Introduction to XML and XQuery Guangjun (Kevin) Xie.

Introduction to XML and XQuery

Guangjun (Kevin) Xie

Nov 28, 2005 York University 2

Road Map

XML data model XML data vs Relational data XPath 2.0 XQuery Processing XQuery


XML Data ModelXML Information Set (Infoset)

Infoset is an abstract data set containing all information in an XML document

provide a consistent set of definitions to refer to the information in a well-formed XML document

Usually, Infosets result from parsing XML documents; but it could also be synthetic

By use of an API, such as DOM By transforming from existing infoset

An infoset consists of a number of information items.


XML Data Model XML Infoset

"information set" and "information item" are similar in meaning to the generic terms "tree" and "node”

An information item is an abstract description of some part of an XML document.

Each information item has a set of associated named properties, indicated as [property name]


XML Data Model Information Items

11 types of information items1. Document Information Item 2. Element Information Items 3. Attribute Information Items 4. Character Information Items 5. Processing Instruction Information Items 6. Unexpanded Entity Reference Information Items 7. Comment Information Items 8. The Document Type Declaration Information Item 9. Unparsed Entity Information Items 10. Notation Information Items 11. Namespace Information Items

We will discuss the first 3 today


XML Data Model Document Information Item

Exactly one doc item in an infoset Other information accessible thru its

properties: [children] – containing PIs, comments, etc [document element] – element item

corresponding to the document element [version] – XML version of the document … etc


XML Data Model Element Information Items

One element item for each element in XML document

The “root” element item is the [document element] prop. of document info item

Properties: [namespace name] – the ns part of tag name [local name] – the local part of tag name [children] – all other info items inside [attributes] – attributes elems of this item [parent] – info. Item containing this item … etc.


XML Data Model Attribute information items

One attribute item for each attribute in an XML element

Properties: [namespace name] – the ns part of tag name [local name] – the local part of tag name [attribute type] – the data type of this attribute [owner element] – the element info item containing

this attr … etc


XML Data Model Infoset example

<?xml version="1.0"?><msg:message doc:date="19990421" xmlns:doc=“http://doc.example.org/namespaces/doc” xmlns:msg="http://message.example.org/" >Phone home!</msg:message>

The information set contains: A document information item. An element information item with namespace name

"http://message.example.org/", local part "message", and prefix "msg". An attribute information item with the namespace name

"http://doc.example.org/namespaces/doc", local part "date", prefix "doc", and normalized value "19990421".

Three namespace information items for the http://www.w3.org/XML/1998/namespace, http://doc.example.org/namespaces/doc, and http://message.example.org/ namespaces.

Two attribute information items for the namespace attributes. Eleven character information items for the character data.


XML Data Model Infoset Example

Version=1.0

msg:message

xmlns:msgxmlns:doc

P h o en h o em !

doc:date

Legend:

Document info. Item Element info. Item Attribute info. Item Character info. Item


Road Map



XML Data vs Relational Data Relational DB stems from commercial data

processing Information usually has regular structure

XML has roots in text documents processing Often have irregular structure.

Both are general model and capable of representing all forms of information.

Different heritages cause them to be optimized for different types of applications.


XML Data vs Relational Data Nesting

XML Model Deeply nested structure Flexible (un-predefined) Query easily handled by “descendants” axis

in XPath 2.0

Relational Model Flat table structure Primary-foreign keys represent nesting

relationship Complex and flexible nesting may result in

awkward queries


XML Data vs Relational Data Metadata

XML Model Metadata mixed with ordinary data Hight ratio of metadata to ordinary data

Relational Model Metadata easily factored out Difficult when query involve metadata

Ex: find the names of columns containing the value “red”


XML Data vs Relational Data Ordering

XML Model Intrinsic ordering can’t derived from value

Ex: sentences in a book is essential Impose challenge for the query language

Relational Model Ordering is dependent on values Rows not considered to have ordering


XML Data vs Relational Data Null Values

XML Model Representing missing value by absence of

element Retrieving missing value results empty list Need rule on how handle empty list

Relational Model “null” value to represent missing value Rules for operators in the presence of null


XML Data vs Relational Data Structural Transformations

XML Model Queries on XML documents and generate

new XML documents XPath 2.0 – navigating inside a document XQuery – joining elements, constructing new

elements/structures

Relational Model Queries on tables and generate new tables


XML Data vs Relational Data Data Definition

XML Model Mixture of primitive data and nested

elements Elements may be optional Constraints on cardinality and order Impose challenges on type inference

Ex: proving output satisfies a given schema?

