Download presentation
Presentation is loading. Please wait.
1
Introduction to XML Extensible Markup Language
2
What is XML XML stands for eXtensible Markup Language.
A markup language is used to provide information about a document. Tags are added to the document to provide the extra information. HTML tags tell a browser how to display the document. XML tags give a reader some idea what some of the data means.
3
What is XML Used For? XML documents are used to transfer data from one place to another often over the Internet. HTML is used for displaying data.
4
Advantages of XML XML is text (Unicode) based. Takes up less space.
Can be transmitted efficiently.
5
With XML You Invent Your Own Tags
XML language has no predefined tags. The tags used in HTML are predefined. HTML documents can only use tags defined in the HTML standard (like <p>, <h1>, etc.). XML allows the author to define his/her own tags and his/her own document structure.
6
XML is Used to Create New Internet Languages
A lot of new Internet languages are created with XML. Here are some examples: XHTML WSDL for describing available web services WAP and WML as markup languages for handheld devices RSS languages for news feeds RDF and OWL for describing resources and ontology SMIL for describing multimedia for the web
7
Example of an HTML Document
<head><title>Example</title></head. <body> <h1>This is an example of a page.</h1> <h2>Some information goes here.</h2> </body> </html>
8
Example of an XML Document
<?xml version=“1.0”/> <address> <name>Alice Lee</name> <phone> </phone> <birthday> </birthday> </address>
9
Difference Between HTML and XML
HTML tags have a fixed meaning and browsers know what it is. XML tags are different for different applications, and users know what they mean. HTML tags are used for display. XML tags are used to describe documents and data.
10
XML Documents Form a Tree Structure
XML documents must contain a root element. This element is "the parent" of all other elements. <root> <child> <subchild>.....</subchild> </child> </root>
11
XML is not… A replacement for HTML (but HTML can be generated from XML) A presentation format (but XML can be converted into one) A programming language (but it can be used with almost any language) A network transfer protocol (but XML may be transferred over a network) A database (but XML may be stored into a database)
12
XML Rules Tags are enclosed in angle brackets.
Tags come in pairs with start-tags and end-tags. Tags must be properly nested. <name>< >…</name></ > is not allowed. <name>< >…</ ><name> is. Tags that do not have end-tags must be terminated by a ‘/’. <br /> is an html example.
13
More XML Rules Tags are case sensitive.
<address> is not the same as <Address> XML in any combination of cases is not allowed as part of a tag. Tags may not contain ‘<‘ or ‘&’. Tags follow Java naming conventions, except that a single colon and other characters are allowed. They must begin with a letter and may not contain white space. Documents must have a single root tag that begins the document. XML Attribute Values Must be Quoted
14
XML by Example … and what about this XML document:
<data> ch37fhgks73j5mv9d63h5mgfkds8d984lgnsmcns983 </data> Impossible to understand for human users Not expressive (no semantics along with the data) Unstructured, read and write only with special programs
15
Well-Formed Documents
An XML document is said to be well-formed if it follows all the rules. An XML parser is used to check that all the rules have been obeyed. Recent browsers such as Internet Explorer 5 and Netscape 7 come with XML parsers. Parsers are also available for free download over the Internet. One is Xerces, from the Apache open-source project. Java 1.4 also supports an open-source parser.
16
XML Example Revisited <?xml version=“1.0”/> <address> <name>Alice Lee</name> <phone> </phone> <birthday> </birthday> </address> Markup for the data aids understanding of its purpose. A flat text file is not nearly so clear. Alice Lee
17
Expanded Example <?xml version = “1.0” ?> <address>
<name> <first>Alice</first> <last>Lee</last> </name> <phone> </phone> <birthday> <year>1983</year> <month>07</month> <day>15</day> </birthday> </address>
18
XML Files are Trees address name email phone birthday first last year
month day
19
XML Trees An XML document has a single root node.
The tree is a general ordered tree. A parent node may have any number of children. Child nodes are ordered, and may have siblings. Preorder traversals are usually used for getting information out of the tree.
20
A Simple XML Document End Tag Element Start Tag <article>
<author>Gerhard Weikum</author> <title>The Web in Ten Years</title> <text> <abstract>In order to evolve...</abstract> <section number=“1” title=“Introduction”> The <index>Web</index> provides the universal... </section> </text> </article> Element Content of the Element (Subelements and/or Text) End Tag
21
A Simple XML Document <article>
<author>Gerhard Weikum</author> <title>The Web in Ten Years</title> <text> <abstract>In order to evolve...</abstract> <section number=“1” title=“Introduction”> The <index>Web</index> provides the universal... </section> </text> </article> Attributes with name and value
22
Elements vs. Attributes
Elements may have attributes (in the start tag) that have a name and a value, e.g. <section number=“1“>. What is the difference between elements and attributes? Only one attribute with a given name per element (but an arbitrary number of subelements) Attributes have no structure, simply strings (while elements can have subelements) Example: <person born=“ “ died=“ “> Alan Turing</person> proved that…
23
XML Encoding <?xml version="1.0" encoding="UTF-8"?>
XML documents can contain international characters, like Norwegian æøå, or French êèé. To avoid errors, you should specify the encoding used, or save your XML files as UTF-8. UTF = Universal character set Transformation Format. Eg. <?xml version="1.0" encoding="UTF-8"?>
24
Displaying your XML Files with CSS?
It is possible to use CSS to format an XML document.
