Dickson K'W' Chiu

1
CSIT600b XML Programming Xlink, XPointer, XQuery

• Dickson K.W. Chiu
• PhD, SMIEEE
• Thanks to Prof. Francis Lau (HKU)

2
Problem of HTML Linking

• Growth of the Web attributed to the ability of
  an HTML page to (hyper)link to another page
• lta hrefhttp//www.ust.hk/gt
• Limitations
• Involves only two resources
• One-way (the back button is a browsers thing)
• The source must be HTML
• The whole document is loaded even if your link
  points to a section
• ltimg srchttp//www.dot.comjpg5gt
• The target page must contain explicit section
  markups

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XML Linking

• XLink to link resources, XPointer to point to
  fragments of XML documents
• Tutorial http//zvon.org/xxl/xlink/OutputExamples
  /xlinksimple_intro.html
• W3C Recommendation 1.0, Jun 2001
• Example
• One-way and two-way
• One link, involving 4 resources
• Information about this link can be in a
  completely separated file

A.html
B.xml
C.html
D.xml
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XLink

• Example
• ltname xmlnshttp//dot.com/name
  xmlnsxlinkhttp//www.w3.org/1999/xlinkgtltfirst
  gtTommylt/firstgtltlast xlinktypesimple
  xlinkhrefhttp//dot.com/tleegtLeelt/lastgtlt/nam
  egt
• XLinks global attributes
• type, href, label, role, arcrole, title, show,
  actuate, from, to
• Can be added to elements that are in any
  arbitrary namespace

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The type Attribute

• Mandatory, to define a link
• Six types (the first 2 are link types, the others
  are for providing more info about a link)
• Simple
• Extended
• Title to provide human-readable titles
• Locator to indicate remote resources
• Resource to define local resources involved
• Arc to indicate the rules for traversing

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title, label, and role

• title and label are used to label the functions
  of various resources in the link
• label is machine-readable, title human-readable
• ltlast xlinklabellastName
  xlinktypesimple xlinkhrefpeople.xml
  xlinktitleLast name xlinkrolehttp//d
  ot.com/namesgtLast namelt/lastgt
• role is a URI that references a resource that
  describes the meaning of the link

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actuate and show

• The actuate attribute specifies when the resource
  should be retrieved
• onLoad (default)
• onRequest
• The show attribute specifies how to display the
  resource when it is loaded
• new new window
• replace current window
• embed (default) insert here like lthtmlimg
  src... gt
• The application can provide other values, using
  QNames, but the application should know how to
  handle them
• xlinkactuateopEveryFiveMinutes

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from and to

• A link can involve multiple resources, and be
  traversed in multiple directions
• ltelement xlinkfrommyappfirst
  xlinktomyapplast xlinkshowreplace
  xlinkactuateonRequestgt Click for
  lastlt/elementgt
• When clicked, the first link resource will be
  replaced by the last link resource

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Simple Links

• Like HTML links 2 resources
• ltelement xlinktypesimple xlinkhref
  xlinkshownewgtClick me!lt/elementgt
• Simple links are inline links because the
  links own content (i.e., Click me) is the
  resource

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Extended Links

• An element to describe links among sets of
  document(s), classified by labels
• Extended links can be out of line
• You could create a link from A to B even though
  you have no access rights for A and B
• Locator-type to indicate remote resources, and
  arc-type to specify rules for traversals
• Attribute arcrole is used to describe the
  relationship between the resources

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Extended Links Example
ltextendedlink xlinktype"extended"gt ltloc
xlinktype"locator" xlinkhref"..."
xlinklabel"parent" xlinktitle"p1" /gt ltloc
xlinktype"locator" xlinkhref"..."
xlinklabel"parent" xlinktitle"p2" /gt ltloc
xlinktype"locator" xlinkhref"..."
xlinklabel"child" xlinktitle"c1" /gt ltloc
xlinktype"locator" xlinkhref"..."
xlinklabel"child" xlinktitle"c2" /gt ltloc
xlinktype"locator" xlinkhref"..."
xlinklabel"child" xlinktitle"c3" /gt ...
lt!-- arc-type elements would go here
--gt lt/extendedlinkgt

• ltgo xlinktypepararc" xlinkfrom"parent"
  xlinkto"child" /gt
• links from parents to children (6 links total)
• ltgo xlinktypechildarc" xlinkto"child" /gt
• links from parents to children and children to
  children (15 links total)
• Upon clicking on a item, say p1, the rendering
  software (need not be a browser) displays a list
  of linked items for the user to choose.

