WWW / Internet

1
WWW / Internet

• Aaron Bloomfield
• CS 415
• Fall 2005

2
Impact of Internet on Programming Languages
3
Formatting Languages
4
HTML Background

• HyperText Markup Language
• Tim Berners-Lee 1989
• Subset/Instance of SGML
• Developed to support WWW
• Developed as a document-layout language

5
Markup Languages

• Used to encode formatting
• Markup tags embedded in text
• Output device interpreted tags
• Originally used in word processing

6
SGML

• Standard General Markup Language
• Rules for defining logical structure of a
  document
• Basis for creating markup languages
• Essential info easily transferred

7
HTML

• HTML file processed and displayed by Web Browser
• Passive language
• Program that displays the html code decides how
  to interpret the description

8
Tags

• Tell Web Browser how to format text on screen
• Always enclosed in angle brackets lttaggt
• Not case sensitive
• Whitespace does not matter

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Anchors

• Allow jumping to different spots
• HREF
• Inserts a hyperlink
• ltA HREFhttp//www.virginia.edugtUVAlt/Agt
• Name
• Allows a different spot in the document to be
  jumped to directly
• ltA NAMEsec2gtSection 2lt/Agt

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Images

• Only need image URL
• SRC tag
• Images can be placed anywhere
• Align

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HTML Evolution

• W3C IETF HTML standards
• Internet Drafts published, tested, commented on,
  and become Document Type Definitions
• Browser authors add to HTML
• Support it in their browsers
• Community accepts or abandons additions

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PDF

• Portable Document Format
• The second generation of PostScript
• PDF files retain their formatting across
  different viewing environments
• Applications exist for converting documents to
  PDF
• Can contain hyperlinks

13
Tex

• Document preparation system
• Typesetting for math and technical material
• Very close control over document

14
Tex File Creation

• Tex file created with regular text editor
• Tex converts it into a DVI (DeVice Independent)
  file
• DVI file read by another program
• Creating DVI file allows for 1 file to produce
  the same output by different reading programs

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LaTeX

• Macro package for Tex
• Used for document preparation
• Author does not format document
• Specify defaults for document classes
• You can create your own document classes

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Latex Example

• \documentclassarticle
• \titleLatex Example
• \begindocument
• Body text goes here.
• \enddocument

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PL Concepts

• Formatting languages are not PLs
• But their use employs
• Parsing
• Generating output in a different form
• Nesting

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XML

• the eXensible Markup Language

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What is XML?

• XML is a markup languge used to represent data in
  a structured, portable manner
• It allows programmers to use a standard parser
  for many different types of data without having
  to worry about small changes in document
  structure affecting their parsing code
• It allows for easy interchange of data between
  heterogenous systems
• Why do we care about XML? Its not a programming
  language.

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Example Gradebook

• Without XMLDoe, John 80 75 60 92Doe, Jane 81
  90 54 84
• With XMLltgradesgt ltstudent nameDoe,
  Johngt ltgrade namehw1gt80lt/gradegt ltgrade
  namehw2gt75lt/gradegt ... lt/studentgt ...lt/gra
  desgt

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XML isn't perfect

• For some applications the tags make up a
  significant fraction of a documents size
• In general, this doesn't matter
• XML by itself doesn't provide a whole lot of
  services
• Things like linking, templating, parsing, and
  defining schemas are provided by other languages
• It isn't really that revolutionary
• It is very similar to SGML and ASN1

22
XML DTD

• lt?xml version1.0?gt
• lt!ELEMENT grades (student)gt
• lt!ELEMENT student (grade)gt
• lt!ATTLIST student name CDATA REQUIREDgt
• lt!ATTLIST student id CDATAgt
• lt!ELEMENT grade (CDATA)gt
• lt!ATTLIST grade name CDATA REQUIREDgt

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Why do we use DTDs

• They show an agreement between two groups on a
  specific way of expressing some data.
• There are tools that will verify a document to a
  DTD
• They don't let you enforce restrictions beyond
  the structure of the document
• Without another tool there isn't a way to require
  that a grade tag only encloses a number.

