Sw Chapter - XML - V2

8/2/2019 Sw Chapter - XML - V2

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eXtensible Markup Language (XML)


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Introduction to the Semantic WebXML2

An HTML Example

Nonmonotonic Reasoning: Context-

Dependent Reasoningby V. Marek and

M. Truszczynski

Springer 1993
ISBN 0387976892


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Introduction to the Semantic Web3

The Same Example in XML

Nonmonotonic Reasoning: Context-Dependent Reasoning

V. Marek

M. Truszczynski

Springer

1993

0387976892

XML


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HTML versus XML: Similarities

Both use tags (e.g. and )

Tags may be nested (tags within tags) Human users can read and interpret both

HTML and XML representations quite easily

But how about machines?

XML


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Problems with Automated

Interpretation of HTML Documents

An intelligent agent trying to retrieve the namesof the authors of the book

Authors names could appear immediatelyafter the titleor immediately after the word by

Are there two authors Or just one, called V.

Marek and M. Truszczynski?

XML


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HTML vs XML: Structural Information

HTML documents do not contain structuralinformation: pieces of the document and their

relationships.

XML more easily accessible to machines because

Every piece of information is described.

Relations are also defined through the nesting structure.

E.g., the tags appear within the tags, sothey describe properties of the particular book.

XML


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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 four digits

XML


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HTML vs XML: Formatting

The HTML representation provides more

than the XML representation: The formatting of the document is also described

But a weakness of HTML

he 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 differentways

XML


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HTML vs XML: Another Example

In HTMLRelationship force-mass

F = M a In XML

Relationship force-mass

F M a

XML


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HTML vs XML: Different Use of Tags

Both previous HTML docs use same tags

While XML use completely different tags

HTML tags define display: color, lists

XML tags not fixed: user definable tags

XML meta markup language: language fordefining markups

XML


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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)

XML


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Lecture Outline

1. Introduction

2. Detailed Description of XML3. Structuring

a) DTDs

b) XML Schema

4. Namespaces5. Navigating XML documents: XPath

6. Transformations: XSLT

XML


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Prolog of an XML Document

The prolog consists of

an XML declaration and an optional reference to external structuring

documents

XML


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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

Shahid Waseem

XML


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XML Elements (2)

Tag names can be chosen almost freely.

The first character must be a letter, anunderscore, or a colon

No name may begin with the string xml inany combination of cases

E.g. Xml,xML

XML


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Content of XML Elements

Content may be text, or other elements, or nothing

Shahid Waseem +92 7 3875 507

If there is no content, then the element is calledempty; it is abbreviated as follows: for

XML


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XML Attributes

An empty element is not necessarily

meaningless It may have some properties in terms of attributes

An attribute is a name-value pair inside theopening tag of an element


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XML Attributes: An Example


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The Same Example without Attributes

23456

Mrs AkramOctober 15, 2011

a5281

c8173

XML


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XML Elements vs Attributes

Attributes can be replaced by elements

When to use elements and when attributes isa matter of taste

But attributes cannot be nested

XML


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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 Lee Hong

Attributes within an element have unique names

Element and tag names must be permissible

XML


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The Tree Model of XML Documents:

An Example

Semantic Web Lecture

AoA, when is the next Semantic Web lecture and whichroom? Is there any assignment pending?

XML


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The Tree Model of XML Documents:

An Example (2)

XML


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The Tree Model of XML Docs

The tree representation of an XML documentis 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 order of elements is important

but the order of attributes is not important

XML


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Lecture Outline

1. Introduction

2.

Detailed Description of XML3. Structuringa) DTDs

b) XML Schema



XML


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Structuring XML Documents

Define all the element and attribute namesthat 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

XML


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Structuring XML Dcuments (2)

An XML document is valid if

it is well-formed respects the structuring information it uses

There are two ways of defining the structureof XML documents:

DTDs (the older and more restricted way) XML Schema (offers extended possibilities)

XML


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DTD: Element Type Definition

David Billington

+61 7 3875 507

DTD for above element (and all lecturer elements)?

XML


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The Meaning of the DTD

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

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

A name element and a phone element may haveany content

In DTDs, #PCDATA is the only atomic type forelements

XML


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DTD: Disjunction in Element Type

Definitions

We express that a lecturer element containseithera name element ora phone element asfollows:

A lecturer element contains a name element

and a phone element in any order.

XML


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Example of an XML Element

XML


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The Corresponding DTD

customer CDATA #REQUIREDdate CDATA #REQUIRED>

quantity CDATA #REQUIREDcomments CDATA #IMPLIED>

XML


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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

XML


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Comments on the DTD (2)

In addition to defining elements, we defineattributes

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

XML


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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 attributecarrying 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.

