EXtensible Markup Language (XML) a W3C standard to complement HTML A markup language much like HTML

Transcription

1 XML and XPath

2 EXtensible Markup Language (XML) a W3C standard to complement HTML A markup language much like HTML origins: structured text SGML motivation: HTML describes presentation XML describes content HTML XML SGML (version 2, 10/2000) Web Services: XML+XPath 2

3 HTML Describes the Presentation Web Services: XML+XPath 3

4 HTML Describes the Presentation <h1>bibliography</h1> <p><i>foundations of Databases</i> Abiteboul, Hull, Vianu <br>addison Wesley, 1995 <p><i>data on the Web</i> Abiteoul, Buneman, Suciu <br>morgan Kaufmann, 1999 Web Services: XML+XPath 4

5 XML Describes the Contents <bibliography> <book><title> Foundations </title> <author> Abiteboul </author> <author> Hull </author> <author> Vianu </author> <publisher> Addison Wesley </publisher> <year> 1995 </year> </book> </bibliography> Web Services: XML+XPath 5

6 More on XML XML was designed to describe data contents XML tags are not predefined in XML. You must invent 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 Web Services: XML+XPath 6

7 Applications and Impact of XML Data can be stored outside HTML Data can be exchanged between incompatible systems Financial information can be exchanged over the Internet Plain text files can be used to share data Data is available to more users Used to create new languages WML, WSDL, BPEL, Web Services: XML+XPath 7

8 Benefits of Using XML XML is structured XML documents are easily committed to a persistence layer XML is platform independent, textual information XML is an open standard XML is language independent DOM and SAX are open, language-independent set of interfaces XML is web enabled XML is totally extensible XML supports shareable structure (using DTDs) XML enables interoperability Web Services: XML+XPath 8

9 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 Web Services: XML+XPath 9

10 Attributes are Alternative Ways to Represent Data <book price = 55 currency = USD > <title>foundations of Databases</title> <author>abiteboul</author> <year> 1995 </year> </book> Web Services: XML+XPath 10

11 CDATA Section Syntax: <![CDATA[...any text here...]]> <script> <![CDATA[ function matchwo (a, b) { if (a < b && a < 0) then { return 1 } else { return 0 } } ]]> </script> Web Services: XML+XPath 11

12 Entity References Syntax: &entityname; Example: <element> this is less than < </element> Some entities: < > & &apos; " & < > & Unicode char Web Services: XML+XPath 12

13 Processing Instructions Syntax: <?target argument?> Example: <product><name> Alarm Clock </name> <?ringbell 20?> <price>19.99</price> </product> What do they mean? Web Services: XML+XPath 13

14 XML Comments Syntax <!--... comment text... --> Yes, they are part of the data model!!! Web Services: XML+XPath 14

15 Name Conflicts <table> <tr> <td>apples</td> <td>bananas</td> </tr> </table> <table> <name>african Coffee Table </name> <width>80</width> <length>120</length> </table> Solution: prefix <h:table> <h:tr> <h:td>apples</h:td> <h:td>bananas</h:td> </h:tr> </h:table> <f:table> <f:name>african Coffee Table </f:name> <f:width>80</f:width> <f:length>120</f:length> </f:table> Web Services: XML+XPath 15

16 XML Namespaces syntactic: <number>, <isbn:number> semantic: provide URL for schema <tag xmlns:mystyle = http: // > <mystyle:title> </mystyle:title> <mystyle:number> </tag> Web Services: XML+XPath 16

17 XML Namespaces (1/99) name ::= [prefix:]localpart <book xmlns:isbn= > <title> </title> <number> 15 </number> <isbn:number> </isbn:number> </book> Web Services: XML+XPath 17

18 XPath (11/99) Building block for other W3C standards: XSL Transformations (XSLT) XML Link (XLink) XML Pointer (XPointer) XML Query Was originally part of XSL Web Services: XML+XPath 18

