> B123 </office>
<product> ... </product>
...
</company>

25. DTD: The Content Model <!ELEMENT tag (CONTENT)> Content model:
Complex = a regular expression over other elements
Text-only = #PCDATA
Empty = EMPTY
Any = ANY
Mixed content = (#PCDATA | A | B | C)*
content model

26. DTD: Regular Expressions
XML
sequence
<!ELEMENT name (firstName, lastName))
<name>
<firstName> </firstName>
<lastName> </lastName>
</name>
optional
<!ELEMENT name (firstName?, lastName))
<person>
<name> </name>
<phone> </phone>
</person>
Kleene star
<!ELEMENT person (name, phone*))
alternation
<!ELEMENT person (name, (phone| )))

27. Attributes in DTDs <!ELEMENT person (ssn, name, office, phone?)>
<!ATTLIS person age CDATA #REQUIRED>
<person age=“25”>
<name> ....</name>
...
</person>

28. Attributes in DTDs <!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>

29. Attributes in DTDs Types: 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 this
Kind:
#REQUIRED
#IMPLIED = optional
value = default value
value #FIXED = the only value allowed

30. Using DTDs Must include in the XML document
Either include the entire DTD:
<!DOCTYPE rootElement [ ]>
Or include a reference to it:
<!DOCTYPE rootElement SYSTEM “
Or mix the two... (e.g. to override the external definition)

31. DTDs as Grammars <!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

32. DTDs 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| )*)>

33. XML Schemas generalizes DTDs uses XML syntax
two documents: structure and datatypes
XML Schemas
Elements v. Types
Regular expressions
Expressive power
XML-Schema is very complex
often criticized
some alternative proposals

34. DTD: <!ELEMENT paper (title,author*,year, (journal|conference))>
XML 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>
DTD: <!ELEMENT paper (title,author*,year, (journal|conference))>

35. Elements v.s. Types in XML 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” 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)>

36. Elements v.s. Types in XML Schema
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

37. Simple Types String Token Byte unsignedByte Integer positiveInteger
Int (larger than integer)
unsignedInt
Long
Short
...
Time
dateTime
Duration
Date ID
IDREF
IDREFS

38. Facets of Simple Types Examples length minLength maxLength pattern
Facets = additional properties restricting a simple type
15 facets defined by XML Schema
Examples
length
minLength
maxLength
pattern
enumeration
whiteSpace
maxInclusive
maxExclusive
minInclusive
minExclusive
totalDigits
fractionDigits

39. Facets of Simple Types
Can further restrict a simple type by changing some facets
Restriction = subset

40. Not so Simple Types List types: Union types Restriction types
<xs:simpleType name="listOfMyIntType">
<xs:list itemType="myInteger"/>
</xs:simpleType>
<listOfMyInt> </listOfMyInt>

41. Local and Global Types in XML 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

42. Local v.s. Global Elements in XML 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

43. Regular Expressions in XML 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”> ..</...> = (...)?

44. Local 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>
name has
different meanings
in person and
in product

45. Subtle 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: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

46. Attributes 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>
Attributes are associated to the type, not to the element
Only to complex types; more trouble if we want to add attributes
to simple types.

47. “Mixed” Content, “Any” Type
<xs:complexType mixed="true">
Better than in DTDs: can still enforce the type, but now may have text between any elements
Means anything is permitted there
<xs:element name="anything" type="xs:anyType"/>

48. “All” Group A restricted form of & in SGML Restrictions:
<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>
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

49. Derived 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"/>
</extension>
</complexContent>
Corresponds to inheritance

50. Derived 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>
Corresponds to set inclusion