XML, XMLSchema, RDF and RDFSchema

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XML, XML-Schema, RDF and RDF-Schema

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XML What is XML?

• XML (eXstensible Markup Language) is a framework
  for defining markup languages
• XML derives from SQML
• XML is a standardization effort by W3C
• XML conforms to ISO 8879
• XML is more a syntax than a language i.e. there
  is no fixed set of markup tags

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XML What was XML designed for?

• To seperate syntax from semantics to provide a
  common framework for structuring information
• To allow tailor-made markup for any possibly
  application domain
• To support internationalization and platform
  independence
• To be the future of structured information

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XML How does XML differ from HTML?

• New tags and attributes can be defined
• Document structures can be nested to any level of
  complexity
• An XML document can contain or refer to optional
  descriptions of its grammar for use by
  applications that need to perform structure
  validation

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XML How does XML differ from HTML?

• We can structure the same information in

HTML and XML
lt?xml version1.0?gt ltemployeesgt ltmarketinggt
ltemployee id"1834"gt ltnamegtGustav
Sielmannlt/namegt ltemailgtgsielmann_at_Dot.comlt/em
ailgt lttelgt43/0662/723942-124lt/telgt
ltfaxgt43/0662/723942-800lt/faxgt lt/employeegt
lt/marketinggt lt/employeesgt
lthtmlgt ltheadgt lttitlegtEmployeeslt/titlegt lt/headgt
ltbodygt lth1gtMarketinglt/h1gt lth2gtGustav Sielman
(1834)lt/h2gt ltpgte-mail gsielmann_at_Dot.comlt/pgt
ltpgtTel. 43/0662/723942-124lt/pgt
ltpgtFax.43/0662/723942-800lt/pgt lt/bodygt lt/htmlgt
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XML XML in a Nutshell

• XML provides a standardized syntax for markup
  languages
• XML uses elements and attributes to define a tree
  structure
• An XML document can have a tree structure of
  arbitrary level of complexity

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XML The structure of an XML document

• An XML document is composed of
• Prolog
• Elements
• Attributes
• Entitiy References
• Comments
• Possibly a DTD (Document Type Definition)

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XML The Prolog

• The Prolog is the first structural element in the
  XML document
• It is usually divided into an XML declaration and
  (optional) a DTD
• E.g.

lt?xml version1.0 encodingUTF-8
standaloneyes?gt
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XML Elements

• All subsequent elements must be within one
  document element
• XML elements must contain a start tag and a
  matching end tag prefixed by a slash. E.g.
  ltYEARgt1976lt/YEARgt
• Empty elements can be written ltYEAR/gt instead of
  using both tags without content
• XML is case-sensitive!
• Element names must begin with an underscore or a
  letter. Subsequent letters in the element name
  may include letters, digits, underscores,
  hyphens and periods

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XML Attributes

• XML attributes are attached to elements
• They are a way of associating values to an
  element without making them part of the actual
  content
• They must begin with a letter or an underscore
  and must not contain any white spaces

ltemployee nameGustav Sielmanngt
gsielman_at_Dot.com lt/employeegt
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XML Entity References

• Entity references are used to reference data that
  is not directly in the structure
• Entity references can be internal external
• Pre-built entitiy references are used to
  represent , lt, gt, and .
• e.g. the string PeterTom(Dont cry for me)
  would be written

PeterampTom(quotDonapost cry for mequot)
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XML Why use Entitiy References?

• We use Entity References

• to make maintenance easy and scalable
• out of comfort
• to use symbols we could not use else

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XML Comments

• Comments are a special set of tags that start
  with lt!-- and end with --gt
• All data written between these two tags is
  ignored by the XML processor.
• Comments are usually used to make small notes
  inside the XML document or to comment out entire
  sections of XML code

lt!-- I HAVE TO GET GUSTAVS EMAIL ltemployee
nameGustav Sielmann gt ltemail/gt
lt/employeegt --gt
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XML Well-formdness and Valdity
With an XML parser an XML document can be checked
for two things

• Well-formdness i.e. if the document obeys the
  syntactical rules of XML (has a prolog, a
  document element, all elements closed,)
• Validity i.e. if the document obeys the rules in
  a DTD or in an XML-Schema

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XML Document Type Definitions

• DTDs (Document Type Definitions) containt a list
  of elements, tags, attributes and entity
  references contained in an XML document and
  describes their relationships to each other.
• A DTD specifies a set of rules for the structure
  of a document therefore making it easy to share
  data with everyone that conforms to the same
  encoding standard

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XML Why use DTDs?

