Web Data Management
XML Data Model
1
Semi-structured Data Model
• A data model, based on graphs, for representing
both regular and irregular data.
• Basic ideas
• Self-describing data. The content comes with its own
description;
– contrast with the relational model, where schema and
content are represented separately.
• Flexible typing. Data may be typed (i.e., “such nodes
are integer values” or “this part of the graph
complies to this description”); often no typing, or a
very flexible one
• Serialized form. The graph representation is
associated to a serialized form, convenient for
exchanges in an heterogeneous environment.
2
Self-describing data
• Starting point: association lists, i.e., records of
label-value pairs.
{name: "Alan", tel: 2157786, email: "agb@abc.com"}
• Natural extension: values may themselves be
other structures:
{name: {first: "Alan", last: "Black"},
tel: 2157786,
email: "agb@abc.com"}
• Further extension: allow duplicate labels.
{name: “Alan’’, tel: 2157786, tel: 2498762 }
3
Tree-based representation
• Data can be graphically represented as trees:
label structure can be captured by tree edges,
and values reside at leaves.
4
Tree-based representation: labels as nodes
• Another choice is to represent both labels and
values as vertices.
• The XML data model adopts this latter
representation.
5
Representation of regular data
• The syntax makes it easy to describe sets of
tuples as in:
{ person: {name: "alan", phone: 3127786, email: "alan@abc.com"},
person: {name: "sara", phone: 2136877, email: "sara@xyz.edu"},
person: {name: "fred", phone: 7786312, email: "fd@ac.uk"} }
– relational data can be represented
– for regular data, the semi-structure representation
is highly redundant.
6
Representation of irregular data
• Many possible variations in the structure: missing
values, duplicates, changes, etc.
{ person: {name: "alan", phone: 3127786, email: "agg@abc.com"},
person: &314
{ name: {first: "Sara", last: "Green" },
phone: 2136877,
email: "sara@math.xyz.edu",
spouse: &443 },
person: &443
{ name: "fred", Phone: 7786312, Height: 183,
spouse: &314 }}
– Nodes can be identified, and referred to by their
identity. Cycles and objects models can be described
as well.
7
XML represents Semistructured Data
• Do not care about the type of the data
• Serialize the data by annotating each data item
explicitly with its description (e.g. name, phone, etc.)
• Such data is called self-describing
• Serialization: convert data into a byte stream that can
be easily transmitted and reconstructed at the receiver
• Self-describing data wastes space but provides
interoperability (required on the web)
• Semistructured data models – XML, JSON (Javascript
Object Notation)
8
XML as a Semi-structured Data
Explained
• Missing attributes:
– <person> <name> John</name>
<phone>1234</phone>
</person>
– <person><name>Joe</name></person>
no phone !
• Repeated attributes
– <person> <name> Mary</name>
<phone>2345</phone>
<phone>3456</phone>
</person>
9
XML as a Semistructured Data
Explained
• Attributes with different types in different objects
– <person> <name> <first> John </first>
<last> Smith </last>
</name>
complex name !
<phone>1234</phone>
</person>
• Nested collections (no 1NF)
• Heterogeneous collections:
– <db> contains both <book>s and <publisher>s
10
XML in brief
• XML is the World-Wide-Web Consortium (W3C)
standard for Web data exchange.
– XML documents can be serialized in a normalized encoding
(typically iso-8859-1, or utf-8), and safely transmitted on
the Internet.
– XML is a generic format, which can be specialized in
“dialects” for specific domain (e.g., XHTML)
– The W3C promotes companion standards: DOM (object
model), XSchema (typing), XPath (path expression), XSLT
(restructuring), Xquery (query language), and many others.
• XML is a simplified version of SGML, a long-term used
language for technical documents.
11
XML documents
• An XML document is a labeled, unranked, ordered tree:
– Labeled means that some annotation, the label, is
attached to each node.
– Unranked means that there is no a priori bound on the
number of children of a node.
– Ordered means that there is an order between the
children of each node.
• XML specifies nothing more than a syntax: no meaning
is attached to the labels.
• A dialect, on the other hand, associates a meaning to
labels (e.g., title in XHTML).
