WWW8 - Toronto "A Runtime System for Interactive Web Services" May 12, 1999 A Runtime System for Interactive Web Services Claus Brabrand, Anders Møller,

WWW8 - Toronto "A Runtime System for Interactive Web Services" May 12, 1999

A Runtime System for

Interactive Web Services

Claus Brabrand, Anders Møller,

Anders Sandholm, Michael I. Schwartzbach

BRICS, University of Aarhus, Denmark


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.


An Interactive Web Service


Problem: Save, Restore State

<INPUT TYPE=“hidden” NAME=confirmed VALUE=“1”> <INPUT TYPE=“hidden” NAME=fname VALUE=“Claus”> <INPUT TYPE=“hidden” NAME=fee VALUE=“495”>

:

<INPUT TYPE=“hidden” NAME=confirmed VALUE=“1”> <INPUT TYPE=“hidden” NAME=fname VALUE=“Claus”> <INPUT TYPE=“hidden” NAME=fee VALUE=“495”>

:


Problem: Bookmarks


Problem: Bookmarks

Bookmark What?


Problem: Back Button





Pay twice ?!Pay twice ?!


CGI Problems

• Save, Restore State

• Bookmark

• Back Button


CGI Problems


• Bookmark

• Back Button


Components

Internet

client

HTTP server

program

database

CGI HTML

HTMLCGI

restore ;compute ;save


Adding a ”Connector”

Internet

client

HTTP server

program

database

CGI

HTML

CGI

connector

HTML

CGI

HTML

restore ;compute ;save

redirect


CGI Problems


• Bookmark

• Back Button


CGI Problems

• Save, Restore StateConnector

• Bookmark

• Back Button


CGI Problems

• Save, Restore State Connector

• Bookmark

• Back Button


Problem: Bookmarks• Problem:

– CGI URL bookmarked (not HTML response).

• Consequence: – Must complete entire service right away.

• Would like:– Pause service (bookmark), resume later.


Components

Internet

client

HTTP server

program

database

CGI

HTML

CGI

connector

HTML

CGI

HTML


Adding an HTML “Reply File”

Internet

client

HTTP server

program

database

CGI

done!

CGI

connector

jump

CGI

jump

HTMLreplyfile

HTML


CGI Problems


• Bookmark

• Back Button


CGI Problems


• Bookmark Reply File

• Back Button


CGI Problems



• 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.


Components

Internet

client

HTTP server

program

database

CGI

done!

CGI

connector

jump

CGI

jump

HTMLreplyfile

HTML


Components

Internet

client

HTTP server

program

database

CGI

done!

CGI

connector

jump

CGI

jump

HTMLreplyfile

HTML

same URL


CGI Problems



• Back Button


CGI Problems



• Back Button Reply File


Additional Problems


Additional Problems


What is going on?• Error? Abort...

– Package Lost?– Service Crash?– Connection?

• Ok? …or Wait !?– Searching Database?– Long Computation?– Waiting for a Resource?


Problem: User Impatience

• Consequence:– Users leave service.

• Would like:– Explain delays.

• “Searching database … Please wait.”.


Components

Internet

client

HTTP server

program

database

CGI

done!

CGI

connector

jump

CGI

jump

HTMLreplyfile

HTML


Adding a Connector Timeout

Internet

client

HTTP server

program

database

CGI

done

CGI

connector

jump

CGI

jump

HTMLreplyfile

update

Timeout


CGI Problems




• User Impatience


CGI Problems




• User Impatience + Timeout


CGI Problems

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


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.


Components

Internet

client

HTTP server

program

database

CGI

done

CGI

connector

jump

CGI

jump

HTMLreplyfile

update

Timeout


Adding a Safety Controller

Internet

client

HTTP server

program

database

CGI

done

CGI

connector

jump

CGI

jump

HTMLreplyfile

updatecontrollerwait

pass

Timeout


CGI Problems

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


CGI Problems

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


Runtime System• Everything implemented!

– in C for Unix / Linux.

• Available: http://www.brics.dk/bigwig/runwig/– Source– Documentation.– Examples.


<bigwig>

• 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/


<bigwig>

• 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/


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.

Documents

WWW8 - Toronto "A Runtime System for Interactive Web Services" May 12, 1999 A Runtime System for Interactive Web Services Claus Brabrand, Anders Møller,