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XMLXML
eXtensible Markup LanguageeXtensible Markup Language
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XML vs. HTMLXML vs. HTML
HTML is a HyperText Markup languageHTML is a HyperText Markup languageDesigned for a specific application, namely, Designed for a specific application, namely,
presenting and linking hypertext documentspresenting and linking hypertext documentsXML describes XML describes structurestructure and and content content
(“semantics”)(“semantics”)The presentation is defined separately from The presentation is defined separately from
the structure and the contentthe structure and the content
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An Address Book asAn Address Book asan XML documentan XML document
<addresses><person>
<name> Donald Duck</name><tel> 414-222-1234 </tel><email> [email protected] </email>
</person><person>
<name> Miki Mouse</name><tel> 123-456-7890 </tel><email>[email protected]</email>
</person></addresses>
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Main Features of XMLMain Features of XML
No fixed set of tagsNo fixed set of tagsNew tags can be added for new applicationsNew tags can be added for new applications
An agreed upon set of tags can be used in An agreed upon set of tags can be used in many applicationsmany applicationsNamespaces Namespaces facilitate uniform and coherent facilitate uniform and coherent
descriptions of datadescriptions of dataFor example, a namespace for address books For example, a namespace for address books
determines whether to use determines whether to use <<teltel>> or or <<phonephone>>
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Main Features of XMLMain Features of XML (cont’d) (cont’d)
XML has the concept of a schemaXML has the concept of a schemaDTD DTD and the more expressive and the more expressive XML SchemaXML Schema
XML is a data model XML is a data model Similar to the Similar to the semistructured data modelsemistructured data model
XML supports internationalization (XML supports internationalization (UnicodeUnicode) and platform independence (an ) and platform independence (an XML file is just a character file)XML file is just a character file)
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XML is the Standard forXML is the Standard forData ExchangeData Exchange
Web services (e.g., ecommerce) require Web services (e.g., ecommerce) require exchanging data between various exchanging data between various applications that run on different platformsapplications that run on different platforms
XML (augmented with namespaces) is the XML (augmented with namespaces) is the preferred syntax for data exchange on the preferred syntax for data exchange on the WebWeb
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XML is not AloneXML is not Alone XML SchemasXML Schemas strengthen the data-modeling strengthen the data-modeling
capabilities of XML (in comparison to XML with capabilities of XML (in comparison to XML with only DTDs)only DTDs)
XPath XPath is a language for accessing parts of is a language for accessing parts of XML documentsXML documents
XLink XLink and and XPointer XPointer support cross-references support cross-references XSLT XSLT is a language for transforming XML is a language for transforming XML
documents into other XML documents documents into other XML documents (including XHTML, for displaying XML files)(including XHTML, for displaying XML files) Limited styling of XML can be done with Limited styling of XML can be done with CSS CSS alone alone
XQuery XQuery is a lanaguage for querying XML is a lanaguage for querying XML documentsdocuments
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The Two Facets of XMLThe Two Facets of XML
Some XML files are just text documents with Some XML files are just text documents with tags that denote their structure and include tags that denote their structure and include some metadata (e.g., an attribute that gives the some metadata (e.g., an attribute that gives the name of the person who did the proofreading)name of the person who did the proofreading) See an example on the next slideSee an example on the next slide XML is a subset of XML is a subset of SGML (Standard Generalized SGML (Standard Generalized
Markup Language)Markup Language) Other XML documents are similar to database Other XML documents are similar to database
files (e.g., an address book)files (e.g., an address book)
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XML can DescribeXML can Describethe Structure of a Documentthe Structure of a Document
<book year="1994"><book year="1994"><title>TCP/IP Illustrated</title><title>TCP/IP Illustrated</title><author><author>
<last>Stevens</last><last>Stevens</last><first>W.</first><first>W.</first>
</author></author><publisher>Addison-Wesley</publisher><publisher>Addison-Wesley</publisher><price>65.95</price><price>65.95</price>
</book></book>
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XML SyntaxXML Syntax
W3Schools Resources on XML SyntaxW3Schools Resources on XML Syntax
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The Structure of XMLThe Structure of XMLXML consists of XML consists of tagstags and and texttextTags come in pairsTags come in pairs <date> <date> ...... </date> </date>They must be They must be properly nestedproperly nested
goodgood
<date><date> ... ... <day><day> ... ... </day></day> ... ... </date></date>badbad
<date><date> ... ... <day><day> ... ... </date></date>... ... </day></day>
(You can’t do (You can’t do <i><i> ... ... <b><b> ... ... </i></i> ... ...</b></b> in HTML) in HTML)
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A Useful AbbreviationA Useful Abbreviation
Abbreviating elements with empty contents:Abbreviating elements with empty contents: <<brbr/> /> forfor < <brbr></></brbr>> <<hrhr widthwidth=“=“1010”/> ”/> forfor < <hrhr widthwidth=“=“1010”></”></hrhr>>For example:For example:
<<familyfamily>> <<personperson idid = “ = “lisalisa”>”>
<<namename> > LisaLisa SimpsonSimpson </ </namename> > <<mothermother idrefidref = “ = “margemarge”/>”/>
<<fatherfather idrefidref = “ = “homerhomer”/>”/></</personperson>>......
