COS 381

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COS 381

• Day 17

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Agenda

• Questions??
• Resources
• Source Code Available for examples in Text Book
  in Blackboard
• Also _at_ http//perleybrook.umfk.maine.edu/SourceCod
  e/
• Html and XHTML examples
• http//perleybrook.umfk.maine.edu/samples/
• In Class Work
• http//perleybrook.umfk.maine.edu/SourceCode/incla
  ssWork/
• Assignment 3 Not corrected
• Assignment 4 is posted
• Due April 4
• Quiz 2 is not corrected
• One student has yet to take quiz
• Finish Discussion on XML

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XML Schemas
- Problems with DTDs 1. Syntax is different
from XML - cannot be parsed with an XML
parser 2. It is confusing to deal with two
different syntactic forms 3. DTDs do not
allow specification of particular kinds of
data XML Schemas is one of the alternatives to
DTD - Two purposes 1. Specify the structure
of its instance XML documents 2. Specify the
data type of every element and attribute of its
instance XML documents DTD can be converted to
schemas http//www.hitsw.com/xml_utilites/
Resource http//www.w3.org/XML/Schema
4
XML Schemas (continued)

• - Schemas are written using a namespace
• http//www.w3.org/2001/XMLSchema
• - Every XML schema has a single root, schema
• The schema element must specify the namespace
  for schemas as its xmlnsxsd attribute
• - Every XML schema itself defines a tag set,
  which must be named
• targetNamespace
• http//cs.uccs.edu/planeSchema
• For this class
• http//perleybrook.umfk.maine.edu/ home
  directory
• If we want to include nested elements, we must
  set the elementFormDefault attribute to qualified
• - The default namespace must also be specified
• xmlns "http//cs.uccs.edu/planeSchema"

5
XML Schemas (continued)
- - A complete example of a schema element
ltxsdschema lt!-- Namespace for the schema itself
--gt ltxmlnsxsd "http//www.w3.org/
2001/XMLSchema" lt!-- Namespace where elements
defined here will be placed --gt
lttargetNamespace "http//cs.uccs.edu/planeSchema"
lt!-- Default namespace for this document --gt
xmlns "http//cs.uccs.edu/planeSchema" lt!--
Next, specify non-top-level elements to be in the
target namespace --gt elementFormDefault
"qualified"gt
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XML Schemas (continued)
- - A complete example of a schema element
ltschema lt!-- Namespace for the schema itself --gt
ltxmlns "http//www.w3.org/2001/XMLS
chema" lt!-- Namespace where elements defined
here will be placed --gt lttargetNamespace
"http//cs.uccs.edu/planeSchema" lt!-- Default
namespace for this document --gt xmlnsplanes
"http//cs.uccs.edu/planeSchema" lt!-- Next,
specify non-top-level elements to be in the
target namespace --gt elementFormDefault
"qualified"gt
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XML Schemas (continued)
- Defining an instance document - The root
element must specify the namespaces it uses
1. The default namespace 2. The standard
namespace for instances
(XMLSchema-instance) 3. The location
where the default namespace is defined, using
the schemaLocation attribute, which is assigned
two values ltplanes xmlns "http//cs.uccs.edu
/planeSchema" xmlnsxsi
http//www.w3.org/2001/XMLSchema-instance"
xsischemaLocation "http//cs.uccs.edu/pla
neSchema planes.xsd" gt Data Type
Categories 1. Simple (strings only, no
attributes and no nested elements) 2.
Complex (can have attributes and nested elements)
8

