dr. alexandra i. cristea acristea/ xml
TRANSCRIPT
Dr. Alexandra I. Cristea
http://www.dcs.warwick.ac.uk/~acristea/
XML
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XML history• Inception: circa 1996 • The Extensible Markup Language (XML)
became a W3C Recommendation 10. February 1998.
• It’s being used currently in very many places – see HESA
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What is XML?• XML stands for EXtensible Markup
Language • XML was designed to describe data • XML is more of a standard and
supporting structure than a standalone programming language
• XML is a markup language much like HTML – wrong!: meta-language
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How does XML work?• XML tags are not predefined. You must
define your own tags • XML uses a Document Type
Definition (DTD) or an XML Schema to describe the data
• XML with a DTD or XML Schema is designed to be self-descriptive
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XML is Free and Extensible• XML tags are not predefined. You must
"invent" your own tags.• The tags used to mark up HTML documents
and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard (like <p>, <h1>, etc.).
• XHTML is XML but not vice-versa.
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XML does not DO anything• XML was created to structure, store and to send
information
<note> <to>John</to> <from>Jane</from>
<heading>Reminder</heading> <body>Don't forget the book!</body>
</note>
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Main Difference XML, HTML• XML was designed to carry data.• XML is not a replacement for HTML.
XML and HTML were designed with different goals:– XML was designed to describe data and to focus on what
data is.
– HTML was designed to display data and to focus on how data looks.
• HTML is about displaying information, while XML is about describing information.
• Syntax: XML is well formed, just like XHTML
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XML is a Complement to HTML
• XML is not a replacement for HTML.– In Web development XML is used to
describe the data, while HTML is used to format and display the same data.
• XML is a cross-platform, software and hardware independent tool for transmitting information.
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Benefits XML• extensibility and structured nature of XML
allows it to be used for communication between different systems
• from one source of XML-based information you can format and distribute it via a multitude of different channels – XSL files act as templates, allowing a single
stylesheet to be used to format multiple pages or the same content for multiple distribution channels
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XML in Web Development
• XML is everywhere.• the XML standard has been developed
quickly and a large number of software vendors have adopted it.
• XML might be the most common tool for all data manipulation and data transmission.
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XML Can be Used to Create New Languages• XML is the mother of WAP and WML.
– WAP: standard for web browser for mobile devices
– The Wireless Markup Language (WML), used to markup Internet applications for handheld devices like mobile phones, is written in XML.
• And many others … search for more as homework
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• Question: When should I use XML?• Answer: When you need a buzzword in
your resume.
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Viewing XML• to view XML documents hierarchically or view
their output, you need an XML parser and processor.
• there are a number of these tools available:• See examples at: • http://www.stylusstudio.com/xml_download.html • http://www.w3schools.com/xml/xml_parser.asp • Please note, however: XML was not designed to
display data.
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The basic XML flow
XML-based languages
• RSS• Twitter API• MathML• SVG• SOAP• WSDL• Microsoft Office (pptx, docx, xlsx)• Open Office XML• SMIL• RDF
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XML Rules1. Every start-tag must have a matching end-tag.
2. Tags cannot overlap. Proper nesting is required.
3. XML documents can only have one root element.
4. Element names must obey the following XML naming conventions: a) Names must start with letters or the "_" character.
Names cannot start with numbers of punctuation characters.
b) After the first character, numbers and punctuation characters are allowed.
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XML Rules (cont.)
c) Names cannot contain spaces. d) Names should not contain the ":" character as it is a
"reserved" character. e) Names cannot start with the letters "xml" in any
combination of case. f) The element name must come directly after the "<" without
any spaces between them.
5. XML is case sensitive. 6. XML preserves white space within text. 7. Elements may contain attributes. If an attribute is
present, it must have a value, even if it is an empty string "".
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Spot the error!
<?xml version="1.0" encoding="ISO-8859-1"?> <note date=12/11/2002>
<to>Tove</to> <from>Jani</from>
</note>
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Spot the error!
<?xml version="1.0" encoding="ISO-8859-1"?> <note date="12/11/2002">
<to>Tove</to> <from>Jani</from>
</note>
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With XML, CR / LF is converted to LF
• Windows: CR + LF• Unix: LF• Macintosh: CR
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There is Nothing Special About XML
• plain text w XML tags • Software that can handle plain text can
also handle XML. • In an XML-aware application, the XML
tags can be handled specially: – Visibility,– Functional meaning, etc.
