XML, XML Schema, Xpath and Xquery

1
XML, XML Schema, Xpath and Xquery
Slides collated from various sources, many from
Dan Suciu at Univ. of Washington
2
XML

• W3C standard to complement HTML
• origins structured text SGML
• motivation
• HTML describes presentation
• XML describes content
• http//www.w3.org/TR/2000/REC-xml-20001006
  (version 2, 10/2000)

3
From HTML to XML
HTML describes the presentation
4
HTML

• lth1gt Bibliography lt/h1gt
• ltpgt ltigt Foundations of Databases lt/igt
• Abiteboul, Hull, Vianu
• ltbrgt Addison Wesley, 1995
• ltpgt ltigt Data on the Web lt/igt
• Abiteboul, Buneman, Suciu
• ltbrgt Morgan Kaufmann, 1999

5
XML

• ltbibliographygt
• ltbookgt lttitlegt Foundations lt/titlegt
• ltauthorgt Abiteboul lt/authorgt
• ltauthorgt Hull lt/authorgt
• ltauthorgt Vianu lt/authorgt
• ltpublishergt Addison Wesley
  lt/publishergt
• ltyeargt 1995 lt/yeargt
• lt/bookgt
• lt/bibliographygt

XML describes the content
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XML Terminology

• tags book, title, author,
• start tag ltbookgt, end tag lt/bookgt
• elements ltbookgtltbookgt,ltauthorgtlt/authorgt
• elements are nested
• empty element ltredgtlt/redgt abbrv. ltred/gt
• an XML document single root element

well formed XML document if it has matching tags
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More XML Attributes

• ltbook price 55 currency USDgt
• lttitlegt Foundations of Databases lt/titlegt
• ltauthorgt Abiteboul lt/authorgt
• ltyeargt 1995 lt/yeargt
• lt/bookgt

attributes are alternative ways to represent data
8
More XML Oids and References

• ltperson ido555gt ltnamegt Jane lt/namegt lt/persongt
• ltperson ido456gt ltnamegt Mary lt/namegt
• ltchildren
  idrefo123 o555/gt
• lt/persongt
• ltperson ido123 mothero456gtltnamegtJohnlt/namegt
• lt/persongt

oids and references in XML are just syntax
9
More XML CDATA Section

• Syntax lt!CDATA .....any text here...gt
• Example
• ltexamplegt lt!CDATA some text here lt/notAtaggt
  ltgtgt
• lt/examplegt

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XML Namespaces

• http//www.w3.org/TR/REC-xml-names (1/99)
• name prefixlocalpart

ltbook xmlnsisbnwww.isbn-org.org/defgt
lttitlegt lt/titlegt ltnumbergt 15 lt/numbergt
ltisbnnumbergt . lt/isbnnumbergt lt/bookgt
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XML Namespaces

• syntactic ltnumbergt , ltisbnnumbergt
• semantic provide URL for schema

lttag xmlnsmystyle http//gt
ltmystyletitlegt
lt/mystyletitlegt ltmystylenumbergt
lt/taggt
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XML Data Model

• Several competing models
• Document Object Model (DOM)
• http//www.w3.org/TR/2001/WD-DOM-Level-3-CMLS-2001
  0209/ (2/2001)
• class hierarchy (node, element, attribute,)
• objects have behavior
• defines API to inspect/modify the document
• Infoset - PSV (post schema validation)
• XML Query data model

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XML Schemas

• http//www.w3.org/TR/xmlschema-1/10/2000
• generalizes DTDs
• uses XML syntax
• two documents structure and datatypes
• http//www.w3.org/TR/xmlschema-1
• http//www.w3.org/TR/xmlschema-2
• XML-Schema is complex

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XML Schemas

• ltxsdelement namepaper typepapertype/gt
• ltxsdcomplexType namepapertypegt
• ltxsdsequencegt
• ltxsdelement nametitle
  typexsdstring/gt
• ltxsdelement nameauthor
  minOccurs0/gt
• ltxsdelement nameyear/gt
• ltxsd choicegt lt xsdelement
  namejournal/gt
• ltxsdelement
  nameconference/gt
• lt/xsdchoicegt
• lt/xsdsequencegt
• lt/xsdelementgt

