XML and XPath. Web Services: XML+XPath2 EXtensible Markup Language (XML) a W3C standard to...

XML and XPath

Web Services: XML+XPath 2

EXtensible Markup Language (XML)

a W3C standard to complement HTML A markup language much like HTML origins: structured text SGML motivation:

HTML describes presentationXML describes content

HTML XML SGML

http://www.w3.org/TR/2000/REC-xml-20001006 (version 2, 10/2000)


HTML Describes the Presentation


HTML Describes the Presentation

<h1>Bibliography</h1><p><i>Foundations of Databases</i> Abiteboul, Hull, Vianu <br>Addison Wesley, 1995<p><i>Data on the Web</i> Abiteoul, Buneman, Suciu <br>Morgan Kaufmann, 1999


XML Describes the Contents

<bibliography><book><title> Foundations… </title>

<author> Abiteboul </author><author> Hull </author><author> Vianu </author><publisher> Addison Wesley </publisher><year> 1995 </year>

</book>…

</bibliography>


More on XML

XML was designed to describe data contents XML tags are not predefined in XML.

You must “invent” your own tags XML uses a Document Type Definition (DTD) or

an XML Schema to describe the data XML with a DTD or XML Schema is designed

to be self-descriptive


Applications and Impact of XML

Data can be stored outside HTML Data can be exchanged between incompatible

systems Financial information can be exchanged over the

Internet Plain text files can be used to share data Data is available to more users Used to create new languages

WML, WSDL, BPEL, ……


Benefits of Using XML

XML is structured XML documents are easily committed to a

persistence layer XML is platform independent, textual information XML is an open standard XML is language independent DOM and SAX are open, language-independent

set of interfaces XML is web enabled XML is totally extensible XML supports shareable structure (using DTDs) XML enables interoperability


XML Terminology

tags: book, title, author, … start tag: <book>, end tag: </book> elements: <book>…</book>,

<author>…</author> elements are nested empty element: <red></red> abbrv. <red/> an XML document: single root element

well formed XML document: if it has matching tags


Attributes are Alternative Ways to Represent Data

<book price = “55” currency = “USD”> <title>Foundations of Databases</title> <author>Abiteboul</author> … <year> 1995 </year></book>


CDATA Section

Syntax: <![CDATA[ .....any text here...]]>

<script><![CDATA[function matchwo (a, b){if (a < b && a < 0) then

{return 1}else{return 0}

}]]></script>


Entity References

Syntax: &entityname; Example:

<element> this is less than < </element> Some entities:

< <

> >

& &

' ‘

" “

&Unicode

char


Processing Instructions

Syntax: <?target argument?> Example:

<product><name> Alarm Clock </name> <?ringBell 20?> <price>19.99</price></product>

What do they mean ?


XML Comments

Syntax 

Yes, they are part of the data model !!!


Name Conflicts

Solution: prefix

<table><tr><td>Apples</td><td>Bananas</td></tr>

</table>

<table><name>African Coffee

Table</name>

<width>80</width><length>120</length>

</table>

<h:table><h:tr><h:td>Apples</

h:td><h:td>Bananas</

h:td></h:tr>

</h:table>

<f:table><f:name>African Coffee

Table</f:name><f:width>80</f:width><f:length>120</f:length>

</f:table>


<tag xmlns:mystyle = “http: // …”>…<mystyle:title> … </mystyle:title><mystyle:number> …

</tag>

XML Namespaces

syntactic: <number> , <isbn:number> semantic: provide URL for schema


XML Namespaces

http://www.w3.org/TR/REC-xml-names (1/99) name ::= [prefix:]localpart

<book xmlns:isbn“www.isbn-org.org/def”> <title> … </title> <number> 15 </number> <isbn:number> … </isbn:number></book>


http://www.w3.org/TR/xpath (11/99) Building block for other W3C standards:

XSL Transformations (XSLT) XML Link (XLink)XML Pointer (XPointer)XML Query

Was originally part of XSL

XPath


Example for XPath Queries<bib>

<book> <publisher> Addison-Wesley </publisher> <author> Serge Abiteboul </author> <author> <first-name> Rick </first-name> <last-name> Hull </last-name></author> <author> Victor Vianu </author> <title> Foundations of Databases </title> <year> 1995 </year>

</book><book price=“55”>

<publisher> Freeman </publisher> <author> Jeffrey D. Ullman </author> <title> Principles of Database and Knowledge Base Systems </title> <year> 1998 </year>

</book></bib>


Data Model for XPath

bib

book book

publisher author . . . .

Addison-Wesley Serge Abiteboul

The root

The root elementProcessing instruction

Comment


Simple Expressions

/bib/book/year

Result: <year> 1995 </year> <year> 1998 </year>

/bib/paper/year

Result: empty (there were no papers)


Restricted Kleene Closure

//author

Result: <author> Serge Abiteboul </author> <author><first-name> Rick </first-name>

<last-name> Hull </last-name> </author> <author> Victor Vianu </author> <author> Jeffrey D. Ullman </author>

/bib//first-name

Result: <first-name> Rick </first-name>


Functions

/bib/book/author/text()

Result: Serge Abiteboul Victor Vianu Jeffrey D. UllmanRick Hull doesn’t appear because he has firstname,

lastname

Functions in XPath:text() = matches the text valuenode() = matches any node (= * or @* or

text())name() = returns the name of the current tag


Wildcard

//author/

Result: <first-name> Rick </first-name>

<last-name> Hull </last-name>

Matches any element


Attribute Nodes

/bib/book/@price

Result: “55”

@price means that price is has to be an attribute


Qualifiers

/bib/book/author[first-name]

Result: <author><first-name> Rick </first-name> <last-name> Hull </last-name> </author>

/bib/book/author[firstname][address[//zip][city]]/lastname

Result: <lastname> … </lastname> <lastname> … </lastname>


More Qualifiers

/bib/book[@price < “60”]

/bib/book[author/@age < “25”]

/bib/book[author/text()]


XPath Summary

bib matches a bib element matches any element/ matches the root element/bib matches a bib element under

rootbib/paper matches a paper in bibbib//paper matches a paper in bib, at any

depth//paper matches a paper at any depthpaper|book matches a paper or a book@price matches a price attributebib/book/@price matches price attribute in book,

in bibbib/book[@price<“55”]/author/lastname

matches…


XPath: More Details

An XPath expression, p, establishes a relation between:A context node, andA node in the answer set

In other words, p denotes a function:S[p] : Nodes -> {Nodes}

Examples:author/firstname. = self.. = parentpart///subpart/../name =

part//[subpart]/name


The Root

<bib><paper>1</paper><paper>2</paper></bib>

bib is the document element The root is above bib

/bib = returns the document element / = returns the root

Why? Because we may have comments before and after <bib>; they become siblings of <bib>

This is advanced xmlogy


XPath Navigation We can navigate along 13 axes:

ancestorancestor-or-selfattributechilddescendantdescendant-or-selffollowingfollowing-siblingnamespaceparentprecedingpreceding-siblingself

We’ve only seen these, so far


Examples

Examples:child::author/child::lastname =

author/lastnamechild::author/descendant::zip = author//zipchild::author/parent:: = author/..child::author/attribute::age = author/@age

What does this mean ?paper/publisher/parent::/author/bib//address[ancestor::book]/bib//author/ancestor:://zip


More Examples

name() = the name of the current node/bib//[name()=book] same as /bib//book

What does this mean ?/bib//[ancestor::[name()!=book]]

Navigation axis gives us strictly more power !

Date post:	27-Dec-2015
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XML and XPath. Web Services: XML+XPath2 EXtensible Markup Language (XML) a W3C standard to...

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