XML Extensible Markup Language

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XML Extensible Markup Language

• Aleksandar Bogdanovski
• Programing Enviroment LABoratory
• alebo_at_ida.liu.se

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What is XML ?

• Unformal definition
• XML is a markup language for representation of
• documents which contain stuctured information.

New in XML ?
http//www.w3.org/XML/1999/XML-in-10-points.html
http//www.w3.org/XML/1999/XML-in-10-points.html
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Document

• The word "document" refers not only to
  traditional documents, but also to
• the countless number of other XML "data
  formats". These include vector
• graphics, e-commerce transactions, mathematical
  equations, object meta-
• -data, server APIs, and a thousand other kinds of
  structured information.

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SGML XML HTML

• SGML provides arbitrary structure. Full SGML
  systems solve large, complex problems that
  justify their expense.
• XML is defined as an application profile of SGML,
  or roughly speaking, a restricted form of SGML.
  XML specifies neither semantics nor a tag set.
  XML provides a facility to define tags and the
  structural relationships between them.
• In HTML, both the tag semantics and the tag set
  are fixed.

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10 Commandmends of XML

1. XML shall be straightforwardly usable over the
   Internet.
2. XML shall support a wide variety of applications.
3. XML shall be compatible with SGML.
4. It shall be easy to write programs which process
   XML documents.
5. The number of optional features in XML is to be
   kept to the absolute minimum, ideally zero.
6. XML documents should be human-legible and
   reasonably clear.
7. The XML design should be prepared quickly.
8. The design of XML shall be formal and concise.
9. XML documents shall be easy to create.
10. Terseness in XML markup is of minimal importance.

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Look and feel of XML Document

• A Simple XML Document
• lt?xml version"1.0"?gt
• ltoldjokegt
• ltburnsgtSay ltquotegtgoodnightlt/quotegt,
  Gracie.lt/burnsgt
• ltallengtltquotegtGoodnight, Gracie.lt/quotegtlt/allengt
• ltapplause/gt
• lt/oldjokegt

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Markup in XML

• There are six kinds of markup in XML
• Elements
• Entity references
• Comments
• Processing instructions (Pis)
• Marked (CDATA) sections
• Document type declarations (DTD)

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Elements

• Elements are the most common form of markup.
• Elements identify the nature of the content they
  surround.
• Some elements may be empty, in which case they
  have no content.
• Element begins with a start-tag, ltelementgt, ends
  with an end-tag, lt/elementgt,
• and has some content in between.
• Example
• ltburnsgtSay ltquotegtgoodnightlt/quotegt,
  Gracie.lt/burnsgt
• Attributes are name-value pairs that occur in
  start-tags after the element name.
• Example
• ltvolvo types40gt
• In XML, all attribute values must be quoted.

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Entity references

• To represent special characters in XML, entities
  are used. Entities are
• also used to refer to often repeated or varying
  text and to include the
• content of external files.
• Every entity must have a unique name.
• A special form of entity reference, called a
  character reference, can be
• used to insert arbitrary Unicode characters into
  your document.
• Character references take one of two forms
  decimal references, 8478,
• and hexadecimal references, x211E.

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Comments

• Comments begin with lt!-- and end with --gt.
  Comments can contain
• any data except the literal string --.
• Comments can be placed anywhere between markup in
  the document.
• Comments are not part of the textual content of
  an XML document. An
• XML processor is not required to pass them along
  to an application.

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Processing instructions (PIs)

• Like comments, Pis are not textually part of the
  XML document, but the
• XML processor is required to pass them to an
  application.
• Processing instructions have the form lt?name
  pidata?gt.
• The name, called the PI target, identifies the PI
  to the application. Any
• data that follows the PI target is optional.
• The names used in PIs may be declared as
  notations in order to formally
• identify them.
• PI names beginning with xml are reserved for XML
  standardization.

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CDATA sections

• CDATA section instructs the parser to ignore most
  markup characters.
• Example
• lt!CDATA
• p q
• b (i lt 3)
• gt
• Between the start of the section, lt!CDATA and
  the end of the section, gt,
• all character data is passed directly to the
  application, without interpretation.
• The only string that cannot occur in a CDATA
  section is gt.

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Document Type Declaration (DTD)

• One of the greatest strengths of XML is that it
  allows you to create your
• own tag names. But it is not meaningful for tags
  to occur in a completely
• arbitrary order
• Example
• ltgraciegtltquotegtltoldjokegtGoodnight,
• ltapplause/gtGracielt/oldjokegtlt/quotegt
• ltburnsgtltgraciegtSay ltquotegtgoodnightlt/quotegt,
• lt/graciegtGracie.lt/burnsgt
• This doesnt make any sence, but syntactically
  theres nothing wrong. For
• the document to have a meaning, some constraints
  on the sequence and
• nesting of tags should be imposed.