DTD lt!ELEMENT paper (title,author,year,
(journalconference))gt
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Elements v.s. Types in XML Schema
ltxsdelement namepersongt ltxsdcomplexTypegt
ltxsdsequencegt ltxsdelement namename
typexsdstring/gt
ltxsdelement nameaddress
typexsdstring/gt lt/xsdsequencegt
lt/xsdcomplexTypegtlt/xsdelementgt
ltxsdelement nameperson
typetttgtltxsdcomplexType nametttgt
ltxsdsequencegt ltxsdelement namename
typexsdstring/gt
ltxsdelement nameaddress
typexsdstring/gt lt/xsdsequencegtlt/xsdco
mplexTypegt
DTD lt!ELEMENT person (name,address)gt
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Elements v.s. Types in XML Schema

• Types
• Simple types (integers, strings, ...)
• Complex types (regular expressions, like in DTDs)
• Element-type-element alternation
• Root element has a complex type
• That type is a regular expression of elements
• Those elements have their complex types...
• ...
• On the leaves we have simple types

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Local and Global Types in XML Schema

• Local type
• ltxsdelement namepersongt
  define locally the persons type
  lt/xsdelementgt
• Global type ltxsdelement nameperson
  typettt/gt ltxsdcomplexType nametttgt
  define here the type ttt
  lt/xsdcomplexTypegt

Global types can be reused in other elements
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Local v.s. Global Elements inXML Schema

• Local element
• ltxsdcomplexType nametttgt
  ltxsdsequencegt ltxsdelement
  nameaddress type.../gt...
  lt/xsdsequencegt lt/xsdcomplexTypegt
• Global element ltxsdelement nameaddress
  type.../gt ltxsdcomplexType nametttgt
  ltxsdsequencegt ltxsdelement
  refaddress/gt ... lt/xsdsequencegt
  lt/xsdcomplexTypegt

Global elements like in DTDs
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Regular Expressions in XML Schema

• Recall the element-type-element alternation
• ltxsdcomplexType name....gt
  regular expression on
  elements lt/xsdcomplexTypegt
• Regular expressions
• ltxsdsequencegt A B C lt/...gt
  A B C
• ltxsdchoicegt A B C lt/...gt
  A B C
• ltxsdgroupgt A B C lt/...gt
  (A B C)
• ltxsd... minOccurs0 maxOccursunboundedgt
  ..lt/...gt (...)
• ltxsd... minOccurs0 maxOccurs1gt ..lt/...gt
  (...)?

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Attributes in XML Schema
ltxsdelement namepaper typepapertype/gt ltxsd
complexType namepapertypegt
ltxsdsequencegt ltxsdelement
nametitle typexsdstring/gt . .
. . . . lt/xsdsequencegt ltxsdattribute
namelanguage" type"xsdNMTOKEN"
fixedEnglish"/gt lt/xsdcomplexTypegt
Attributes are associated to the type, not to the
element Only to complex types more trouble if we
want to add attributes to simple types.
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Mixed Content, Any Type
ltxsdcomplexType mixed"true"gt . . . .

• Better than in DTDs can still enforce the type,
  but now may have text between any elements
• Means anything is permitted there

ltxsdelement name"anything" type"xsdanyType"/gt
. . . .
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Derived Types by Extensions
ltcomplexType name"Address"gt ltsequencegt
ltelement name"street" type"string"/gt
ltelement name"city"
type"string"/gt lt/sequencegt lt/complexTypegt
ltcomplexType name"USAddress"gt
ltcomplexContentgt ltextension
base"ipoAddress"gt ltsequencegt ltelement
name"state" type"ipoUSState"/gt
ltelement name"zip"
type"positiveInteger"/gt lt/sequencegt
lt/extensiongt lt/complexContentgt lt/complexTypegt
Corresponds to inheritance
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Derived Types by Restrictions

