Διδάσκων: Ν. Βασιλειάδης Αναπλ. Καθ. Τμ. Πληροφορικής...

ΤΜΗΜΑ ΠΛΗΡΟΦΟΡΙΚΗΣ, ΑΠΘ ΜΕΤΑΠΤΥΧΙΑΚΟ ΠΡΟΓΡΑΜΜΑ ΣΠΟΥΔΩΝ

Κατεύθυνση Πληροφοριακών Συστημάτων - 1ο Εξάμηνο

Σημασιολογικός Ιστόςlpis.csd.auth.gr/mtpx/sw/index.htm

Διδάσκων: Ν. ΒασιλειάδηςΑναπλ. Καθ. Τμ. Πληροφορικής ΑΠΘ

Μαθήματα: 2-3-4

Chapter 2Structured Web Documents in XML

Grigoris AntoniouFrank van Harmelen

A Semantic Web Primer, 2nd Edition2-3

Introduction

Today HTML (HyperText Markup Language) is the standard language for Web pages.

HTML was derived from SGML (Standard Generalized Markup Language)

SGML Applications– HTML: Developed because SGML is too complex for

Internet-related purposes. – XML (eXtensible Markup Language): Its development

was driven by shortcomings of HTML.


An HTML Example

<h2>Nonmonotonic Reasoning: Context-Dependent Reasoning</h2>

<i>by <b>V. Marek</b> and <b>M. Truszczynski</b></i><br>

Springer 1993<br>ISBN 0387976892


The Same Example in XML

<book><title>Nonmonotonic Reasoning: Context-

Dependent Reasoning</title><author>V. Marek</author><author>M. Truszczynski</author><publisher>Springer</publisher><year>1993</year><ISBN>0387976892</ISBN>

</book>


HTML versus XML: Similarities

Both use tags (e.g. <h2> and </year>) Tags may be nested (tags within tags) Human users can read and interpret

both HTML and XML representations quite easily

… But how about machines?


HTML versus XML: Differences

All tags in XML must be closed – E.g. for an opening tag <title> there must be a closing

tag </title>– The enclosed content, together with its opening and

closing tags, is called element In HTML some tags (<br>), may be left open. XHTML brings HTML more in line with XML

– Opening and closing tags in XHTML are balanced– Any valid XHTML document is also a valid XML

document


Problems with Automated Interpretation of HTML Documents

An intelligent agent trying to retrieve the namesof the authors of the book Authors’ names could appear immediately

after the title or immediately after the word by Are there two authors? Or just one, called “V. Marek and M.

Truszczynski”?


HTML vs XML: Structural Information

HTML documents do not contain structural information: pieces of the document and their relationships.

XML more easily accessible to machines:– Every piece of information is described. – Relations are also defined through the nesting

structure– E.g., <author> tags appear within <book> tags, so

they describe properties of the particular book.


HTML vs XML: Structural Information (2)

A machine processing the XML document would be able to deduce that – the author element refers to the enclosing book

element– rather than by proximity considerations

XML allows the definition of constraints on values– E.g. a year must be a number of 4 digits


HTML vs XML: Formatting

The HTML representation provides more than the XML representation: – The formatting of the document is also described

Τhe main use of an HTML document is to display information: it must define formatting

XML: separation of content from display– Same information can be displayed in different ways – Content may be used for purposes other than display


HTML vs XML: Another Example

In HTML<h2>Relationship matter-energy</h2><i> E = M × c2 </i>

In XML<equation>

<meaning>Relationship matter energy</meaning>

<leftside> E </leftside><rightside> M × c2 </rightside>

</equation>


HTML vs XML: Different Use of Tags

Both HTML docs have the same tags. In XML completely different tags are used!

HTML tags define display: color, lists … XML tags not fixed: user definable tags XML meta markup language: language for

defining markup languages


XML Vocabularies

Web applications must agree on common vocabularies to communicate and collaborate

Communities and business sectors are defining their specialized vocabularies– mathematics (MathML)– bioinformatics (BSML)– human resources (HRML) – …


Data Exchange

The main use of XML today is as a uniform data exchange format between applications. – Rather than a document markup language.

Companies retrieve information from their partners, and update their databases accordingly.– If there is not an agreed common standard, then specialized

processing and querying software must be developed for each partner separately

– Technical overhead– The software must be updated every time a partner decides to

change its own database format.


Lecture Outline

1. Introduction2. Detailed Description of XML3. Structuring

a) DTDsb) XML Schema

4. Namespaces5. Accessing, querying XML documents: XPath6. Transformations: XSLT


The XML Language

An XML document consists of a prolog a number of elements an optional epilog (not discussed)


Prolog of an XML Document

The prolog consists of an XML declaration and an optional reference to external structuring

documents

<?xml version="1.0" encoding="UTF-16"?>

<!DOCTYPE book SYSTEM "book.dtd">


XML Elements

The “things” the XML document talks about– E.g. books, authors, publishers

An element consists of:– an opening tag– the content– a closing tag

<lecturer>David Billington</lecturer>


XML Elements (2)

Tag names can be chosen almost freely. The first character must be a letter, an

underscore, or a colon No name may begin with the string “xml” in

any combination of cases – E.g. “Xml”, “xML”


Content of XML Elements

Content may be text, or other elements, or nothing

<lecturer><name>David Billington</name><phone> +61 − 7 − 3875 507 </phone>

</lecturer>

If there is no content, then the element is called empty; it is abbreviated as follows:<lecturer/> for <lecturer></lecturer>


XML Attributes

An empty element is not necessarily meaningless– Its presence alone may “mean” something– It may have some properties in terms of attributes

An attribute is a name-value pair inside the opening tag of an element<lecturer name="David Billington" phone="+61 − 7 − 3875 507"/>


XML Attributes: An Example

<order orderNo="23456“customer="John Smith" date="October 15, 2002">

<item itemNo="a528" quantity="1"/><item itemNo="c817" quantity="3"/>

</order>


The Same Example without Attributes

<order><orderNo>23456</orderNo><customer>John Smith</customer><date>October 15, 2002</date><item>

<itemNo>a528</itemNo><quantity>1</quantity>

</item><item>

<itemNo>c817</itemNo><quantity>3</quantity>

</item></order>


XML Elements vs Attributes

Attributes can be replaced by elementsWhen to use elements and when

attributes is a matter of tasteBut attributes

– Cannot be nested – Cannot have two attributes with the same name in

the same element

Mixed Content

Elements with mixed content contain both text and other elements at the same time

<letter> Dear Mr.<name>John Smith</name>.

