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Fall 2001CSE330 1
Query Languages for XML
Fall 2001CSE330 2
Why a query language? Extracting, Restructuring, Integration, Browsing…
XML-QL http://www.w3.org/TR/NOTE-xml-ql
http://db.cis.upenn.edu/XML-QL/
XPATH (part of a query language) http:www.w3.org/TR/xpath XSLT
http://www.w3.org/TR/xslt
http://www.mulberrytech.com/quickref/XSLTquickref.pdf
QUILT http://www.almaden.ibm.com/cs/people/chamberlin/quilt.html
http://db.cis.upenn.edu/Kweelt/
Fall 2001CSE330 3
XML-QL (XML Query Language)
• W3C proposal, August 1998
• authors: – Mary Fernandez AT&T– Dana Florescu INRIA– Alon Levy Univ. of Washington– Dan Suciu AT&T– Alin Deutsch Univ. of Pennsylvania
Fall 2001CSE330 4
Address Book Revisited<addrBook>
<person SSN=“111-22-3333”>
<name> Caesar </name>
<greet> Caesar Imperator</greet>
<addr> The Capitol </addr>
<addr> Rome, OH 98765 </addr>
<tel> (321) 786 2543 </tel>
<fax> (321) 786 2543 <fax>
<tel> (321) 786 2543 </tel>
<email> [email protected]
</email>
</person>
</addrBook>
Fall 2001CSE330 5
XML-QL: Pattern Matching
Find Caesar’s e-mail address:
where <addrBook> <person> <name>Caesar</name> <email>$e</email> </person> </addrBook> in “http://db.cis.upenn.edu/~peter/address.xml”construct $e
<XML>[email protected]</XML>
Data Extraction
Fall 2001CSE330 6
XML-QL: Constructing New XML Data
Whom can we contact electronically?
where <addrBook> <person> <greet>$g</greet> <email>$e</email> </person> </addrBook> in “http://...”construct <e-contact> <who>$g</who> <where>$e</where> </e-contact>
<XML> <e-contact> <who>Caesar Imperator</who> <where>[email protected] </where> </e-contact> <e-contact> <who>Brutus</who> <where>[email protected] </where> </e-contact> ...</XML>
Data Restructuring
Fall 2001CSE330 7
XML-QL: Joins
Who of our contacts was involved in a movie?
where <addrBook> <person> <greet>$g</greet> <email>$e</email> </person> </addrBook> in “http://…address.xml” <movie><title>$t</> <character>$g</> </movie> in “http://www.imdb.com”construct <cine-contact> <who>$g</who> <movie>$t</movie> <where>$e</where> </cine-contact>
Fall 2001CSE330 8
XML-QL: Joins (cont’d)
<XML> <cine-contact> <who>Caesar Imperator</who> <where>[email protected]</where> <movie>Asterix and Cleopatra</movie> </cine-contact>
<cine-contact> <who>Dr. Strangelove</who> <where>[email protected]</where> <movie>Dr. Strangelove or How I Stopped ...</movie> </cine-contact>...</XML>
Data Integration
Fall 2001CSE330 9
XML-QL Data Model
• Directed, labeled graph
• Tags represented as edge labels
• Sets of attribute name-value pairs as node labels
• Two models: ordered and unordered
Fall 2001CSE330 10
XML-QL Data Model (cont’d)
<person SSN=“111-22-3333”>
<name> Caesar </name>
<greet> Caesar Imperator </greet>
<addr> The Capitol </addr>
<addr> Rome, OH 98765 </addr>
<tel> (321) 786 2543 </tel>
<fax> (321) 786 2543 <fax>
<tel> (321) 786 2543 </tel>
<email> [email protected]
</email>
</person>
person
name tel fax tel emailgreet
addr addr
SSN=“111-…”
Caesar
addrBook
Caesar Imperator
The Capitol Rome, OH
(321) 786 2543
Fall 2001CSE330 11
XML-QL Semantics: Variable Bindings
person
name tel fax tel emailgreet
addr addr
SSN=“111-…”
Caesar
addrBook
Caesar Imperator
The Capitol Rome, OH
(321) 786 2543
name tel fax tel emailgreet
addr addr
SSN=“111-…”
Stragelove
Dr. Strangelove
The Capitol Washington, DC
person
strangelov@[email protected]