XML Schemas (continued)
- XMLS defines over 40 data types http//www.w3.o
rg/TR/xmlschema-2/built-in-datatypes -
Primitive string, Boolean, float, -
Derived byte, decimal, positiveInteger, -
User-defined (derived) data types specify
constraints on an existing type (the base type)
- Constraints are given in terms of facets
(totalDigits, maxInclusive, etc.) - Both
simple and complex types can be either named or
anonymous - DTDs define global elements
(context is irrelevant) - With XMLS, context
is essential, and elementscan be either
1. Local, which appears inside an element that is
a child of schema, or 2. Global, which
appears as a child of schema
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XML Schemas (continued)
- Defining a simple type - Use the element
tag and set the name and type attributes
ltxsdelement name "bird" type
"xsdstring" /gt - An instance could have
ltbirdgt Yellow-bellied sap sucker lt/birdgt -
Element values can be constant, specified with
the fixed attribute fixed "three-toed" -
User-Defined Types - Defined in a simpleType
element, using facets specified in the content of
a restriction element - Facet values are
specified with the value attribute
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XML Schemas (continued)
ltxsdsimpleType name "middleName" gt
ltxsdrestriction base "xsdstring" gt
ltxsdmaxLength value "20" /gt
lt/xsdrestrictiongt lt/xsdsimpleTypegt -
Categories of Complex Types 1. Element-only
elements (elements no text) 2. Text-only
elements (text no elements) 3.
Mixed-content elements (both text and elements
4. Empty elements - Element-only elements
- Defined with the complexType element - Use
the sequence tag for nested elements that must be
in a particular order - Use the all tag if
the order is not important
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XML Schemas (continued)
ltxsdcomplexType name "sports_car" gt
ltxsdsequencegt ltxsdelement name "make"
type "xsdstring" /gt ltxsdelement name
"model " type "xsdstring" /gt
ltxsdelement name "engine" type "xsdstring"
/gt ltxsdelement name "year" type
"xsdstring" /gt lt/xsdsequencegt
lt/xsdcomplexTypegt - Nested elements can include
attributes that give the allowed number of
occurrences (minOccurs, maxOccurs,
unbounded) - We can define nested elements
elsewhere ltxsdelement name "year" gt
ltxsdsimpleTypegt ltxsdrestriction base
"xsddecimal" gt ltxsdminInclusive value
"1990" /gt ltxsdmaxInclusive value
"2003" /gt lt/xsdrestrictiongt
lt/xsdsimpleTypegt lt/xsdelementgt
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XML Schemas (continued)
- The global element can be referenced in the
complex type with the ref attribute
ltxsdelement ref "year" /gt - Validating
Instances of XML Schemas - Can be done with
several different tools - One of them is xsv,
which is available from http//www.ltg.ed.ac.uk
/ht/xsv-status.html - Note If the schema is
incorrect (bad format), xsv reports that it can
find the schema planes.xsd Plane.xml
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Modified Plane example from text
lt?xml version "1.0"?gt lt!-- plane.xml A
simple XML document for illustrating a schema
The schema is in planes.xsd
--gt lt?xml-stylesheet type"text/css"
href"planes.css"?gt ltplane xmlns
"http//perleybrook.umfk.maine.edu/examples/planes
" xmlnsxsi "http//www.w3.org/2001/XMLSchema-
instance" xsischemaLocation
"http//perleybrook.umfk.maine.edu/examples/planes
planes.xsd"gt ltmakegt Cessna lt/makegt
ltmakegt Piper lt/makegt ltmakegt Beechcraft
lt/makegt lt/planegt
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Cont
lt?xml version "1.0"?gt lt!-- planes.xsd A
simple schema for plane.xml --gt ltxsdschema
xmlnsxsd "http//www.w3.org/2001/XMLSchema
" targetNamespace "http//perleybrook.umfk.m
aine.edu/examples/planes" xmlns
"http//perleybrook.umfk.maine.edu/examples/planes
" elementFormDefault "qualified"gt
ltxsdelement name "planes"gt
ltxsdcomplexTypegt ltxsdallgt
ltxsdelement name "make"
type "xsdstring"
minOccurs "1"
maxOccurs "unbounded" /gt
lt/xsdallgt lt/xsdcomplexTypegt
lt/xsdelementgt lt/xsdschemagt
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Validating Instances of Schemas

• Various systems for validating instances against
  schemas
• Online http//www.w3.org/2001/03/webdata/xsv
• XML support libraries include validation Xerces
  from Apache, Saxon, Altova XML tools
• Some IDEs have automatic validation Altova Spy,
  Eclipse with Oxygen, Eclipse with XML Buddy Pro
• Certain IDEs will use schemas to provide support
  for XML file creation

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Displaying Raw XML Documents
- There is no presentation information in an XML
document - An XML browser should have a default
style sheet for an XML document that does not
specify one - You get a stylized listing of
the XML
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Displaying XML Documents with CSS
- A CSS style sheet for an XML document is just
a list of its tags and associated styles -
The connection of an XML document and its style
sheet is made through an xml-stylesheet
processing instruction lt?xml-stylesheet
type "text/css" href
"mydoc.css"?gt --gt SHOW planescss.xml and
planes.css
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7.9 Overview of XSLT

• A functional style programming language
• Basic syntax is XML
• There is some similarity to LISP and Scheme
• An XSLT processor takes an XML document as input
  and produces output based on the specifications
  of an XSLT document

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8.9 XSLT Style Sheets
Resources http//www.w3.org/Style/XSL/ http//www.
vbxml.com/xsl/tutorials/intro/default.asp http//w
ww.w3.org/TR/xsl/ -An XSLT processor merges an
XML document into an XSLT style sheet -
This merging is a template-driven process - An
XSLT style sheet can specify page layout,
page orientation, writing direction, margins,
page numbering, etc.
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7.9 XSLT Style Sheets

• A family of specifications for transforming XML
  documents
• XSLT specifies how to transform documents
• XPath specifies how to select parts of a
  document and compute values
• XSL-FO specifies a target XML language
  describing the printed page
• XSLT describes how to transform XML documents
  into other XML documents such as XHTML
• XSLT can be used to transform to non-XML
  documents as well

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Figure 7.5 XSLT processing
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7.9 XSLT Structure

• An XSLT document contains templates
• XPath is used to specify patterns of elements to
  which the templates should apply
• The content of a template specifies how the
  matched element should be processed
• The XSLT processor will look for parts of the
  input document that match a template and apply
  the content of the template when a match is found
• Two models
• Template-driven works with highly regular data
• Data-driven works with more loosely structured
  data with a recursive structure (like XHTML
  documents)