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Is this an error?
<note>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this weekend!</body>
</note>
<heading>Reminder</heading>
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XML Elements have Relationships
• Elements are related as parents and children.
• Root element / Parents• Children / Siblings
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Elements• An element consists of all the information from the
beginning of a start-tag to the end of an end-tag including everything in between.
• E.g. from (X)HTML, all of the following would be the equivalent of one element, named h1:
<h1>This is a heading.</h1> – Where, <h1> is the start tag, </h1> is the end tag, and the
content is in between. • Each XML document has a root element within which
all other elements are nested.
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Examples• See at:
– http://www.dcs.warwick.ac.uk/~acristea/courses/CS253/2009/books.xml
– http://feeds.bbci.co.uk/news/rss.xml– Search more by yourself and familiarize
yourself with the syntax!
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XML Attributes• XML elements can have attributes.
• From HTML you will remember this: <IMG SRC="computer.gif">
• The SRC attribute provides additional information about the IMG element.
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Attributes versus Elements• <person sex="female">
<firstname>Anna</firstname> <lastname>Smith</lastname> </person>
• <person> <sex>female</sex> <firstname>Anna</firstname> <lastname>Smith</lastname> </person>
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Comments• same as in any other languages with line(s) of
code whose sole purpose is to provide the developer, and anyone reading the code in the future, information about the code.
<!-- all the comments go in here -->
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XML Validation: Well Formed-ness
• An XML document is well formed, if all the XML rules are obeyed.
(with 7 XML rules as defined in slides 16-17)
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XML declaration
• Every XML document begins with a declaration (not mandatory, good practice)
<?xml version="1.0"?> • Or, using optional attributes:<?xml version="1.0" encoding=“UTF-16” standalone="yes"?>
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Document Type Definition (DTD)
• which tags and attributes are allowed, • where they can be placed, and • whether or not they can be nested
within a given document.
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Document Type Declaration (DOCTYPE)
• <!DOCTYPE MovieCatalog SYSTEM "movie_catalog.dtd">
Root document element
URL to DTD(external subset via a system identifier)
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Internal vs External DTD declaration
Internal:
<!DOCTYPE foo [ <!ENTITY greeting "hello"> ]>
External, public:
<!DOCTYPE html PUBLIC "//W3C//DTD HTML 4.01//EN” >
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Valid XML Documents• A "Valid" XML document is a "Well Formed"
XML document, which also conforms to the rules of a Document Type Definition (DTD):
<?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE note SYSTEM "Note.dtd"> <note> <to>Tom</to> <from>Jane</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body>
</note>
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Validators• http://xmlvalidator.new-studio.org/
• Also at: http://validator.w3.org/#validate_by_input
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Internal DTD<?xml version="1.0"?> <!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> ]> <note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>
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External DTD
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
>> saved as file Note.dtd
Attributes in DTDs• Syntax:
<!ATTLIST element-name attribute-name attribute-type attribute-value>
• Example:<!ATTLIST body lang CDATA "EN">
• Usage (in XML doc):<body lang="EN"/>
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Attribute-value can be an actual value, or #REQUIRED or #IMPLIED or even #FIXED value
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XML Schema (XSD)• XML Schema is an XML based
alternative to DTD. • W3C supports an alternative to DTD
called XML Schema:http://www.w3.org/XML/Schema
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Displaying your XML Files with CSS?• It is possible to use CSS to format an XML document.• Example:• XML file: The CD catalog• style sheet: The CSS file• product: The CD catalog formatted with the CSS file• Below is a fraction of the XML file. The second line,
<?xml-stylesheet type="text/css" href="cd_catalog.css"?>, links the XML file to the CSS file
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Displaying XML with XSL• XSL is the preferred style sheet language
of XML.• XSL (the eXtensible Stylesheet Language) is
far more sophisticated than CSS. • examples:
– View the XML file, the XSL style sheet, and View the result.