Your order <orderid>1032</orderid>will be shipped on <shipdate>2001-07-13</shipdate>.

</letter>


Mixed Content

An element has also mixed content if it has attributes and text

<lecturer phone="+61 − 7 − 3875 507">David Billington

</lecturer>



Further Components of XML Docs

Comments– A piece of text that is to be ignored by parser– 

Processing Instructions (PIs)– Define procedural attachments– <?stylesheet type="text/css"

href="mystyle.css"?>


Well-Formed XML Documents

Syntactically correct documents Some syntactic rules:

– Only one outermost element (called root element)– Each element contains an opening and a

corresponding closing tag– Tags may not overlap

<author><name>Lee Hong</author></name>– Attributes within an element have unique names– Element and tag names must be permissible


The Tree Model of XML Documents: An Example

<email><head>

<from name="Michael Maher"

address="[email protected]"/><to name="Grigoris Antoniou"

address="[email protected]"/><subject>Where is your draft?</subject>

</head><body>

Grigoris, where is the draft of the paper you promised

me last week?</body>

</email>

Root

email

head

from

name

Michael Maher

address

[email protected]

to

name

Grigoris Antoniou

address

[email protected]

subject

Where is your draft?

body

Grigoris, where is the draft of the

paper you promised me last week?

A Tree Example



The Tree Model of XML Docs

The tree representation of an XML document is an ordered labeled tree:– There is exactly one root– There are no cycles– Each non-root node has exactly one parent– Each node has a label.


The Tree Model of XML Docs (2)

Element nodes are different from attribute nodes– The order of elements is important – … but the order of attributes is not important – Attribute nodes are always terminal– Element nodes may be terminal or inner nodes

There is difference between:– the root of the tree (representing the XML document)– the root element (email)– This distinction is important for addressing and querying

XML documents.


Lecture Outline





Why Structuring XML Documents?

An XML document is well-formed if it respects certain syntactic rules.

These rules say nothing specific about the structure of the document.

Imagine 2 applications that try to communicate– They wish to use the same vocabulary


Structuring XML Documents

Define all the element and attribute names that may be used

Define the structure – what values an attribute may take– which elements may or must occur within other

elements, etc. If such structuring information exists, the

document can be validated


Structuring XML Documents (2)

An XML document is valid if – it is well-formed– respects the structuring information it uses

There are two ways of defining the structure of XML documents: – DTDs (the older and more restricted way)– XML Schema (offers extended possibilities)


DTD: Element Type Definition

<lecturer><name>David Billington</name><phone> +61 − 7 − 3875 507 </phone>

</lecturer>DTD for above element (and all lecturer elements):

<!ELEMENT lecturer (name,phone)><!ELEMENT name (#PCDATA)><!ELEMENT phone (#PCDATA)>


The Meaning of the DTD

The element types lecturer, name, and phone may be used in the document

A lecturer element contains a name element and a phone element, in that order (sequence)

A name element and a phone element may have any content

In DTDs, #PCDATA is the only atomic type for elements


DTD: Disjunction in Element Type Definitions

We express that a lecturer element contains either a name element or a phone element as:<!ELEMENT lecturer (name | phone)>

Both elements below are validated:<lecturer>

<name>David Billington</name></lecturer><lecturer>

<phone> +61 − 7 − 3875 507 </phone></lecturer>

A lecturer with both name and phone is not validated!


DTD: Element Type Definitions – Any order

A lecturer element contains a name element and a phone element in any order. <!ELEMENT lecturer ((name,phone) | (phone,name))>

Both elements below are validated:<lecturer>

<name>David Billington</name><phone> +61 − 7 − 3875 507 </phone>

</lecturer><lecturer>

<phone> +61 − 7 − 3875 507 </phone><name>David Billington</name>

</lecturer>


Example of an XML Element

<order orderNo="23456" customer="John Smith" date="October 15, 2002">

<item itemNo="a528" quantity="1"/><item itemNo="c817" quantity="3"/>

</order>


The Corresponding DTD

<!ELEMENT order (item+)><!ATTLIST order

orderNo ID #REQUIREDcustomer CDATA #REQUIREDdate CDATA #REQUIRED>

<!ELEMENT item EMPTY><!ATTLIST item

itemNo ID #REQUIREDquantity CDATA #REQUIREDcomments CDATA #IMPLIED>


Comments on the DTD

The item element type is defined to be empty + (after item) is a cardinality operator:

– ?: appears zero times or once– *: appears zero or more times– +: appears one or more times– No cardinality operator means exactly once


Comments on the DTD (2)

In addition to defining elements, we define attributes

This is done in an attribute list containing:– Name of the element type to which the list applies – A list of triplets of attribute name, attribute type,

and value type Attribute name: A name that may be used in

an XML document using a DTD


DTD: Attribute Types

Similar to predefined data types, but limited selection The most important types are

– CDATA, a string (sequence of characters)– ID, a name that is unique across the entire XML document– IDREF, a reference to another element with an ID attribute

carrying the same value as the IDREF attribute– IDREFS, a series of IDREFs– (v1| . . . |vn), an enumeration of all possible values

Limitations: no dates, number ranges etc.


DTD: Attribute Value Types

#REQUIRED– Attribute must appear in every occurrence of the

element type in the XML document #IMPLIED

– The appearance of the attribute is optional "value"

– This specifies the default value for the attribute #FIXED "value"

– Every element must have this attribute


Referencing with IDREF and IDREFS

<!ELEMENT family (person*)><!ELEMENT person (name)><!ELEMENT name (#PCDATA)><!ATTLIST person id ID #REQUIRED

mother IDREF #IMPLIED father IDREF #IMPLIED children IDREFS #IMPLIED>


An XML Document Respecting the DTD

<family><person id="bob" mother="mary" father="peter">

<name>Bob Marley</name></person><person id="bridget" mother="mary">

<name>Bridget Jones</name></person><person id="mary" children="bob bridget">

<name>Mary Poppins</name></person><person id="peter" children="bob">

<name>Peter Marley</name></person>

</family>


The email example

<email><head>

<from name="Michael Maher"

address="[email protected]"/><to name="Grigoris Antoniou"

address="[email protected]"/><subject>Where is your draft?</subject>

</head><body>

Grigoris, where is the draft of the paper you promised

me last week?</body>

</email>

The email example slightly modified

<email><head>

<from name="Michael Maher" address="mm@cs..."/><to name="Grigoris Antoniou"

address="grigoris@cs..."/><subject>Where is your draft?</subject>

</head><body>

<text>Grigoris, where is the draft of the paper you promised me last week?</text>