Relational Model Specifying the properties of columns All rows have same columns Relatively simple


Road Map



XPath 2.0What’s XPath?

XPath is a specification for defining parts of an XML document. XPath 2.0 provides a method to locate individual node or set of nodes in

a XML data model.

XPath 2.0 is close related to XQuery Same data model based on XML data model (infoset) XQuery uses XPath to refer to information in the data model

XPath 2.0 uses path expressions to navigate in XML documents XPath 2.0 uses path expressions to select nodes in an XML document. An XPath expression evaluates to a sequence of nodes These path expressions look very much like the expressions you see whe

n you work with a traditional computer file system.

XPath 2.0 is a W3C recommendation


XPath 2.0Data model

Represent various values including the input and the output of a query all values of expressions used during the intermediate

calculations.

Based on XML infoset data model Shared with XQuery Model XML data as trees

Sequence based data model Using sequence to represent set of trees or tree fragments Everything is sequence Sequences never contain other sequences


XPath 2.0Data model

A tree whose root node is a Document Node is referred to as a document.

A tree whose root node is not a Document Node is referred to as a fragment.


XPath 2.0Data model

Every instance of the data model is a sequence

A sequence may contain nodes, atomic values, or any mixture of nodes and atomic values

A sequence is an ordered collection of zero or more items

An item is either a node or an atomic value A single item appearing on its own is

modeled as a sequence containing one item.


XPath 2.0Data model

There are seven kinds of Nodes in the data model: Document node Element node Attribute node Text node Namespace node processing instruction node Comment node


XPath 2.0Sample XML Document

<?xml version="1.0" encoding="ISO-8859-1"?> <bookstore>

<book category="COOKING"> <title lang="en">Everyday Italian</title> <author>Giada De Laurentiis</author> <year>2005</year> <price>30.00</price> </book>

<book category="CHILDREN"> <title lang="en">Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price> </book>

<book category="WEB"> <title lang="en">XQuery Kick

Start</title>

<author>James McGovern</author> <author>Per Bothner</author> <author>Kurt Cagle</author> <author>James Linn</author> <author>Vaidyanathan Nagarajan</author> <year>2003</year> <price>49.99</price> </book>

<book category="WEB"> <title lang="en">Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> <price>39.95</price> </book>

</bookstore>

Books.xml


XPath 2.0Example

<book category="COOKING"> <title lang="en">Everyday Italian</title> <author>Giada De Laurentiis</author> <year>2005</year> <price>30.00</price> </book>

<book category="CHILDREN"> <title lang="en">Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price> </book>

<book category="WEB"> <title lang="en">XQuery Kick Start</title>

<author>James McGovern</author> <author>Per Bothner</author> <author>Kurt Cagle</author> <author>James Linn</author> <author>Vaidyanathan Nagarajan</author> <year>2003</year> <price>49.99</price> </book>

<book category="WEB"> <title lang="en">Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> <price>39.95</price> </book>

/bookstore/book evaluated to a sequence of nodes, each node corresponding to a book element:

//book evaluated to the same result


XPath 2.0Example

<book category="WEB"> <title lang="en">XQuery Kick Start</title> <author>James McGovern</author> <author>Per Bothner</author> <author>Kurt Cagle</author> <author>James Linn</author> <author>Vaidyanathan Nagarajan</author> <year>2003</year> <price>49.99</price> </book>

<book category="WEB"> <title lang="en">Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> <price>39.95</price></book>

//book[@category=“WEB”] evaluates to a sequence containing 2 book element nodes:


XPath 2.0Example

some $x in //book satisfies $x/price > 49 evaluates to a sequence containing a atomic value TRUE

every $x in //book satisfies $x/price > 49 evaluates to a sequence containing a atomic value FALSE


XPath 2.0Example

<book category="COOKING">

<title lang="en">Everyday Italian</title>

<author>Giada De Laurentiis</author>

<year>2005</year>

<price>30.00</price>

</book>

/bookstore/book[position()=1] evaluated to a sequence containing one element node:


Road Map



XQueryWhat’s XQuery?