12
XML documents are trees
XML:
person
name
phone
John
3634
row
name
“John”
Sue
6343
Dick
6363
person
row
row
phone name phone
3634 “Sue”
name
6343 “Dick”
phone
6363
<person>
<row> <name>John</name>
<phone> 3634</phone></row>
<row> <name>Sue</name>
<phone> 6343</phone>
<row> <name>Dick</name>
<phone> 6363</phone></row>
</person> Serialized representation
13
XML and Semistructured Data:
Similarities and Differences
<person id=“o123”>
<name> Alan </name>
<age> 42 </age>
<email> ab@com </email>
</person>
<person father=“o123”> …
</person>
father
person
{ person: &o123
{ name: “Alan”,
age: 42,
email: “ab@com” }
}
{ person: { father: &o123 …}
}
person father
name age email
name
Alan
age
42
email
ab@com
Alan
similar on trees, different on graphs
42 ab@com
14
XML describes structured content
• Applications cannot interpret unstructured content:
The book ‘‘Fundations of Databases’’, written by Serge Abiteboul, Rick Hull
and Victor Vianu, published in 1995 by Addison-Wesley
• XML provides a means to structure this content:
<bibliography>
<book>
<title> Foundations of Databases </title>
<author> Abiteboul </author>
<author> Hull </author>
<author> Vianu </author>
<publisher> Addison Wesley </publisher>
<year> 1995 </year> </book>
<book>...</book>
</bibliography>
• Now, an application can access the XML tree, extract some parts,
rename the labels, reorganize the content into another structure,
etc.
15
Applications associate semantics to
XML docs
• Letter document
<letter>
<header>
<author>...</author>
<date>...</date>
<recipient>...</recipient>
<cc>...<cc>
</header>
<body>
<text>...</text>
<signature>...</signature>
</body>
</letter>
16
Applications associate semantics to
XML docs
• Letter style sheet
if letter then ...
if header then ...
if author then ...
if date then ...
if recipient then ...
if cc then ...
if body then ...
if text then ...
if signature then ...
• Some software then produces the actual letter to
mail or email.
17
Serialized and tree-based forms
• The serialized form is a textual, linear representation
of the tree; it complies to a (sometimes complicated)
syntax;
• Tree-based forms implement in a specific context,
object-oriented model, the abstract tree
representation (Document Object Model)
• Typically, an application gets a document in serialized
form, parse it in tree form, and serializes it back at
the end.
18
Serialized and tree-based forms: text
and elements
• The basic components
of an XML document
are element and text.
• Here is an element,
whose content is a text.
• The tree form of the
document, modeled in
DOM: each node has a
type, either Document
or Text.
<elt_name>
Textual content
</elt_name>
19
Serialized and tree-based forms:
nesting elements
• Serialized form: The
• Tree-based form: the
content of an element is
subtree rooted at the
the part between the
corresponding Element
opening and ending
node (in DOM)
tags
<elt1>
Textual content
<elt2>
Another content
</elt2>
</elt1>
20
Serialized and tree-based forms:
attributes
• Serialized form: Attributes
are pairs of name/value
attached to an element
• The content of an attribute
is always atomic text (no
nesting)
• Attributes are not ordered,
and there cannot be two
attributes with the same
name in an element
<elt1 att1=’12’ att2=’fr’>
Textual content
</elt1>
• Tree-based form:
Attributes are special
child nodes of the
Element node (in DOM)
21
Serialized and tree-based forms: the
document root
• Document content must always be enclosed in a single
opening/ending tag, called the element root
• The first line of the serialized form must always be the prologue if
there is one:
<?xml version="1.0"encoding="utf-8"?>
• A document with its
prologue, and element
root
<?xml version="1.0“ encoding="utf-8" ?>
<elt>
Document content.
</elt>
• In the DOM representation,
the prologue appears as a
Document node, called the
root node.
22
Web Data Management with XML
• Publishing
– an XML document can easily be converted to another XML
document (same content, but another structure)
– Web publishing is the process of transforming XML
documents to XHTML.
• Integration
– XML documents from many sources can be transformed in
a common dialect, and constitute a collection.