25
The CD Catalog <CATALOG> <DVD> <TITLE>Empire Burlesque</TITLE> <ARTIST>Bob Dylan</ARTIST> <COUNTRY>USA</COUNTRY> <COMPANY>Columbia</COMPANY> <PRICE>10.90</PRICE> <YEAR>1985</YEAR> </DVD> </CATALOG>
26
The CSS File CATALOG { background-color: #ffffff; width: 100%; }
DVD { display: block; margin-bottom: 30pt; margin-left: 0; } TITLE { color: #FF0000; font-size: 20pt; } ARTIST { color: #0000FF; font-size: 20pt; } COUNTRY,PRICE,YEAR,COMPANY { display: block; color: #000000; margin-left: 20pt; }
27
The CD catalog formatted with the CSS file
<?xml version="1.0" encoding="UTF-8"?> <?xml-stylesheet type="text/css" href="cd_catalog.css"?> <CATALOG> <CD> <TITLE>Empire Burlesque</TITLE> <ARTIST>Bob Dylan</ARTIST> <COUNTRY>USA</COUNTRY> <COMPANY>Columbia</COMPANY> <PRICE>10.90</PRICE> <YEAR>1985</YEAR> </CD> </CATALOG>
28
Output
29
XML DTD An XML document with correct syntax is called "Well Formed".
An XML document validated against a DTD is "Well Formed" and "Valid".
30
Valid XML Documents A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a DTD: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE note SYSTEM "Note.dtd"> <note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>
31
XML DTD The purpose of a DTD is to define the structure of an XML document. It defines the structure with a list of legal elements: <!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> ]>
32
#PCDATA means parse-able text data.
Explanation The DTD above is interpreted like this: !DOCTYPE note defines that the root element of the document is note !ELEMENT note defines that the note element contains four elements: "to, from, heading, body" !ELEMENT to defines the to element to be of type "#PCDATA" !ELEMENT from defines the from element to be of type "#PCDATA" !ELEMENT heading defines the heading element to be of type "#PCDATA" !ELEMENT body defines the body element to be of type "#PCDATA" #PCDATA means parse-able text data.
33
DTD for address Example
<!ELEMENT address (name, , phone, birthday)> <!ELEMENT name (first, last)> <!ELEMENT first (#PCDATA)> <!ELEMENT last (#PCDATA)> <!ELEMENT (#PCDATA)> <!ELEMENT phone (#PCDATA)> <!ELEMENT birthday (year, month, day)> <!ELEMENT year (#PCDATA)> <!ELEMENT month (#PCDATA)> <!ELEMENT day (#PCDATA)>
34
Using DTD for Entity Declaration
A doctype declaration can also be used to define special characters and character strings, used in the document: Example <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE note [ <!ENTITY writer "Writer: Donald Duck."> <!ENTITY copyright "Copyright: W3Schools."> ]>
35
Use <note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> <footer>&writer;©right;</footer> </note> An entity has three parts: an ampersand (&), an entity name, and a semicolon (;).
36
Schemas Schemas are themselves XML documents.
They were standardized after DTDs and provide more information about the document. They have a number of data types including string, decimal, integer, boolean, date, and time. They divide elements into simple and complex types. They also determine the tree structure and how many children a node may have.
37
Schema for First address Example
<?xml version="1.0" encoding="ISO " ?> <xs:schema xmlns:xs=" <xs:element name="address"> <xs:complexType> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name=" " type="xs:string"/> <xs:element name="phone" type="xs:string"/> <xs:element name="birthday" type="xs:date"/> </xs:sequence> </xs:complexType> </xs:element> </xs:schema>
38
Explanation of Example Schema
<?xml version="1.0" encoding="ISO " ?> ISO , Latin-1, is the same as UTF-8 in the first 128 characters. <xs:schema xmlns:xs=" contains the schema standards. <xs:element name="address"> <xs:complexType> This states that address is a complex type element. <xs:sequence> This states that the following elements form a sequence and must come in the order shown. <xs:element name="name" type="xs:string"/> This says that the element, name, must be a string. <xs:element name="birthday" type="xs:date"/> This states that the element, birthday, is a date. Dates are always of the form yyyy-mm-dd.
39
XSLT Extensible Stylesheet Language Transformations
XSLT is used to transform one xml document into another, often an html document. The Transform classes are now part of Java 1.4. A program is used that takes as input one xml document and produces as output another. If the resulting document is in html, it can be viewed by a web browser. This is a good way to display xml data.
40
A Style Sheet to Transform address.xml
<?xml version="1.0" encoding="ISO "?> <xsl:stylesheet version="1.0" xmlns:xsl=" <xsl:template match="address"> <html><head><title>Address Book</title></head> <body> <xsl:value-of select="name"/> <br/><xsl:value-of select=" "/> <br/><xsl:value-of select="phone"/> <br/><xsl:value-of select="birthday"/> </body> </html> </xsl:template> </xsl:stylesheet>
41
The Result of the Transformation
Alice Lee
42
Parsers There are two principal models for parsers.
SAX – Simple API for XML Uses a call-back method Similar to javax listeners DOM – Document Object Model Creates a parse tree Requires a tree traversal
43
References Elliotte Rusty Harold, Processing XML with Java, Addison Wesley, 2002. Elliotte Rusty Harold and Scott Means, XML Programming, O’Reilly & Associates, Inc., 2002. W3Schools Online Web Tutorials,
Similar presentations