• We use DTDs

• to define a grammar for one of several XML
  documents
• to check XML documents against this grammar

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XML DTDs

• Internal, i.e. placed in the prolog of an XML
  document or
• External, beeing identified by an URL, thus
  making it easy to share the same encoding
  standard with other people

Document Type Definitions can be
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XML Structure of a DTD

• A DTD always starts with lt!DOCTYPE and always
  ends with gt
• Directly after the lt!DOCTYPE comes the name of
  the document element followed by a
• Then comes a list of all elements and attributes
  contained in the XML file, including the document
  element

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XML Example of a DTD
ltemployeesgt ltmarketinggt ltemployee
id"1834"gt ltnamegtGustav Sielmannlt/namegt
ltemailgtgsielmann_at_Dot.comlt/emailgt
lttelgt43/0662/723942-124lt/telgt
ltfaxgt43/0662/723942-800lt/faxgt lt/employeegt
lt/marketinggt lt/employeesgt
XML Structure
lt!DOCTYPE employees lt!ELEMENT employees
(marketing)gt lt!ELEMENT marketing
(employee)gt lt!ELEMENT employee
(name,email,tel,fax?)gt lt!ATTLIST employee id
CDATAIMPLIEDgt lt!ELEMENT name (PCDATA)gt lt!ELEMENT
email (PCDATA)gt lt!ELEMENT tel
(PCDATA)gt lt!ELEMENT fax (PCDATA)gt gt
DTD
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XML Companion Standards

• XML Namespaces allow for modular document
  definition, multiple inheritance and collision
  avoidance
• XPath or the XML Path Language allows navigation
  of the document tree
• XPointer allows tree components as targets
• The XML Linking Language defines linking
  capability

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XML Companion Standards

• The XML Style Language degines presentation
  capbility
• XSLT provides for the transformation of documents
• XML Schema to allow DTDs to be defined as XML
  documents and to define custom data types in
  order for content value control

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XML XML Namespaces

• The XML namespaces recommendation defines a way
  to distinguish between duplicate element type and
  attribute names.
• An XML namespace is a collection of element type
  and attribute names. The namespace is identified
  by a unique name, which is a URI.
• XML namespaces are declared with an xmlns
  attribute, which can associate a prefix with the
  namespace.

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XML XPath

• XPath is a non-XML language used to identify
  particular parts of XML documents.
• XPath lets you write expressions that refer to
  the document's first person element, the seventh
  child element of the third person element, the ID
  attribute of the first person element whose
  contents are the string "Fred Jones,
• XSLT and XPointer use XPath to identify
  particular points in an XML document.

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XML XPointer

• XPointer defines an addressing scheme for
  individual parts of an XML document.
• XPointers enable you to target a given element by
  number, name, type, or relation, to other
  elements in the document.
• XPointers uses the XPath syntax to identify the
  parts of the document they point to.

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XML XML Linking Language

• The XML Linking Language (XLink) allows elements
  to be inserted into XML documents in order to
  create and describe links between resources.
• XLink provides a framework for creating both
  basic unidirectional links and more complex
  linking structures, e.g. linking relationships
  among more than two resources, associate metadata
  with a link,

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XML XML Style Language

• XSL (XML Style Language) is a language for
  expressing stylesheets for XML documents
• XSL describes how to display an XML document of a
  given type
• XSL defines a set of elements called Formatting
  Objects and attributes (in part borrowed from
  CSS2 properties and adding more complex ones)

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XML XSLT

• XSLT (XSL Transformations) is a language for
  transforming XML documents into other XML
  documents
• XSLT is also designed to be used independently of
  XSL. However, XSLT is not intended as a
  completely general-purpose XML transformation
  language. Rather it is designed primarily for the
  kinds of transformations that are needed when
  XSLT is used as part of XSL.
• A transformation expressed in XSLT describes
  rules for transforming a source tree into a
  result tree.

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XML-Schema Why use XML-schema?
In order to validate an XML document you use
XML-schema to specify

• The allowed structure of an XML document
• The allowed data types contained in one (or
  several) XML documents

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XML-Schema Why use schemas instead of DTDs?

• XML-schema documents themselves are XML documents
  and therefore use the same syntax and can
  themselves be validated with schemas
• XML-schema has more powerful possibilites to
  define custom data types

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XML-Schema Why use schemas instead of DTDs?

