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XML, XML Schema, Xpath and XQuery

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XML, XML Schema, Xpath and XQuery. Slides collated from various sources, many from Dan Suciu at Univ. of Washington. XML. W3C standard to complement HTML origins: structured text SGML motivation: HTML describes presentation XML describes content
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XML, XML Schema, Xpath and XQuery Slides collated from various sources, many from Dan Suciu at Univ. of Washington 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)
  • CS561 - Spring 2005. From HTML to XML HTML describes the presentation CS561 - Spring 2005. HTML <h1> Bibliography </h1> <p> <i> Foundations of Databases </i> Abiteboul, Hull, Vianu <br> Addison Wesley, 1995 <p> <i> Data on the Web </i> Abiteboul, Buneman, Suciu <br> Morgan Kaufmann, 1999 CS561 - Spring 2005. XML <bibliography> <book> <title> Foundations… </title> <author> Abiteboul </author> <author> Hull </author> <author> Vianu </author> <publisher> Addison Wesley </publisher> <year> 1995 </year> </book> … </bibliography> XML describes the content CS561 - Spring 2005. 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 CS561 - Spring 2005. More XML: Attributes <bookprice = “55” currency = “USD”> <title> Foundations of Databases </title> <author> Abiteboul </author> … <year> 1995 </year> </book> attributes are alternative ways to represent data CS561 - Spring 2005. More XML: Oids and References <personid=“o555”> <name> Jane </name> </person> <personid=“o456”> <name> Mary </name> <childrenidref=“o123 o555”/> </person> <personid=“o123” mother=“o456”><name>John</name> </person> oids and references in XML are just syntax CS561 - Spring 2005. XML Namespaces
  • http://www.w3.org/TR/REC-xml-names (1/99)
  • name ::= [prefix:]localpart
  • <bookxmlns:isbn=“www.isbn-org.org/def”> <title> … </title> <number> 15 </number> <isbn:number> …. </isbn:number> </book> CS561 - Spring 2005. defined here XML Namespaces
  • syntactic: <number> , <isbn:number>
  • semantic: provide URL for schema
  • <tagxmlns:mystyle = “http://…”> … <mystyle:title> … </mystyle:title> <mystyle:number> … </tag> CS561 - Spring 2005. 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
  • CS561 - Spring 2005. XML Schemas <xsd:elementname=“paper” type=“papertype”/> <xsd:complexTypename=“papertype”> <xsd:sequence> <xsd:elementname=“title” type=“xsd:string”/> <xsd:elementname=“author” minOccurs=“0”/> <xsd:elementname=“year”/> <xsd:choice> < xsd:elementname=“journal”/> <xsd:elementname=“conference”/> </xsd:choice> </xsd:sequence> </xsd:element> DTD: <!ELEMENT paper (title,author*,year, (journal|conference))> CS561 - Spring 2005. Elements v.s. Types in XML Schema <xsd:elementname=“person”> <xsd:complexType> <xsd:sequence> <xsd:elementname=“name” type=“xsd:string”/> <xsd:elementname=“address”type=“xsd:string”/> </xsd:sequence> </xsd:complexType></xsd:element> <xsd:elementname=“person”type=“ttt”><xsd:complexType name=“ttt”> <xsd:sequence> <xsd:elementname=“name” type=“xsd:string”/> <xsd:elementname=“address”type=“xsd:string”/> </xsd:sequence></xsd:complexType> DTD: <!ELEMENT person (name,address)> CS561 - Spring 2005. 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
  • CS561 - Spring 2005. Local and Global Types in XML Schema
  • Local type: <xsd:elementname=“person”> [define locally the person’s type] </xsd:element>
  • Global type: <xsd:elementname=“person” type=“ttt”/> <xsd:complexType name=“ttt”> [define here the type ttt] </xsd:complexType>
  • CS561 - Spring 2005. Global types: can be reused in other elements Local v.s. Global Elements inXML Schema
  • Local element: <xsd:complexType name=“ttt”> <xsd:sequence> <xsd:elementname=“address” type=“...”/>... </xsd:sequence> </xsd:complexType>
  • Global element: <xsd:elementname=“address” type=“...”/> <xsd:complexType name=“ttt”> <xsd:sequence><xsd:elementref=“address”/> ... </xsd:sequence> </xsd:complexType>
  • Global elements: like in DTDs CS561 - Spring 2005. Regular Expressions in XML Schema Recall the element-type-element alternation: <xsd:complexType name=“....”> [regular expression on elements] </xsd:complexType> Regular expressions:
  • <xsd:sequence> A B C </...> = A B C
  • <xsd:choice> A B C </...> = A | B | C
  • <xsd:group> A B C </...> = (A B C)
  • <xsd:... minOccurs=“0”maxOccurs=“unbounded”> ..</...> = (...)*
  • <xsd:... minOccurs=“0”maxOccurs=“1”> ..</...> = (...)?