– Search engines, or portals, provide browsing and searching
services on collections of XML documents.
• Distributed Data Processing
– many softwares can be adapted to consume/produce XMLrepresented data.
– Web services provide remote services for XML data
processing.
23
Web Publishing: restructuring to XHTML
• The Web application produces some XML content,
structured in some application-dependent dialect, on
the server.
• In a second phase, the XML content is transformed in
an XHTML document that can be visualized by
humans.
• The transformation is typically expressed in XSLT, and
can be processed either on the server or on the
client.
24
Web publishing: content +
presentation instructions
• XML content
<bibliography>
<book>
<title> Foundations of Databases </title>
<author> Abiteboul </author>
<author> Hull </author>
<author> Vianu </author>
<publisher> Addison Wesley </publisher>
<year> 1995 </year> </book>
<book>...</book>
</bibliography>
• Document in XHTML
<h1> Bibliography </h1>
<p> <i> Foundations of Databases </i>
Abiteboul, Hull, Vianu
<br/> Addison Wesley, 1995 </p>
<p> <i> Data on the Web </i>
Abiteoul, Buneman, Suciu
<br/> Morgan Kaufmann, 1999 </p>
25
Web publishing
• The same content may be published using
different means:
– Web publishing: XML  XHTML
– WAP (Wireless Application Protocol): XML  WML
26
Web publishing
• Data obtained from a relational database and
from XML files
• XSLT restructures the XML data
• Produces XHTML pages for a browser
27
Web Integration: gluing together
heterogeneous sources
• The portal receives (possibly continuously) XMLstructured content, each source using its own
dialect.
• Each feed provides some content, extracted with
XSLT or XQuery, or any convenient XML processing
tool (e.g., SAX).
28
Data integration
29
Distributed Data Management with
XML
• XML encoding is used to exchange information
between applications.
• A specific dialect, WDSL, is used to describe
Web Services Interfaces.
30
Exploiting XML documents
31
XML dialects
• Dialects define specialized structures, constraints and
vocabularies to construct ad hoc XML contents that can
be used and exchanged in a specific application area
• RSS is an XML dialect for describing content updates
that is heavily used for blog entries, news headlines or
podcasts.
• WML (Wireless Mark-up Language) is used in Web sites
by wireless applications based on the Wireless
Application Protocol (WAP).
• MathML (Mathematical Mark-up Language) is an XML
dialect for describing mathematical notation and
capturing both its structure and content.
32
XML dialects
• Xlink (XML Linking Language) is an XML dialect for
defining hyperlinks between XML documents.
These links are expressed in XML and may be
introduced inside XML documents.
• SVG (Scalable Vector Graphics) is an XML dialect
for describing two-dimensional vector graphics,
both static and animated. With SVG, images may
contain outbound hyperlinks in XLinks.
33
XML dialects – SVG example
<?xml version="1.0" encoding="UTF-8" ?>
<svg xmlns="http://www.w3.org/2000/svg">
<polygon points="0,0 50,0 25,50"
style="stroke:#660000; fill:#cc3333;"/>
Some SVG text
<text x="20" y="40">Some SVG text</text>
</svg>
34
XML standards
• SAX (Simple API for XML) sees an XML document
as a sequence of tokens (its serialization).
• DOM (Document Object Model) is an object
model for representing (HTML and) XML
document independently of the programming
language.
• XPath (XML Path Language) that we will study, is
a language for addressing portions of an XML
document.
35
XML standards
• XQuery (that we will study) is a flexible query
language for extracting information from
collections of XML documents.
• XSLT (Extensible Stylesheet Language
Transformations), that we will study, is a
language for specifying the transformation of
XML documents into other XML documents.
• Web services provide interoperability
between machines based on Web protocols.
36
Processing an XML Document with SAX
and DOM
• A SAX parser transforms an XML document into a
flow of events.
– Examples of events: start/end of a document, the
start/end of an element, a text token, a comment, etc.
• Example: Load data in XML format into a relational
database
1. when document start is received, connect to the database;
2. when a Movie open tag is received, create a new Movie record;
(a) when a text node is received, assign its content to X;
(b) when a Title close tag is received, assign X to Movie.Title;
(c) when a Year close tag is received, assign X to Movie.Year, etc.