• XML-schema allows to define elements with nil
  content
• XML-schema allows to define multiple elements
  with the same name but different content
• XML-schema uses XML namespaces

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XML-Schema A Simple XML-Schema
lt?xml version1.0 encodingUTF-8?gt ltmarketing
xmlnsxsi http//www.w3c.org/2001/XMLSchema
-Instance xsinoNameSpaceSchemaLocation
http//www.Dot.com/mySchema.xsdgt
ltemployeegtGustav Sielmannlt/employeegt
ltemployeegtArnold Rummerlt/employeegt
ltemployeegtJohann Neumeierlt/employeegt lt/marketinggt
lt?xml version1.0 encodingUTF-8?gt ltxsdschema
xmlnsxsd http//www.w3c.org/2001/XMLSchemagt
ltxsdelement name marketinggt
ltxsdcomplexTypegt ltxsdsequencegt
ltxsdelement name employee type
xsdstring maxOccurs
unbounded/gt lt/xsdsequencegt
lt/xsdcomplexTypegt lt/xsdelementgt lt/xsdschemagt
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XML-Schema XML-Schema Structure
An XML-schema is composed of

• The Schema Element
• Element Definitions
• Attribute Definitions
• Annotations
• Type Definitions

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XML-Schema The Schema Element

• The schema element is the container element where
  all elements, attributes and data types contained
  in an XML document are stored
• The schema element refers to the XML-schema
  definition at W3C

ltxsdschema xmlnsxsd http//www.w3c.org/2001/X
MLSchemagt . . . . . lt/xsdschemagt
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XML-Schema Defining Elements

• Elements must have a name and a type
• Elements can contain simple, predefined data
  types
• Elements can be defined in regard to their
  cardinality
• Elements can refer to other element definitions

ltxsdelement name employee type
xsdstring maxOccurs unbounded/gt
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XML-Schema Defining Attributes

• Like elements, attributes must have a name and
  type
• Attributes can use custom data types
• Attributes can be restricted in regard to
  cardinality or default values
• Attributes can refer to other attribute
  definitions

ltxsdattribute name country type
xsdstring fixed Austria/gt
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XML-Schema Annotations

• XML-schema provides several tags for annotating a
  schema documentation (intended for human
  readers), appInfo (intended for applications) and
  annotation
• Documentation and appInfo usually appear as
  subelements of annotation

ltxsdannotationgt ltxsddocumentation xmllang
engt here goes the documentation text for
the schema lt/xsddocumentationgt lt/xsdannotation
gt
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XML-Schema Data Type Definitions

• Pre-built Simple Types
• Derived from Simple Types
• Complex Types

XML-schema data types are either
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XML-Schema Simple Types

• Simple types are elements that contain data
• Simple types may not contain attributes or
  sub-elements
• New simple types are defined by deriving them
  from built-in simple types

ltxsdsimpleType name mySimpleDayOfMothgt
ltxsdrestriction base xsdpositiveIntegergt
lt!--positiveInteger defines the minimum to be
1--gt ltxsdmaxInclusion value 31gt
lt/xsdrestrictiongt lt/xsdsimpleTypegt
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XML-Schema Some Built-in Simple Types
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XML-Schema Complex Types

• Complex types are elements that allow
  sub-elements and/or attributes
• Complex types are defined by listing the elements
  and/or attributes nested within
• Complex types are used if one wants to define
  groups or choices of elements

ltxsdcomplexType name myAdressTypegt
ltxsdsequencegt ltxsdelement name Name
type xsdstringgt ltxsdelement name
Email type xsdstringgt ltxsdelement
name Tel type xsdstringgt
lt/xsdsequencegt lt/xsdcomplexTypegt
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XML-Schema Complex Types
In complex types elements can be com-bined using
the following constructs

• Group collection of elements, usually used to
  refer to a common group of elements
• Sequence all the named elements must apear in
  the sequence listed
• Choice one and only one of the elements must
  appear
• All all the named elements must appear, but in
  no specific order

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XML-Schema Mixed, Empty and Any Content

• Mixed content is used if you want to model
  elements that includes both subelements and
  character data
• Empty content is used to define elements that are
  not to include any subelements and character data
• Any content (the most basic data type) does not
  constrain the content in any way

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XML-Schema Inheritance

• XML-Schema provides a pseudo inheritance via
  type-derivations
• In XML-Schema all inheritance has to be defined
  explicitly
• New types can only be created by extending or
  restricting existing types
• Types can only be derived from one type
  multiple inheritance is not supported

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XML-Schema Restricting a Type

• New simple types can be derived by constraining
  facets of a simple type
• The XSDRESTRICTION element is used to state the
  base type

ltxsdsimpleType name AustrianPostalCodegt
ltxsdrestriction base xsdintegergt
ltxsdminInclusive value 1000gt
ltxsdmaxInclusive value 9999gt
lt/xsdrestrictiongt lt/xsdsimpleTypegt
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XML-Schema Extending a Type

• New complex types can be derived by extending
  simple types
• The XSDEXTENSION element is used to state the
  base type

ltxsdcomplexTypegt ltxsdsimpleContentgt
ltxsdextension base "xsddecimal"gt
ltxsdattribute name "currency"
type"xsdstring"/gt lt/xsdextensiongt
lt/xsdsimpleContentgt lt/xsdcomplexTypegt