• () may restrict cardinalities, e.g. (0,infty)
  to (1,1) may restrict choices other
  restrictions

ltcomplexContentgt ltrestriction
base"ipoItemsgt rewrite the entire
content, with restrictions...
lt/restrictiongt lt/complexContentgt
Corresponds to set inclusion
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Keys in XML Schema
XML
ltpurchaseReportgt ltregionsgt ltzip code"95819"gt
ltpart number"872-AA" quantity"1"/gt ltpart
number"926-AA" quantity"1"/gt ltpart
number"833-AA" quantity"1"/gt ltpart
number"455-BX" quantity"1"/gt lt/zipgt ltzip
code"63143"gt ltpart number"455-BX"
quantity"4"/gt lt/zipgt lt/regionsgt ltpartsgt
ltpart number"872-AA"gtLawnmowerlt/partgt ltpart
number"926-AA"gtBaby Monitorlt/partgt ltpart
number"833-AA"gtLapis Necklacelt/partgt ltpart
number"455-BX"gtSturdy Shelveslt/partgt
lt/partsgt lt/purchaseReportgt
XML Schema
ltkey name"NumKey"gt ltselector
xpath"parts/part"/gt ltfield xpath"_at_number"/gt lt
/keygt
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Keys in XML Schema

• In general, two flavors

ltkey namesomeDummyNameHere"gt ltselector
xpathp"/gt ltfield xpathp1"/gt ltfield
xpathp2"/gt . . . ltfield
xpathpk"/gt lt/keygt
ltunique namesomeDummyNameHere"gt ltselector
xpathp"/gt ltfield xpathp1"/gt ltfield
xpathp2"/gt . . . ltfield
xpathpk"/gt lt/keygt
Note all Xpath expressions start at the
element currently being defined The fields must
identify a single node
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Keys in XML Schema

• Unique guarantees uniqueness
• Key guarantees uniqueness and existence
• All Xpath expressions are restricted
• /a/b /a/c OK for selector
• //a/b//c OK for field
• Note better than DTDs ID mechanism

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Keys in XML Schema

• Examples

ltkey name"fullName"gt ltselector
xpath".//person"/gt ltfield xpath"forename"/gt
ltfield xpath"surname"/gt lt/keygt ltunique
name"nearlyID"gt ltselector xpath".//"/gt
ltfield xpath"_at_id"/gt lt/uniquegt
Recall must have A single forename, Single
surname
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Foreign Keys in XML Schema

• Example

ltkeyref name"personRef" refer"fullName"gt
ltselector xpath".//personPointer"/gt ltfield
xpath"_at_first"/gt ltfield xpath"_at_last"/gt lt/keyrefgt
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XPATH
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XPath

• Goal permit to access some nodes from document
• XPath main construct axis navigation
• XPath path consists of one or more navigation
  steps, separated by /
• Navigation step axis node-test predicates
• Examples
• /descendantnode()/childauthor
• /descendantnode()/childauthorparent/attribute
  booktitle XML2
• XPath also offers shortcuts
• no axis means child
• // º /descendant-or-selfnode()/

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XPath- Child axis navigation

• author is shorthand for childauthor. Examples
• aaa -- all the child nodes labeled aaa (1,3)
• aaa/bbb -- all the bbb grandchildren of aaa
  children (4)
• /bbb all the bbb grandchildren of any child
  (4,6)
• . -- the context node
• / -- the root node

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XPath- child axis navigation

• /doc -- all the doc children of the root
• ./aaa -- all the aaa children of the context node
  (equivalent to aaa)
• text() -- all the text children of the context
  node
• node() -- all the children of the context node
  (includes text and attribute nodes)
• .. -- parent of the context node
• .// -- the context node and all its descendants
• // -- the root node and all its descendants
• //text() -- all the text nodes in the document

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Predicates

• 2 -- the second child node of the context node
• chapter5 -- the fifth chapter child of the
  context node
• last() -- the last child node of the context
  node
• chaptertitleintroduction -- the chapter
  children of the context node that have one or
  more title children whose string-value is
  introduction (the string-value is the
  concatenation of all the text on descendant text
  nodes)
• person.//firstname joe -- the person
  children of the context node that have in their
  descendants a firstname element with string-value
  Joe

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Axis navigation

• So far, nearly all our expressions have moved us
  down by moving to child nodes. Exceptions were
• . -- stay where you are
• / go to the root
• // all descendants of the root
• .// all descendants of the context node
• XPath has several axes ancestor,
  ancestor-or-self, attribute, child, descendant,
  descendant-or-self, following, following-sibling,
  namespace, parent, preceding, preceding-sibling,
  self
• Some of these (self, parent) describe single
  nodes, others describe sequences of nodes.