3. when a Movie close tag is received, insert the Movie record in the
database (and commit the transaction);
4. when document end is received, close the database connection.
37
Sax
• SAX is a good choice when the content of a
document needs to be examined once
• SAX handler written in Java
– It features methods that handle SAX events:
opening and closing tags; character data
– See next slide
38
import org.xml.sax.*;
import org.xml.sax.helpers.LocatorImpl;
public class SaxHandler implements ContentHandler {
/** Constructor */
public SaxHandler() {
super(); }
/** Handler for the beginning and end of the document */
public void startDocument() throws SAXException {
out.println("Start the parsing of document"); }
public void endDocument() throws SAXException {
out.println("End the parsing of document"); }
/** Opening tag handler */
public void startElement(String nameSpaceURI, String localName, String rawName, Attributes attributes) throws
SAXException {
out.println("Opening tag: " + localName);
// Show the attributes, if any
if (attributes.getLength() > 0) {
System.out.println(" Attributes: ");
for (int index = 0;
index < attributes.getLength(); index++) {
out.println(" - " + attributes.getLocalName(index) + " = " + attributes.getValue(index)); } } }
/** Closing tag handler */
public void endElement(String nameSpaceURI, String localName, String rawName)
throws SAXException {
out.print("Closing tag : " + localName);
out.println(); }
/** Character data handling */
public void characters(char[] ch, int start,
int end) throws SAXException {
out.println("#PCDATA: " + new String(ch, start, end)); }}
39
DOM (Document Object Model)
• A DOM parser transforms an XML document
into a tree and offers an object API for that
tree.
• A partial view of the Class hierarchy of DOM
40
Parsing XML Documents
 A parser checks XML documents for wellformedness or validates it against a
schema
 So, what is parsing? well, in computer
terminology..
‘to analyze or separate (input, for example) into more easily
processed components’
 XML parsers load XML documents and
provide access to it’s contents in the form
of objects
Parsing XML Documents
 A Validating Parser: can use a DTD or schema to verify
that a document is properly constructed
 A Non-Validating Parser: only requires the document
to be well formed; many free parsers on the Web are
non-validating
 Stream-Based Parsers: read through the document
and signal the application every time a new component
appears
 Tree-Based Parsers: read the entire document and give
the application a tree structure corresponding to the
element structure of the document
Parsing XML Documents
 DOM API: language & platform independent
interfaces for accessing & manipulating info. in
XML documents
 Document checked to see if it’s well formed and
valid
 Parser then converts information into a tree of
nodes
 A tree starts at one root node; in DOM terms,
called a document object instance
 You can modify, delete and create leaves and
branches on the tree using interfaces in API
Parsing XML Documents
 Titles.xml; a sample XML document
<?xml version="1.0" encoding="UTF-8"?>
<BookList>
<Book>
<book_id>BU1111</book_id>
<title>Cooking with Computers: Surreptitious Balance Sheets</title>
<type>business</type>
<pub_id>1389</pub_id>
<price>11.95</price>
<advance>5000</advance>
<royalty>10</royalty>
<ytd_sales>3876</ytd_sales>
<notes>Helpful hints on how to use your electronic...</notes>
<pubdate>1991-06-09T05:00:00</pubdate>
</Book>
<Book>
<book_id>BU7832</book_id>
<title>Straight Talk About Computers</title>
<type>business</type>
<pub_id>1389</pub_id>
<price>19.99</price>
<advance>5000</advance>
<royalty>10</royalty>
<ytd_sales>4095</ytd_sales>
<notes>Annotated analysis of what computers can do for you</notes>
<pubdate>1991-06-22T05:00:00</pubdate>
</Book>
</BookList>
Parsing XML
Documents
DOM
 DOM provides interfaces in it’s hierarchy of Node
objects
 Node: an XML Document object created after a
DOM parser reads an XML file
 Inheritance relationship between important
interfaces
DOM
A sample document object tree
Methods of Node Object
Method
Description
hasChildNodes()
finds out if a Node has children, takes no parameters,
returns a Boolean
getNodeType()
returns the type of a particular Node. The type is a constant
integer used to identify different types of Nodes
appendChild()
adds a new child object, which is passed to the method, to
the current Node
cloneNode()
returns a duplicate of the Node
hasAttributes()
returns a Boolean true if the Node has any attributes. This
method was added in DOM Level 2
insertBefore()
takes a new child Node and a reference child Node and
inserts the new child Node before the reference Node
isSupported()
tests whether or not this implementation of the DOM
supports a specific feature. This method was added in DOM
Level 2 and takes a version number and a feature as
parameters
normalize()
puts all text nodes in the full depth of the sub-tree
underneath this Node
removeChild()
removes the specified child
replaceChild()
replaces the specified child with the new child passed
Methods of Node Object
Method
Description
getAttribute()
retrieves the specified attribute.