<attachment file=“draft.doc” encoding=“mime”/><attachment file=“contract.pdf” encoding=“mime”/>

</body></email>2-51 A Semantic Web Primer, 2nd Edition


A DTD for an Email Element

<!ELEMENT email (head, body)><!ELEMENT head (from, to+, cc*, subject)><!ELEMENT from EMPTY><!ATTLIST from name CDATA #IMPLIED

address CDATA #REQUIRED><!ELEMENT to EMPTY><!ATTLIST to name CDATA #IMPLIED

address CDATA #REQUIRED>


A DTD for an Email Element (2)

<!ELEMENT cc EMPTY><!ATTLIST cc name CDATA #IMPLIED

address CDATA #REQUIRED>

<!ELEMENT subject (#PCDATA)><!ELEMENT body (text, attachment*)><!ELEMENT text (#PCDATA)><!ELEMENT attachment EMPTY><!ATTLIST attachment

encoding (mime | binhex) "mime" file CDATA

#REQUIRED>


Interesting Parts of the DTD

A head element contains (in that order):– a from element– at least one to element– zero or more cc elements– a subject element

In from, to, and cc elements – the name attribute is not required– the address attribute is always required


Interesting Parts of the DTD (2)

A body element contains – a text element– possibly followed by a number of attachment

elements The encoding attribute of an attachment

element must have either the value “mime” or “binhex”– “mime” is the default value


Remarks on DTDs

A DTD can be interpreted as an Extended Backus-Naur Form (EBNF)– <!ELEMENT email (head, body)>– is equivalent to email ::= head body

Recursive definitions possible in DTDs <!ELEMENT bintree ((bintree, root, bintree) | emptytree)> <!ELEMENT root (#PCDATA)><!ELEMENT emptytree EMPTY>


DTD for the “original” Email example

<!ELEMENT email (head, body)>…<!ELEMENT body (#PCDATA)>

DTD for Mixed Content

<letter> Dear Mr.<name>John Smith</name>. Your order <orderid>1032</orderid> will be shipped on <shipdate>2001-07-13</shipdate>.

</letter><!ELEMENT letter

(#PCDATA | name | orderid | shipdate)*><!ELEMENT cname (#PCDATA)><!ELEMENT orderid (#PCDATA)><!ELEMENT shipdate (#PCDATA)>


What if the email body had mixed content?

<email><head>



</head><body>Grigoris, where is the draft of the paper you promised me last week?


</body></email>

2-59 A Semantic Web Primer, 2nd Edition


A DTD for Email with mixed content

<!ELEMENT email (head, body)>…<!ELEMENT body (#PCDATA | attachment)*><!ELEMENT attachment EMPTY><!ATTLIST attachment

encoding (mime | binhex) "mime" file CDATA

#REQUIRED>


Lecture Outline





XML Schema

Significantly richer language for defining the structure of XML documents

Its syntax is based on XML itself– not necessary to write separate tools (e.g. parser)

Reuse and refinement of schemas– Expand or restrict already existent data types

Sophisticated set of data types– compared to DTDs (which only supports strings)


XML Schema (2)

An XML schema is an element with an opening tag like

<schema version="1.0" xmlns="http://www.w3.org/2000/10/XMLSchema">– Uses the schema found at the W3C Web site as a

basis on which new schemas can be built. Structure of schema elements

– Definitions of element and attribute types using data types


Element Types

<element name="email"/><element name="head" minOccurs="1"

maxOccurs="1"/><element name="to" minOccurs="1"/> Cardinality constraints: minOccurs="x" (default value 1) maxOccurs="x" (default value 1)

– Generalizations of *,?,+ offered by DTDs


Attribute Types

<attribute name="id" type="ID" use="required"/>

<attribute name="speaks" type="Language" default="en"/>

Existence: use="x", where x may be optional or required

Default value: default="x" Fixed value: fixed="x"

Incompatible


Data Types

There is a variety of built-in data types – Numerical data types: integer, Short etc. – String types: string, ID, IDREF, CDATA etc.– Date and time data types: time, Month etc.

There are also user-defined data types – simple data types, which cannot use elements or

attributes– complex data types, which can use these


Data Types (2)

Complex data types are defined from already existing data types by defining some attributes (if any), and using:– sequence, a sequence of existing data type

elements (order is important)– all, a collection of elements that must appear

(order is not important)– choice, a collection of elements, of which one will

be chosen


A Data Type Example

<complexType name="lecturerType"><sequence>

<element name="firstname" type="string"minOccurs="0"

maxOccurs="unbounded"/><element name="lastname" type="string"/>

</sequence><attribute name="title" type="string" use="optional"/>

</complexType><element name=“lecturer"

type="lecturerType"/>


Data Type Extension Already existing data types can be extended by new

elements or attributes. Example:<complexType name="extendedLecturerType">

<complexContent><extension base="lecturerType">

<sequence><element name="email"

type="string"

minOccurs="0" maxOccurs="1"/></sequence><attribute name="rank"

type="string" use="required"/></extension>

</complexContent></complexType>


Resulting Data Type

<complexType name="extendedLecturerType"><sequence>

<element name="firstname" type="string"minOccurs="0" maxOccurs="unbounded"/>

<element name="lastname" type="string"/><element name="email" type="string"

minOccurs="0" maxOccurs="1"/></sequence><attribute name="title" type="string" use="optional"/><attribute name="rank" type="string" use="required"/>

</complexType>


Data Type Extension (2)

A hierarchical relationship exists between the original and the extended type– Instances of the extended type are also

instances of the original type– They may contain additional information,

but neither less information, nor information of the wrong type


Data Type Restriction

An existing data type may be restricted by adding constraints on certain values

New type and use attributes may be added minOccurs, maxOccurs may be tightened


Example of Data Type Restriction

<complexType name="restrictedLecturerType"><complexContent>

<restriction base="lecturerType"><sequence>

<element name="firstname" type="string"

minOccurs="1" maxOccurs="2"/>

</sequence><attribute name="title" type=“string”

use="required"/></restriction>

</complexContent></complexType>


Data Type Restriction

Restriction is not the opposite from extension – Elements or attributes cannot be deleted

