XML Data and Technologies

1
XML Data and Technologies

• Chapter 30.2.2, 30.3.2 - 30.3.5, 30.4, 30.5 (but
  30.5.1, 30.5.2, 30.5.4 30.5.6)

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XML Document Modeling

• XML vocabularies
• Are designed for a specific type of content
• Conform general XML standards
• All documents from the same application must also
  conform to a consistent set of rules
• Modeling tools
• XML Data Type Definitions (DTDs)
• XML schemas

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Data Type Definitions

• DTD forms a vocabulary
• Defines a set of allowable elements
• Defines a set of allowable attributes
• DTD forms the grammar
• Content model is a pattern which determines the
  element and attribute appearance
• DTD facilitates content management

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Declaring a DTD

• Internal DTD is placed within the same document
• lt!DOCTYPE root_element
• declarations gt
• External DTD all declarations are placed to a
  separate file with extension .dtd

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Declaring an External DTD

• Private external DTD is stored locally on the
  server
• lt!DOCTYPE root_element SYSTEM URLgt
• Public external DTD
• lt!DOCTYPE root_element
• PUBLIC FPI URLgt,
• Where FPI formal public identifier

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Declaring Document Elements

• lt!ELEMENT element content-modelgt
• Content-model specifies a type of element
  content
• Any element no restriction
• Empty element cannot store any content
• Character data text string
• Elements contains child (nested) elements
• Mixed contains both a character data and child
  elements

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Element Definition ANY Content

• lt!ELEMENT element_name ANYgt
• Definition
• lt!ELEMENT card ANYgt
• Element appearance in XML document
• ltcardgt ltnamegt Toon Mermaid lt/namegt
• ltkindgt Monster lt/kindgtlt/cardgt
• Or
• ltcardgt Toon Mermaid lt/cardgt

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Element Definition EMPTY Content

• lt!ELEMENT element_name EMPTYgt
• Definition
• lt!ELEMENT attack EMPTYgt
• Element appearance in XML document
• ltattackgtlt/attackgt
• Or
• ltattack/gt

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Element Definition Character Data Only Content

• lt!ELEMENT element_name (PCDATA)gt
• Where PCDATA parsed-character data
• Definition
• lt!ELEMENT rarity (PCDATA)gt
• Element appearance in XML document
• ltraritygt Super rare foillt/raritygt
• NOT VALID appearance
• ltraritygt ltclassgtSuper rarelt/classgt
• lttypegt foillt/typegtlt/raritygt

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Element Definition Element Content

• lt!ELEMENT element_name (child_elements)gt
• Definition
• lt!ELEMENT rarity (class)gt
• Element appearance in XML document
• ltraritygtltclassgt Super rare foillt/classgtlt/raritygt
  
• NOT VALID appearance
• ltraritygt ltclassgtSuper rarelt/classgt
• lttypegt foillt/typegtlt/raritygt

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List of Child Elements

• Sequence is a list of elements with a defined
  order
• lt!ELEMENT element_name (child1,,childN)gt
• Choice lists possible elements
• lt!ELEMENT element_name (child1child2)gt
• Only one child-element is allowed
• Choice and sequence can be combined

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Occurrence of Elements

• Modifying symbols
• Allow zero or one - element?
• Allow one or more - element
• Allow zero or more - element
• Modifying symbols can be applied to a sequence or
  choice

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Working with Mixed Content

• lt!ELEMENT element_name (PCDATAChild1Child2)gt
  
• Definition
• lt!ELEMENT rarity (PCDATAtype)gt
• Element appearance in XML document
• ltraritygt Super rare foillt/raritygt Or
• ltraritygt lttypegt Super rare foillt/typegtlt/raritygt
• Restricts the control of the document structure

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Defining Element Attributes

• Attribute-list declaration
• List of the names of attributes associated with a
  specific element
• Attribute data types
• Indicates whether the attribute is required or
  optional
• Default value for the attribute

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Attribute Declaration Syntax

• lt!ATTLIST element
• attribute1 type1 default1
• attribute2 type2 default2gt
• Or
• lt!ATTLIST element attribute1 type1 default1gt
• lt!ATTLIST element attribute2 type2 default2gt
• lt!ATTLIST element attribute3 type3 default3gt

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Attribute Types

• String types CDATA
• attribute CDATA
• Enumerated types
• attribute (value1value2)
• lt!ATTLIST card kind (MagicTrap)gt
• Tokenized type specifies some rules for the
  format and content
• attribute token