getAttributeNS()
retrieves the specified attribute by local name and
namespace. This method was added in Level 2.
getAttributeNode()
retrieves an Attr node by name.
getAttributeNodeNS()
retrieves an Attr node by local name and namespace.
This method was added in Level 2.
getElementsByTagName()
returns a NodeList of all child elements of a given tag
name in the order in which they are encountered.
getElementsByTagNameNS()
returns a NodeList of all child elements of a given tag by
local name and namespace in the order in which they
are encountered. This method was added in Level 2.
hasAttribute()
returns a Boolean true if the specified attribute is
present. Returns Boolean false otherwise.
hasAttributeNS()
returns a Boolean true if the specified attribute, by local
name and namespace, is present. Returns Boolean false
otherwise. This method was added in Level 2.
removeAttribute()
removes the specified attribute.
removeAttributeNS()
removes the attribute specified by local name and
namespace. This method was added in Level 2.
Methods of Node Object
Method
Description
removeAttributeNode()
removes the specified Attr node.
setAttribute()
adds a new attribute. If an attribute of the same name
exists, its value is changed to the specified value.
setAttributeNS()
adds a new attribute. If an attribute of the same local name
and namespace exists, its value is changed to the specified
value. This method was added in Level 2.
setAttributeNode()
adds a new Attr node. If an Attr node of the same name
exists, its value is changed to the specified value.
setAttributeNodeNS()
adds a new Attr node. If an Attr node of the same local name
and namespace exists, its value is changed to the specified
value. This method was added in Level 2.
DOM
 Node Interface: NodeList is an iterator for a Nodes list
A DOM NodeList object
 NodeList has only a single method, item(); it returns
the Node at the indexed position passed to the method
SAX
 SAX Parser: stream in documents according to specific
events
 SAX parser doesn't have a default object model
 SAX parser read in a XML document and start events
based on the following:




open or start of elements
closing or end of documents
#PCDATA and CDATA sections
processing instructions, comments & entity declarations
 3 steps to using SAX in your applications:
 creating a custom object model, like a Book class
 creating a SAX parser
 creating a document handler to turn your document
into instances of your custom object model
SAX
 Document Handler: is a listener for the various events
fired by the SAX parser
 Events are fired based on all registered document
event listeners and translated into method calls
A SAX event order
 SAX parser exposes the document as a series of events
that are translated into method calls
DOM Vs SAX
 The following are DOM benefits you should focus
on:




it allows random access to the document
complex searches can be easily implemented
the DTD or schema is available
the DOM is read/write
 The following list contains some of the most
useful benefits of SAX:




it can parse files of any size
it is a fast processing method
you can build your own data structure
you can access only a small subset of info. if desired
Example Parsers
 MSXML: first parser which can perform both SAX
and DOM-based parsing, from Microsoft
 Xerces: available in three languages, from the
Apache Group at http://xml.apache.org
 IBM's XML for Java: http:// www.alphaworks.ibm.com/
formula/xml
 Microstar's Ifred: http://home.pacbell.net/david-b/xml/
 Sun's Java API for XML: http://java.sun.com/products/xml
 Oracle's XML Parser for Java: http://technet.oracle.com/
XPath
• Language for expressing paths in an XML
document
– Navigation: child, descendant, parent, ancestor