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XPath Navigation Axes
ancestor
following-sibling
preceding-sibling
self
child
attribute
following
preceding
namespace
descendant
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XPath abbreviated syntax
(nothing) child _at_ attribute // /descendan
t-or-selfnode() . selfnode() .// descendan
t-or-selfnode .. parentnode() / (document
root)
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XPath

• Reasonably widely adopted -- in XML-Schema and
  query languages.
• Neither more expressive nor less expressive than
  regular path expressions

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Quilt

• proposed by Chamberlin, Robbie and Florescu
• (from the authors slides)
• Leverage the most effective features of several
  existing and proposed query languages
• Design a small, clean, implementable language
• Cover the functionality required by all the XML
  Query use cases in a single language
• Write queries that fit on a slide
• Design a quilt, not a camel

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Quilt/Kweelt URLs
Quilt (the language) http//www.almaden.ibm.com/
cs/people/chamberlin/quilt_lncs.pdf Kweelt (the
implementation) http//db.cis.upenn.edu/Kwee
lt/ http//db.cis.upenn.edu/Kweelt/useCases
(examples in these notes)
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Quilt XPathcomprehension

• XML -QL
• Quilt

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Examples of Quilt(http//db.cis.upenn.edu/Kweelt/
useCases/R/Q1.qlt )
lt?xml version"1.0" ?gt lt!DOCTYPE items
lt!ELEMENT items (item_tuple)gt lt!ELEMENT
item_tuple (itemno, description, offered_by,
start_date?,
end_date?, reserve_price? )gt lt!ELEMENT
itemno (PCDATA)gt lt!ELEMENT description
(PCDATA)gt lt!ELEMENT offered_by (PCDATA)gt
lt!ELEMENT start_date (PCDATA)gt lt!ELEMENT
end_date (PCDATA)gt lt!ELEMENT reserve_price
(PCDATA)gt gt
lt?xml version"1.0" ?gt lt!DOCTYPE bids
lt!ELEMENT bids (bid_tuple)gt lt!ELEMENT
bid_tuple (userid, itemno, bid, bid_date)gt
lt!ELEMENT userid (PCDATA)gt lt!ELEMENT itemno
(PCDATA)gt lt!ELEMENT bid (PCDATA)gt
lt!ELEMENT bid_date (PCDATA)gt gt
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The data
ltitemsgt ltitem_tuplegt ltitemnogt1001lt/itemnogt ltdescr
iptiongtRed Bicyclelt/descriptiongt ltoffered_bygtU01lt/
offered_bygt ltstart_dategt1999-01-05lt/start_dategt lte
nd_dategt1999-01-20lt/end_dategt ltreserve_pricegt40lt/r
eserve_pricegt lt/item_tuplegt ltitem_tuplegt ltitemnogt
1002lt/itemnogt ltdescriptiongtMotorcyclelt/description
gt ltoffered_bygtU02lt/offered_bygt ltstart_dategt1999-02
-11lt/start_dategt ltend_dategt1999-03-15lt/end_dategt lt
reserve_pricegt500lt/reserve_pricegt lt/item_tuplegt
lt/itemsgt
ltbidsgt ltbid_tuplegt ltuseridgtU02lt/useridgt ltitemnogt1
001lt/itemnogt ltbidgt35lt/bidgt ltbid_dategt99-01-07lt/bid
_dategt lt/bid_tuplegt ltbid_tuplegt ltuseridgtU04lt/user
idgt ltitemnogt1001lt/itemnogt ltbidgt40lt/bidgt ltbid_dategt
99-01-08lt/bid_dategt lt/bid_tuplegt lt/bidsgt
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Query 1
simple function definitions
FUNCTION date() "1999-02-01" ltresultgt
( FOR i IN document("items.xml")//item_tuple
WHERE i/start_date LEQ date() AND
i/end_date GEQ date() AND
contains(i/description, "Bicycle") RETURN
ltitem_tuplegt i/itemno ,
i/description lt/item_tuplegt SORTBY
(itemno) ) lt/resultgt
XPath expressions in orange
dates are formatted so that lexicographic
ordering gives the right result
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Output from Q1
lt?xml version"1.0" ?gt ltresultgt ltitem_tuplegt
ltitemnogt 1003 lt/itemnogt ltdescriptiongt Old
Bicycle lt/descriptiongt lt/item_tuplegt
ltitem_tuplegt ltitemnogt 1007 lt/itemnogt
ltdescriptiongt Racing Bicycle lt/descriptiongt