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Attribute Tokens
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Entities

• An entity physical storage unit
• Entity reference the method to refer to the
  storage unit
• Entities are introduced for
• To refer to often repeated text
• To include the content of external files
• Entity reference in XML documents
• entity_name

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Defining Entities

• Internal entity
• lt!ENTITY entity_name valuegt
• Example
• Definition
• lt!ENTITY effect1 Destroys one opponents
  monstergt
• In XML document lteffectgteffect1lt/effectgt
• External entity
• lt!ENTITY entity_name SYSTEM URLgt

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Attribute Defaults
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Merging XML Documents

• XML documents created based on a few XML
  documents
• Name collision
• Declaring a namespace in the document
• Assigning a prefix to the namespace
• Applying the prefix to corresponding elements

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Namespaces

• Namespace defined collection of element and
  attribute names
• Declaring a namespace
• lt?xmlnamespace nsURI prefixpr_name?gt

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Combine a Few XML Documents

• Although namespaces can be used to distinguish
  elements from different XML documents in a given
  document, to check validity of the document new
  DTD must be created
• DTD cannot be associated with a namespace

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DTDs Limitations

• Written in a different (non-XML) syntax- Extended
  Backus Naur Form
• Doesnt work well with namespaces
• Limited data typing
• Limited control on mixed content

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XML Schema

• A definition of a specific XML structure
• It is an XML document
• Defines
• Each element type of the structure
• Each data type associated with the element type
• Schema dialects

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Creating XML Schema

• W3C Schema Working Group
• File written in the XML Schema dialect with
  extension .xsd
• Single root element schema
• ltxsdschema
• xmlnsxsdhttp//www.w3.org/2001/XMLSchemagt
• Element declarations
• lt/xsdschemagt

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Schema Element Types

• Simple type an element contains no attribute or
  child element
• Complex type an element contains attributes
  and/or child element
• Complex type is defined based on a compositor and
  attribute declaration

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Compositors

• Sequence compositor forces elements in the XML
  document to be entered in the same order as in
  the schema
• Choice compositor specifies that only one of the
  elements in the list to be used in the XML
  document
• All compositor allows any of the elements to
  appear in the XML document
• Compositors can be nested

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Element Declaration. Simple type

• ltxsdelement nameelement_name
  typexsddata_type/gt
• Where data_type can be
• string
• decimal
• integer, positiveInteger, and other
• boolean
• date
• .

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Element Declaration. Complex type

• ltxsdelement nameelement_namegt
• ltxsdcomplexTypegt
• ltxsdcompositorgt
• element declarations
• lt/ xsdcompositorgt
• attribute declaration
• lt/xsdcompelexTypegt
• lt/xsdelementgt

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Element Cardinality

• The number of possible occurances
• The minimum number
• minOccurs
• The maximum number
• maxOccur
• Default value is 1 for both attributes

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Declaring Attributes

• An attribute must be declared along with the
  element it belongs to
• ltxsdattribute nameattr_name
  typexsddata_type useIs_required?
  defaultdefault_value fixedfixed_values /gt
• Is_required can be required, optional, prohibited

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Elements with Simple Content and Attributes

• ltxsdelement nameelement_namegt
• ltxsdcomplexTypegt
• ltxsdsimpleContentgt
• ltxsdextension basedata_typegt
• attribute declarations
• lt/xsdextensiongt
• lt/xsdsimpleContentgt
• lt/xsdcomplexTypegt
• lt/xsdelementgt

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Using Schemas in a Combined Documents

• To attach the schemas to different parts of the
  document
• Add the XML Schema-instance namespace to the
  documents root element
• Assign namespaces to the different parts of the
  document
• Add schemaLocation attribute to the parent
  element of each part

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Example

• lt?xml version1.0?gt
• ltmcset xmlnsxsihttp//www.w3.org/2001/XMLSchem
  a-instance
• xmlnsmchttp//deck/monster/ns
• xsischemaLocationURI schemagt
• ltcardgt
• lt/mcsetgt

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Structuring a Schema

• Russian Doll design set of nested declarations
• Flat Catalog design all element declarations
  are made globally
• References
• ltxsdelement refelement_name/gt

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Displaying Contents of XML Documents