<?xml version="1.0" encoding="ISO-8859-1"?> <?xml-stylesheet type="text/xsl" href=“simple.xsl"?>
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XML Conclusions• We have learned:
– XML history– What it is– How it works– Differences to (X)HTML– XML flow– XML Rules– XML Elements, Relationships, Attributes,
Comments– Well-formed-ness concept– XML supporting frame: XML Schema or DTD– Generics on displaying XML
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Why an XML Editor?• XML Schema to define XML structures and data
types • XSLT to transform XML data • SOAP to exchange XML data between applications • WSDL to describe web services • RDF to describe web resources • XPath and XQuery to access XML data • SMIL to define graphics • Altova's XMLSpy
– 30 days free trial– http://www.altova.com/xmlspy.html– http://www.altova.com/products/xmlspy/xsl_xslt_editor.html
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• Next:– We look at how to access elements and
attributes inside the XML– This can be done via …
– XPATH
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• Previously we looked at:– XML
• Next:– XPath– Namespaces
Validity versus well-formedness• Checking for well-formedness:
– http://www.xmlvalidation.com/– http://www.w3schools.com/xml/xml_validator.asp
• Checking for validity:– http://www.validome.org/xml/validate/
• As a homework, check the validity and well-formedness of various XML documents in this course and on the web. Pay attention to the difference.
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XPath• XPath is a syntax for defining parts of an XML
document • XPath uses path expressions to navigate in XML
documents • XPath contains a library of standard functions • XPath is a major element in XSLT • XPath is a W3C recommendation, thus a
Standard (16. November 1999; newest Dec. 2010 )
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XPath Path Expressions• Uses path expressions to select nodes
or node-sets in an XML document. – These path expressions look very much
like the expressions you see when you work with a traditional computer file system.
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XPath Standard Functions• over 100 built-in functions.
– string values, – numeric values, – date and time comparison, – node and QName manipulation, – sequence manipulation, – Boolean values, – and more.
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XPath Terminology• Nodes• Atomic values• Items (atomic values or nodes)• Relationships of nodes
– Parent– Children– Siblings– Ancestors– Descendants
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XPath Nodes• 7 kinds of nodes:
1. element,
2. attribute,
3. text,
4. namespace,
5. processing-instruction,
6. comment, and
7. document (root) nodes. • XML documents are treated as trees of nodes. The root
of the tree is called the document node (or root node).
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Nodes Examples<?xml version="1.0" encoding="ISO-8859-1"?> <bookstore> <book> <title lang="en">Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price> </book>
</bookstore>
Document (root) node
Element node
Attribute node
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Atomic values Examples*<?xml version="1.0" encoding="ISO-8859-1"?> <bookstore> <book> <title lang="en">Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price> </book> </bookstore>
*nodes with no children or parent
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Selecting nodes
Expression Description
nodename Selects all child nodes with this name
/ Selects from the root node
// Selects nodes in the document from the current node down that match the selection no matter where they are
. Selects the current node
.. Selects the parent of the current node
@ Selects attributes
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Examples of selecting nodesPath Expression Result
bookstore Selects all the bookstore elements
/bookstore Selects the root element bookstoreNote: If the path starts with a slash ( / ) it always represents an absolute path to an element!
bookstore/book Selects all book elements that are children of bookstore
//book
bookstore//book
//@lang Selects all attributes that are named lang
Selects all book elements no matter where they are in the document
Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
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Predicates• Predicates are used to find a specific
node or a node that contains a specific value.
• Predicates are always embedded in square brackets.
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Example predicates
Path Expression Result
/bookstore/book[1] Selects the first book element that is the child of the bookstore element
/bookstore/book[last()] Selects the last book element that is the child of the bookstore element
/bookstore/book[last()-1]
/bookstore/book[position()<3]
Selects the last but one book element thatis the child of the bookstore element
Selects the first two book elements that are children of the bookstore element
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Example predicates – cont. Path Expression Result
//title[@lang] Selects all the title elements that have an attribute named lang
//title[@lang='eng'] Selects all the title elements that have an attribute named lang with a value of 'eng'
/bookstore/book[price>35.00]
/bookstore/book[price>35.00]/title
Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00
Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00
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Selecting Unknown Nodes
Wildcard Description
* Matches any element node
@* Matches any attribute node
node() Matches any node of any kind
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Example: selecting several paths
Path Expression Result//book/title | //book/price Selects all the title as well as price
elements of all book elements
//title | //price
/bookstore/book/title | //priceSelects all the title as well as price elements in the documentSelects all the title elements of the book element of the bookstore element as well as all the price elements in the document
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XPath Axesself
child parent
ancestor descendant
ancestor-or-self descendant-or-self
preceding-sibling following-sibling
preceding following
attribute
namespace
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axisname::nodetest[predicate] • //DDD/parent::*
<AAA> <BBB> <DDD>
</DDD> </BBB>
</AAA>
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axisname::nodetest[predicate] • //BBB/child::*
<AAA> <BBB> <DDD>
</DDD> </BBB>
</AAA>
Note: /AAA is equivalent to /child::AAA
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More examples• http://zvon.org/comp/r/tut-XPath_1.html
• Check basics, //, *, predicates, attributes, functions (new ones: count, name, normalize-space, starts-with, contains, string-length, floor, ceiling), axes, operators (mod)– Note: The ancestor, descendant, following,
preceding and self axes partition a document (ignoring attribute and namespace nodes): they do not overlap and together they contain all the nodes in the document. (see example)
XPath Try-out• XPath online:
http://www.freeformatter.com/xpath-tester.html#ad-output
• You can use an existing XML:– http://www.dcs.warwick.ac.uk/~acristea/courses/CS25
3/2008/books.xml
• Use XPath snippets from module or create your own:– //title | //price– /bookstore/book[last()]– /bookstore/book[last()-1]– /bookstore/book[position()<3] etc.