lt/item_tuplegt lt/resultgt
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Query Q2
For all bicycles, list the item number,
description, and highest bid (if any), ordered by
item number. ltresultgt ( FOR i IN
document("items.xml")//item_tuple LET b
document("bids.xml")//bid_tupleitemno
i/itemno WHERE contains(i/description,
"Bicycle") RETURN ltitem_tuplegt
i/itemno , i/description , IF
(b) THEN lthigh_bidgt
NumFormat(".", max(-1, b/bid))
lt/high_bidgt ELSE "" lt/item_tuplegt
SORTBY (itemno) ) lt/resultgt
use of variable in Xpath
lots of coercion
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Output from Q2
ltresultgt ltitem_tuplegt
ltitemnogt 1001 lt/itemnogt
ltdescriptiongt Red Bicycle lt/descriptiongt
lthigh_bidgt 55 lt/high_bidgt
lt/item_tuplegt ltitem_tuplegt
ltitemnogt 1003 lt/itemnogt
ltdescriptiongt Old Bicycle lt/descriptiongt
lthigh_bidgt 20 lt/high_bidgt
lt/item_tuplegt ltitem_tuplegt
ltitemnogt 1007 lt/itemnogt
ltdescriptiongt Racing Bicycle lt/descriptiongt
lthigh_bidgt 225 lt/high_bidgt
lt/item_tuplegt ltitem_tuplegt
ltitemnogt 1008 lt/itemnogt
ltdescriptiongt Broken Bicycle lt/descriptiongt
lt/item_tuplegt lt/resultgt
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Query Q3
Find cases where a user with a rating worse
(alphabetically greater than "C" ) offers an item
with a reserve price of more than
1000. ltresultgt ( FOR u IN
document("users.xml")//user_tuple, i IN
document("items.xml")//item_tuple WHERE
u/rating GT 'C' AND i/reserve_price GT
1000 AND i/offered_by u/userid
RETURN ltwarninggt
ltuser_namegtu/name/text()lt/user_namegt,
ltuser_ratinggtu/rating/text()lt/user_ratinggt,
ltitem_descriptiongti/description/text()lt/item
_descriptiongt, i/reserve_price
lt/warninggt ) lt/resultgt
Comparing sets with singletons Same rules as in
XPath? In this case the DTD gives uniqueness
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Quilt -- Attributes and IDs
ltcensusgt ltperson name "Bill" job
"Teacher"gt ltperson name "Joe" job
"Painter" spouse "Martha"gt ltperson name
"Sam" job "Nurse"gt ltperson name
"Fred" job "Senator" spouse "Jane"gt
lt/persongt lt/persongt ltperson name
"Karen" job "Doctor" spouse "Steve"gt
lt/persongt lt/persongt ltperson name "Mary"
job "Pilot"gt ltperson name "Susan" job
"Pilot" spouse "Dave"gt lt/persongt
lt/persongt lt/persongt ltperson name "Frank"
job "Writer"gt ltperson name "Martha" job
"Programmer" spouse "Joe"gt ltperson name
"Dave" job "Athlete" spouse "Susan"gt
lt/persongt lt/persongt ...
lt/persongt lt/censusgt
lt?xml version"1.0" ?gt lt!DOCTYPE census
lt!ELEMENT census (person)gt lt!ELEMENT person
(person)gt lt!ATTLIST person name ID
REQUIRED spouse IDREF IMPLIED
job CDATA IMPLIED gt gt
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Query Q1
Find Martha's spouse FOR m IN
document("census.xml")//person_at_name"Martha" RET
URN shallow(m/_at_spouse-gtperson_at_name)
A hack. Kweelt does not read the DTD
The shallow function strips an element of its
subelements.
Dereferencing
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Query Q6
Find Bill's grandchildren. ltresultgt (
FOR b IN document("census.xml")//person_at_name
"Bill" , c IN b/person
b/_at_spouse-gtperson_at_name/person , g IN
c/person c/_at_spouse-gtperson_at_name/person
RETURN shallow(g) ) lt/resultgt
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Query Languages - XQuery
52
Summary of XQuery

• FLWR expressions
• FOR and LET expressions
• Collections and sorting
• Resources
• XQuery A Query Language for XML Chamberlin,
  Florescu, et al.
• W3C recommendation www.w3.org/TR/xquery/

53
XQuery

• Based on Quilt (which is based on XML-QL)
• http//www.w3.org/TR/xquery/2/2001
• XML Query data model (ordered)

54
FLWR (Flower) Expressions

• FOR ... LET... FOR... LET...
• WHERE...
• RETURN...