24
Real-world uses of XML

• Data exchange is great, but how is XML really
  used?
• RSS/RDF
• FOAF
• SOAP/XMLRPC
• Content Management/Syndication
• Streaming Video (SML)
• Microsoft Word
• ... and much, much more

25
Content Mangement

• Many businesses like to write content once, and
  format it for a variety of destinations
• We want to have a version for the web (HTML),
  cellphones (WML), and print (SGML).
• We don't want to have to make each version by
  hand
• Gererally it works like this
• A story is written and marked up in XML
• CMS software uses stylesheets to create the
  different output from the same source
• Everybody is happy

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Style sheets for XML

• The most common style sheet language is XSLT the
  eXensible StyLesheet and Templating language.
• It allows us to transform one XML document into
  another document.
• Unlike XML, XSLT is a programming language
• XSLT programs just are expressed in XML
• XSLT is interpreted
• XSLT is dynamically typed and type-safe, does
  dynamic type checking, and is statically scoped

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Example gradebook stylesheet

• ltxslstylesheet version '1.0'
  xmlnsxsl'http//www.w3.org/1999/XSL/Transform'gt
• ltxsltemplate match/gt
• ltxslapply-templates /gt
• ltxsltemplate /gt
• ltxsltemplate matchstudentgt
• lth1gtltxslvalue-of select_at_namegtlt/h1gt
• lttablegtltxslapplytemplates /gt
• lt/tablegt
• lt/xsltemplategt

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Gradebook continued

• ltxsltemplate matchgradegt
• lttrgt
• lttdgtltxslvalue-of select_at_name/gtlt/tdgt
• lttdgtltxslvalue-of select./gtlt/tdgt
• lt/trgt
• lt/xsltemplategt
• lt/xslstylesheetgt

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More XSLT

• We can also do conditional processing
• ltxslvariable namethisgrade select./gtltxsli
  f testthisgrade lt 60gtlth2gtltxslvalue-of
  select./gtlt/h2gtltxslif/gtltxslif testnot
  (thisgrade lt 60)gt ltxslvalue-of
  select./gtltxslif/gt
• ...and other thingsltxslvalue-of sum(./grade)
  div count(./grade) /gt

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Internet Applications and Multimedia
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History

• People like to be able to use their senses
• However, the space that digital pictures, sounds,
  and video required was far more than a disk could
  hold
• 1994 the Internet became more popular in the
  common household
• However, browsers were originally mostly text
  based and connections were too slow to support
  large files

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Flash

• Macromedia created Flash which, in one simple
  program allowed people to develop multimedia
  content
• Flash uses vector graphics, which is very space
  efficient and incorporates other methods for
  compressing media types
• Also provides streaming content, extremely useful
  to an internet user

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ActionScript

• ActionScript is Flashs scripting language
• From a programmers point of view, makes Flash a
  lot easier to work with
• The programmer has complete control over what is
  going on in their application
• Enhances ones ability to create an interactive
  application, be that a presentation, a game, or a
  movie

34
ActionScript cont.

• ActionScript and Flash are primarily used today
  as a 2D graphics environment.
• However, people are also using ActionScript to
  create interactive forms on the web
• Another useful application is that a company
  could store something on its main server, and
  when they have to give a presentation out in
  Seattle, they could just access that and have
  real time stream and interactivity

35
More on ActionScript

• In ActionScript, we dont need to specify what
  type the variable is.
• ex. favColor pink sets the variable named
  favColor to a string with the value pink.
• Also, favColor can later be changed to another
  type.
• ex. (following first example) favColor 1 sets
  the variable favColor to the number 1.