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Document Type Declaration (DTD)

• Constarints are expresed in the Declarations.
• Declarations allow a document to communicate
  meta-information to the
• parser about its content.
• There are four kinds of declarations in XML
• Element Type Declarations
• Attribute List Declarations
• Entity Declarations
• Notation Declarations

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Element Type Declaration

• Element type declarations identify the names of
  elements and the nature
• of their content.
• Example
• lt!ELEMENT oldjoke  (burns, allen, applause?)gt
• lt!ELEMENT burns    (PCDATA quote)gt
• lt!ELEMENT allen    (PCDATA quote)gt
• lt!ELEMENT quote    (PCDATA)gt
• lt!ELEMENT applause EMPTYgt

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Attribute List Declarations

• Attribute list declarations identify which
  elements may have attributes,
• what attributes they may have, what values the
  attributes may hold, and
• what value is the default.
• Example
• lt!ATTLIST oldjoke    
• name  
• ID               
• REQUIRED    
• label 
• CDATA            
• IMPLIED    
• status ( funny notfunny ) 'funny'gt
• Each attribute in a declaration has 3 parts a
  name, a type, and default
• value.

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Attribute List Declarations
There are six possible attribute types

• CDATA
• CDATA attributes are strings, any text is
  allowed.
• ID
• The value of an ID attribute must be a name. All
  of the ID values used in document
• must be different. IDs uniquely identify
  individual elements in a document. Elements
• can have only a single ID attribute.
• IDREF or IDREFS
• An IDREF attribute's value must be the value of a
  single ID attribute on some element
• in the document. The value of an IDREFS attribute
  may contain multiple IDREF
• values separated by white space.

ENTITY or ENTITIES An ENTITY attribute's value
must be the name of a single entity. The value of
an ENTITIES attribute may contain multiple
entity names separated by white space. NMTOKEN
or NMTOKENS Restricted form of string attribute.
NMTOKEN attribute must consist of a single word
, but there are no additional constraints. The
value of an NMTOKENS attribute may contain
multiple NMTOKEN values separated by white space.
A list of names The value of an attribute must
be taken from a specific list of names. This is
frequently called an enumerated type.
Alternatively, you can specify that the names
must match a notation name.
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Attribute List Declarations
There are four possible default values

• REQUIRED
• The attribute must have an explicitly specified
  value on every occurrence of the element in the
• document.
• IMPLIED
• The attribute value is not required, and no
  default value is provided. If a value is not
  specified, the
• XML processor must proceed without one.
• "value"
• An attribute can be given any legal value as a
  default. The attribute value is not required on
  each
• element in the document, and if it is not
  present, it will appear to be the specified
  default.
• FIXED "value"
• An attribute declaration may specify that an
  attribute has a fixed value. In this case, the
  attribute is
• not required, but if it occurs, it must have the
  specified value. If it is not present, it will
  appear to
• be the specified default.

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Entity Declarations

• Entity declarations allow you to associate a name
  with some other fragment
• of content. That construct can be a chunk of
  regular text, a chunk of the
• document type declaration, or a reference to an
  external file containing
• either text or binary data.
• Example
• lt!ENTITY ATI "ArborText, Inc."gt
• lt!ENTITY boilerplate SYSTEM "/standard/legalnotice
  .xml"gt
• lt!ENTITY ATIlogo SYSTEM "/standard/logo.gif"
  NDATA GIF87Agt
• There are three kinds of entities
• Internal Entities
• External Entities
• Parameter Entities

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Internal Entities

• The internal entities associate a name with a
  string of literal text.
• Example
• lt!ENTITY ATI "ArborText, Inc."gt
• Internal entities allow to define shortcuts for
  frequently typed text or
• text that is expected to change, such as the
  revision status of a
• document.
• The XML specification predefines five internal
  entities
• lt produces the left angle bracket, lt
• gt produces the right angle bracket, gt
• amp produces the ampersand,
• apos produces a single quote character (an
  apostrophe), '
• quot produces a double quote character, "

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External Entities

• External entities associate a name with the
  content of another file.
• External entities contain either text or binary
  data.
• Example
• lt!ENTITY boilerplate SYSTEM "/standard/legalnotic
  e.xml"gt
• lt!ENTITY ATIlogo SYSTEM "/standard/logo.gif"
  NDATA GIF87Agt
• The textual content of the external file is
  inserted at the point of
• reference and parsed as part of the referring
  document.
• Binary data is not parsed and may only be
  referenced in an attribute.

