INF 523 Web Technologies with XML

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INF 523 Web Technologies (with XML)

• Week 3
• Bahadir K. Akcam
• Fall 2006

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Case Assignment

• Due on November 13
• Read By Invitation Only by Galen Gruman at CIO
• http//www.cio.com/archive/090106/col_tec.html
• Find an XML implementation case
• Evaluate the Grumans article and your case to
  discuss
• how organizations use xml technologies in their
  work,
• their expectations from these technologies,
• and current opportunities and obstacles for
  implementing XML
• Max 4 pages

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XML Namespaces

• XML Namespaces provide a method to avoid element
  name conflicts.
• When different XML documents are shared, same
  element names may be used for different purposes

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XML Namespaces

• Document 1)
• lttablegt
• lttrgt
• lttdgtAppleslt/tdgt
• lttdgtBananaslt/tdgt
• lt/trgt
• lt/tablegt

• Document 2)
• lttablegt
• ltnamegtTea tablelt/namegt ltwidthgt80lt/widthgt
  ltlengthgt120lt/lengthgt lt/tablegt

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Using Prefix

• Document 1)
• lthtablegt
• lthtrgt
• lthtdgtAppleslt/htdgt
• lthtdgtBananaslt/htdgt
• lt/htrgt
• lt/htablegt

• Document 2)
• ltftablegt
• ltfnamegtTea tablelt/fnamegt ltfwidthgt80lt/fwidthgt
  ltflengthgt120lt/flengthgt lt/ftablegt

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Using namespaces

• An XML Namespace is simply a group of names,
  usually with a related purpose or context, where
  the group has a globally unique name (the
  namespace name).
• This is often ensured by using a domain name
  (from Internet DNS) as the first part of the
  namespace name.
• xmlnsnamespace-prefix"namespaceURI"

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Using namespaces

• ltftable xmlnsf"http//furniturez.com/furniture"
  gt ltfnamegtAfrican Coffee Tablelt/fnamegt
  ltfwidthgt80lt/fwidthgt ltflengthgt120lt/flengthgt
• lt/ftablegt

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Namespaces

• When a namespace is defined in the start tag of
  an element, all child elements with the same
  prefix are associated with the same namespace.
• Default Namespaces Defining a default namespace
  for an element saves us from using prefixes in
  all the child elements.
• xmlns"namespaceURI"

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Namespaces

• Namespaces are NOT
• Resources that exist anywhere (other than
  conceptually)
• Directly related to DTDs or XML schemas

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DTDs and Valid XML Documents

• lt?xml version"1.0"?gt
• lt!DOCTYPE note
• lt!ELEMENT note (to,from,heading,body)gt
  lt!ELEMENT to (PCDATA)gt
• lt!ELEMENT from (PCDATA)gt
• lt!ELEMENT heading (PCDATA)gt
• lt!ELEMENT body (PCDATA)gt
• gt
• ltnotegt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekendlt/bodygt
• lt/notegt

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CDATA and PCDATA

• CDATA means character data
• PCDATA means parsed character data.
• All text in an XML document will be parsed by the
  parser.
• Only text inside a CDATA section will be ignored
  by the parser.

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Parsed Data

• ltmessagegtThis text is also parsedlt/messagegt
• ltnamegtltfirstgtBilllt/firstgtltlastgtGateslt/lastgtlt/namegt
  
• ltnamegt
• ltfirstgtBilllt/firstgt
• ltlastgtGateslt/lastgt
• lt/namegt

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Escape Characters

• Illegal XML characters (lt, gt, , , ) have to be
  replaced by entity references.
• ltmessagegtif salary lt 1000 thenlt/messagegt
• ltmessagegtif salary lt 1000 thenlt/messagegt
• Everything inside a CDATA section is ignored by
  the parser.
• "lt!CDATA" and ends with "gt"
• If your text contains a lot of "lt" or ""
  characters - as program code often does - the XML
  element can be defined as a CDATA section.

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XML Validation

• (1) XML with correct syntax is Well Formed XML.
• (2) XML validated against a DTD is Valid XML.

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Well Formed XML Documents

• A "Well Formed" XML document has correct XML
  syntax.
• XML documents must have a root element
• XML elements must have a closing tag
• XML tags are case sensitive
• XML elements must be properly nested
• XML attribute values must always be quoted

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Valid XML Documents

• A "Valid" XML document is a "Well Formed" XML
  document, which also conforms to the rules of a
  Document Type Definition (DTD)
• Remember DTD rules!
• Preventing having different elements with
  different formats into your XML files

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XML Schema

• XML Schema is an XML-based alternative to DTDs.
• An XML Schema describes the structure of an XML
  document.
• The XML Schema language is also referred to as
  XML Schema Definition (XSD).

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XML Schema

• The purpose of an XML Schema is to define the
  legal building blocks of an XML document, just
  like a DTD.
• An XML Schema defines
• elements that can appear in a document
• attributes that can appear in a document
• which elements are child elements
• the order of child elements
• the number of child elements
• whether an element is empty or can include text
• data types for elements and attributes
• default and fixed values for elements and
  attributes

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XML Schema

• XML Schemas are the Successors of DTDs
• XML Schemas are extensible to future additions
• XML Schemas are richer and more powerful than
  DTDs
• XML Schemas are written in XML
• XML Schemas support data types
• XML Schemas support namespaces

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Why Use XML Schemas?