where <addrBook> <person> <name>$n</> <email>$e</> </> </>
$n $eCaesar [email protected] [email protected]
Fall 2001CSE330 12
XML-QL Semantics: XML Output
$n $eCaesar [email protected] [email protected]
construct <e-contact> <who>$n</who> <where>$e</where> </e-contact>
XML
e-contact e-contact
who where who where
Caesar [email protected] Strangelove [email protected]
Fall 2001CSE330 13
Advanced XML-QL
Find tags of person subelements:
where <addrBook.person.$tag></> in “http://db.cis.upenn.edu/~peter/address.xml”construct <childOfPerson>$tag</>
Find all email addresses and fax numbers :
where <addrBook._*. (email | fax)>$eORf</> in “http://db.cis.upenn.edu/~peter/address.xml”construct <emailOrFax>$eORf</>
Schema browsing
Fall 2001CSE330 14
More Advanced XML-QL
Find attributes of person elements:
where <_*.person $attrName=$attrVal></> in “http://db.cis.upenn.edu/~peter/address.xml”construct <personAttribute> <name>$attrName</> <value>$attrVal</> </>
Schema browsing
Fall 2001CSE330 15
XPath• Reasonably widely adopted -- in XML-Schema and query
languages.• Neither more expressive nor less expressive than regular
path expressions (can’t do (ab)* )• Primary goal = to permit to access some nodes from a
given document• XPath main construct : axis navigation• An XPath path consists of one or more navigation steps,
separated by /• A navigation step is a triplet: axis + node-test + list of
predicates
• Examples– /descendant::node()/child::author– /descendant::node()/child::author[parent/attribute::booktitle = “XML”]
[2]
• XPath also offers some shortcuts– no axis means child– // /descendant-or-self::node()/
Fall 2001CSE330 16
XPath- child axis navigation• author is shorthand for child::author. 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
aaa
bbb
ccc aaa
aaa bbb ccc
1 2 3
4 5 6 7
context node
Fall 2001CSE330 17
XPath- child axis navigation (cont)– /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– //para -- all the para nodes in the document– //text() -- all the text nodes in the document– @font the font attribute node of the context node
Fall 2001CSE330 18
Predicates
– [2] -- the second child node of the context node– chapter[5] -- the fifth chapter child of the context node– [last()] -- the last child node of the context node– chapter[title=“introduction”] -- 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”
Fall 2001CSE330 19
Unions of Path Expressions
• employee | consultant -- the union of the employee and consultant nodes that are children of the context node
• For some reason person/(employee|consultant) --as in regular path expressions -- is not allowed
• However person/node()[boolean(employee|consultant)] is allowed!!
• From the XPATH specification:– The boolean function converts its argument to a boolean as
follows:• a number is true if and only if it is neither positive or negative zero
nor NaN
• a node-set is true if and only if it is non-empty
• a string is true if and only if its length is non-zero
• an object of a type other than the four basic types is converted to a boolean in a way that is dependent on that type
Fall 2001CSE330 20
Axis navigation
• So far, nearly all our expressions have moved us down the 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
• All other expressions have been abbreviations for child::… e.g. child::para. child:is an example of an axis
• 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.