Hierarchical relationship: – Instances of restricted type are also instances of

original type – They satisfy at least the constraints of original

type


Restriction of Simple Data Types

<simpleType name="dayOfMonth"><restriction base="integer">

<minInclusive value="1"/><maxInclusive value="31"/>

</restriction></simpleType>


Data Type Restriction: Enumeration

<simpleType name="dayOfWeek"><restriction base="string">

<enumeration value="Mon"/><enumeration value="Tue"/><enumeration value="Wed"/><enumeration value="Thu"/><enumeration value="Fri"/><enumeration value="Sat"/><enumeration value="Sun"/>


The email example (again…)

<email><head>



</head><body>

<text>Grigoris, where is the draft of the paper you promised me last week?</text>


</body></email>2-77 A Semantic Web Primer, 2nd Edition


XML Schema: The Email Example

<element name="email" type="emailType"/>

<complexType name="emailType"><sequence>

<element name="head" type="headType"/><element name="body" type="bodyType"/>

</sequence></complexType>


XML Schema: The Email Example (2)

<complexType name="headType"><sequence>

<element name="from" type="nameAddress"/><element name="to" type="nameAddress"

minOccurs="1" maxOccurs="unbounded"/>

<element name="cc" type="nameAddress"minOccurs="0"

maxOccurs="unbounded"/><element name="subject" type="string"/>

</sequence></complexType>



<complexType name="nameAddress"><attribute name="name"

type="string" use="optional"/><attribute name="address"

type="string" use="required"/>

</complexType>Notice how an empty complex type is defined in XML Schema



<complexType name="bodyType"><sequence>

<element name="text" type="string"/><element name="attachment" minOccurs="0"

maxOccurs="unbounded"><complexType>

<attribute name="encoding" use=“optional" default ="mime">

<simpleType><restriction

base="string"><enumeration

value="mime"/><enumeration

value="binhex"/></restriction>

</simpleType></attribute><attribute name="file" type="string"

use="required"/>…


Remarks for the e-Mail Example

Some data types are defined separately and given names

Other data types are defined (anonymously) within other types – E.g. the types for the attachment element and the

encoding attribute If a type is only used once, it makes sense to

define it anonymously for local use.– However, this approach reaches its limitations

quickly if nesting becomes too deep.


XML Schema: The Email Example (4a)

<complexType name="bodyType"><sequence><element name="text" type="string"/><element name="attachment" type=“attachmentType”minOccurs="0" maxOccurs="unbounded“/><sequence>

</complexType>

<complexType name=“attachmentType”><attribute name="encoding" type=“encodingType” use=“optional" default ="mime“/><attribute name="file" type="string" use="required"/>

</complexType>


XML Schema: The Email Example (4b)

<simpleType name=“encodingType”><restriction base="string">

<enumeration value="mime"/><enumeration value="binhex"/>


XML Schema for Mixed Content

<xs:element name="letter"> <xs:complexType mixed="true"> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="orderid"

type="xs:positiveInteger"/> <xs:element name="shipdate" type="xs:date"/> </xs:sequence> </xs:complexType></xs:element>

2-85

<letter> Dear Mr.<name>John Smith</name>. Your order <orderid>1032</orderid> will be shipped on <shipdate>2001-07-13</shipdate>.

</letter> A Semantic Web Primer, 2nd Edition

What if the email body had mixed content?

<email><head>



</head><body>Grigoris, where is the draft of the paper you promised me last week?


</body></email>



XML Schema for Email with mixed content

<complexType name="bodyType"><sequence><element name="text" type="string"/><element name="attachment" type=“attachmentType”minOccurs="0" maxOccurs="unbounded“/><sequence>

</complexType>

<complexType name="bodyType" mixed="true"><sequence><element name="attachment" type=“attachmentType”minOccurs="0" maxOccurs="unbounded"/><sequence>

</complexType>

Old

New


Lecture Outline





Namespaces

An XML document may use more than one DTD or schema

Since each structuring document was developed independently, name clashes may appear

The solution is to use a different prefix for each DTD or schema – prefix:name


An Example

<vu:instructors xmlns:vu="http://www.vu.com/empDTD"xmlns:gu="http://www.gu.au/empDTD"xmlns:uky="http://www.uky.edu/empDTD">

<uky:faculty uky:title="assistant professor" uky:name="John Smith" uky:department="Computer Science"/>

<gu:academicStaff gu:title="lecturer" gu:name="Mate Jones" gu:school="Information

Technology"/></vu:instructors>


Namespace Declarations

Namespaces are declared within an element and can be used in that element and any of its children (elements and attributes)

A namespace declaration has the form:– xmlns:prefix="location"– location is the address of the DTD or schema

If a prefix is not specified: xmlns="location" then the location is used by default


Namespace without prefix example

<vu:instructors xmlns:vu="http://www.vu.com/empDTD" xmlns="http://www.gu.au/empDTD" xmlns:uky="http://www.uky.edu/empDTD">

<uky:faculty uky:title="assistant professor" uky:name="John Smith" uky:department="Computer Science"/>

<academicStaff title="lecturer“ name="Mate Jones" school="Information Technology"/>

</vu:instructors>


Lecture Outline





Addressing and Querying XML Documents

In relational databases, parts of a database can be selected and retrieved using SQL– Same necessary for XML documents– Query languages: XQuery, XQL, XML-QL

The central concept of XML query languages is a path expression – Specifies how a node or a set of nodes, in the tree

representation of the XML document can be reached


XPath

XPath is core for XML query languages Language for addressing parts of an XML

document. – It operates on the tree data model of XML– It has a non-XML syntax

XPath expressions can be used for purposes other than querying– For transforming XML documents.


