XML 20 -Mar-18 What is XML XML

HTML and XML, III HTML is for humans HTML describes web pages You don’t want to see error messages about the web pages you visit Browsers ignore and/or correct as many HTML errors as they can, so HTML is often sloppy XML is for computers XML describes data The rules are strict and errors are not allowed In this way, XML is like a programming language Current versions of most browsers can display XML However, browser support of XML is spotty at best 26

SGML(ISO 8879) Standard Generalized Markup Language The international standard for defining descriptions of structure and content in text documents Interchangeable: device-independent, system-independent Tags are not predefined Using DTD to validate the structure of the document Large, powerful, and very complex Heavily used in industrial and commercial for over a decade Slide 27 XML Introdution

HTML(RFC 1866) Hyper. Text Markup Language A small SGML application used on web (a DTD and a set of processing conventions) Can only use a predefined set of tags Slide 28 XML Introdution

What Is XML? e. Xtensible Markup Language A simplified version of SGML Maintains the most useful parts of SGML Designed so that SGML can be delivered over the Web XHTML -- a reformulation of HTML 4 in XML 1. 0 Slide 29 XML Introdution

XML Syntax All XML elements must have a closing tag XML tags are case sensitive All XML elements must be properly nested All XML documents must have a root tag Attribute values must always be quoted With XML, white space is preserved With XML, a new line is always stored as LF Slide 30 XML Introdution

XML-related technologies DTD (Document Type Definition) and XML Schemas are used to define legal XML tags and their attributes for particular purposes CSS (Cascading Style Sheets) describe how to display HTML or XML in a browser XSLT (e. Xtensible Stylesheet Language Transformations) and XPath are used to translate from one form of XML to another DOM (Document Object Model), SAX (Simple API for XML, and JAXP (Java API for XML Processing) are all APIs for XML parsing 31

7/14/97 North Place, NX" src="https://present5.com/presentation/ca86014c2f99ba5fcce7726521cb4d8c/image-32.jpg" alt="Example XML document 7/14/97 North Place, NX" /> Example XML document 7/14/97 North Place, NX USA High Temp: 103 Low Temp: 70 Morning: Partly cloudy, Hazy Afternoon: Sunny & hot Evening: Clear and Cooler 32

The Basic Rules XML is case sensitive This is incorrect This is correct

The Basic Rules All start tags must have end tags Mozart l Empty Element

The Basic Rules Elements must be properly nested This is incorrect nesting This is correct nesting

The Basic Rules XML declaration must be the first statement

The Basic Rules Every document must contain a root element . . .

Ani" src="https://present5.com/presentation/ca86014c2f99ba5fcce7726521cb4d8c/image-38.jpg" alt="The Basic Rules Attribute values must be quoted with inverted commas Ani" /> The Basic Rules Attribute values must be quoted with inverted commas Ani John

The Basic Rules Certain characters are reserved for parsing if salary < 1000 then if salary < 1000 then

Predefined entities < < less than > > greater than & & &ersand ' ' apostrophe " " quotation mark

XML Building blocks--Prolog The part of an XML document that precedes the XML data Includes A declaration: version [, encoding, standalone] An optional DTD (Document Type Definition ) Example Slide 41 XML Introdution

Tags are used to specify a name for a given piece of information. A tag consists of opening and closing angular brackets (<>) that enclose the name of the tag. Example Nick Shaw Slide 42 XML Introdution

Elements are represented using tags. An XML document must always have a root element. General format: … Empty element: Example John Smith Slide 43 XML Introdution

Elements XML Elements are Extensible XML documents can be extended to carry more information XML Elements have Relationships Elements are related as parents and children Elements have Content Elements can have different content types: element content, mixed content, simple content, or empty content and attributes XML elements must follow the naming rules Slide 44 XML Introdution

Content refers to the information represented by the elements of an XML document. Character or data content Element content Combination or mixed content Example The Painted House Slide 45 XML Introdution

Attributes Located in the start tag of elements Provide additional information about elements Often provide information that is not a part of data Must be enclosed in quotes Should I use an element or an attribute? metadata (data about data) should be stored as attributes, and that data itself should be stored as elements Slide 46 XML Introdution

Entities An entity is a name that is associated with a block of data. . Internal Entities: < , > … General Entities General entities are declared in Document Type Definitions (DTD) Example For more information, please visit &nyt; Thank you! Parameter Entities Are only declared and used in DTDs Slide 47 XML Introdution