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XQuery

• Find all book titles published after 1995

FOR x IN document("bib.xml")/bib/book WHERE
x/year gt 1995 RETURN x/title
Result lttitlegt abc lt/titlegt lttitlegt def
lt/titlegt lttitlegt ghi lt/titlegt
56
XQuery

• For each author of a book by Morgan Kaufmann,
  list all books she published

FOR a IN distinct(document("bib.xml")
/bib/bookpublisherMorgan
Kaufmann/author) RETURN ltresultgt
a, FOR t IN
/bib/bookauthora/title
RETURN t lt/resultgt
distinct a function that eliminates duplicates
57
XQuery

• Result
• ltresultgt
• ltauthorgtJoneslt/authorgt
• lttitlegt abc lt/titlegt
• lttitlegt def lt/titlegt
• lt/resultgt
• ltresultgt
• ltauthorgt Smith lt/authorgt
• lttitlegt ghi lt/titlegt
• lt/resultgt

58
XQuery

• FOR x in expr -- binds x to each element in
  the list expr
• LET x expr -- binds x to the entire list
  expr
• Useful for common subexpressions and for
  aggregations

59
XQuery
ltbig_publishersgt FOR p IN
distinct(document("bib.xml")//publisher)
LET b document("bib.xml")/bookpublisher
p WHERE count(b) gt 100 RETURN
p lt/big_publishersgt
count a (aggregate) function that returns the
number of elms
60
XQuery

• Find books whose price is larger than average

LET aavg(document("bib.xml")/bib/book/_at_price) FO
R b in document("bib.xml")/bib/book WHERE
b/_at_price gt a RETURN b
61
XQuery

• Summary
• FOR-LET-WHERE-RETURN FLWR

FOR/LET Clauses
List of tuples
WHERE Clause
List of tuples
RETURN Clause
Instance of Xquery data model
62
FOR v.s. LET

• FOR
• Binds node variables ? iteration
• LET
• Binds collection variables ? one value

63
FOR v.s. LET
Returns ltresultgt ltbookgt...lt/bookgtlt/resultgt
ltresultgt ltbookgt...lt/bookgtlt/resultgt ltresultgt
ltbookgt...lt/bookgtlt/resultgt ...
FOR x IN document("bib.xml")/bib/book RETURN
ltresultgt x lt/resultgt
LET x document("bib.xml")/bib/book RETURN
ltresultgt x lt/resultgt
Returns ltresultgt ltbookgt...lt/bookgt
ltbookgt...lt/bookgt
ltbookgt...lt/bookgt ... lt/resultgt
64
Collections in XQuery

• Ordered and unordered collections
• /bib/book/author an ordered collection
• Distinct(/bib/book/author) an unordered
  collection
• LET a /bib/book ? a is a collection
• b/author ? a collection (several authors...)

Returns ltresultgt ltauthorgt...lt/authorgt
ltauthorgt...lt/authorgt
ltauthorgt...lt/authorgt
... lt/resultgt
RETURN ltresultgt b/author lt/resultgt
65
Sorting in XQuery
ltpublisher_listgt FOR p IN distinct(document("
bib.xml")//publisher) RETURN ltpublishergt
ltnamegt p/text() lt/namegt ,
FOR b IN document("bib.xml")//bookpublisher
p RETURN ltbookgt

b/title ,
b/_at_price
lt/bookgt SORTBY(price DESCENDING)
lt/publishergt SORTBY(name)
lt/publisher_listgt
66
Sorting in XQuery

• Sorting arguments refer to name space of RETURN
  clause, not FOR clause
• To sort on an element you dont want to display,
  first return it, then remove it with an
  additional query.

67
If-Then-Else
FOR h IN //holding RETURN ltholdinggt
h/title, IF
h/_at_type "Journal"
THEN h/editor ELSE
h/author lt/holdinggt SORTBY
(title)
68
Existential Quantifiers
FOR b IN //book WHERE SOME p IN b//para
SATISFIES contains(p, "sailing") AND
contains(p, "windsurfing") RETURN b/title
69
Universal Quantifiers
FOR b IN //book WHERE EVERY p IN b//para
SATISFIES contains(p, "sailing") RETURN
b/title