</</familyfamily>>
Note that a tag may have a set of attributes, each consisting of a name and a value
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XML TextXML Text
XML has only one “basic” type – XML has only one “basic” type – texttext
It is bounded by tags, e.g.,It is bounded by tags, e.g., <<titletitle>> TheThe Big SleepBig Sleep </</titletitle>> <<yearyear>> 19351935 </ </ yearyear>> – 1935 is still text – 1935 is still text
XML text is called PCDATA XML text is called PCDATA (for parsed character data)(for parsed character data)
It uses a 16-bit encoding, e.g., It uses a 16-bit encoding, e.g., \&\#x0152\&\#x0152 for for the Hebrew letter the Hebrew letter MemMem
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XML StructureXML Structure
Nesting tags can be used to express Nesting tags can be used to express various structures, e.g., a tuple (record):various structures, e.g., a tuple (record):
<person><name> Lisa Simpson</name><tel> 02-828-1234 </tel><tel> 054-470-777 </tel><email> [email protected] </email>
</person>
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XML Structure (cont’d)XML Structure (cont’d)
We can represent a list by using the We can represent a list by using the same same tag repeatedly:tag repeatedly:
<addresses><person> … </person><person> … </person><person> … </person><person> … </person>…
</addresses>
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XML Structure (cont’d)XML Structure (cont’d)
<addresses><person>
<name> Donald Duck</name><tel> 04-828-1345 </tel><email> [email protected] </email>
</person><person>
<name> Miki Mouse</name><tel> 03-426-1142 </tel><email>[email protected]</email>
</person></addresses>
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TerminologyTerminologyThe segment of an XML document The segment of an XML document between an opening and a corresponding between an opening and a corresponding closing tag is called an closing tag is called an element element
<person> <name> Bart Simpson </name>
<tel> 02 – 444 7777 </tel> <tel> 051 – 011 022 </tel>
<email> [email protected] </email> </person>
element
element, a sub-element of
not an element
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An XML Document is a TreeAn XML Document is a Tree
person
name emailtel tel
Bart Simpson
02 – 444 7777
051 – 011 022
Leaves are either empty or contain PCDATA
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Mixed ContentMixed Content
An element may contain a mixture of sub-An element may contain a mixture of sub-elements and PCDATAelements and PCDATA
<<airlineairline>> <<namename>> British AirwaysBritish Airways </</namename>> <<mottomotto> > World’sWorld’s <<dubiousdubious>> favoritefavorite</</dubiousdubious>>
airline airline </</mottomotto>></</airlineairline>>
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The Header TagThe Header Tag
<?xml <?xml versionversion=="1.0""1.0" standalonestandalone=="yes/no""yes/no" encodingencoding=="UTF-8""UTF-8"?>?>StandaStandallone=“no” means tone=“no” means thhat there is an at there is an
external Dexternal DTTDDYou can leave out the encoding attribute and You can leave out the encoding attribute and
the processor will use the UTF-8 defaultthe processor will use the UTF-8 default
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Processing InstructionsProcessing Instructions
<?xml version="1.0"?><?xml version="1.0"?><?xml-stylesheet href="doc.xsl" type="text/xsl"?><?xml-stylesheet href="doc.xsl" type="text/xsl"?>
<!DOCTYPE doc SYSTEM "doc.dtd"><!DOCTYPE doc SYSTEM "doc.dtd">
