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Chapter 2 - Markup and Core Concepts Learning XML by Erik T. Ray

Chapter 2 - Markup and Core Concepts Learning XML by Erik T. Ray

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Chapter 2 - Markup and Core Concepts Learning XML by Erik T. Ray

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  1. Chapter 2 - Markup and Core ConceptsLearning XMLbyErik T. Ray Slides were developed by Jack DavisCollege of Information Scienceand TechnologyRadford University

  2. XML Syntax • “Syntax” refers to the rules of a language • Syntax is needed with any language so that the documents created with that language are consistent • Programs that process documents expect the syntax rules to be followed, otherwise the document may not be interpreted correctly

  3. Components of an XML Document • XML Declaration • Elements • Attributes • Entities • Comments

  4. Components: The XML Declaration • The XML Declaration: • Tells the processing program that the document is an XML document, along with other optional information • The declaration is always the first line of an XML document • Attributes that can be used in the Declaration: • version • encoding • standalone • Example: <?xml version=“1.0”? Encoding=“UTF-8” standalone=“yes”?>

  5. Document Type Declaration • Document type declarations are used to define entities or default attribute values. Secondly, they are used to support validation, a special mode of parsing that checks grammar and vocabulary of markup. A validating parser needs to read a list of declarations for element rules before it can begin to parse. In both cases, this is done in document type declaration section. • A document type declaration consists of:- delimeter <!DOCTYPE- element name identifies the type element- dtd id local path or url- entity decl optional list of entity declara. • dtd identifier supports two methods of identification: system-specific and public<!DOCTYPE doc SYSTEM "/usr/simple.dtd"><!DOCTYPE html PUBLIC "-//w3c//DTD HTML 3.2//EN" "http://www.w3.org/TR … >

  6. XML Syntax • “Syntax” refers to the rules of a language • Syntax is needed with any language so that the documents created with that language are consistent • Programs that process documents expect the syntax rules to be followed, otherwise the document may not be interpreted correctly

  7. Components: XML Elements • Elements: • Used to describe the data. Consist of: • A start tag • Content • An end tag • Example:<element>Content</element> • The “root” element of a document is the outermost element, and contains all of the other elements in the document. There can be only one root element in a single document • An element that does not contain any content is known as an “empty element”

  8. Element Nesting • The term “nesting” refers to the process of containing elements within other elements • Terminology: • Child elements – elements that are contained within other elements • Parent elements – elements that contain other elements • Sibling elements – elements that share the same parent element

  9. Nesting Example 1 <family_tree> 2 <mother>Sally</mother> 3 <father>Joe</father> 4 <children> 5 <child>Larry</child> 6 <child>Curly</child> 7 <child>Mo</child> 8 </children> 9 </family_tree>

  10. Components: XML Attributes • Attributes help to describe XML elements • Attributes are always contained in the start tag of the element they are describing • Attributes are known as “name-value pairs” • Example:address=“123 Main Street”

  11. Components: XML Entities • Two types of entities: • General – placeholders for information contained in the XML document • Parameter – used within a DTD to reference a grouping of elements • Three types of general entities: • Character – used in place of special characters • Content – used for blocks of frequently used text • Unparsed – used for binary or non-text data, like image files

  12. Examples of Entities • Character entity: • Character: > • Entity reference: &gt; or &#62; • Usage: <formula> x &gt; y </formula> • Content entity: • Declaration:<!ENTITY address “123 Main St”> • Usage: <ship_address> &address; <ship_address> • Unparsed entity: • Declaration:<!ENTITY image SYSTEM “sunset.gif” NDATA GIF> • Usage: <picture> &aimage; </picture>

  13. Components: Comments • An XML comment is ignored by applications that process XML • Comments are commonly used for documentation, or to add information for others viewing the document • The content of the comment is surrounded by special comment tags: <!– and --> • Example:<!-- This is a comment -->

  14. Well-Formed XML Documents • A “well-formed” document is one which adheres to the syntax rules for XML: • An XML document contains one root element • All elements must have start and end tags, except for empty elements • Elements must be properly nested • All attributes must have a value • Attributes can only appear in the start tag and must be unique to that element • Element names are case-sensitive • Special characters must be written as entities • Names of element can start only with letters or an underscore, and can contain letters, numbers, hyphens, periods and underscores

  15. XML Parsers • A “parser” is a program that checks the syntax of an XML document to ensure that the document is well-formed • Two types of parsers: • Non-validating – only checks for syntax • Validating – checks syntax and verifies the document against a DTD or Schema