Types of Path Expressions

Absolute (starting at the root of the tree)– Syntactically they begin with the symbol /– It refers to the root of the document

(situated one level above the root element of the document)

Relative to a context node


An XML Example

<library location="Bremen"><author name="Henry Wise">

<book title="Artificial Intelligence"/><book title="Modern Web Services"/><book title="Theory of Computation"/>

</author><author name="William Smart">

<book title="Artificial Intelligence"/></author><author name="Cynthia Singleton">

<book title="The Semantic Web"/><book title="Browser Technology Revised"/>

</author></library>

A Semantic Web Primer, 2nd Edition

root

library

location

Bremen

author

name

Henry Wise

book

title

Artificial Intelligence

book

title

Modern Web

Services

book

title

Theory of Computation

author

name

William Smart

book

title

Artificial Intelligen

ce

author

name

Cynthia Singleton

book

title

The Semantic

Web

book

title

Browser Technolo

gy Revised

Tree Representation

2-98


Examples of Path Expressions in XPath

Address all author elements/library/author

Addresses all author elements that are children of the library element node, which resides immediately below the root

/t1/.../tn, where each ti+1 is a child node of ti, is a path through the tree representation


2-100

Examples of Path Expressions in XPath (2)

Address all author elements//author

Here // says that we should consider all elements in the document and check whether they are of type author

This path expression addresses all author elements anywhere in the document


2-101


Address the location attribute nodes within library element nodes

/library/@location

The symbol @ is used to denote attribute nodes


2-102


Find if there are title attribute nodes within

book elements anywhere in the document,

which have the value “Artificial Intelligence”

//book/@title="Artificial Intelligence"


root

library

location

Bremen

author

name

Henry Wise

book

title


book

title

Modern Web

Services

book

title


author

name

William Smart

book

title


ce

author

name

Cynthia Singleton

book

title

The Semantic

Web

book

title

Browser Technolo

gy Revised

Tree Representation of Query 4

2-103

Non-empty set; return true


2-104


Address all books with title “Artificial Intelligence”

//book[@title="Artificial Intelligence"] Test within square brackets: a filter expression

– It restricts the set of addressed nodes. Difference with query 4.

– Q5 addresses book elements, the title of which satisfies a certain condition.

– Q4 tests if there are title attribute nodes of book elements with a certain characteristic

root

library

location

Bremen

author

name

Henry Wise

book

title


book

title

Modern Web

Services

book

title


author

name

William Smart

book

title


ce

author

name

Cynthia Singleton

book

title

The Semantic

Web

book

title

Browser Technolo

gy Revised

Tree Representation of Query 5


2-105


2-106


Address the first author element node in the XML document

//author[1] Address the last book element within the first

author element node in the document//author[1]/book[last()]

Address all book element nodes without a title attribute

//book[not(@title)]

More XPath

How can we address the first book of each author?

//author/book[1] The following will work as well

//book[1]



2-108

General Form of Path Expressions

A path expression consists of a series of steps, separated by slashes

A step consists of – An axis specifier, – A node test, and – An optional predicate


2-109

General Form of Path Expressions (2)

An axis specifier determines the tree relationship between the nodes to be addressed and the context node– E.g. parent, ancestor, child (the default),

sibling, attribute node– // is such an axis specifier: descendant or

self


2-110


A node test specifies which nodes to address – The most common node tests are element

names E.g. //author/book E.g., * addresses all element nodes

– comment() addresses all comment nodes


2-111


Predicates (or filter expressions) are optional and are used to refine the set of addressed nodes– E.g., the expression [1] selects the first node– [position()=last()] selects the last node– [position() mod 2 =0] selects the even nodes

XPath has a more complicated full syntax. – We have only presented the abbreviated syntax


2-112

More XPath Examples (1)

para selects the para element children of the context node

* selects all element children of the context node text() selects all text node children of the context

node @* selects all the attributes of the context node */para selects all para grandchildren of the

context node


2-113


/doc/chapter[5]/section[2] selects the 2nd section of the 5th chapter of the doc

chapter//para selects the para element descendants of the chapter element children of the context node

//olist/item selects all the item elements in the same document as the context node that have an olist parent


2-114


. selects the context node .//para selects the para element descendants of

the context node .. selects the parent of the context node ../@lang selects the lang attribute of the parent

of the context node


para[@type="warning"][5] selects the 5th para child of the context node that has a type attribute with value warning

para[5][@type="warning"] selects the 5th para child of the context node if that child has a type attribute with value warning – Could be written also as:

para[position()=5 and @type="warning"] 2-115 A Semantic Web Primer, 2nd Edition


chapter[title="Introduction"] selects the chapter children of the context node that have one or more title children with string-value equal to Introduction

chapter[title] selects the chapter children of the context node that have one or more title children

employee[@secretary and @assistant] selects all the employee children of the context node that have both a secretary attribute and an assistant attribute



2-117

Lecture Outline





2-118

Displaying XML Documents

So far we have not provided any information about how XML documents can be displayed.

Such information is necessary because unlike HTML documents, XML documents do not contain formatting information.

The advantage is that a given XML document can be presented in various ways, when different style sheets are applied to it.


2-119

Displaying XML Documents

<author><name>Grigoris Antoniou</name><affiliation>University of Bremen</affiliation><email>[email protected]</email>

</author>may be displayed in different ways:

Grigoris Antoniou Grigoris AntoniouUniversity of Bremen University of [email protected] [email protected]


2-120

Style Sheets

Style sheets can be written in various languages– E.g. CSS2 (cascading style sheets level 2)– XSL (extensible stylesheet language)

XSL includes – a transformation language (XSLT)– a formatting language– Both are XML applications


2-121

XSL Transformations (XSLT)

XSLT specifies rules with which an input XML document is transformed to– another XML document– an HTML document – plain text

The output document may use the same DTD or schema, or a completely different vocabulary

XSLT can be used independently of the formatting language


2-122

XSLT (2)

Move data and metadata from one XML representation to another

XSLT is chosen when applications that use different DTDs or schemas need to communicate

XSLT can be used for machine processing of content without any regard to displaying the information for people to read.