XML


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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

#FIXED "value"

Every element must have this attribute

"value"

This specifies the default value for the attribute

XML


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Referencing with IDREF and IDREFS

mother IDREF#IMPLIED

father IDREF#IMPLIED

children IDREFSXML


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An XML Document Respecting the DTD

Kalsoom Yonus

Muhammad Ali

Khalida Yonus

Muhammad Yonus

XML


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Introduction to the Semantic Web

XML Entities

An XML entity can play the role as

a placeholder for repeatable characters

a section of external data

a part of a declaration for elements

We can use the entity reference &thisyearinstead ofthe value " 2007 "

39 XML


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A DTD for an Email Element

#IMPLIED

address CDATA

#REQUIRED>

address CDATA#REQUIRED>XML


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A DTD for an Email Element (2)

CDATA #IMPLIEDaddress CDATA#REQUIRED>

encoding (mime|binhex)

"mime" fileXML


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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

XML


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Interesting Parts of the DTD (2)

A body element contains

a text element

possibly followed by a number of attachmentelements

The encoding attribute of an attachment

element must have either the value mimeor binhex

mime is the default value

XML


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Lecture Outline

1. Introduction

2. Detailed Description of XML

3. Structuringa) DTDs

b) XML Schema



XML


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XML Schema

Significantly richer language for defining thestructure of XML documents

Its syntax is based on XML itself not necessary to write separate tools

Reuse and refinement of schemas

Expand or delete already existent schemas Sophisticated set of data types, compared to

DTDs (which only supports strings)

XML


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XML Schema (2)

An XML schema is an element with an opening taglike

Structure of schema elements

Element and attribute types using data types


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Element Types

Cardinality constraints:

minOccurs="x" (default value 1) maxOccurs="x" (default value 1)

Generalizations of *,?,+ offered by DTDs


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Attribute Types

< attribute name="speaks" type="Language"

use="default" value="en"/>

Existence: use="x", where x may be

optional or required Default value: use="x" value="...", where x

may be default or fixed


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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 orattributes

complex data types, which can use elements or/andattributes


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Data Types (2)

Complex data types are defined from already existing datatypes by defining some attributes (if any) and using indicators:

Order indicators sequence, a sequence of existing data type elements (order is

important)

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

choice, a collection of elements, of which one will be chosen

Occurrence Indicators maxOccurs

minOccurs


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An Example

XML51


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A Data Type Example


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Data Type Extension

Already existing data types can be extended by new elementsor attributes. Example:


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Resulting Data Type


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Data Type Extension (2)

A hierarchical relationship exists between theoriginal and the extended type

Instances of the extended type are also instancesof the original type

They may contain additional information, butneither less information, nor information of thewrong type


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Data Type Restriction

An existing data type may be restricted by addingconstraints on certain values

Restriction is not the opposite from extension Restriction is not achieved by deleting elements or attributes

The following hierarchical relationship still holds:

Instances of the restricted type are also instances of the

original type They satisfy at least the constraints of the original type


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Mixed Content Example

Dear Mr.John Smith.

Your order 1032

will be shipped on 2001-07-13.

XML57


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Example of Data Type Restriction


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Restriction of Simple Data Types


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Data Type Restriction: Enumeration


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XML Schema: The Email Example


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XML Schema: The Email Example (2)


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XML Schema: The Email Example (3)

Similar for bodyType


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Lecture Outline

1. Introduction



b) XML Schema




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Namespaces

An XML document may use more than oneDTD or schema

Since each structuring document wasdeveloped independently, name clashes mayappear

The solution is to use a different prefix foreach DTD or schema

prefix:name


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An Example


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Namespace Declarations

Namespaces are declared within an elementand can be used in that element and any ofits 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


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Lecture Outline

1. Introduction



b) XML Schema




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Addressing and Querying XML

Documents

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

The central concept of XML query languagesis a path expression


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XPath

XPath is core for XML query languages

Language for addressing parts of an XMLdocument.

It operates on the tree data model of XML

It specifies how a node or a set of nodes, in the

tree representation of the XML document can bereached

It has a non-XML syntax


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Tree Structure of an XML Document

The root node

Element nodes

Text nodes

Attribute nodes

Comment nodes

Processing-instruction nodes

Namespace nodes

XML71


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Tree Structure of an XML Document (II)

XML72


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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 onelevel above the root element of the document)

Relative to a context node


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An XML Example


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Tree Representation

Anything

missing ??


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Examples of Path Expressions in

XPath

Address all author elements

/library/author

Addresses all author elements that arechildren of the library element node, whichresides immediately below the root.

EditiX also shows the attributes of elements

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


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General Form of Path Expressions

A path expression consists of one or more steps, each steprepresents an individual location path and is separated by a

/ (slash)

An absolute location path:/step/step/...

A relative location path:step/step/...

