XML Instructor: Charles Moen CSCI/CINF 4230

2 XML  Extensible Markup Language  A set of rules that allow you to create your own markup language  Designed for delivering data over the Web in text files that are self-describing and readable both by computer programs and by humans  The XML specification has been maintained by the World Wide Web Consortium (W3C)‏ since 1998 XML (Spainhour, Ray, W3Schools)‏

Example of an XML File XML declaration is always on the first line. XML uses markup tags, like HTML, but developers can invent their own tag names. As long as the tags follow the XML syntax rules, we can invent whatever tags and attributes are needed to describe our data. XML (Spainhour, Ray, W3Schools)‏

Problem with HTML 4 Beginning ASP.NET 3.5 in C# 2008 Matthew MacDonald It’s difficult to get the meaning of this data by looking at the HTML elements. XML (Yue)‏ HTML provides the structure of a Web page, but not the semantic meaning of its content. Beginning ASP.NET 3.5 in C# 2008 Matthew MacDonald XML can provide the semantic meaning through its markup tags.

5 XML is Portable Data  XML files are plain text files that contain markup tags  Any software that can process plain text can read XML Hardware independent Software independent XML can be used to exchange data between incompatible systems  XML-aware applications Can process XML data as long as the application “knows” the meaning of the tags Meaning of the tags depends on the application XML (Ding, W3Schools)‏

6 XML Technologies  XML  XML Namespaces  DTD (Document Type Definition) For describing your markup language  XML Schema An XML-based method of describing your markup language  XSL (Extensible Stylesheet Language) For displaying and transforming XML documents  DOM (Document Object Model) Object library for manipulating an XML document as a tree XML (Yue)‏

7 XML documents must be well-formed An XML document that conforms to the minimal XML syntax rules is well-formed  Elements must always have a closing tag  Tag names and attribute names are case-sensitive  Elements must be properly nested  All attributes must have a value  All attribute values must be surrounded with quotes or apostrophes  The XML declaration is on the first line  The document has a single root element XML (Spainhour, Ray, W3Schools)‏

Root Element Root element XML (Spainhour, Ray, W3Schools)‏ The top-level element Only one All other elements must be nested within it In an XHTML document, the root element is

9 Tag Names  There are no predefined tag names; you must invent your own (or use tags that another developer invented)  Should be descriptive, so that the document can be self- describing  Should be short and concise  Can contain letters, numbers, and other characters  Must not start with a number or punctuation character, including the dollar sign, caret, percent symbol, semicolon, etc.  Must not start with the letters “xml”  Cannot contain spaces  Should not contain the characters “:” or “.” XML (Spainhour, Ray, W3Schools)‏

10 Element Content The text between the start tag and end tag Content can be any of the following:  Empty, without content  Nested elements  Character data  Character entities  Processing instructions  Comments  CDATA sections XML (Spainhour, Ray, W3Schools)‏ 5.99 < > & " &apos; <?xml-stylesheet type="text/xsl" href="simple.xsl"?>

5.99 <![CDATA[ Bacon, lettuce, & tomato ]]> 11 CDATA  Can be inserted anywhere that character data can occur  All characters within a CDATA section are treated as a literal part of the character data Begins with these special characters All characters within are treated as literals and are not parsed as XML XML (Spainhour, Ray, W3Schools)‏ Ends with these special characters

12 Attributes ‏ Attribute  Name-value pair that describes a property of the element  Can be included in the start tag or an empty tag  A particular attribute can appear only once in the same tag XML (Spainhour, Ray, W3Schools)‏

13 Validation ‏  A DTD describes your XML markup language  Which tags can be used  What each element can contain  A document can be tested with the DTD, and if it passes then it is valid Must be well-formed Must be free of mistakes ‒ No misspelled tag names ‒ No improper nesting ‒ No missing elements  Important when used by software that expects a particular document structure; and when separate groups of people need to agree on a common language for data exchange XML (Spainhour, Ray, W3Schools)‏

14 DTD ‏  Defines the structure or grammar of an XML document by describing your markup language  Used to test whether the XML document is valid  Can be internal or external  Can contain the following types of markup declarations ELEMENT – the XML elements ATTLIST – attributes of the elements ENTITY – characters referenced using the “&...;” syntax NOTATION – description of the data format Processing instructions Comments XML (Yue, Spainhour, Ray, W3Schools)‏

15 DTD Example ‏ If we want to maintain a phone list as an XML document, the DTD might look like the following: XML (Yue, Spainhour, Young, W3Schools)‏ This DTD defines a phone list that contains the name, area code and phone number of each person in the list.