In the following we use XSLT only to display XML documents

Process of XSL Transformations

2-123

Altova XML Spy

Any modern browser


2-124

XSLT Transformation into HTML

<xsl:template match="/author"><html>

<head><title>An author</title></head><body bgcolor="white">

<b><xsl:value-of select="name"/></b><br>

<xsl:value-of select="affiliation"/><br><i><xsl:value-of select="email"/></i>

</body></html>

</xsl:template>


2-125

Style Sheet Output

<html><head><title>An author</title></head><body bgcolor="white">

<b>Grigoris Antoniou</b><br>University of Bremen<br><i>[email protected]</i>

</body></html>


2-126

Observations About XSLT

XSLT documents are XML documents – XSLT resides on top of XML

The XSLT document defines a template– In this case an HTML document, with some

placeholders for content to be inserted xsl:value-of retrieves the value of an element

and copies it into the output document– It places some content into the template


2-127

A Template

<html><head><title>An author</title></head><body bgcolor="white">

<b>...</b><br>...<br><i>...</i>

</body></html>


2-128

Auxiliary Templates

We have an XML document with details of several authors

It is a waste of effort to treat each author element separately

In such cases, a special template is defined for author elements, which is used by the main template


2-129

Example of an Auxiliary Template

<authors><author>

<name>Grigoris Antoniou</name><affiliation>University of Bremen</affiliation><email>[email protected]</email>

</author><author>

<name>David Billington</name><affiliation>Griffith University</affiliation><email>[email protected]</email>

</author></authors>


2-130

Desired Output


2-131

Example of an Auxiliary Template (2)

<xsl:template match="/"><html>

<head><title>Authors</title></head><body bgcolor="white">

<xsl:apply-templates select="authors"/>



</body></html>

</xsl:template>


2-132

Example of an Auxiliary Template (3)

<xsl:template match="authors"><xsl:apply-templates select="author"/>

</xsl:template><xsl:template match="author">

<h2><xsl:value-of select="name"/></h2>Affiliation:<xsl:value-of

select="affiliation"/><br>Email: <xsl:value-of select="email"/><p>

</xsl:template>


2-133

Multiple Authors Output

<html><head><title>Authors</title></head><body bgcolor="white">

<h2>Grigoris Antoniou</h2>Affiliation: University of Bremen<br>Email: [email protected]<p><h2>David Billington</h2>Affiliation: Griffith University<br>Email: [email protected]<p>

</body></html>


2-134

Explanation of the Example

xsl:apply-templates element causes all children of the context node to be matched against the selected path expression– E.g., if the current template applies to /, then the element

xsl:apply-templates applies to the root element– I.e. the authors element (/ is located above the root

element)– If the current context node is the authors element, then

the element xsl:apply-templates select="author" causes the template for the author elements to be applied to all author children of the authors element


2-135

Explanation of the Example (2)

It is good practice to define a template for each element type in the document– Even if no specific processing is applied to certain

elements, the xsl:apply-templates element should be used

– E.g. authors In this way, we work from the root to the leaves

of the tree, and all templates are applied

Alternative XSLT

<xsl:template match="/"><html><head><title>Authors</title></head><body bgcolor="white"><xsl:apply-templates select=“//author"/></body></html>

</xsl:template><xsl:template match="author">

<h2><xsl:value-of select="name"/></h2>Affiliation:<xsl:value-of select="affiliation"/><br>Email: <xsl:value-of select="email"/><p></xsl:template> Lectures 2 & 3: Information Sharing

on the Web: XML

2-136


2-137

Processing XML Attributes

Suppose we wish to transform the following element:

<person firstname="John" lastname="Woo"/>– to

<person name="John Woo"/>

Processing XML Attributes Wrong solution

<xsl:template match="person"> <person name="<xsl:value-of select="@firstname"> <xsl:value-of select="@lastname">"/></xsl:template>

– Not well-formed because tags are not allowed within the values of attributes

– XSL commands are ignored because they are included in double quotes2-

138 A Semantic Web Primer, 2nd Edition

Processing XML AttributesCorrect Solution

We wish to add attribute values into template

<xsl:template match="person"> <person name="{@firstname} {@lastname}"/></xsl:template>


Transforming an XML Document to Another

Root

authors

author

name

Grigoris Antonio

u

affiliation

University of

Bremen

email

[email protected]

author

name

David Billingto

n

affiliation

Griffith Universi

ty

email

[email protected].

net

2-140

Root

authors

author

name

Grigoris Antonio

u

contact

institute

University of

Bremen

email

[email protected]

author

name

David Billingto

n

contact

institute

Griffith Universi

ty

email

[email protected].

net


2-141

Transforming an XML Document to Another (2)

<xsl:template match="/"><?xml version="1.0" encoding="UTF-16"?><authors>

<xsl:apply-templates select="authors"/></authors>

</xsl:template>

<xsl:template match="authors"><author>

<xsl:apply-templates select="author"/></author>

</xsl:template>


2-142

Transforming an XML Document to Another (3)

<xsl:template match="author"><name><xsl:value-of select="name"/></name><contact>

<institution><xsl:value-of select="affiliation"/>

</institution><email><xsl:value-of

select="email"/></email></contact>

</xsl:template>

More XSLT constructsxsl:for-each

Allows you to do looping in XSLT by selecting every XML element of a specified node-set

Sometimes the same effect can be performed using xsl:apply-templates, but not always– When the “specified node-set” cannot be determined

using a proper X-Path expression, then it is necessary to use xsl:for-each

– E.g. when the “selection” condition is very complex


2-143

More XSLT constructsxsl:for-each

<xsl:template match="/"> <html> <body> <h2>My CD Collection</h2> <table border="1"> <tr bgcolor="#9acd32"> <th>Title</th> <th>Artist</th> </tr> <xsl:for-each select="catalog/cd"> <tr> <td><xsl:value-of select="title"/></td> <td><xsl:value-of select="artist"/></td> </tr> </xsl:for-each> </table> </body> </html></xsl:template> A Semantic Web Primer, 2nd Edition

2-144

XML input document

<catalog><cd> <title>Empire Burlesque</title>

<artist>Bob Dylan</artist><country>USA</country><company>Columbia</company><price>10.90</price><year>1985</year>

</cd><cd> <title>Hide your heart</title>

<artist>Bonnie Tyler</artist><country>UK</country><company>CBS Records</company><price>9.90</price><year>1988</year>

</cd>…</catalog>


2-145

HTML output document


2-146

More XSLT constructsxsl:for-each (alternative solution)<xsl:template match="/">

<html> <body><h2>My CD Collection</h2><table border="1"><tr bgcolor="#9acd32"><th>Title</th><th>Artist</th></tr><xsl:apply-templates select="catalog/cd"/></table></body> </html></xsl:template><xsl:template match="cd"><tr><td><xsl:value-of select="title"/></td><td> <xsl:value-of select="artist"/></td></tr></xsl:template> A Semantic Web Primer, 2nd Edition