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XPath Conclusion• We have learned:
– XPath definition– Path expressions– Standard functions– Terminology– Predicates– Location paths– Axes– Some operators
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• Before we go on, one more thing about XML:
• XML Namespaces
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Naming ambiguity
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The Idea to Solve it
• Assign a URI (~ URL) to every sub-language:– E.g., for XHTML 1.0:
http://www.w3.org/1999/xhtml• Qnames: Qualify element names with
URIs:– {http://www.w3.org/1999/xhtml}head
Web Naming and Addressing Overview (URIs, URLs, ...)
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The actual solution• Namespace declarations bind URIs to
prefixes:• Default namespace (no prefix) declared
with: xmlns=“…”• Lexical Scope• Attribute names can also be prefixed
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Applying namespaces
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• Next we look at how to query XML• This can be done, to some extent, as
we have seen, within XPath (or XSLT), • but the main language developed for
this purpose is …
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• Previously we looked at:– XPath– Namespaces
• Next:– XQuery
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What is XQuery?• XQuery is the language for querying XML data • XQuery for XML is like SQL for databases • XQuery is built on XPath expressions • XQuery is defined by the W3C • XQuery is supported by all the major database
engines (IBM, Oracle, Microsoft, etc.) • XQuery is a W3C recommendation (Jan 2007;
latest 14 Dec 2010) thus a standard
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XQuery - Examples of Use
• Extract information to use in a Web Service • Generate summary reports • Transform XML data to XHTML • Search Web documents for relevant
information
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XQuery compared to XPath
• XQuery 1.0 and XPath 2.0 share the same data model and support the same functions and operators.
• XQuery 1.0 is a strict superset of XPath 2.0• XPath 2.0 expression is directly an XQuery 1.0
expression (a query)• The extra expressive power is the ability to:
– Join information from different sources and– Generate new XML fragments
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XQuery ‘compilers’
• Download: http://www.altova.com/altovaxml.html
• Syntax check at: http://www.w3.org/2007/01/applets/xqueryApplet.html
• XPath, XQuery tester:http://www.xpathtester.com/xqueryhttp://brettz9.github.io/xqueryeditor/
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XQuery query makeup
• Prolog– Like XPath, XQuery expressions are evaluated
relatively to a context– explicitly provided by a prolog (header)~ header with definitions
• Body– The actual query
• Select• Join• Generate
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XQuery Ex.: Prolog + Query
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XQuery Prolog (i.e., header(s))• Settings define various parameters for the XQuery processor language,
such as:xquery version "1.0";
declare base-uri "http://example.org";declare default element namespace
"http://example.org/names";declare namespace xs= "http://www.w3.org/2001/XMLSchema";import module "http://www.w3.org/2003/05/xpath-functions"
at "logo.xq";declare variable $x as xs:integer := 7;declare function addLogo($root as node()) as node()*{ };(: etc :)
Module definition
xquery version "1.0";module namespace mylib = "http://www.example.com/test_library";
declare variable $mylib:foo as xs:string := "foo";
declare function mylib:foobar() as xs:string
{
concat ($mylib:foo, "bar")
};
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Body: Constructors
Direct constructors in XQuery:
<XMLfragment>my fragment </XMLfragment>
– Evaluates to the given XML fragment
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Explicit constructors
computed constructors
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Variable bindings (implicit constructors)
<employee empid="{$id}"> <name>{$name}</name>
{$job} <deptno>{$deptno}</deptno> <salary>{$SGMLspecialist+100000}</salary>
</employee>
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How to Select Nodes with XQuery?