– Tests on the nature of the node
– More complex selection predicates
• Means to specify portions of a document
• Basic tool for other XML languages: Xlink,
XSLT, Xquery
56
XQuery
• Query language: “SQL for XML”
• Like SQL: select portions of the data and reconstruct a
result
• Query structure: FLW (pronounced "flower")
FOR $p IN document("bib.xml")//publisher
LET $b := document("bib.xml)//book[publisher = $p]
WHERE count($b) > 100
RETURN $p
•
•
•
•
$p : scans the sequence of publishers
$b : scans the sequence of books for a publisher
WHERE filters out some publishers
RETURN constructs the result
57
XSLT
• Transformation language: “Perl for XML”
• An XSLT style sheet includes a set of
transformation rules: pattern/template
• Pattern: based on XPATH expressions; it specifies
a structural context in the tree
• Template: specifies what should be produced
• Principle: when a pattern is matched in the
source document, the corresponding templates
produces some data
58
XLINK
• XML Linking Language
• Advanced hypertext primitives
• Allows inserting in XML documents descriptions
of links to external Web resources
• Simple mono-directional links ala (HREF) HTML
• Multidirectional links
• XLink relies on XPath for addressing portions of
XML documents
59
XLink
• Generalizes HTML’s href
• XLink links resources, which include documents,
audio, video, database data, etc.
• Many types: simple, extended, locator, arc,
resource, or title
<person xmlns:xlink=“http:///.w3.org/1999/xlink” required attributes
xlink:type=“simple”
xlink:href=http://a.b.c/myhomepage.html
xlink:role="http://www.example.com/studentlist"
xlink:title=“The Homepage”
xlink:show=“replace”
xlink:actuate=“onRequest”>
optional attributes
.....
</person>
60
XLink
• The linking element (i.e., person) that references document2 is called a
local resource.
• The resource referenced is called the remote resource.
• Traversal Path between the local and remote resources is to get from
resource A to resource B by following the defined link.
• Arc: how to traverse a pair of resources, including the direction of
traversal and possibly application behavior information as well.
• Outbound arc: An arc that has a local starting resource and a remote
ending resource
• Inbound arc: If an arc's ending resource is local but its starting resource is
remote
• Third party arc: If neither the starting resource nor the ending resource is
local
61
XLink
• show attribute specifies how to display a resource when it is
loaded and can be
–
–
–
–
“new”, to display in new window
”replace”, to replace current resource with the linked resource
”embed”, replace current element with the linked resource
”other”, XLink-aware application can decide how to display
• actuate attribute specifies when the resource should be
retrieved and can be
–
–
–
–
“onLoad”, retrieve as soon as it is loaded
”onRequest”, retrieve resource by clicking on the link
”other”, XLink-aware applications can decide when to load
”none”, no information when to load the resource
62
XLink
• The use of XLink elements and attributes
requires declaration of the XLink
namespace,
<person xmlns:xlink=“http:///.w3.org/1999/xlink”…..
• href attribute defines the remote resource's
URI
• Role attribute is a URI that references a
resource that describes the link
• Title attribute is a descriptive title for the
link.
63
XLink
• Extended Links
– for linking multiple combinations of local and remote
resources.
– The figure shows two unidirectional links
– With XLink, we can create multidirectional links for
traversing between resources
64
XLink
• Multidirectional links are not limited to just two
resources, but can link any number of resources
• The links need not be traversed sequentially.
