A Runtime System for Interactive Web Services

1
A Runtime System forInteractive Web Services

• Claus Brabrand, Anders Møller,
• Anders Sandholm, Michael I. Schwartzbach

BRICS, University of Aarhus, Denmark
2
Plan

• Illustrate problems with CGI
• example interactive web service.
• Solve problems one by one
• building on top of CGI.
• Additional problems and solutions.
• Package solutions into runtime system.
• Conclusion.

3
An Interactive Web Service
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Problem Save, Restore State
ltINPUT TYPEhidden NAMEconfirmed VALUE1gt
ltINPUT TYPEhidden NAMEfname VALUEClausgt
ltINPUT TYPEhidden NAMEfee VALUE495gt

5
Problem Bookmarks
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Problem Bookmarks
Bookmark What?
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Problem Back Button
8
Problem Back Button
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Problem Back Button
Pay twice ?!
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CGI Problems

• Save, Restore State
• Bookmark
• Back Button

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CGI Problems

• Save, Restore State
• Bookmark
• Back Button

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Components
client
CGI
HTML
Internet
HTTP server
HTML
CGI
restore compute save
program
database
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Adding a Connector
client
CGI
HTML
Internet
HTTP server
CGI
HTML
connector
redirect
HTML
CGI
restore compute save
program
database
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CGI Problems

• Save, Restore State
• Bookmark
• Back Button

15
CGI Problems

• Save, Restore State Connector
• Bookmark
• Back Button

16
CGI Problems

• Save, Restore State Connector
• Bookmark
• Back Button

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Problem Bookmarks

• Problem
• CGI URL bookmarked (not HTML response).
• Consequence
• Must complete entire service right away.
• Would like
• Pause service (bookmark), resume later.

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Components
client
CGI
HTML
Internet
HTTP server
CGI
HTML
connector
HTML
CGI
program
database
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Adding an HTML Reply File
client
CGI
jump
Internet
HTTP server
CGI
jump
connector
done!
CGI
HTML reply file
program
HTML
database
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CGI Problems

• Save, Restore State Connector
• Bookmark
• Back Button

21
CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button

22
CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button

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Problem Back Button

• Problem History of old requests
• Annoying.
• No longer make sense.
• Dangerous! (for client and server)
• Would like
• Back should take us back.
• Never see old CGI requests.

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Components
client
CGI
jump
Internet
HTTP server
CGI
jump
connector
done!
CGI
HTML reply file
program
HTML
database
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Components
client
CGI
jump
Internet
HTTP server
CGI
jump
connector
same URL
done!
CGI
HTML reply file
program
HTML
database
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CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button

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CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button Reply File

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Additional Problems
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Additional Problems
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What is going on?

• Error? Abort...
• Package Lost?
• Service Crash?
• Connection?
• Ok? or Wait !?
• Searching Database?
• Long Computation?
• Waiting for a Resource?

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Problem User Impatience

• Consequence
• Users leave service.
• Would like
• Explain delays.
• Searching database Please wait..

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Components
client
CGI
jump
Internet
HTTP server
CGI
jump
connector
done!
CGI
HTML reply file
program
HTML
database
33
Adding a Connector Timeout
client
CGI
jump
Internet
HTTP server
CGI
jump
connector
Timeout
done
CGI
HTML reply file
program
update
database
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CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button Reply File
• User Impatience

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CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button Reply File
• User Impatience Timeout

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CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button Reply File
• User Impatience Timeout
• Concurrency Control

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Concurrency Control

• Problem Parallel service processes.
• Access shared resources.
• Require synchronization.
• Solution
• Allow separate specification of constraints.
• Use safety controller process
• Ensures that service obeys constraints.

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Components
client
CGI
jump
Internet
HTTP server
CGI
jump
connector
Timeout
done
CGI
HTML reply file
program
update
database
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Adding a Safety Controller
client
CGI
jump
Internet
HTTP server
CGI
jump
connector
Timeout
done
CGI
wait
HTML reply file
program
controller
update
pass
database
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CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button Reply File
• User Impatience Timeout
• Concurrency Control

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CGI Problems

• Save, Restore State Connector
• Bookmark Reply File
• Back Button Reply File
• User Impatience Timeout
• Concurrency Control Controller

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Runtime System

• Everything implemented!
• in C for Unix / Linux.
• Available http//www.brics.dk/bigwig/runwig/
• Source
• Documentation.
• Examples.

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ltbigwiggt

• Research project at BRICS.
• Domain specific high-level language
• Rapid construction of interactive web services.
• Compiles into
• HTML, CGI, Java, JavaScript,
• Uses our runtime system extensively.

http//www.brics.dk/bigwig/
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ltbigwiggt

• Research project at BRICS.
• Domain specific high-level language
• Rapid construction of interactive web services.
• Compiles into
• HTML, CGI, Java, JavaScript,
• Uses our runtime system extensively.

Released June 1999
http//www.brics.dk/bigwig/
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Conclusion

• CGI widely used, but inherently low-level.
• Our Runtime System
• Higher level.
• Built on top of CGI.
• Compact and efficient.
• Solves the problems discussed.

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The CGI Model
Client
Server
read fill-out submit
CGI
restore compute save
HTML
read fill-out submit
CGI
restore compute save
HTML
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Adding a Connector
Client
Server
read fill-out submit
CGI
awake compute sleep
HTML
read fill-out submit
CGI
awake compute sleep
HTML