2-147

More XSLT constructsxsl:sort Used to sort the output Where to put the Sort Information

– Inside an <xsl:for-each> element– Inside an <xsl:apply-templates> element


2-148

More XSLT constructsxsl:sort<xsl:template match="/"> <html> <body> <h2>My CD Collection</h2> <table border="1"> <tr bgcolor="#9acd32"> <th>Title</th> <th>Artist</th> </tr> <xsl:for-each select="catalog/cd"> <xsl:sort select="artist"/> <tr> <td><xsl:value-of select="title"/></td> <td><xsl:value-of select="artist"/></td> </tr> </xsl:for-each> </table> </body> </html></xsl:template>


2-149

More XSLT constructsxsl:sort (alternative solution)<xsl:template match="/">

<html> <body><h2>My CD Collection</h2><table border="1">

<tr bgcolor="#9acd32"><th>Title</th><th>Artist</th></tr><xsl:apply-templates select="catalog/cd">

<xsl:sort select="artist"/></xsl:apply-templates>

</table></body> </html>

</xsl:template><xsl:template match="cd">

<tr><td><xsl:value-of select="title"/></td><td> <xsl:value-of select="artist"/></td>

</tr></xsl:template> A Semantic Web Primer, 2nd Edition

2-150



2-151

Sorted

More XSLT constructsxsl:if To put a conditional test against the content of the XML

– Usually for optional element / attributes in the XML document – Output something only when the element is present

Syntax<xsl:if test="expression"> ...some output if the expression is true...</xsl:if> Where to Put the <xsl:if> Element

– E.g. inside an <xsl:for-each> element– E.g. inside an <xsl:template> element


2-152

More XSLT constructsxsl:if<xsl:template match="/"> <html> <body> <h2>My CD Collection</h2> <table border="1"> <tr bgcolor="#9acd32"> <th>Title</th> <th>Artist</th> </tr> <xsl:for-each select="catalog/cd"> <xsl:if test="price > 10"> <tr> <td><xsl:value-of select="title"/></td> <td><xsl:value-of select="artist"/></td> </tr> </xsl:if> </xsl:for-each> </table> </body> </html></xsl:template>


2-153

More XSLT constructsxsl:if (alternative solution - 1)

<xsl:template match="/"><html> <body><h2>My CD Collection</h2><table border="1"><tr bgcolor="#9acd32"><th>Title</th><th>Artist</th></tr><xsl:apply-templates select="catalog/cd"/></table></body> </html></xsl:template><xsl:template match="cd"><xsl:if test="price > 10"><tr><td><xsl:value-of select="title"/></td><td> <xsl:value-of select="artist"/> </td> </tr></xsl:if></xsl:template> A Semantic Web Primer, 2nd Edition

2-154

More XSLT constructsxsl:if (alternative solution - 2)

<xsl:template match="/"><html> <body><h2>My CD Collection</h2><table border="1"><tr bgcolor="#9acd32"><th>Title</th><th>Artist</th></tr><xsl:apply-templates select="catalog/cd[price > 10]"/></table></body> </html></xsl:template><xsl:template match="cd"><tr><td><xsl:value-of select="title"/></td><td> <xsl:value-of select="artist"/> </td> </tr></xsl:template> A Semantic Web Primer, 2nd Edition

2-155



2-156

Filtered

More XSLT constructsxsl:choose Expresses multiple conditional tests

– Used in conjunction with <xsl:when>, <xsl:otherwise> Syntax<xsl:choose> <xsl:when test="expression"> ... some output ... </xsl:when>… <xsl:otherwise> ... some output .... </xsl:otherwise></xsl:choose>


2-157

More XSLT constructsxsl:choose<xsl:template match="/">

<html><body><h2>My CD Collection</h2><table border="1"><tr bgcolor="#9acd32"><th>Title</th><th>Artist</th></tr><xsl:apply-templates select="catalog/cd"/></table></body></html>

</xsl:template> A Semantic Web Primer, 2nd Edition

2-158

More XSLT constructsxsl:choose<xsl:template match="cd">

<tr> <td><xsl:value-of select="title"/></td>

<xsl:choose><xsl:when test="price > 10">

<td bgcolor="#ff00ff"><xsl:value-of select="artist"/> </td> </xsl:when> <xsl:when test="price > 9"> <td bgcolor="#cccccc"><xsl:value-of select="artist"/></td> </xsl:when> <xsl:otherwise> <td><xsl:value-of select="artist"/></td> </xsl:otherwise> </xsl:choose>

</tr></xsl:template> A Semantic Web Primer, 2nd Edition

2-159



2-160

Colored

More XSLT constructsxsl:variable

Used to declare a local or global variable. The variable is global if it's declared as a top-

level element, and local if it's declared within a template.

Once you have set a variable's value, you cannot change or modify that value!

You can add a value to a variable by the content of the <xsl:variable> element OR by the select attribute!


2-161

More XSLT constructsxsl:variable - Syntax

<xsl:variable name="name“ select="expression"> </xsl:variable>

Attributes– name: Required. Specifies the name of the variable– select: Optional expression. Defines the value of the

variable


2-162

XML input documentxsl:variable example (1)<catalog>

<cd catid="cd0001"> <title>Empire Burlesque</title><artist>Bob Dylan</artist><country>USA</country><company>Columbia</company><price>10.90</price><year>1985</year>

</cd><cd catid="cd0028"> <title>Hide your heart</title>

<artist>Bonnie Tyler</artist><country>UK</country><company>CBS Records</company><price>9.90</price><year>1988</year>

</cd>…</catalog> A Semantic Web Primer, 2nd Edition

2-163


2-164

XML input documentxsl:variable example (2)

<order orderNo=“o23456" customer="John Smith" date="October 15, 2002"><item itemNo="i123" productID="cd0001" quantity="1"/><item itemNo="i124" productID="cd0028" quantity="3"/>

</order>

XML input documentxsl:variable example (3)

<eshop><catalog><cd catid="…"> … </cd>…</catalog><orders><order> … </order>…</orders>

</eshop>A Semantic Web Primer, 2nd Edition

2-165

More XSLT constructsxsl:variable - example

We want to generate a list of orders, where each list will contain – ID and Date of the order – name of the client– List of items with their name (not id), quantity and

item price Later we could add

– total price per ordered items– Total price of the order


2-166

xsl:variable – exampleHTML Output

2-167

xsl:variable – example (1)