Fall 2001CSE330
XPath Navigation Axes(merci, Arnaud Sahuguet)
ancestor
descendant
followingpreceding
following-siblingpreceding-sibling
child
attribute
namespace
self
Fall 2001CSE330
XPath abbreviated syntax
(nothing) child::@ attribute::// /descendant-or-self::node(). self::node().// descendant-or-self::node.. parent::node()/ (document root)
Fall 2001CSE330 23
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
Fall 2001CSE330 24
Quilt = XPath + “comprehension” syntax
• XML -QL
• Quilt
where <pattern> in <XML-expression> <pattern> in <XML-expression> … <condition>construct <expression>
bind variables
use variables
for x in <XPath-expression> y in <XPath-expression> …where <condition>return <expression>
bind variables
use variables
Fall 2001CSE330 25
Examples of Quilt(from http://db.cis.upenn.edu/Kweelt/useCases/R/Q1.qlt )
Relational data -- two DTDs:<?xml version="1.0" ?><!DOCTYPE items [ <!ELEMENT items (item_tuple*)> <!ELEMENT item_tuple (itemno, description, offered_by, start_date?, end_date?, reserve_price? )> <!ELEMENT itemno (#PCDATA)> <!ELEMENT description (#PCDATA)> <!ELEMENT offered_by (#PCDATA)> <!ELEMENT start_date (#PCDATA)> <!ELEMENT end_date (#PCDATA)> <!ELEMENT reserve_price (#PCDATA)>]>
<?xml version="1.0" ?> <!DOCTYPE bids [ <!ELEMENT bids (bid_tuple*)> <!ELEMENT bid_tuple (userid, itemno, bid, bid_date)> <!ELEMENT userid (#PCDATA)> <!ELEMENT itemno (#PCDATA)> <!ELEMENT bid (#PCDATA)> <!ELEMENT bid_date (#PCDATA)>]>
Fall 2001CSE330 26
The data
<items>
<item_tuple><itemno>1001</itemno><description>Red Bicycle</description><offered_by>U01</offered_by><start_date>1999-01-05</start_date><end_date>1999-01-20</end_date><reserve_price>40</reserve_price></item_tuple>
<item_tuple><itemno>1002</itemno><description>Motorcycle</description><offered_by>U02</offered_by><start_date>1999-02-11</start_date><end_date>1999-03-15</end_date><reserve_price>500</reserve_price></item_tuple>
…
</items>
<bids>
<bid_tuple><userid>U02</userid><itemno>1001</itemno><bid>35</bid><bid_date>99-01-07</bid_date></bid_tuple>
<bid_tuple><userid>U04</userid><itemno>1001</itemno><bid>40</bid><bid_date>99-01-08</bid_date></bid_tuple>
…
</bids>
Fall 2001CSE330 27
Query 1
FUNCTION date(){ "1999-02-01"}
<result> ( 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 <item_tuple> $i/itemno , $i/description </item_tuple> SORTBY (itemno) )</result>
XPath expressionsin orange
simple function definitions
dates are formatted sothat lexicographic ordering gives the rightresult
Fall 2001CSE330 28
Output from Q1
<?xml version="1.0" ?><result> <item_tuple> <itemno> 1003 </itemno> <description> Old Bicycle </description> </item_tuple> <item_tuple> <itemno> 1007 </itemno> <description> Racing Bicycle </description> </item_tuple></result>
Fall 2001CSE330 29
Query Q2
For all bicycles, list the item number, description, and highest bid (if any), ordered by item number.
<result> ( FOR $i IN document("items.xml")//item_tuple LET $b := document("bids.xml")//bid_tuple[itemno = $i/itemno] WHERE contains($i/description, "Bicycle") RETURN <item_tuple> $i/itemno , $i/description , IF ($b) THEN <high_bid> NumFormat("#####.##", max(-1, $b/bid)) </high_bid> ELSE "" </item_tuple> SORTBY (itemno) )</result>
use of variablein Xpath
lots of coercion
Fall 2001CSE330 30
Output from Q2
<result> <item_tuple> <itemno> 1001 </itemno> <description> Red Bicycle </description> <high_bid> 55 </high_bid> </item_tuple> <item_tuple> <itemno> 1003 </itemno> <description> Old Bicycle </description> <high_bid> 20 </high_bid> </item_tuple> <item_tuple> <itemno> 1007 </itemno> <description> Racing Bicycle </description> <high_bid> 225 </high_bid> </item_tuple> <item_tuple> <itemno> 1008 </itemno> <description> Broken Bicycle </description> </item_tuple></result>
Fall 2001CSE330 31
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.
<result> ( 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 = $u/userid RETURN <warning> <user_name>$u/name/text()</user_name>, <user_rating>$u/rating/text()</user_rating>, <item_description>$i/description/text()</item_description>, $i/reserve_price </warning> )</result>
Comparing sets with singletonsSame rules as in XPath? In thiscase the DTD gives uniqueness
Fall 2001CSE330 32
Conclusions
• XML is a data format for which there are an increasing number of useful tools for– Constructing schemas– Programming– Querying
• Although it is likely that a query language will soon emerge as a standard, there is less agreement or understanding on how to store XML data efficiently.
• Many other database issues remain to make it useful for manipulating large amounts of data.