• Cascading Style Sheets have limitations
• Cant change the format of the content (like date
  format)
• Cant add additional text
• Hard to work with images and hyperlinks
• Are applied to the elements, but not attributes
• Extensible Style Sheet Language
• XSL-Formatting Objects (page layout and design)
• XSLTransformations (transforms XML content into
  another presentation format)
• XPath (locates information and performs
  operations)

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XSLT Style Sheets

• Convert source document (XML document) into a
  result document
• Transformation is performed by XSLT processor
• Server side transformation
• Client side transformation
• Browsers support for XSLT
• Internet Explorer 6.0 fully supports W3CXSLT
  specifications

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XSLT Transformation

• XSLT allows to create a result document as HTML,
  XML, or text file.
• ltxsloutput methodhtml version4.0/gt
• Some of XSLT processors generate result documents
  according to specification.

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Creating XSLT

• lt?xml version"1.0" ?gt
• ltxslstylesheet version1.0 xmlnsxsl
• "http//www.w3.org/1999/XSL/Transform"gt
• Content
• lt/xslstylesheetgt
• XSLT file has an extension .xsl

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XSLT Content

• Template a set of elements that defines how a
  part of the source document should be transformed
  in the result document
• Template
• ltxsltemplate matchnode
• XSLT and Literal result Elements
• lt/ xsltemplategt
• Where node either /, name, or XPath expression

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Template

• XSLT elements commands to XSLT processor
• Literal result element text sent to the result
  document, but not processed by XSLT processor
• The example HTML tags

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Referencing Parts of XML Documents

• XPath is the language for referencing the content
  of an XML document
• XML document is viewed as a node tree.
• Similar to Unix or DOS specifications for file
  paths
• Reaching elements
• /child1/child2
• Reaching attribute of child2
• /child1/_at_child

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Working with XSLT

• Inserting a node expression into XSLT document
• ltxslvalue-of selectXPath_expression/gt
• Applying XSLT to XML document
• lt?xmlstylesheet typetext/xsl hrefURL ?gt

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Querying XML Data

• XML Query Working Group
• Basic Documents
• XML Query Requirements
• XML Query Data Model
• XML Query Algebra
• XQuery

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Query Requirements

• Language must be declarative
• Independent of any protocol
• Data model must
• Represent XML 1.0 data types of Schema
  specification
• Support references within and outside of the
  document
• The language must support specific operations

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XML Query Data Model

• A node basic construct
• Node types
• Document,
• Element,
• Value,
• Attribute,
• Namespace,
• Processing instruction (PI) ,
• Comment

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Node Document

• Root node is connected to all the nodes that are
  reachable directly or indirectly from it
• Connected nodes form a tree
• Every node belongs to exactly one tree
• Every tree has exactly one root node

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XML Query Algebra

• Projection
• Selection
• Iteration
• Join
• Sorting
• Aggregation

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XQuery

• Is applied to XML
• Returns a sequence of XML fragments or atomic
  values
• XQuery relies on XPath and XML Schema data types.
  
• XQuery is not an XML language

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XQuery Expressions

• Path expressions
• Element constructors
• FLWOR ("flower") expressions
• List expressions
• Conditional expressions
• Quantified expressions
• Datatype expressions

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FLWOR Expression

• For-Let-Where-Order-Return
• Similar to SELECT-FROM-WHERE- GROUP-BY from SQL
• For binds values to one or more variables using
  path expression, is used when iteration is
  required
• Generates list of bindings per variable

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FLWOR Expression (cont)

• Let binds values to one or more variables
  without iteration
• Single binding per each variable
• Where specifies qualification condition
• Return constructs the output of the expression
• Node
• Set of nodes

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XML and Databases

• Databases store data for machine processing
• Data-centric model
• Data is stored in a database
• Data is transferred as XML documents
• Document-centric model
• Documents are designed for human consumption

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XML Storing to and Retrieving from a Database

• Documents with simple recordsets
• Relational mapping
• Documents with hierarchical recordsets
• Object-relational mapping
• Object oriented mapping
• Schema-independent representation
• Relations are used to describe structure of XML
  document

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Converting a Relation into XML Document
Root/Relation
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SQL and XML

• SQL/XML Standard
• Oracle XML
• XML SQL Utility
• Directly serves and stores XML from the database
• Takes SQL queries and generates XML documents
  from results
• Flexible XML output can be produced as Text or as
  DOM trees
• Generates DTDs and XML schemas from database
  schemas