Overall structure An XML document may start with one or more processing instructions (PIs) or directives: Following the directives, there must be exactly one root element containing all the rest of the XML: . . . 48

XML building blocks Aside from the directives, an XML document is built from: elements: high in 103 tags, in pairs: 103 attributes: 103 entities: Sunny & hot character data, which may be: parsed (processed as XML)--this is the default unparsed (all characters stand for themselves) 49

Elements and attributes Attributes and elements are somewhat interchangeable Example using just elements: David Matuszek Example using attributes: You will find that elements are easier to use in your programs--this is a good reason to prefer them Attributes often contain metadata, such as unique IDs Generally speaking, browsers display only elements (values enclosed by tags), not tags and attributes 50

Well-formed XML Every element must have both a start tag and an end tag, e. g. 51 . . . But empty elements can be abbreviated: . XML tags are case sensitive XML tags may not begin with the letters xml, in any combination of cases Elements must be properly nested, e. g. not bold and italic Every XML document must have one and only one root element The values of attributes must be enclosed in single or double quotes, e. g. Character data cannot contain < or &

Entities Five special characters must be written as entities: & for < for > for " for ' for & < > " ' (almost always necessary) (not usually necessary) (necessary inside double quotes) (necessary inside single quotes) These entities can be used even in places where they are not absolutely required These are the only predefined entities in XML 52

XML declaration The XML declaration looks like this: The XML declaration is not required by browsers, but is required by most 53 XML processors (so include it!) If present, the XML declaration must be first--not even whitespace should precede it Note that the brackets are version="1. 0" is required (this is the only version so far) encoding can be "UTF-8" (ASCII) or "UTF-16" (Unicode), or something else, or it can be omitted standalone tells whethere is a separate DTD

XML Encoding XML documents can contain international characters, like 54 Norwegian æøå, or French êèé. To avoid errors, you should specify the encoding used, or save your XML files as UTF-8. Unicode is an industry standard for character encoding of text documents. It defines (nearly) every possible international character by a name and a number. Unicode has two variants: UTF-8 and UTF-16. UTF = Universal character set Transformation Format.

XML Encoding UTF-8 uses a single byte (8 -bits) to represent commonly 55 used characters and two (or three) bytes for the rest. UTF-16 uses two bytes (16 bits) for most characters, and three bytes for the rest. UTF-8 Web Standard UTF-8 is the standard character encoding on the web. UTF-8 is the default character encoding for HTML-5, CSS, Java. Script, PHP, SQL, and XML.

Processing instructions PIs (Processing Instructions) may occur anywhere in the XML 56 document (but usually first) A PI is a command to the program processing the XML document to handle it in a certain way XML documents are typically processed by more than one program Programs that do not recognize a given PI should just ignore it General format of a PI: Example:

Comments Comments can be put anywhere in an XML document Comments are useful for: Explaining the structure of an XML document Commenting out parts of the XML during development and testing Comments are not elements and do not have an end tag The blanks after are optional The character sequence -- cannot occur in the comment The closing bracket must be --> Comments are not displayed by browsers, but can be seen by anyone who looks at the source code 57

CDATA By default, all text inside an XML document is parsed You can force text to be treated as unparsed character data by 58 enclosing it in Any characters, even & and <, can occur inside a CDATA Whitespace inside a CDATA is (usually) preserved The only real restriction is that the character sequence ]]> cannot occur inside a CDATA is useful when your text has a lot of illegal characters (for example, if your XML document contains some HTML text)

Names in XML Names (as used for tags and attributes) must begin with a letter or underscore, and can consist of: Letters, both Roman (English) and foreign Digits, both Roman and foreign . (dot) - (hyphen) _ (underscore) : (colon) should be used only for namespaces Combining characters and extenders (not used in English) 59

Namespaces Recall that DTDs are used to define the tags that can be used in an XML document An XML document may reference more than one DTD Namespaces are a way to specify which DTD defines a given tag XML, like Java, uses qualified names This helps to avoid collisions between names Java: my. Object. my. Variable XML: my. DTD: my. Tag Note that XML uses a colon (: ) rather than a dot (. ) 60

XML is case sensitive" src="https://present5.com/presentation/ca86014c2f99ba5fcce7726521cb4d8c/image-61.jpg" alt="Review of XML rules Start with XML is case sensitive" /> Review of XML rules Start with XML is case sensitive You must have exactly one root element that encloses all the 61 rest of the XML Every element must have a closing tag Elements must be properly nested Attribute values must be enclosed in double or single quotation marks There are only five predeclared entities