• XML Schemas Support Data Types
• It is easier
• to describe allowable document content
• to validate the correctness of data
• to work with data from a database
• to define data facets (restrictions on data)
• to define data patterns (data formats)
• to convert data between different data types

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Why Use XML Schemas?

• XML Schemas use XML Syntax
• Another great strength about XML Schemas is that
  they are written in XML.
• You don't have to learn a new language
• You can use your XML editor to edit your Schema
  files
• You can use your XML parser to parse your Schema
  files
• You can manipulate your Schema with the XML DOM
• You can transform your Schema with XSLT

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Why Use XML Schemas?

• XML Schemas Secure Data Communication
• When sending data from a sender to a receiver, it
  is essential that both parts have the same
  "expectations" about the content.
• With XML Schemas, the sender can describe the
  data in a way that the receiver will understand.
• A date like "03-11-2004" will, in some
  countries, be interpreted as 3.November and in
  other countries as 11.March.
• However, an XML element with a data type like
  this ltdate type"date"gt2004-03-11lt/dategt
• ensures a mutual understanding of the content,
  because the XML data type "date" requires the
  format "YYYY-MM-DD".

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Why Use XML Schemas?

• XML Schemas are Extensible
• XML Schemas are extensible, because they are
  written in XML.
• With an extensible Schema definition you can
• Reuse your Schema in other Schemas
• Create your own data types derived from the
  standard types
• Reference multiple schemas in the same document

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Why Use XML Schemas?

• Well-Formed is not Enough
• A well-formed XML document is a document that
  conforms to the XML syntax rules, like
• it must begin with the XML declaration
• it must have one unique root element
• start-tags must have matching end-tags
• elements are case sensitive
• all elements must be closed
• all elements must be properly nested
• Even if documents are well-formed they can still
  contain errors, and those errors can have serious
  consequences.

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XSD How To?

• XML documents can have a reference to a DTD or to
  an XML Schema
• Remember our famous XML document
• lt?xml version"1.0"?gt
• ltnotegt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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XSD How To?

• A DTD File
• lt!ELEMENT note (to, from, heading, body)gt
• lt!ELEMENT to (PCDATA)gt
• lt!ELEMENT from (PCDATA)gt
• lt!ELEMENT heading (PCDATA)gt
• lt!ELEMENT body (PCDATA)gt

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XSD How To?

• An XML Schema called note.xsd
• lt?xml version"1.0"?gt
• ltxsschema xmlnsxs"http//www.w3.org/2001/XMLSch
  ema" targetNamespace"http//www.albany.edu"
  xmlns"http//www.albany.edu" elementFormDefault
  "qualified"gt
• ltxselement name"note"gt
• ltxscomplexTypegt
• ltxssequencegt
• ltxselement name"to" type"xsstring"/gt
• ltxselement name"from" type"xsstring"/gt
  ltxselement name"heading" type"xsstring"/gt
• ltxselement name"body" type"xsstring"/gt
• lt/xssequencegt
• lt/xscomplexTypegt
• lt/xselementgt
• lt/xsschemagt

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XSD How To?

• A Reference to an XML Schema
• lt?xml version"1.0"?gt
• ltnote xmlns"http//www.albany.edu"
  xmlnsxsi"http//www.w3.org/2001/XMLSchema-instan
  ce" xsischemaLocation"http//www.albany.edu
  note.xsd"gt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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ltSchemagt Element

• The ltschemagt element is the root element of every
  XML Schema.
• lt?xml version"1.0"?gtltxsschemagt...
  ...lt/xsschemagt
• ltxsschema xmlnsxs"http//www.w3.org/2001/XMLSch
  ema" targetNamespace"http//www.albany.edu"
  xmlns"http//www.albany.edu" elementFormDefault"
  qualified"gt... ...lt/xsschemagt

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ltSchemagt Element

• xmlnsxs"http//www.w3.org/2001/XMLSchema"
• the elements and data types used in the schema
  come from the "http//www.w3.org/XMLSchema"
  namespace.
• It also specifies that the elements and data
  types that come from the "http//www.w3.org/2001/X
  MLSchema" namespace should be prefixed with xs
• targetNamespace"http//www.albany.edu"
• the elements defined by this schema (note, to,
  from, heading, body) come from the
  "http//www.albany.edu" namespace.
• xmlns"http//www.albany.edu"
• the default namespace is "http//www.albany.edu".
  
• elementFormDefault"qualified"
• any elements used by the XML instance document
  which were declared in this schema must be
  namespace qualified.

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Referencing a Schema in an XML Document

• lt?xml version"1.0"?gt
• ltnote xmlns"http//www.albany.edu
• xmlnsxsi"http//www.w3.org/2001/XMLSchema-instan
  ce
• xsischemaLocation"http//www.albany.edu
  note.xsd"gt
• lttogtTovelt/togt ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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Referencing a Schema in an XML Document

• xmlns"http//www.albany.edu"
• specifies the default namespace declaration.
• xmlnsxsi"http//www.w3.org/2001/XMLSchema-instan
  ce"
• Refer to XML Schema Instance namespace
• xsischemaLocation"http//www.albany.edu
  note.xsd"
• This attribute has two values. The first value is
  the namespace to use. The second value is the
  location of the XML schema to use for that
  namespace.

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NEXT WEEK

• Continue on XML Schema
• More time to develop our projects XSD in class
• Make a start to XPath on Wednesday

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References

• www.w3schools.com
• Birbeck et.al. (2001) Professional XML 2nd
  Edition, Wrox Press Ltd. Birmingham, UK