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"><xsl:output method="html" version="1.0" encoding="UTF-8" indent="yes"/><xsl:template match="/"><html><head><title>Order list</title></head><body><h1>List of Orders</h1><xsl:apply-templates select="eshop/orders/order"/></body></html></xsl:template>


2-168


<xsl:template match="order"><h2>Order No. <xsl:value-of select="@orderNo"/> of <xsl:value-of select="@customer"/> </h2><h3>Date: <xsl:value-of select="@date"/> </h3><p>Items:</p><table border="1"><tbody><tr><th>Title</th> <th>Price per item</th> <th>Quantity</th></tr><xsl:apply-templates select="item"/></tbody></table>

</xsl:template>A Semantic Web Primer, 2nd Edition

2-169


<xsl:template match="item"><xsl:variable name="product" select="@productID"/><tr><td><xsl:value-of select="//cd[@catid=$product]/title"/></td><td><xsl:value-of select="//cd[@catid=$product]/price"/></td><td><xsl:value-of select="@quantity"/></td></tr>


2-170

xsl:variable – example (extended)HTML Output


2-171

xsl:variable – extended example (2’)

<xsl:template match="order"><h2>Order No. <xsl:value-of select="@orderNo"/> of <xsl:value-of select="@customer"/> </h2><h3>Date: <xsl:value-of select="@date"/> </h3><p>Items:</p><table border="1"><tbody><tr><th>Title</th> <th>Price per item</th> <th>Quantity</th><th>Total price per item</th></tr><xsl:apply-templates select="item"/><tr><th>TOTAL</th> <th/><th><xsl:value-of select="sum(item/@quantity)"/></th><th/></tr></tbody></table>


2-172

xsl:variable – extended example (3’)

<xsl:template match="item"><xsl:variable name="product" select="@productID"/><tr><td><xsl:value-of select="//cd[@catid=$product]/title"/></td><td><xsl:value-of select="//cd[@catid=$product]/price"/></td><td><xsl:value-of select="@quantity"/></td><td><xsl:value-of select="//cd[@catid=$product]/price * @quantity"/></td></tr>

</xsl:template>A Semantic Web Primer, 2nd Edition

2-173

More XSLT constructsxsl:variable – extended example

It is extremely difficult to calculate the total price for the order


2-174

It requires calling templates recursively with parameters

… but it is doable!

xsl:variable/param – example (extended++)HTML Output

2-175

xsl:param – extended example++ (2’’)

<xsl:template match="order"><h2>Order No. <xsl:value-of select="@orderNo"/> of <xsl:value-of

select="@customer"/></h2><h3>Date: <xsl:value-of select="@date"/></h3><p>Items:</p><table border="1"> <tbody><tr><th>Title</th><th>Price per item</th><th>Quantity</th><th>Total price per

item</th></tr><xsl:apply-templates select="item"/><tr><th>TOTAL</th> <th/><th> <xsl:value-of select="sum(item/@quantity)"/> </th><th> <xsl:call-template name="sum"><xsl:with-param name="nodes" select="item" /></xsl:call-template></th></tr></tbody> </table>

</xsl:template>

2-176 Lectures 2 & 3: Information Sharing on the Web: XML

xsl:param – extended example (4)

<xsl:template name="sum"> <xsl:param name="nodes" /><xsl:param name="sum" select="0" /><xsl:variable name="curr" select="$nodes[1]" /><xsl:variable name="product" select="$curr/@productID"/><xsl:if test="$curr">  <xsl:variable name="runningsum" select="$sum + //cd[@catid=$product]/price * $curr/@quantity" /> <xsl:call-template name="sum"><xsl:with-param name="nodes" select="$nodes[position() > 1]" /><xsl:with-param name="sum" select="$runningsum" /> </xsl:call-template></xsl:if><xsl:if test="not($curr)"> <xsl:value-of select="$sum" /></xsl:if>

</xsl:template>

2-177 Lectures 2 & 3: Information Sharing on the Web: XML

xsl:param

Similar to xsl:variable, but… The value specified on the xsl:param variable

is only a default value for the binding When the template or stylesheet within which

the xsl:param element occurs is invoked, parameters may be passed that are used in place of the default values.


2-178


More details on XSLT & XPath

XSLT Tutorial: http://www.w3schools.com/xsl/ XPath Tutorial:

http://www.w3schools.com/xpath/ XSLT 2.0: http://www.w3.org/TR/xslt20/ XSLT 1.0: http://www.w3.org/TR/xslt XPath 2.0: http://www.w3.org/TR/xpath20/ XPath 1.0: http://www.w3.org/TR/xpath/

2-179

http://www.w3schools.com/xsl/

http://www.w3schools.com/xpath/

http://www.w3.org/TR/xslt20/

http://www.w3.org/TR/xslt

http://www.w3.org/TR/xpath20/

http://www.w3.org/TR/xpath/


XML tools

Altova XML Spy (http://www.altova.com/xml-editor/) <oXygen/> (http://www.oxygenxml.com/) EditiX (http://www.editix.com/) Liquid XML Studio (http://www.liquid-technologies.com/) Free editors

– XML Copy Editor (http://xml-copy-editor.sourceforge.net/)– EditiX Lite (http://free.editix.com/)– XML Notepad 2007 (

http://www.microsoft.com/download/en/details.aspx?id=7973)2-180

http://www.altova.com/xml-editor/

http://www.oxygenxml.com/

http://www.editix.com/

http://www.liquid-technologies.com/

http://xml-copy-editor.sourceforge.net/

http://free.editix.com/

http://www.microsoft.com/download/en/details.aspx?id=7973


2-181

XML Summary

Metalanguage that allows users to define markup – Nesting of tags introduces structure. – The structure of documents can be enforced using

schemas or DTDs. Separates content and structure from formatting De facto standard for the representation and

exchange of structured information on the Web – XML supports machine processing of information.

Supported by query languages


2-182

Points for Discussion in Subsequent Chapters

Tag nesting does not have standard meaning Semantics of XML documents is not accessible

to machines, only to people Collaboration-exchange supported if there is

shared understanding of the vocabulary XML is well-suited for close collaboration, where

community-based vocabularies are used – It is not so well-suited for global communication.

Chapter 2Structured Web Documents in XML

Grigoris AntoniouFrank van Harmelen

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