36
More on ActionScript

• However, if you want a function to only take a
  certain type and only return a certain type, you
  can do something like this
• ex. Function doThis(myWordString)Number
• Also, ActionScript (being part of Flash) was
  designed with interaction in mind.
• ex.
• on (release)
• clip2._visible false

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More on ActionScript

• There are currently other languages out there
  which are intended to achieve the same results as
  ActionScript.
• The popular ones include JavaScript and upcoming
  Avalon.
• Using ActionScript, a programmer can extremely
  enhance a presentation with sound, graphics,
  video, and their overall layout

38
More on ActionScript

• Both ActionScript and JavaScript are based on the
  ECMA-262 (The European Computers Manufacturers
  Association)
• One big difference is that ActionScript doesnt
  support browser specific objects and commands.
• Microsofts future OS is planning on distributing
  Avalon as a feature with it. Will support 2D and
  3D vector graphics.

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Internet Applications

• (Applets)

40
Applets

• One common misconception is that an applet refers
  to Java applets, which isnt necessarily the case
• Something to note about these applications is
  that they can use the computing power of the
  server or of the user

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Java Applets

• Even though we have stated that applets do not
  necessarily have to be Java, this is a
  predominant form
• One crucial feature of Java and Javas Virtual
  Machine is that it is machine-independent
• To do this, applets need to be able to access
  some information about the users machine, but
  Java Applets are not allowed/able to read or
  write files on/to the users machine

42
Interpreted/Compiled

• Originally, the Java Applets for the Java Virtual
  Machine were intended to be Interpreted
• This has its weaknesses, so there are two other
  methods that the JVM can use

43
More on the JVM

• One thing that the JVM can do is look at what
  part of the program that is being most heavily
  used and convert that into machine code
• The other option is the Just-in-Time (JIT)
  Compiler
• This takes the Java bytecode and converts it to
  instructions that can be directly performed by
  the processor (also using machine code)

44
More on the JVM

• Users of ActionScript like to point out that
  whatever they create will look the same on any
  machine (though you do need to download the Flash
  viewer) whereas JavaScript can be interpreted
  differently in different (especially the less
  mainstream) browsers
• Along the same lines, Java applets (as previously
  stated) were designed to be machine independent
  and could potentially even work on someones cell
  phone

45
PERL CGI

• Practical Extraction Reporting Language
  (Pathologically Eclectic Rubbish Lister)

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Agenda

• Brief History
• Language Overview
• Benefits of using Perl (Efficiency, Portability)
• Common Gateway Interface (CGI)

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Brief History

• Developed by Larry Wall
• Perl 1.000 released in 1987
• Perl 3.000 released in 1988 under GNU Public
  License
• Current stable release Perl 5.8.1
• Today, Perl comes standard on most operating
  systems (e.g. Solaris, Redhat, Mac OS X)
• 3rd party companies offer pre-built Perl
  distributions for other OSs (e.g. Windows)

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What is Perl?

• Interpreted language
• Wall originally intended Perl for
• Scanning arbitrary text files
• Extracting information
• Printing reports from extracted info
• System management tasks
• Expression syntax borrows heavily from other
  languages (C, sed, awk, sh)

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Wall on Perl

• Perl is a language for getting your job done.
• Perl is designed to make easy jobs easy, without
  making hard jobs impossible.

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• str Hello, world!
• sub PrintHello
• while(1)
• if (str m/o..w/)
• print str\n
• else
• print NO MATCH\n
• break
• PrintHello

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Language Overview - Types

• 3 primitive types scalars, _at_arrays, and hashes
  (associative arrays)
• A scalar variable may be a number or a string
• Conversion between the two is automatic pending
  on your operator usage (e.g. OR eq)
• _at_arrays and hashes are dynamically sized
• A hash consist of a set of key-data pairs

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Type Examples

• helloStr Hello, world!
• someNum 415
• _at_myArray (helloStr, someNum, 1, 2.2, 3)
• myHashkey data

