XML. XML Syntax. An example of XML:

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1 XML Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. Defined in the XML 1.0 Specification produced by the W3C. Similar to HTML, but with a different purpose: HTML was designed to display data, with a focus on what data looks like. XML was designed to transport and store data, with a focus on what data is. XML Syntax An example of XML: <?xml version="1.0" encoding="iso "?>  <class_list> <student active="true"> <name>robert</name> <grade>a+</grade> </student> <student active="false"> <name>lenard</name> <grade>a-</grade> </student> </class_list>

2 XML Document Syntax An XML document is made up of a small group of building blocks. XML Prolog o Prolog XML Declaration Document Type Declaration (DTD) or XML Schema Definition (XSD) (optional) o Root Element (Document) Elements (Nested Elements) Element Attributes and Values Data The XML prolog is an optional piece of information that must come before the root element when used. There are two pieces that make up the prolog: the XML declaration and the Document Type Declaration (DTD). XML Declaration The XML declaration defines the XML version (1.0) and the encoding used (ISO = Latin-1/West European character set). <?xml version="1.0" encoding="iso "?> All XML parsers are required to support the Unicode UTF-8 and UTF-16 encodings; many XML parser support other encodings as well. It is legal for a transfer protocol like HTTP to override the encoding value that you put in the XML declaration, so you cannot guarantee that the document will actually use the encoding provided in the XML declaration.

3 Document Type Declaration (DTD) / XML Schema Definition (XSD) The optional DTD or XSD describes the rules the XML document must follow. It defines the structure of the document with a list of legal elements. The original DTD specification has largely been superseded by the newer XSD specification. The DTD and XSD syntax is beyond the scope of this lecture, but tutorials can easily be found online. XML Root Element (Document) The root element, also referred to as the document, dictates what kind of XML document this is (a class list, for example). When creating an HTML file that is XML complaint, the root element will be <html>. In an XML file, it may be anything. The root element must be the first element in an XML document and there can only be one root element per file. The root element must encapsulate all of the other elements. <class_list>... </class_list>

4 XML Element The meat of an XML document comes from the elements that are contained within the root element. Each element represents a different type of data that is being stored in the document. An element can contain: o other elements o text o attributes o or a mix of all of the above... Most XML elements will be enclosed by a tag pair an opening tag and a closing tag. <name>robert</name> An element that has no text may instead be signified by using a modified opening tag sometimes called a solo tag. <element> </element> <element/> Opening tag used to signify the beginning of an element. Closing tag used to signify the end of an element. Solo tag used alone to signify an element with no data. Tags are case-sensitive. Their names are programmer-defined and should both descriptive and self-explanatory. Tags must be properly nested. Elements opened first must be closed last. o That means that the root element, the first element in an XML document, must also be closed last. o Nested elements, ones that occur in the middle of the document, must be closed before those that came before them.

5 XML Attributes Attributes provide additional information about elements. <student active="true"> Attribute values must always be quoted. Either single or double quotes may be used. There are no rules about when to use attributes or when to use elements, but attributes can be difficult to read and maintain: o Attributes cannot contain multiple values (elements can) o Attributes cannot contain tree structures (elements can) o Attributes are not easily expandable (for future changes) Data should generally be stored as elements, while attributes should be reserved for metadata (data about the data).

6 References A reference allows you to include additional text or markup in an XML document. References always begin with the character & (which is reserved) and end with the character ;. XML has two kinds of references: o An entity reference, like &, contains a name (in this case, amp ) between the start and end delimiters. The name refers to a predefined string of text and/or markup. There are five predefined entities: > > < < & & " " ' ' XML also allows you to define your own custom entities in the DTD or XSD for your XML document. o A character references, like &, contains a hash mark ( # ) followed by a number. The number always refers to the Unicode code for a single character, such as 65 for the letter A.

7 XML Comments An XML document may contain comments. XML comments have the same syntax as HTML comments:  You can comment out XML code to temporarily remove it from an XML document:

8 A Larger XML Example <?xml version="1.0" encoding="utf-8"?> <customer> <firstname>john</firstname> <lastname>smith</lastname> <age>25</age> <address> <streetaddress>21 2nd Street</streetAddress> <city>new York</city> <state>ny</state> <postalcode>10021</postalcode> </address> <contactinfo> <phonenumber> <type>home</type> <number> </number> </phonenumber> <phonenumber> <type>fax</type> <number> </number> </phonenumber> </contactinfo> </customer>

9 References BRAY, T., PAOLI, J., SPERBERG-MCQUEEN, C.M., MALER E., and YERGEAU, F. eds., Extensible Markup Language (XML) 1.0, Fifth Edition. W3C. w3schools.com. XML tutorial.

XML (Extensible Markup Language

XML (Extensible Markup Language XML is a markup language. XML stands for extensible Markup Language. The XML standard was created by W3C to provide an easy to use and standardized way to store self describing