  • CS561 - Spring 2005. Derived Types by Extensions <complexTypename="Address"> <sequence> <elementname="street" type="string"/> <elementname="city" type="string"/> </sequence> </complexType> <complexTypename="USAddress"> <complexContent> <extensionbase="ipo:Address"> <sequence> <elementname="state" type="ipo:USState"/> <elementname="zip" type="positiveInteger"/> </sequence> </extension> </complexContent> </complexType> CS561 - Spring 2005. Corresponds to inheritance Keys in XML Schema XML:
  • <purchaseReport>
  • <regions>
  • <zipcode="95819">
  • <partnumber="872-AA" quantity="1"/>
  • <partnumber="926-AA" quantity="1"/>
  • <partnumber="833-AA" quantity="1"/>
  • <partnumber="455-BX" quantity="1"/>
  • </zip>
  • <zip code="63143">
  • <partnumber="455-BX" quantity="4"/>
  • </zip>
  • </regions>
  • <parts>
  • <partnumber="872-AA">Lawnmower</part>
  • <partnumber="926-AA">Baby Monitor</part>
  • <partnumber="833-AA">Lapis Necklace</part>
  • <partnumber="455-BX">Sturdy Shelves</part>
  • </parts>
  • </purchaseReport>
  • XML Schema: <keyname="NumKey"> <selectorxpath="parts/part"/> <fieldxpath="@number"/> </key> CS561 - Spring 2005. Keys in XML Schema
  • In general, two flavors:
  • <keyname=“someDummyNameHere"> <selectorxpath=“p"/> <fieldxpath=“p1"/> <fieldxpath=“p2"/> . . . <fieldxpath=“pk"/> </key> <uniquename=“someDummyNameHere"> <selectorxpath=“p"/> <fieldxpath=“p1"/> <fieldxpath=“p2"/> . . . <fieldxpath=“pk"/> </key> Note: all Xpath expressions “start” at the element currently being defined The fields must identify a single node CS561 - Spring 2005. 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 DTD’s ID mechanism
  • CS561 - Spring 2005. Keys in XML Schema
  • Examples
  • <keyname="fullName">
  • <selectorxpath=".//person"/>
  • <fieldxpath="forename"/>
  • <fieldxpath="surname"/>
  • </key>
  • <uniquename="nearlyID">
  • <selectorxpath=".//*"/>
  • <fieldxpath="@id"/>
  • </unique>
  • Recall: must have A single forename, Single surname CS561 - Spring 2005. Foreign Keys in XML Schema
  • Example
  • <keyrefname="personRef" refer="fullName">
  • <selectorxpath=".//personPointer"/>
  • <fieldxpath="@first"/>
  • <fieldxpath="@last"/>
  • </keyref>
  • CS561 - Spring 2005. XPATH 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
  • /descendant::node()/child::author
  • /descendant::node()/child::author[parent/attribute::booktitle =“XML”][2]
  • XPath also offers shortcuts
  • no axis means child
  • // º /descendant-or-self::node()/
  • CS561 - Spring 2005. context node aaa ccc aaa aaa ccc 2 3 1 bbb bbb 4 5 6 7 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
  • CS561 - Spring 2005. 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
  • CS561 - Spring 2005. 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”
  • CS561 - Spring 2005. 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.