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Control Statements

• Conditional branching
• if (condition) statement(s)
• else statement(s)
• elsif (condition) statement(s)
• unless (condition) statement(s)

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Control Statements - contd

• Iteration
• while (condition) statement(s)
• until (condition) statement(s)
• for ( initialize condition re-initialize )
• foreach scalar (_at_list)

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Functions Scopes

• Perl allows for recursion with proper scoping
  declarations
• Defining a subroutine
• sub subname
• statement(s)
• Calling a subroutine
• subname
• subname()
• Scoping keywords my, our, and local

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Regular Expressions

• One of Perls primary purposes was to process
  text
• Perl has built-in pattern matching useful for
  searching and manipulating strings
• Perls regular expressions are derived from
  established regular expressions found in popular
  tools like sed, awk, grep, and vi
• regex operators
• matches, ! doesnt match
• m/ PATTERN /
• s/ PATTERN / PATTERN /
• tr/ PATTERN / PATTERN /

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Perl Benefits - Portability

• Perl programs are not platform dependant
• Comes standard on many different operating
  systems
• Avoid Cs IFDEF statements
• Does not guarantee that a program uses platform
  dependant tools
• regex widely used (grep, sed, awk, ed, vi, emacs,
  etc)
• Perl is a semantic superset of the above
• any regex that can be described in the above can
  also be described in Perl (but maybe using
  different characters

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Perl Benefits Efficiency

• Use of hashes instead of linear searches through
  an array
• Use of foreach instead of for loops
• No need to have extra operation on counter
• regex for fast pattern matching for searching
  large amounts of data
• Use of AutoLoader module
• Defines functions the first time theyre called

59
Common Gateway Interface (CGI)

• CGI script a program on the web server which
  runs on demand to generate the content of a web
  page
• You can find CGI scripts everywhere on-line
• Used to access and manipulate databases
• On-line shopping
• Popular CGI scripting languages
• Perl, PHP, ASP, Python
• But really, anything that is executable on the
  server

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What happens when a script runs?
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CGI with Perl

• Why use Perl to create CGI scripts?
• Free software
• Fast and powerful string manipulation (imagine
  doing the same thing with C/C)
• Built-in types and functions that are useful for
  handling records and information (arrays and
  hashes)
• Comes standard on almost all web servers
• Standard CGI module

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CGI Example Server-side

• !/usr/bin/perl
• use CGI 'standard'
• print header, start_html('Hello World'), b('And
  hello to you too'), end_html

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CGI Example Client-side

• Content-type text/html
• ltHTMLgtltHEADgtltTITLEgtHello Worldlt/TITLEgtltBODYgt
• ltSTRONGgtAnd hello to you toolt/STRONGgt
• lt/BODYgtlt/HTMLgt

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Perl/CGI forms
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Example 1 Standard CGI script

• Purpose was to allow computations of the form ne
  mod m
• In particular, where the numbers involved were
  500 digit integers
• Used in RSA encryption
• Provided to my CS 202 class
• The script creates the HTML page
• Ive provided the HTML page separately to show
  what the HTML code looks like
• Note that the script is synchronous
• It requires the page be re-loaded with the new
  data

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Example 2 AJAX script

• AJAX stands for Asynchronous Java And Xml
• Does not require the page be re-loaded to display
  new data
• Google Maps is an example of an AJAX script
• Two files involved
• ajax.html has the HTML and Javascript necessary
  to load the content without reloading the page
• ajax the Perl script itself, its pretty simple

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URLs

• Example 1
• Script can be run at http//www.cs.virginia.edu/cg
  i-bin/cgiwrap/cs415/modpow
• Script can be viewed at http//www.cs.virginia.edu
  /cs415/cgi-bin/modpow
• Example 2
• ajax.html http//www.cs.virginia.edu/cs415/code/
  ajax.html
• ajax script http//www.cs.virginia.edu/cs415/cgi
  -bin/ajax