19 Example for XPath Queries <bib> <book> <publisher> Addison-Wesley </publisher> <author> Serge Abiteboul </author> <author> <first-name> Rick </first-name> <last-name> Hull </last-name></author> <author> Victor Vianu </author> <title> Foundations of Databases </title> <year> 1995 </year> </book> <book price= 55 > <publisher> Freeman </publisher> <author> Jeffrey D. Ullman </author> <title> Principles of Database and Knowledge Base Systems </title> <year> 1998 </year> </book> </bib> Web Services: XML+XPath 19

20 Data Model for XPath The root Processing instruction Comment bib The root element book book publisher author.... Addison- Wesley Serge Abiteboul Web Services: XML+XPath 20

21 Simple Expressions /bib/book/year Result: <year> 1995 </year> <year> 1998 </year> /bib/paper/year Result: empty (there were no papers) Web Services: XML+XPath 21

22 Restricted Kleene Closure //author Result: <author> Serge Abiteboul </author> <author><first-name> Rick </first-name> <last-name> Hull </last-name> </author> <author> Victor Vianu </author> <author> Jeffrey D. Ullman </author> /bib//first-name Result: <first-name> Rick </first-name> Web Services: XML+XPath 22

23 Functions /bib/book/author/text() Result: Serge Abiteboul Victor Vianu Jeffrey D. Ullman Rick Hull doesn t appear because he has firstname, lastname Functions in XPath: text() = matches the text value node() = matches any node (= * or text()) name() = returns the name of the current tag Web Services: XML+XPath 23

24 Wildcard //author/ Result: <first-name> Rick </first-name> <last-name> Hull </last-name> Matches any element Web Services: XML+XPath 24

25 Attribute Nodes Result: means that price is has to be an attribute Web Services: XML+XPath 25

26 Qualifiers /bib/book/author[first-name] Result: <author><first-name> Rick </first-name> <last-name> Hull </last-name> </author> /bib/book/author[firstname][address[//zip][city]]/lastname Result: <lastname> </lastname> <lastname> </lastname> Web Services: XML+XPath 26

27 More Qualifiers < 60 ] /bib/book[author/@age < 25 ] /bib/book[author/text()] Web Services: XML+XPath 27

28 XPath Summary bib matches a bib element matches any element / matches the root element /bib matches a bib element under root bib/paper matches a paper in bib bib//paper matches a paper in bib, at any depth //paper matches a paper at any depth paper book matches a paper or a matches a price attribute bib/book/@price matches price attribute in book, in bib bib/book[@price< 55 ]/author/lastname matches Web Services: XML+XPath 28

29 XPath: More Details An XPath expression, p, establishes a relation between: A context node, and A node in the answer set In other words, p denotes a function: S[p] : Nodes -> {Nodes} Examples: author/firstname. = self.. = parent part/ / /subpart/../name = part/ / [subpart]/name Web Services: XML+XPath 29

30 The Root <bib><paper>1</paper><paper>2</paper></bib> bib is the document element The root is above bib /bib = returns the document element / = returns the root Why? Because we may have comments before and after <bib>; they become siblings of <bib> This is advanced xmlogy Web Services: XML+XPath 30

31 XPath Navigation We can navigate along 13 axes: ancestor ancestor-or-self attribute child We ve only seen these, so far descendant descendant-or-self following following-sibling namespace parent preceding preceding-sibling self Web Services: XML+XPath 31

32 Examples Examples: child::author/child::lastname = author/lastname child::author/descendant::zip = author//zip child::author/parent:: = author/.. child::author/attribute::age = author/@age What does this mean? paper/publisher/parent:: /author /bib//address[ancestor::book] /bib//author/ancestor:: //zip Web Services: XML+XPath 32

33 More Examples name() = the name of the current node /bib// [name()=book] same as /bib//book What does this mean? /bib// [ancestor:: [name()!=book]] Navigation axis gives us strictly more power! Web Services: XML+XPath 33