The language for querying XML data XQuery is a language for finding and extracting elements

and attributes from XML documents.

XQuery for XML is like SQL for relational databases

Lots of the concepts and techniques used in SQL processing and optimization can be applied to XQuery processing and optimization.



XQuery is built on XPath 2.0 expressions XQuery 1.0 and XPath 2.0 share the same data model Support the same functions and operators. Understanding XPath 2.0 is essential to understanding XQ

uery.

Supported by all the major database venders

IBM Oracle Microsoft etc



closed with respect to a data model value of every expression in the language is guaranteed t

o be in the data model. XPath 2.0 is also closed

Designed to be a functional language No side-effect Processing and producing sequences

XQuery is becoming a W3C standard Current draft version is XQuery 1.0 Not yet a W3C Recommendation (XQuery is a Working Dra

ft)


XQueryFLWOR expression

For expression binds a variable with each element in a sequence iteratively

Let expression binds a variable with a sequence

Where expression applies conditions during For expression binding

Order By sort the output of the For expression

Return expression returns a sequence

York University 35

XQuerysample XML document – bib.xml<bib> <book year="1994"> <title>TCP/IP Illustrated</title> <author><last>Stevens</last><first>W.</first></author> <publisher>Addison-Wesley</publisher> <price>65.95</price> </book> <book year="1992"> <title>Advanced Programming in the Unix environment</title> <author><last>Stevens</last><first>W.</first></author> <publisher>Addison-Wesley</publisher> <price>65.95</price> </book> <book year="2000"> <title>Data on the Web</title> <author><last>Abiteboul</last><first>Serge</first></author> <author><last>Buneman</last><first>Peter</first></author> <author><last>Suciu</last><first>Dan</first></author> <publisher>Morgan Kaufmann Publishers</publisher> <price>39.95</price> </book> <book year="1999"> <title>The Economics of Technology and Content for Digital TV</title> <editor> <last>Gerbarg</last><first>Darcy</first> <affiliation>CITI</affiliation> </editor> <publisher>Kluwer Academic Publishers</publisher> <price>129.95</price> </book></bib>


XQuerysample XML document – reviews.xml<reviews> <entry> <title>Data on the Web</title> <price>34.95</price> <review> A very good discussion of semi-structured database systems and XML. </review> </entry> <entry> <title>Advanced Programming in the Unix environment</title> <price>65.95</price> <review> A clear and detailed discussion of UNIX programming. </review> </entry> <entry> <title>TCP/IP Illustrated</title> <price>65.95</price> <review> One of the best books on TCP/IP. </review> </entry></reviews>


XQuerysample XML document – prices.xml

<prices> <book> <title>Advanced Programming in the Unix environment</title> <source>bstore2.example.com</source> <price>65.95</price> </book> <book> <title>Advanced Programming in the Unix environment</title> <source>bstore1.example.com</source> <price>65.95</price> </book> <book> <title>TCP/IP Illustrated</title> <source>bstore2.example.com</source> <price>65.95</price> </book> <book> <title>TCP/IP Illustrated</title> <source>bstore1.example.com</source> <price>65.95</price> </book> <book> <title>Data on the Web</title> <source>bstore2.example.com</source> <price>34.95</price> </book> <book> <title>Data on the Web</title> <source>bstore1.example.com</source> <price>39.95</price> </book></prices>


XQueryExample 1

Solution in XQuery:

<bib> { for $b in doc("bib.xml")/bib/book where $b/publisher = "Addison-Wesley" and $b/@year > 1991 return <book year="{ $b/@year }"> { $b/title } </book> }</bib>