16 Element Declarations ELEMENT’s are the “building blocks” of an XML document. The first line declares that a “phonelist” element has element content, and it can contain zero or more “person” child elements. Begins the element declaration Tag name of this element Content can be zero or more “person” elements * Zero or more + One or more ? Zero or one These three characters can be used to specify the number of elements Ends the element declaration XML (Yue, Spainhour, Young, W3Schools)‏

Element Declarations 17 The second line declares that a “person” element has element content, and it must contain exactly one of each of the elements “name” and “phonenumber,” in that order. Tag name of this element When there are multiple child elements with commas separating the names, then the child elements must appear in that specific sequence XML (Yue, Spainhour, Young, W3Schools)‏

Element Declarations 18 The third line declares that the content of the “name” element is simple character data. Tag name of this element “PCDATA” stands for “parsed character data,” text that will be parsed by the XML parser. Tags inside the text will be treated as markup and entities will be expanded. It can also be empty. XML (Ding,Yue, Young, W3Schools)‏

Element Declarations 19 What can you say about the next three declarations? XML (Yue, Spainhour, Young, W3Schools)‏

Element Declarations 20 Is the following XML document valid, according to this DTD? <?xml version="1.0" encoding="UTF-8"?> Charles Moen XML (Yue, Spainhour, Young, W3Schools)‏

Using an External DTD 21 Use the DOCTYPE instruction to connect the xml document with an external DTD <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE phonelist SYSTEM "phonelist.dtd"> Charles Moen XML (Yue, Spainhour, Young, W3Schools)‏ phonelist.dtd phonelist.xml <!DOCTYPE phonelist SYSTEM "phonelist.dtd"> The root element Describes the location of the DTD, and can be relative or fully qualified, such as: " Either SYSTEM or PUBLIC (if PUBLIC, then must be followed by both a name and URI)

Using an Internal DTD An internal DTD is placed in the DOCTYPE instruction of the XML document. <!DOCTYPE phonelist [ ] > Charles Moen XML (Yue, Spainhour, Young, W3Schools)‏ phonelist.xml

23 More about Element Declarations ELEMENT content can be specified in several forms. The “choice” form specifies a series of possible child elements XML (Yue, Spainhour, Young, W3Schools)‏ The “sequence” form specifies a required sequence of child elements The “ANY” keyword means the element can have any legal content, in any order. The “EMPTY” keyword means the element must have no content.

24 Attribute-List Declarations All attributes must be explicitly declared with an “ATTLIST” declaration. Here, the “title” attribute is required; it must be CDATA; and it defaults to “Dr”. XML (Yue, Spainhour, Young, W3Schools)‏ Here, the “title” attribute is not required; it must be one of the three values that are enumerated; and it defaults to “Dr”.

XML Namespaces 25 Charles Moen CSCI/CINF 4230 XML (Yue, Spainhour, Young, W3Schools)‏ We can be sure that there is no conflict with element names by using a namespace. The namespace must be declared before using it, and the declaration is often in the root element. The identifier must be unique, and is usually a URL. (The URL does not have to be a valid URL of a Web page.) The qualified element name consists of the namespace, followed by a colon, followed by the local name.

Just for Fun XSL 26 XML An XSL (Extensible Stylesheet Language) document can be used to transform the data in an XML document to an HTML document, or a document in some other format. Charles Moen Demo XSL Phone List Name Phone number   ( )  Demo XSL Phone List Name Phone number   ( )  The XSL must be linked to the XML

27 References Ding, Wei, “XML” UHCL lecture slides, Ray, Erik T. Learning XML. O'Reilly, Spainhour, Stephen and Robert Eckstein. Webmaster in a Nutshell, 3rd Edition. O'Reilly, W3Schools Online Web Tutorials. “DTD Tutorial". [Online]. Available: W3Schools Online Web Tutorials. "XML Tutorial". [Online]. Available: Young, Michael J., XML Step by Step. Microsoft Press, Yue, Kwok-Bun, “An Introduction to XML” UHCL lecture notes, 2001.