• Functions– XQuery uses functions to extract data from XML
documents.• (X)Path Expressions
– XQuery uses path expressions to navigate through elements in an XML document.
• Predicates– XQuery uses predicates to limit the extracted
data from XML documents.
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Functions• doc()
– function to open a file• Example:
– doc("books.xml")
• Note: A call to a function can appear where an expression may appear.
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Path Expressions
• Example:select all the title elements in the "books.xml"
file:
doc("books.xml")/bookstore/book/title
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Predicates• Example:
select all the book elements under the bookstore element that have a price element with a value that is less than 30 :
doc("books.xml")/bookstore/book[price<30]
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At a glance: function, path, predicate
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FLWOR• For, Let, Where, Order by, Return
= main engine
~ SQL syntax (SFW(GH)O)
~ programs and function calls
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FLWOR by comparison with Path expressions
• select all the title elements under the book elements that are under the bookstore element that have a price element with
a value that is higher than 30.
• Path expression:doc("books.xml")/bookstore/book[price>30]/title
• FLWOR expression: for $x in doc("books.xml")/bookstore/book where $x/price>30 return $x/title
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Sorting in FLWOR• for $x in doc("books.xml")/bookstore/book
where $x/price>30 order by $x/title return $x/title
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Present the Result as HTML List
<ul>
{
for $x in doc("books.xml")/bookstore/book/title
order by $x
return <li>{$x}</li>
}
</ul>
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Result HTML List
<ul> <li><title lang="en">Everyday
Italian</title></li> <li><title lang="en">Harry
Potter</title></li> <li><title lang="en">Learning
XML</title></li> <li><title lang="en">XQuery Kick
Start</title></li> </ul>
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Eliminate element (here: title)
<ul>
{
for $x in doc("books.xml")/bookstore/book/title
order by $x
return <li>{data($x)}</li> (: also text{} :)
}
</ul>
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New result HTML List
<ul>
<li>Everyday Italian</li>
<li>Harry Potter</li>
<li>Learning XML</li>
<li>XQuery Kick Start</li>
</ul>
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Another FLWOR Expression
<doubles>{ for $s in doc("students.xml")//student let $m := $s/major where count($m) ge 2 order by $s/@id return <double>
{ $s/name/text()} </double>}</doubles>
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The Difference between for and let
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The Difference between for and let
:=in
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The Difference between for and let
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The Difference between for and let
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FLWOR Basic Building Blocks
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General rules
• for and let may be used many times in any order
• only one where is allowed • many different sorting criteria can be
specified (descending, ascending, etc.)
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Reversing order• Reverses the order of a sequence, for
nodes or atomic values
• reverse (( 1, 2, 3))
-> 321
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Joining documentsfor $p in doc("www.irs.gov/taxpayers.xml")//person
for $n in doc("neighbors.xml")//neighbor[ssn = $p/ssn]
return
<person>
<ssn> { $p/ssn } </ssn>
{ $n/name }
<income> { $p/income } </income>
</person>
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Two-way join in a where Clause
for $item in doc(“ord.xml”)//item,
$product in doc(“cat.xml”)//product
where $item/@num = $product/number
return
<item num=“{$item/@num}”
name=“{$product/name}”
quan=“{$item/@quantity}” />
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Aggregating• Make summary calculations on grouped
data• Functions:
– sum, avg, max, min, count
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Conditionalsfor $b in doc(“bib.xml”)/book
return <short> {$b/title} <author> {if ( count($b/author) < 3 ) then $b/author else ( $b/author[1], <author>and others</author>) } </author> </short>
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Nesting Conditional Expressions
• Conditional expressions can be nested• ‘else if’ functionality is provided
• if ( count($b/author) = 1 ) then $b/author else if (count($b/author) = 2 )then (: .. :) else ( $b/author[1], <author>and others</author>)
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Logical Expressions• and, or operators:
– and has precedence over or– Parentheses can change precedence
if ($isDiscounted and ($discount > 5 or $discount < 0 ) ) then 5 else $discount
• not function for negations: if (not($isDiscounted)) then 0 else $discount
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XQuery Built-in Functions
XQuery function namespace URI is:http://www.w3.org/2005/02/xpath-functions
default prefix: fn:.• E.g.: fn:string() or fn:concat(). • fn: is the default prefix of the namespace, the
function names does not need to be prefixed when called.
