Designing User Interfaces Spring 1999

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SE 767-NT Software Performance Engineering Robert
Oshana Lecture 24 For more
information, please contact NTU Tape
Orders NTU Media Services [phone]
oshana_at_airmail.net
tapeorders_at_ntu.edu
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Web Applications

• Chapter 13

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Where we are

• Introduction
• SPE Quick View
• SPE and the UML
• Software Execution Models
• Web applications and other distributed systems
• System execution models
• SPE data collection
• Software measurement and instrumentation
• Performance oriented design
• Performance patterns
• Performance anti-patterns
• Implementation solutions
• Web applications
• Embedded and real-time systems
• The SPE process
• Implementing SPE

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Introduction

• Web app is similar to a C/S app deployed using a
  web site
• Static and dynamic content
• Use of a browser
• Complex environments

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Web application
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Performance issues

• Responsiveness
• time to retrieve and display a web page
• End to end time for a business process
• User perceived responsiveness can be improved
  using good design
• Scalability
• Ability to handle more and more users to a site

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Performance issues

• Decisions about amount of data sent over the
  network
• Number of interactions to complete a task
• Integration of legacy applications

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Performance issues

• How much of the app will execute on the server?
• What will execute on the client?
• Should component libraries be used?
• How to access DBs

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SPE models for Web Apps

• Similar to those for distributed systems
• All starts with use cases
• Identify processing steps with greatest impact
• Create SW execution model

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Web application model
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Nachtfliegen.com

• Add navigation and tabs
• Add promotions and deals
• Add functions for flight inquiry
• Support frequent flyer club

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Performance improvements

• More precise specification for findFlights
• Record typical paths through this scenario
• Reduce size and number of messages sent to
  browser
• Combine frames into table

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Performance improvements

• Let user choose which page they want to view
  first
• Reduce size of pages and data

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Typical performance problems

• Failure to control the architecture
• Failure to control the front end interactions
• Failure to control the back end interactions

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Technical architecture chosen before requirements
complete

• Avoid solution looking for a problem
• Select the technical architecture after you have
  defined the performance, system, and software
  requirements

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Lack of a software architect

• Many web sites grow organically
• These eventually become difficult to maintain and
  have erratic performance
• Define an extensible SW architecture using a
  notation that provides a consistent, uniform
  method for specifying architecture and its
  behavior

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System architecture mimics the organization

• Organizations that design systems are constrained
  to produce designs that are copies of the
  communication structures of these organizations
• Data coordination problems
• Data availability schedule
• Question system and SW assumptions that are based
  on organizational boundaries early in the
  development process

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Failure to control front end interactions

• Size of pages, amount of data, amount of code
  transmitted to and from browsers
• Performance problems occur if developers send all
  available data
• Determine the subset of data that users are most
  likely to need together, and send all of that
  data but no more

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Failure to control back end interactions

• Retrieval of information from other servers or
  mainframes and the middleware that supports this
• Middleware may not be suited to access patterns
  and volumes
• Use SPE models to match back-end interactions to
  user needs and to find the best performance
  implementation alternatives to meet those needs

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SE 767-NT Software Performance Engineering Robert
Oshana End of lecture For
more information, please contact NTU Tape
Orders NTU Media Services [phone]
oshana_at_airmail.net
tapeorders_at_ntu.edu