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XPointer

• Provides a method for pointing to pieces of an
  XML document
• W3C Recommendation 1.0, Mar 2003
• Built on XPath, with the following extensions
• Locate information by string matching
• Can be appended to URIs
• Address not only entire nodes, but pieces of
  nodes in an XML document
• Finer than nodes
• A location is any node type allowed in Xpath
• A point is any spot in the XML document
• A range is defined by two points

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XInclude and XBase

• XML 1.0 / 1.1 does not have includes
• XInclude uses XPointer to include portions of
  another document
• The parse attribute has value xml (parsed) or
  text (unparsed)
• XBase is for providing base URIs for relative
  links in a document

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XQuery

• XQuery is a language for querying XML data
• XQuery is built on XPath expressions
• XQuery for XML is like SQL for databases
• http//www.w3c.org/XML/Query
• Updated release of the XQuery 1.0, XPath 2.0
  W3C Oct 2004
• XQuery is not an XML language - a version in XML
  syntax is called XQueryX.
• Tutorial booklet download from DataDirect
  http//www.datadirect.com/news/whatsnew/xquerybook
  /index.ssp
• Brief tutorials
• http//www.brics.dk/amoeller/XML/index.html
• http//www.w3schools.com/xquery/default.asp

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XQuery W3C Requirements

• at least one XML syntax (at least one
  human-readable syntax)
• must be declarative
• must be protocol independent
• must respect XML data model
• must be namespace aware
• must coordinate with XML Schema
• must work even if schemas are unavailable
• must support simple and complex datatypes
• must support universal and existential
  quantifiers
• must support operations on hierarchy and sequence
  of document structures
• must combine information from multiple documents
• must support aggregation
• must be able to transform and to create XML
  structures
• must be able to traverse ID references

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XQuery Basic Concepts

• Expressions are evaluated relative to a context
• namespaces
• variables
• functions
• date and time
• context item (current node or atomic value)
• context position (in the sequence being
  processed)
• context size (of the sequence being processed)

• A query in XQuery is an expression that
• reads a sequence of XML fragments or atomic
  values
• returns a sequence of XML fragments or atomic
  values
• The principal forms of XQuery expressions are
• path expressions (same as XPath)
• element constructors
• FLWOR ("flower") expressions
• list expressions
• conditional expressions
• quantified expressions
• datatype expressions

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XQuery Path Expressions

• The simplest kind of query is just an XPath 2.0
  expression.
• Example
• document("recipes.xml")//recipetitle"Ricotta
  Pie"//ingredient_at_amount
• Some XQuery specific extension of XPath
• location steps may follow a new IDREF axis
• an arbitrary XQuery expression may be used as a
  location step

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XPath 2.0 Major Changes from 1.0

• now using XML Schema primitive types instead of
  just node-set, boolean, number, string
• new type operators cast, treat, assert, instance
  of
• now using sequences instead of node-sets
• also allow non-node types
• new operators for, if, some, every, intersect,
  except
• many new functions
• regular expression match/replace/tokenize
• date formats
• ...

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XQuery FLWOR expressions

• The main engine of XQuery is FLWOR expression
• For-Let-Where-Order-Return
• pronounced "flower"
• generalizes SELECT-FROM-HAVING-WHERE from SQL
• Example
• for d in document("depts.xml")//deptno
• let e document("emps.xml")//employeedeptno
  d
• where count(e) gt 10
• order by avg(e/salary) descending
• return
• ltbig-deptgt d,
• ltheadcountgtcount(e)lt/headcountgt,
  ltavgsalgtavg(e/salary)lt/avgsalgt
• lt/big-deptgt

For loop Let binding once
Only 1 where
list expression
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XQuery FLWOR Join Example

• Sufficient to compute joins of documents
  example
• for p IN document("www.irs.gov/taxpayers.xml")//p
  erson
• for n IN document("neighbors.xml")//neighborssn
  p/ssn
• return
• ltpersongt
• ltssngt p/ssn lt/ssngt
• n/name
• ltincomegt p/income lt/incomegt
• lt/persongt

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XQuery List Expression

• XQuery expressions manipulate lists of values,
  for which many operators are supported
• constant lists (7, 9, ltthirteen/gt)
• integer ranges i to j
• XPath expressions, like all named children of the
  context node name
• concatenation ,
• set operators (or union), intersect, except
• functions remove, index-of, count, avg, max,
  min, sum, distinct-values ...
• When lists are viewed as sets
• XML nodes are compared on node identity
• duplicates are removed
• the order is preserved

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XQuery Qualified Expression

• some-in-satisfies
• for b in document("bib.xml")//book
• where some p in b//paragraph satisfies
• (contains(p,"sailing") AND contains(p,"windsur
  fing"))
• return b/title
• every-in-satisfies
• for b in document("bib.xml")//book
• where every p in b//paragraph satisfies
• contains(p,"sailing")
• return b/title

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XQuery Datatype Expression

• XQuery supports all datatypes from XML Schema,
  both primitive and complex types.
• Constant values can be written
• as literals (like string, integer, float)
• as constructor functions (true(),
  date("2001-06-07"))
• as explicit casts (cast as xsdpositiveInteger(47)
  )
• Arbitrary XML Schema documents can be imported
  into a query.
• An instance of operator allows runtime validation
  of any value relative to a datatype or a schema.
• A typeswitch operator allows branching based on
  types.

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XQuery - Other Features

• Hundreds of built-in operators and functions -
  contains anything you might think of
• Computed element and attribute names - allow more
  flexible queries
• User-defined functions - allow general-purpose
  computations
• Views and updates are still under development

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Status (updated)

• Software? Starting to come up
• http//www.w3.org/XML/Linking
• XLink 1.0 and Xbase 1.0 - June 27, 2001
• XPointer 1.0 - 25 March 2003
• XInclude 1.0 W3C Working Draft 10 Nov 2003
• Updated release of the XQuery 1.0, XPath 2.0, Oct
  2004

Working draft ? Last call working draft
?Candidate recommendation ?Proposed
recommendation ? Recommendation