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Built-in Functions• String-related
– substring, contains, matches, concat, normalize-space, tokenize
• Date-related– current-date, month-from-date, adjust-time-to-
timezone• Number-related
– round, avg, sum, ceiling• Sequence-related
– index-of, insert-before, reverse, subsequence, distinct-values
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Built-in Functions (2)• Node-related
– data, empty, exists, id, idref• Name-related
– local-name, in-scope-prefixes, QName, resolve-QName
• Error handling and trapping– error, trace, exactly-one
• Document and URI-related– collection, doc, root, base-uri
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Function calls
doc("books.xml")//book[substring(title,1,5)='Harry']
let $name := (substring($book/title,1,4))
<name>{upper-case($book/title)}</name>
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for $x in doc("http://www.dcs.warwick.ac.uk/~acristea/courses/CS253/2009/books.xml")//book/title
for $y in data($x)for $name in (substring($y,1,4))
return $name
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User Defined Functions
declare function prefix:function_name($parameter AS datatype)
AS returnDatatype
{ (: ...function code here... :) };
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User-defined Functionsdeclare function depth($e AS xsd:integer) AS xsd:integer
{ if (empty($e/*) then 1 else max(for $c in $e/* return depth($c)) ) +1};
(: usage :) for $b in doc(“bib.xml”)/book
return depth($b)
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Existential and Universal Quantifiers
• for $b in doc(“bib.xml”)/bookwhere some $author in $b/author satisfies $author/text() = “Ullman”return $b
• for $b in doc(“bib.xml”)/bookwhere every $author in $b/author satisfies $author/text() = “Ullman”return $b
Return books where all authors are “Ullman”
Return books where at least one author is “Ullman”
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Comments
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Comparisons• Value comparisons
Eq, ne, lt, le, gt, ge
Used to compare individual values
Each operand must be a single atomic value (or a node containing a single atomic value)
• General comparisons=, !=, <, <=, >, >=
Can be used with sequences of multiple items
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Example
Node comparisons• to compare two nodes, by their identity
or by their document order• Example:• The following comparison is true only if
the left and right sides each evaluate to exactly the same single node:
• /books/book[isbn="1558604820"] is /books/book[call="QA76.9 C3845"]
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Remember direct element constructors?
element book {
attribute isbn {"isbn-0060229357" },
element title { "Harold and the Purple Crayon"},
element author { element first { "Crockett" },
element last {"Johnson" }
}
}
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Using direct element constructors interestingly
let $e := <length units="inches">{5}</length>
return element {fn:node-name($e)}
{$e/@*, 2 * fn:data($e)}
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Other examples node comparison
• The following comparison is false because each constructed node has its own identity:
• <a>5</a> is <a>5</a> • The following comparison is true only if the
node identified by the left side occurs before the node identified by the right side in document order:
• /transactions/purchase[parcel="28-451"] << /transactions/sale[parcel="33-870"]
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XQuery Syntax• Declarative, functional language
~ SQL• Nested expressions• Case sensitive• White spaces:
– Tabs, space, CR, LF– Ignored between language constructs– Significant in quoted strings
• No special EOL character
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Keywords and names• Keywords and operators
– Case-sensitive, generally lower case– May have several meanings depending on the
context• E.g. “*” or “in”
– No reserved words
• All names must be valid XML names – variables, functions, elements, attributes– Can be associated with a namespace
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XQuery gives you a choice:• Path Expressions:
– If you just want to copy certain elements and attributes as is
• FLWOR Expressions:– Allow sorting– Allow adding elements/attributes– Verbose, but can be clearer
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XQuery tools• XStylus Studio 2007
http://www.stylusstudio.com/xml_download.html (free trial version)– See also short XQuery intro at:
http://www.stylusstudio.com/xquery_primer.html
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Other info:
–XQuery on Distributed Resources–Extensions for generic programming with XML
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XQuery on Distributed Sources
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XML and programming
• XSLT, XPath and XQuery provide tools for specialized tasks.
• But many applications are not covered: – domain-specific tools for concrete XML
languages – general tools that nobody has thought of yet
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XML in general-purpose programming languages
• parse XML documents into XML trees • navigate through XML trees • construct XML trees • output XML trees as XML documents • DOM and SAX are corresponding APIs that
are language independent and supported by numerous languages. JDOM is an API that is tailored to Java.
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XQuery Conclusion• We have learned:
– XQuery definition– Usage scenarios– Comparison w. XSLT and XPath– Capabilities– Functions, path expressions and
predicates– FLWOR