Another well-structured example This is the great American novel. It was a dark and stormy night. Suddenly, a shot rang out! 62

Valid XML You can make up your own XML tags and attributes, but. . . . any program that uses the XML must know what to expect! A DTD (Document Type Definition) defines what tags are legal and 63 where they can occur in the XML An XML document does not require a DTD XML is well-structured if it follows the rules given earlier In addition, XML is valid if it declares a DTD and conforms to that DTD A DTD can be included in the XML, but is typically a separate document Errors in XML documents will stop XML programs Some alternatives to DTDs are XML Schemas and RELAX NG

Viewing XML is designed to be processed by computer programs, not to be displayed to humans Nevertheless, almost all current browsers can display XML documents They don’t all display it the same way They may not display it at all if it has errors For best results, update your browsers to the newest available versions Remember: HTML is designed to be viewed, XML is designed to be used 64

Displaying your XML Files with CSS With CSS (Cascading Style Sheets) you can add display information to an XML document. Bob Dylan USA Columbia 10. 90 1985 65

CATALOG { background-color: #ffffff; width: 100%; } CD { display: block; margin-bottom: 30 pt; margin-left: 0; } 66

TITLE { color: #FF 0000; font-size: 20 pt; } ARTIST { color: #0000 FF; font-size: 20 pt; } 67

COUNTRY, PRICE, YEAR, COMPANY { display: block; color: #000000; margin-left: 20 pt; } 68

Why Is XML Important? Plain Text Easy to edit Platform independent Data Identification Tell you what kind of data you have Can be used in different ways by different applications Easily Processed Slide 69 Vendor-neutral standard XML Introdution

Why Is XML Important? Slide 70 Stylability Inherently style-free XSL---Extensible Stylesheet Language Different XSL formats can then be used to display the same data in different ways Inline Reusability Can be composed from separate entities Modularize your documents XML Introdution

Why is XML important? Slide 71 Linkability -- XLink and XPointer Simple unidirectional hyperlinks Two-way links Multiple-target links “Expanding” links Hierarchical Faster to access Easier to rearrange XML Introdution

XML Application 1—Separate data XML can Separate Data from HTML Store data in separate XML files Using HTML for layout and display Using Data Islands can be bound to HTML elements Benefits: Changes in the underlying data will not require any changes to your HTML Slide 72 XML Introdution

XML Application 2—Exchange data XML is used to Exchange Data Text format Software-independent, hardware-independent Exchange data between incompatible systems, given that they agree on the same tag definition. Can be read by many different types of applications Benefits: Reduce the complexity of interpreting data Easier to expand upgrade a system Slide 73 XML Introdution

XML Application 3—Store Data XML can be used to Store Data Plain text file Store data in files or databases Application can be written to store and retrieve information from the store Other clients and applications can access your XML files as data sources Benefits: Accessible to more applications Slide 74 XML Introdution

XML Application 4—Create new language XML can be used to Create new Languages WML (Wireless Markup Language) used to markup Internet applications for handheld devices like mobile phones (WAP) Music. XML used to publishing musical scores RSS. Math. ML. Slide 75 XML Introdution

Overview XML and Structured Data Pre-XML representation of data: XML representation of the same data: “PO-1234”, ”CUST 001”, ”X 9876”, ” 5”, ” 14. 98” PO-1234 CUST 001 X 9876 5 14. 98

Overview Benefits of XML Open W 3 C standard Representation of data across heterogeneous environments Cross platform Allows for high degree of interoperability Strict rules Syntax Structure Case sensitive

Overview Who Uses XML? Submissions by Microsoft IBM Hewlett-Packard Fujitsu Laboratories Sun Microsystems Netscape (AOL), and others… Technologies using XML SOAP, eb. XML, Biz. Talk, Web. Sphere, many others…

Syntax and Structure Components of an XML Document Elements Each element has a beginning and ending tag . . . Elements can be empty () Attributes Describes an element; e. g. data type, data range, etc. Can only appear on beginning tag Processing instructions Encoding specification (Unicode by default) Namespace declaration Schema declaration

Syntax and Structure Components of an XML Document Elements with Attributes Elements Prologue (processing instructions)

Syntax and Structure Rules For Well-Formed XML There must be one, and only one, root element Sub-elements must be properly nested A tag must end within the tag in which it was started Attributes are optional Defined by an optional schema Attribute values must be enclosed in “” or ‘’ Processing instructions are optional XML is case-sensitive and are not the same type of element

82 Comp Sci 346 3/20/2018

83 Comp Sci 346 3/20/2018