Result:

<bib> <book year="1994"> <title>TCP/IP Illustrated</title> </book> <book year="1992"> <title>Advanced Programming in the Unix environment</title> </book></bib>

List books published by Addison-Wesley after 1991, including their year and title


XQueryExample 2

Solution in XQuery:

for $b in doc("bib.xml")/bib/book, $t in $b/title, $a in $b/author return <result> { $t } { $a } </result>

Result:

<result> <title>TCP/IP Illustrated</title> <author><last>Stevens</last><first>W.</first></author></result><result> <title>Advanced Programming in the Unix environment</title> <author><last>Stevens</last><first>W.</first></author></result><result> <title>Data on the Web</title> <author><last>Abiteboul</last><first>Serge</first></author></result><result> <title>Data on the Web</title> <author><last>Buneman</last><first>Peter</first></author></result><result> <title>Data on the Web</title> <author><last>Suciu</last><first>Dan</first></author></result>

Create a flat list of all the title-author pairs


XQueryExample 3

Solution in XQuery:

for $b in doc("bib.xml")/bib/book

return <result> { $b/title } { $b/author } </result>

Result:

<result> <title>TCP/IP Illustrated</title> <author><last>Stevens</last><first>W.</first></author></result><result> <title>Advanced Programming in the Unix environment</title

> <author><last>Stevens</last><first>W.</first></author></result><result> <title>Data on the Web</title> <author><last>Abiteboul</last><first>Serge</first></author

> <author><last>Buneman</last><first>Peter</first></author> <author><last>Suciu</last><first>Dan</first></author></result><result> <title>The Economics of Technology and Content for Digital

TV</title></result>>

For each book in the bibliography, list the title and authors


XQueryExample 4

Solution in XQuery:

<books-with-prices> { for $b in doc("bib.xml")//book, $a in doc("reviews.xml")//entry where $b/title = $a/title return <book-with-prices> { $b/title } <bib-price>

{ $a/price/text() } </bib-price> <review-price> { $b/price/text() } </review-price> </book-with-prices> }</books-with-prices>

Result:

<books-with-prices> <book-with-prices> <title>TCP/IP Illustrated</title> <price-bstore2>65.95</price-bstore2> <price-bstore1>65.95</price-bstore1> </book-with-prices> <book-with-prices> <title>Advanced Programming in the Unix

environment</title> <price-bstore2>65.95</price-bstore2> <price-bstore1>65.95</price-bstore1> </book-with-prices> <book-with-prices> <title>Data on the Web</title> <price-bstore2>34.95</price-bstore2> <price-bstore1>39.95</price-bstore1> </book-with-prices></books-with-prices>

For each book found at both bib.xml and reviews.xml, list the title of the book and its price from each source


XQueryExample 5

Solution in XQuery:

<bib> { for $b in doc("bib.xml")//book where $b/publisher = "Addison-Wesley" and $b/@year > 1991 order by $b/title return <book> { $b/@year } { $b/title } </book> }</bib>

Result:

<bib> <book year="1992"> <title> Advanced Programming in the Unix environment </title> </book> <book year="1994"> <title>TCP/IP Illustrated</title> </book></bib>

List the titles and years of all books published by Addison-Wesley after 1991, in alphabetic order


XQueryExample 6

Solution in XQuery:

<results> { let $doc := doc("prices.xml") for $t in distinct-values($doc//book/title) let $p := $doc//book[title = $t]/price return <minprice title="{ $t }"> <price>{ min($p) }</price> </minprice> }</results>

Result:

<results> <minprice title="Advanced Programming in the Unix environ

ment"> <price>65.95</price> </minprice> <minprice title="TCP/IP Illustrated"> <price>65.95</price> </minprice> <minprice title="Data on the Web"> <price>34.95</price> </minprice></results>

In the document “prices.xml”, find the minimum price for each book, in the form of a “miniprice” element with the book title as its title attribute