Each step is evaluated against the nodes in the current node-set


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XPath (2)

Address all author elements anywhere inthe document

//author

Here // says that we should consider allelements in the document and check

whether they are of type author


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XPath (3)

Address the location attribute nodes withinlibrary element nodes

/library/@location

The symbol @ is used to denote attributenodes


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XPath (4)

Address all title attribute nodes within bookelements anywhere in the document, which

have the value Artificial Intelligence

//book/@title= "Artificial Intelligence

Addressed node is an attribute, therefore theresult is a Boolean value


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XPath (5)

Address all books with title Artificial Intelligence

//book[@title="Artificial Intelligence"]

Test within square brackets: a predicate (or filterexpression)

It restricts the set of addressed nodes.

Query 4 addresses book elements, the title of whichsatisfies a certain condition.


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Tree Representation of Query 4


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Tree Representation of Query 5


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Examples of Filter Expressions

(Predicates)

Address the first author element node in the XML document

//author[1]

Address the title of last book element within the first author elementnode in the document

//author[1]/book[last()]/@title

Address the title of all book elements having price greater than 30

//book[@price>30]/@title

Address all book element nodes without a title attribute

//book[not @title]


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Few more Queries

Selecting several paths: gives the name of all authors and thetitles of their books

//author/@name | //book/@title

Returns the attribute values of title and price of all bookelements

//book/@title | //book/@price

Path expression with wildcard: selects all the elements in thedocument

//*


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Xpath Usage XPath is a major element in W3C's XSLT standard - and

XQuery and XPointer are both built on XPath expressions

XML86


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XPath Summary

Xpath is for finding information in an XML document bynavigating through elements and attributes in the XML

document.

Its adoption has been widespread within other XMLstandards.

XML87


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Lecture Outline

1. Introduction



b) XML Schema

4.

Namespaces5. Navigating XML documents: XPath



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Displaying XML Documents

Grigoris Antoniou

University of [email protected]

may be displayed in different ways:

Grigoris Antoniou Grigoris AntoniouUniversity of Bremen University of Bremen

[email protected] [email protected]


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Style Sheets

Style sheets can be written in variouslanguages

E.g. CSS2 (cascading style sheets level 2)

XSL (extensible stylesheet language)

XSL includes

a transformation language (XSLT) a formatting language (XSL-FO)

Both are XML applications


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Styling a Document

XML91

Practical Examples of Style Sheets in Use


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XSL Transformations (XSLT)

XSLT specifies rules with which an input XMLdocument 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


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XSLT (2)

Move data and metadata from one XMLrepresentation to another

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

XSLT can be used for machine processing of contentwithout any regard to displaying the information for

people to read. In the following we use XSLT only to

transform/display XML documents in HTML


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XSLT Transformation into HTML

Grigoris Antoniou

University of Bremen

[email protected]


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Introduction to the Semantic WebXML

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Style Sheet Output

An author

Grigoris Antoniou

University of Bremen

[email protected]


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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 outputdocument It places some content into the template


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A Template

An author

...

...

...


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Auxiliary Templates

We have an XML document with details ofseveral authors

It is a waste of effort to treat each authorelement separately

In such cases, a special template is defined for

author elements, which is used by the maintemplate


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Example of an Auxiliary Template

Grigoris Antoniou

University of [email protected]

David Billington

Griffith [email protected]

XML


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Example of an Auxiliary Template (2)

Authors

XML


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Example of an Auxiliary Template (3)

Affiliation:

Email:

XML


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Multiple Authors Output

Authors

Grigoris AntoniouAffiliation: University of Bremen
Email: [email protected]

David BillingtonAffiliation: Griffith University

Email: [email protected]

XML


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Explanation of the Example

xsl:apply-templates element causes all children ofthe 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. theauthors 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 thetemplate for the author elements to be applied to all authorchildren of the authors element

XML


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Explanation of the Example (2)

It is good practice to define a template foreach element type in the document

Even if no specific processing is applied to certainelements, the xsl:apply-templates elementshould be used

E.g. authors

In this way, we work from the root to theleaves of the tree, and all templates areapplied

XML


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Processing XML Attributes

Suppose we wish to transform to itself the element:

Wrong solution:

XML


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Processing XML Attributes (2)

Not well-formed because tags are notallowed within the values of attributes

We wish to add attribute values into template

XML


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Transforming an XML Document toAnother

XML


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Transforming an XML Document toAnother (2)

XML


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Transforming an XML Document toAnother (3)

XML


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Show Another Example

XML

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XML Chapters Summary

XML is a metalanguage that allows users to define markup.

Nesting of tags introduces structure. The structure of documentscan be enforced using schemas or DTDs.

XML separates content and structure from formatting.

XML is the de facto standard for the representation and exchangeof structured information on the Web.

XML supports the exchange of structured information across

different applications through markup, structure, andtransformations.

XML is supported by query languages

XML

S


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Points for Discussion in SubsequentChapters

The nesting of tags does not have standard meaning

The semantics of XML documents is not accessible tomachines, only to people

Collaboration and exchange are supported if there is underlyingshared understanding of the vocabulary

XML is well-suited for close collaboration, where domain- orcommunity-based vocabularies are used

It is not so well-suited for global communication.

XML


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