Introduction to XML

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Introduction to XML
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Programming models
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Distributed programming modelsTypical Web-based

• Easy to deploy but slow, not great user experience

database
html browser
WebServer
http

• Many programming models
• JSP
• Servlets
• PHP
• CGI (python, perl, C)
• Cold Fusion

Dynamically Generated html
html
plus optionally JavaScript to jazz up html
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Distributed programming modelsTypical Web-based

• Better user experience. Heavier, less portable,
  requires socket programming to stream to server.

html
database
WebServer
http
applet
socket
Dynamically Generated html
html applet
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Direct Connections
App1
Application client
Remote Procedures
NDS
App2
App3
Examples Javas rmi, CORBA
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XML basics
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XML Basics, cont

• Most modern languages have method of representing
  structured data.
• Typical flow of events in application

Read data (file, db, socket)
Marshal objects
Manipulate in program
Unmarshal (file, db, socket)

• Many language-specific technologies to reduce
  these steps RMI, object
• serialization in any language, CORBA (actually
  somewhat language neutral),
• MPI, etc.
• XML provides a very appealing alternative that
  hits the sweet spot for
• many applications

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User-defined types in programming languages

• XML is a text-based, programming-language-neutral
  way of representing structured information.
  Compare

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Sample XML Schema

• In XML, datatype description is called a schema.
• ema"
• elementFormDefault"qualified"
  attributeFormDefault"unqualified"
• type"xsstring"/
• type"xsstring"/
• type"xsinteger"/
• type"xsdecimal"/

Ignore this For now
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Alternative schema
In this example studentType is defined separately
rather than anonymously


type"xsstring"/ type"xsstring"/ type"xsinteger"/ type"xsdecimal"/

new type defined separately
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Alternative DTD
Can also use a DTD (Document Type Descriptor),
but this is probably becoming obsolete (notice
the lack of types) Each XML file is stored in a document whose name
is the same as the root node -- ELEMENT Student (name,ssn,age,gpa) Student has four attributes --
is parsed character data -- ssn (PCDATA) (PCDATA)

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Creating instances of types
In programming languages, we instantiate
objects struct Student s1, s2 s1.name
Andrew s1.ssn123-45-6789 Student s new
Student() s1.name Andrew s1.ssn123-45-6789
. type(Student) s1 s1name Andrew .
C
Java
Fortran
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Creating XML documents

• XML is not a programming language!
• In XML we make a Student object in an xml file
  (Student.xml)
• Andrew
• 123-45-6789
• 36
• 2.0
• Think of this as like a serialized object.

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XML and Schema

• Note that there are two parts to what we did
• Defining the structure layout
• Defining an instance of the structure
• The first is done with an appropriate Schema or
  DTD.
• The second is the XML part
• Both can go in the same file, or an XML file can
  refer to an external Schema or DTD (typical)
• From this point on we use only Schema

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XMLSpy
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XMLSpy

• Excellent tool for both learning and developing
  XML.
• Many XML books contain free 90-day license.
  Otherwise, free 30-day license on web page for
  professional and totally free home edition
• Try to use XMLSpy to create example just covered.

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Aspects of XML syntax

• It is illegal to omit closing tags
• XML tags are case-sensitive
• XML elements must be properly nested
• XML elements must have a root element
• XML preserves whitespaces
• XML comments

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How is XML Useful

• Part I
• Simple Mortgage Calculator

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Mortgage payment calculator

• Design a simple application which does the
  following
• Accepts user input
• Loan amount
• Loan term
• Interest rate
• Extras (assessments taxes)
• Returns per-month table of
• total payment
• interest
• Principal
• Some other fun stuff

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Mortgage Calculator General Requirements

• Must be
• Clean simple interface (easy)
• Remotely accessible with security
• Portable
• Not require too much installation on the part of
  the user
• Sufficiently fast not to be embarrassing

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Some possible architectures

• Web server
• Server-side scripting with pure html
• Server-side scripting with htmljavascript
• Server-side scripting with htmlapplet
• Direct connection
• Raw sockets
• Distributed objects

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Initial architecture

• Front-end pure html form
• Back end python cgi (similar to java servlet)
• Python generates web page dynamically after
  making calculations
• No use of higher-level web generation libraries
  at this point
• What are advantages/disadvantages of this
  architecture?
• Run application
• http//masters.cs.uchicago.edu/asiegel/courses/cs
  pp53025/caseStudies/mortgage

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Disadvantages

• Two obvious disadvantages are
• Formatted web content in print statements
  low-level, ugly error prone
• Data is not decoupled from formatting. What if we
  want to switch to an application client?
• Several strategies can help with both of these
  (higher-level htmlgen libraries, server-side
  scripting model, beans, etc.) and XML
• We will look at how XML fits in

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XML-based architecture
web browser
hand-rolled XML
WebServer
http
File system
python CGI
hand-rolled XML
XML
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Observations/questions

• What does browser do with XML?
• Can it display
• Does it even understand XML?
• If not, what good is this?
• Do we have to hand roll our programming language
  objects from XML?

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Some answers

• Regarding first point, try this with your web
  browser
• Note that XML is displayed/formatted nicely, but
  not nearly to the same level of utility as the
  html table
• To add formatting instructions, we must associate
  a separate XSL file with the XML file. We will
  study XSL soon.
• Regarding XML-language conversion, we will study
  language binding for various high-level ways of
  doing this! For now, we will hand-roll ourselves!

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XSL

• We will not cover details of XSL until the third
  week.
• However, for now we can easily create XSL at a
  high level using XMLSpy
• See example application

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Lottery application
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Lottery overview

• Given a list of student members of a dormitory,
  perform an ordered randomized sort of the
  students to determine a room draft order.

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Lottery details

• Students are defined by
• Last name
• First name
• Seniority
• Quarters in the House
• Quarters in the College
• The sort keys are
• Quarters in House
• Quarters in College
• Random

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Software requirements

• Secure login
• House name
• Password
• Remotely accessible
• Prototypes
• Standalone excel
• Web-based

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Architectural requirements
filesystem
XML Login Info
login
Web Server
Web Client
XML
XML Student Data
XSL
lottery
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Next Step

• Implement Lottery as specified
• You must have the following
• Student Schema
• Password Schema
• Sample student xml
• Sample password xml
• Simple XSL for display