York University 44

XQuerysample XML document – book.xml

<?xml version="1.0"?><book> <title>Data on the Web</title> <author>Serge Abiteboul</author> <author>Peter Buneman</author> <author>Dan Suciu</author> <section id="intro" difficulty="easy" > <title>Introduction</title> <p>Text ... </p> <section> <title>Audience</title> <p>Text ... </p> </section> <section> <title>Web Data and the Two

Cultures</title> <p>Text ... </p> <figure height="400" width="400"> <title>Traditional client/server

architecture</title> <image source="csarch.gif"/> </figure> <p>Text ... </p> </section> </section> <section id="syntax" difficulty="medium" > <title>A Syntax For Data</title>

<p>Text ... </p> <figure height="200" width="500"> <title>Graph representations of structures</title

> <image source="graphs.gif"/> </figure> <p>Text ... </p> <section> <title>Base Types</title> <p>Text ... </p> </section> <section> <title>Representing Relational Databases</title

> <p>Text ... </p> <figure height="250" width="400"> <title>Examples of Relations</title> <image source="relations.gif"/> </figure> </section> <section> <title>Representing Object Databases</title> <p>Text ... </p> </section> </section></book>


XQueryExample 7

Solution in XQuery:

declare function local:toc( $book-or-section as element()) as element()*

{ for $section in $book-or-section/section return <section> { $section/@*, $section/title, local:toc($section) } </section>};

<toc> { for $s in doc("book.xml")/book return local:toc($s) }</toc>

<toc> <section id="intro" difficulty="easy"> <title>Introduction</title> <section> <title>Audience</title> </section> <section> <title>Web Data and the Two Cultures</title> </section> </section> <section id="syntax" difficulty="medium"> <title>A Syntax For Data</title> <section> <title>Base Types</title> </section> <section> <title>Representing Relational Databases</title> </section> <section> <title>Representing Object Databases</title> </section> </section></toc>

Prepare a (nested) table of contents, listing all sections and their titles. Preserve the original attributes of each <section> element, if any


Road Map



Processing XQueryApproaches for querying XML data

Mapping XML data into relational data Query with SQL May produces too many relations Loses of information may occurs

Ex: ordering, explicit hierarchical relationship between elements

Using specific query languages Usually integrated with SQL and relational data

management SQL/XML or XQuery


Processing XQueryIBM System RX SQL/XQuery compiler

A new XQuery parser is added to the existing relational query processing

All components extended to process XQuery


Processing XQueryOracle XQuery Compilation Engine

Parser convert XQuery into XQueryX

XQueryX is an XML representation of XQuery (another W3C candidate recommendation)

XML parser construct a DOM tree from XQueryX

Work on the DOM afterward

Corresponding components are extended for XQuery too


Processing XQueryMicrosoft XQuery compilation

XQuery compiled into XML algebra tree, which is an internal representation

Algebra tree can be optimized and executed by relational query processor

Optimizations are rule-based

Mapper traverses the algebra tree, converting each XML operator into a relational operator sub-tree


References M. Nicola, Bert van der Linden. Native XML Support in DB2

Universal Database. Proceeding of the 31st VLDB Conference, Trondheim, Norway, 2005

Kevin Beyer, Chun Zhang, etc. System RX: One Part Relational, One Part XML. SIGMOD 2005, Baltimore, Maryland, USA.

Shankar Pal, Istvan Cseri, etc. XQuery Implementation in a Relational Database System. Proceedings of the 31st VLDB Conference

Zhen Hua Liu, Vikas Arora. Native XQuery Processing in Oracle XMLDB. SIGMOD 2005, Baltimore, Maryland, USA

Scott Boag, Don Chamberlin, etc. XQuery 1.0: An XML Query Language. http://www.w3.org/TR/xquery/

Mary Fernandaz, Norman Walsh, etc. XQuery 1.0 and XPath 2.0 Data Model. http://www.w3.org/TR/xpath-datamodel/

Date post:	27-Dec-2015
Category:	Documents
Upload:	antony-underwood
View:	235 times
Download:	3 times

Introduction to XML and XQuery Guangjun (Kevin) Xie.

Documents