65
1 <?xml version = "1.0"?>
2
3 <!-- Fig. 14.8 : booklinks.xml -->
4 <!-- XML document containing extended links -->
5
6 <books xmlns:xlink = "http://www.w3.org/1999/xlink"
7
xlink:type = "extended"
8
xlink:title = "Book Inventory">
9
10 <author xlink:label = "authorDeitel"
11
xlink:type = "locator"
12
xlink:href = "/authors/deitel.xml"
13
xlink:role = "http://deitel.com/xlink/author"
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xlink:title = "Deitel &amp; Associates, Inc.">
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<persons id = "authors">
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<person>Deitel, Harvey</person>
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<person>Deitel, Paul</person>
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</persons>
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</author>
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<publisher xlink:label = "publisherPrenticeHall"
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xlink:type = "locator"
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xlink:href = "/publisher/prenticehall.xml"
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xlink:role = "http://deitel.com/xlink/publisher"
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xlink:title = "Prentice Hall"/>
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<warehouse xlink:label = "warehouseXYZ"
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xlink:type = "locator"
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xlink:href = "/warehouse/xyz.xml"
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xlink:role = "http://deitel.com/xlink/warehouse"
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xlink:title = "X.Y.Z. Books"/>
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Books – root element
A link to the book's authors
with information located at
/authors/deitel.xml
A label's value is used to
link one resource to another
type locator, which
specifies a remote resource
When either Deitel,
Harvey or Deitel, Paul is
selected, the document
deitel.xml will be
retrieved
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Book - a local resource
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<book xlink:label = "JavaBook"
xlink:type = "resource"
xlink:role = "http://deitel.com/xlink/author"
xlink:title = "Textbook on Java">
Java How to Program: Third edition
</book>
<arcElement xlink:type = "arc"
xlink:from = "JavaBook"
xlink:arcrole = "http://deitel.com/xlink/info"
xlink:to = "authorDeitel"
xlink:show = "new"
xlink:actuate = "onRequest"
xlink:title = "About the author"/>
<arcElement xlink:type = "arc"
xlink:from = "JavaBook"
xlink:arcrole = "http://deitel.com/xlink/info"
xlink:to = "publisherPrenticeHall"
xlink:show = "new"
xlink:actuate = "onRequest"
xlink:title = "About the publisher"/>
<arcElement xlink:type = "arc"
xlink:from = "warehouseXYZ"
xlink:arcrole = "http://deitel.com/xlink/info"
xlink:to = "JavaBook"
xlink:show = "new"
xlink:actuate = "onRequest"
xlink:title = "Information about this book"/>
can be linked to (or from) an
author or publisher
create an outbound arc
between the book local
resource and the author
remote resource
arcrole provides information
about the book's author
create an outbound arc
between the book local
resource and the publisher
remote resource
an inbound arc, that has a
starting resource that is
remote, i.e., warehouseXYZ
and an ending resource that is
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local,i.e. JavaBook
XLink
64 <arcElement xlink:type = "arc"
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xlink:from = "publisherPrenticeHall"
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xlink:arcrole = "http://deitel.com/xlink/stock"
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xlink:to = "warehouseXYZ"
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xlink:show = "embed"
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xlink:actuate = "onLoad"
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xlink:title = "Publisher&apos;s inventory"/>
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72 </books>
- a third-party arc, that has starting and ending resources that are both
remote
- Attribute show has value embed, which indicates that the ending
resource should replace the starting resource when the link is traversed
- Attribute actuate has value onLoad, so upon loading the XML
document, the link is traversed
- Because we consider the relationship between the publisher and
warehouse as being different than the previous three arcs, we provide a
different arcrole value for this link
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XPointer
• An extension of XPath
• Usage:
– href=www.a.b.c/document.xml#xpointerExpr
• XPointer can link to
– specific locations (i.e., nodes in an XPath tree),
or even
– ranges of locations, in an XML document.
• XPointer also adds the ability to search XML
documents by using string matching.
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XPointer
• Pointing to a point (=XML element or
character)
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<?xml version = "1.0"?>
<!-- Fig. 14.14 : contacts.xml -->
<!-- contact list document -->
<contacts>
<contact id = "author01">Deitel, Harvey</contact>
<contact id = "author02">Deitel, Paul</contact>
<contact id = "author03">Nieto, Tem</contact>
</contacts>
• Full XPointer form
xlink:href = "/contacts.xml#xpointer(//contact[@id = 'author02'])"
• The name xpointer—called a scheme
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XPointer
• If a document's unique identifier is referenced in an
expression such as
xlink:href = "/contacts.xml#xpointer(id('author01‘))"
• bare-name XPointer address – simplified expression
xlink:href = "/contacts.xml#author01"
• Child sequence: e.g. #xpointer( /1/3/2/5),
#xpointer( /bib/book[3])
• Pointing to a range: e.g. #xpointer(id(3652 to 44))
• Most interesting examples use XPath
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