<doc>Hello, world!<!-- Comment 1 --></doc><doc>Hello, world!<!-- Comment 1 --></doc>
<?pi-without-data?><?pi-without-data?><!-- Comment 2 --><!-- Comment 2 --><!-- Comment 3 --><!-- Comment 3 -->
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Using CDATAUsing CDATA<<HEAD1HEAD1> >
Entering a Kennel Club MemberEntering a Kennel Club Member
</</HEAD1HEAD1>>
<<DESCRIPTIONDESCRIPTION>>Enter the member by the name on his or her papers. Use the Enter the member by the name on his or her papers. Use the NAME tag. The NAME tag has two attributes. Common (all in NAME tag. The NAME tag has two attributes. Common (all in lowercase, please!) is the dog's call name. Breed (also in all lowercase, please!) is the dog's call name. Breed (also in all lowercase) is the dog's breed. Please see the breed reference lowercase) is the dog's breed. Please see the breed reference guide for acceptable breeds. Your entry should look something guide for acceptable breeds. Your entry should look something like this: like this:
</</DESCRIPTIONDESCRIPTION> >
<<EXAMPLEEXAMPLE>><![CDATA[<![CDATA[<NAME common="freddy" breed"=springer-<NAME common="freddy" breed"=springer-spaniel">Sirspaniel">Sir Fredrick of Ledyard's End</NAME>Fredrick of Ledyard's End</NAME>]]>]]>
</</EXAMPLEEXAMPLE> >
We want to seethe text as is,even though
it includes tags
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A Complete XML DocumentA Complete XML Document
http://www.mscs.mu.edu/~praveen/Teachihttp://www.mscs.mu.edu/~praveen/Teaching/fa05/AdvDb/Lectures/bib.xmlng/fa05/AdvDb/Lectures/bib.xml
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Well-Formed XML DocumentsWell-Formed XML Documents
An XML document (with or without a DTD) is An XML document (with or without a DTD) is
well-formedwell-formed if if Tags are syntactically correctTags are syntactically correct
Every tag has an end tagEvery tag has an end tag
Tags are properly nestedTags are properly nested
There is a root tagThere is a root tag
A start tag does not have two occurrences of the A start tag does not have two occurrences of the
same attributesame attribute
An XML document must be well formed
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Representing relational databasesRepresenting relational databases
A relational database for school:A relational database for school:
student:student: course: course:
enroll:enroll:
cno title credit
331 DB 3.0350 Web 3.0… … …
id name gpa
001 J oe 3.0002 Mary 4.0… … …
id cno
001 331001 350002 331… …
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XML representationXML representation<school> <school>
<student id=“001”><student id=“001”>
<name> Joe </name><name> Joe </name> <gpa> 3.0 </gpa><gpa> 3.0 </gpa>
</student></student>
<student id=“002”><student id=“002”>
<name> Mary </name> <gpa> 4.0 </gpa><name> Mary </name> <gpa> 4.0 </gpa>
</student></student>
<course cno=“331”><course cno=“331”>
<title> DB </title> <credit> 3.0 </credit><title> DB </title> <credit> 3.0 </credit>
</course></course>
<course cno=“350”><course cno=“350”>
<title> Web </title> <credit> 3.0 </credit><title> Web </title> <credit> 3.0 </credit>
</course></course>
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XML representationXML representation
<enroll><enroll>
<id> 001 </id><id> 001 </id> <cno> 331 </cno> <cno> 331 </cno>
</enroll></enroll>
<enroll><enroll>
<id> 001 </id><id> 001 </id> <cno> 350 </cno> <cno> 350 </cno>
</enroll></enroll>
<enroll><enroll>
<id> 002 </id><id> 002 </id> <cno> 331 </cno> <cno> 331 </cno>
</enroll></enroll>
</school></school>