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XSLT Style Sheets (continued)
- The processing instruction we used for
connecting a CSS style sheet to an XML document
is used to connect an XSLT style sheet to an XML
document lt?xml-stylesheet type "text/xsl href
"XSLT style sheet"?gt - An example lt?xml
version "1.0"?gt lt!-- xslplane.xml --gt
lt?xml-stylesheet type "text/xsl"
href "xslplane.xsl" ?gt ltplanegt
ltyeargt 1977 lt/yeargt ltmakegt Cessna lt/makegt
ltmodelgt Skyhawk lt/modelgt ltcolorgt Light
blue and white lt/colorgt lt/planegt
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XSLT Style Sheets (continued)
- An XSLT style sheet is an XML document with a
single element, stylesheet, which defines
namespaces ltxslstylesheet xmlnsxsl
http//www.w3.org/1999/XSL/Format xmlns
http//www.w3.org/1999/xhtmlgt - If a style
sheet matches the root element of the XML
document, it is matched with the template
ltxsltemplate match "/"gt - A template can
match any element, just by naming it (in place of
/) ltxsltemplate match plane"gt -
XSLT elements include two different kinds of
elements, those with content and those for which
the content will be merged from the XML doc
- Elements with content often represent xHTML
elements ltspan style "font-size 14"gt
Happy Easter! lt/spangt
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XML Transformations and Style Sheets (continued)

• - XSLT elements that represent xHTML elements are
  simply copied to the merged document
• - The XSLT value-of element
• - Has no content
• - Uses a select attribute to specify part of
  the XML data to be merged into the XSLT
  document
• ltxslvalue-of select CAR/ENGINE" /gt
• - The value of select can be any branch of
  the document tree
• SHOW xslplane.xml xslplane.xsl
• - The XSLT for-each element
• - Used when an XML document has a sequence of
• the same elements
• --gt SHOW xslplanes.xml
• --gt SHOW xslplanes.xsl

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7.9 Producing Transformation Output

• Elements not belonging to XSLT and other text
  will be copied to the output when the containing
  template is applied
• The value-of tag causes the select attribute
  value to be evaluated and the result is put into
  the output
• The value of an element is the text contained in
  it and in sub-elements
• The value of an attribute is the value
• Example xslplane1.xsl transforms the xslplane.xml
  file into XHTML for display purposes
• If the style sheet is in the same directory as
  the XML file, some browsers will pick up the
  transformation and apply it
• This works with Firefox and Internet Explorer but
  not Opera

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7.9 Processing Repeated Elements

• File xslplanes.xml contains data about multiple
  airplanes
• The style sheet xslplanes.xsl uses a for-each
  element to process each plane element in the
  source document
• A sort element could be included to sort output
• The element
• ltxslsort selectyear data-typenumber/gt
• Specifies sorting by year

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Overview
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7.10 XML Processors

• XML processors provide tools in programming
  languages to read in XML documents, manipulate
  them and to write them out

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7.10 Purposes of XML Processors

• Four purposes
• Check the basic syntax of the input document
• Replace entities
• Insert default values specified by schemas or
  DTDs
• If the parser is able and it is requested,
  validate the input document against the
  specified schemas or DTDs
• The basic structure of XML is simple and
  repetitive, so providing library support is
  reasonable
• Examples
• Xerces-J from the Apache foundation provides
  library support for Java
• Command line utilities are provided for checking
  well-formedness and validity
• Two different standards/models for processing
• SAX
• DOM

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7.10 Parsing

• The process of reading in a document and
  analyzing its structure is called parsing
• The parser provides as output a structured view
  of the input document

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7.10 The SAX Approach

• In the SAX approach, an XML document is read in
  serially
• As certain conditions, called events, are
  recognized, event handlers are called
• The program using this approach only sees part of
  the document at a time

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7.10 The DOM Approach

• In the DOM approach, the parser produces an
  in-memory representation of the input document
• Because of the well-formedness rules of XML, the
  structure is a tree
• Advantages over SAX
• Parts of the document can be accessed more than
  once
• The document can be restructured
• Access can be made to any part of the document at
  any time
• Processing is delayed until the entire document
  is checked for proper structure and, perhaps,
  validity
• One major disadvantage is that a very large
  document may not fit in memory entirely

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7.11 Web Services

• Allow interoperation of software components on
  different systems written in different languages
• Servers that provide software services rather
  than documents
• Remote Procedure Call
• DCOM and CORBA provide implementations
• DCOM is Microsoft specific
• CORBA is cross-platform

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7.11 Web Service Protocols

• Three roles in web services
• Service providers
• Service requestors
• Service registry
• The Web Services Definition Language provides a
  standard way to describe services
• The Universal Description, Discovery and
  Integration service provides a standard way to
  provide information about services in response to
  a query
• SOAP is used to specify requests and responses