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Parameter Entities

• Parameter entities can only occur in the document
  type declaration.
• Parameter entity references are immediately
  expanded in the
• Document type declaration and their replacement
  text is part of the
• declaration.
• Example
• lt!ENTITY personcontent "PCDATA quote"gt
• lt!ELEMENT burns (personcontent)gt
• lt!ELEMENT allen (personcontent)gt

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Notation Declaration

• Notation declarations identify specific types of
  external binary data. This
• information is passed to the processing
  application, which may make
• whatever use of it it wishes.
• Example
• lt!NOTATION GIF87A SYSTEM "GIF"gt

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Including a DTD

• The DTD must be the first thing in the document
  after the optional
• processing instructions and comments.
• The DTD identifies the root element of the
  document and may contain
• additional declarations.
• Example
• lt?XML version"1.0" standalone"no"?gt
• lt!DOCTYPE chapter SYSTEM "dbook.dtd
• lt!ENTITY ulink.module "IGNORE"gt
• lt!ELEMENT ulink (PCDATA)gt
• lt!ATTLIST ulink    
• xmllink CDATA  FIXED "SIMPLE"    
• xml-attributes CDATA  FIXED "HREF URL"    
• URL            CDATA  REQUIREDgt gt
• ltchaptergt...lt/chaptergt

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Well-formed Documents

• A document can only be well-formed if it obeys
  the syntax of XML.

The document must meet all of the following
conditions

• The document instance must conform to the grammar
  of XML documents.
• The replacement text for all parameter entities
  referenced inside a markup declaration consists
  of zero or more complete markup declarations.
• No attribute may appear more than once on the
  same start-tag.
• String attribute values cannot contain references
  to external entities.

• Non-empty tags must be properly nested.
• Parameter entities must be declared before they
  are used.
• All entities except the following amp, lt, gt,
  apos, and quot must be declared.
• A binary entity cannot be referenced in the flow
  of content, it can only be used in an attribute
  declared as ENTITY or ENTITIES.
• Neither text nor parameter entities are allowed
  to be recursive, directly or indirectly.

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Valid Documents

• A well-formed document is valid only if it
  contains a proper document type
• declaration and if the document obeys the
  constraints of that declaration
• (element sequence and nesting is valid, required
  attributes are provided,
• attribute values are of the correct type, etc.).
  The XML specification
• identifies all of the criteria in detail.

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The XML family

• Set of modules that offer useful services to
  accomplish important and
• frequently demanded tasks.
• The XML family consists of
• XLink
• XPointer
• XSchemas
• CSS XSL XSLT
• DOM etc.

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XLink

• Some of the highlights of XLink are
• XLink gives you control over the semantics of
  the link
• XLink introduces Extended Links. Extended Links
  can involve more than two resources.
• There are two types of links
• Simple Links
• Extended Links

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Simple Links

• A Simple Link strongly resembles an HTML ltAgt
  link
• Example
• ltlink xmllink"simple" href"locator"gtLink
  Textlt/linkgt
• A Simple Link identifies a link between two
  resources, one of which is the
• content of the linking element itself. This is an
  in-line link.
• The locator identifies the other resource. The
  locator may be a URL, a
• query, or an Extended Pointer.

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Extended Links

• Extended Links allow you to express relationships
  between more than two
• resources
• Example
• ltelink xmllink"extended" role"annotation"gt
• ltlocator xmllink"locator" href"text.loc"gt
• The Textlt/locatorgt
• ltlocator xmllink"locator" href"annot1.loc"gt
• Annotations lt/locatorgt
• ltlocator xmllink"locator" href"annot2.loc"gt
• More Annotationslt/locatorgt
• ltlocator xmllink"locator" href"litcrit.loc"gt
• Literary Criticismlt/locatorgt
• lt/elinkgt

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XPointer

• XPointers offer a syntax that allows you to
  locate a resource by traversing
• the element tree of the document containing the
  resource.
• Example
• child(2,oldjoke).(3,.)
• locates the third child (whatever it may be) of
  the second oldjoke in the
• document.
• XPointers can span regions of the tree.
• Example
• span(child(2,oldjoke),child(3,oldjoke))
• selects the second and third oldjoke s in the
  document.

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XSchemas

• XML Schemas help developers to precisely define
  the
• structures of their own XML-based formats.

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CSS XSL XSLT

• CSS the style sheet language, is applicable to
  XML as it is to HTML.
• XSL is the advanced language for expressing style
  sheets. It is based on
• XSLT a transformation language used for
  rearranging, adding and deleting
• tags and attributes.

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Conclusion

• XML isn't always the best solution, but it is
  always
• worth considering.