  • CS561 - Spring 2005. XPath Navigation Axes ancestor preceding-sibling following-sibling self child attribute preceding following namespace descendant CS561 - Spring 2005. XPath abbreviated syntax (nothing) child:: @ attribute:: // /descendant-or-self::node() . self::node() .// descendant-or-self::node .. parent::node() / (document root) CS561 - Spring 2005. Query Languages - XQuery 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/
  • CS561 - Spring 2005. XQuery
  • Based on Quilt (which is based on XML-QL)
  • http://www.w3.org/TR/xquery/2/2001
  • XML Query data model (ordered)
  • CS561 - Spring 2005. FLWR (“Flower”) Expressions FOR ... LET... FOR... LET... WHERE... RETURN... CS561 - Spring 2005. XQuery Find all book titles published after 1995: FOR$xINdocument("bib.xml")/bib/book WHERE$x/year > 1995 RETURN$x/title Result: <title> abc </title> <title> def </title> <title> ghi </title> CS561 - Spring 2005. XQuery For each author of a book by Morgan Kaufmann, list all books she published: FOR$aINdistinct(document("bib.xml")/bib/book[publisher=“Morgan Kaufmann”]/author) RETURN <result> $a, FOR$tIN /bib/book[author=$a]/title RETURN$t </result> distinct = a function that eliminates duplicates CS561 - Spring 2005. XQuery Result: <result> <author>Jones</author> <title> abc </title> <title> def </title> </result> <result> <author> Smith </author> <title> ghi </title> </result> CS561 - Spring 2005. XQuery
  • FOR$x in expr -- binds $x to each element in the list expr
  • LET$x = expr -- binds $x to the entire list expr
  • Useful for common subexpressions and for aggregations
  • CS561 - Spring 2005. XQuery <big_publishers> FOR$pINdistinct(document("bib.xml")//publisher) LET$b := document("bib.xml")/book[publisher = $p] WHEREcount($b) > 100 RETURN$p </big_publishers> count = a (aggregate) function that returns the number of elms CS561 - Spring 2005. XQuery Find books whose price is larger than average: LET$a=avg(document("bib.xml")/bib/book/@price) FOR$b in document("bib.xml")/bib/book WHERE$b/@price > $a RETURN$b CS561 - Spring 2005. XQuery Summary:
  • FOR-LET-WHERE-RETURN = FLWR
  • FOR/LET Clauses List of tuples WHERE Clause List of tuples RETURN Clause CS561 - Spring 2005. Instance of Xquery data model FOR v.s. LET FOR
  • Binds node variables iteration LET
  • Binds collection variables one value
  • CS561 - Spring 2005. FOR v.s. LET Returns: <result> <book>...</book></result> <result> <book>...</book></result> <result> <book>...</book></result> ... FOR$xINdocument("bib.xml")/bib/book RETURN <result> $x </result> LET$x:=document("bib.xml")/bib/book RETURN <result> $x </result> Returns: <result> <book>...</book> <book>...</book> <book>...</book> ... </result> CS561 - Spring 2005. Collections in XQuery
  • Ordered and unordered collections
  • /bib/book/author = an ordered collection
  • Distinct(/bib/book/author) = an unordered collection
  • LET$a = /bib/book $a is a collection
  • $b/author  a collection (several authors...)
  • Returns: <result> <author>...</author> <author>...</author> <author>...</author> ... </result> RETURN <result> $b/author </result> CS561 - Spring 2005. Sorting in XQuery <publisher_list> FOR$pINdistinct(document("bib.xml")//publisher) RETURN <publisher> <name> $p/text() </name> , FOR$bIN document("bib.xml")//book[publisher = $p] RETURN <book> $b/title , $b/@price </book> SORTBY(priceDESCENDING) </publisher> SORTBY(name) </publisher_list> CS561 - Spring 2005. Sorting in XQuery
  • Sorting arguments: refer to name space of RETURN clause, not FOR clause
  • To sort on an element you don’t want to display, first return it, then remove it with an additional query.
  • CS561 - Spring 2005. If-Then-Else FOR$h IN //holding RETURN <holding> $h/title, IF$h/@type = "Journal" THEN$h/editor ELSE$h/author </holding> SORTBY (title) CS561 - Spring 2005. Existential Quantifiers FOR$b IN //book WHERESOME$p IN $b//paraSATISFIES contains($p, "sailing") AND contains($p, "windsurfing") RETURN$b/title CS561 - Spring 2005. Universal Quantifiers FOR$b IN //book WHEREEVERY$p IN $b//paraSATISFIES contains($p, "sailing") RETURN$b/title CS561 - Spring 2005.
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