Software Architecture in Practice

1
Software Architecturein Practice

• RiSEs Seminars
• Basss at all Book Chapters 13
• Fred Durão

2
Summary

• The world wide web A case study in
  Interoperability (Chapter 13)
• The original requirements
• Architectural Solution
• The evolution of web based e-commerce
  architecture
• The architectural business cycle today

3
The word wide web A case study in
Interoperability
4
History
The World Wide Web Chapter 13

• Tim Berners Lee and CERN members seen the need of
  creating a information network
• In 1989, Tim Berners Lee created a document named
  Information Management A proposal
• In 1990, a reformulated version of his document
  became a project named World Wide Web

5
The www original requirements
The World Wide Web Chapter 13

• Remote access across networks
• Heterogeneity
• Noncentralization
• Access to existing data
• Ability for users to add data
• Private links
• Bells and whistles the data display was on 24 x
  80 character ASCII Terminal
• Data analysis
• Live links given that information changes all
  the time
• Some non requirements became requirements like
  SSL (Secure Socket Layer) and HTTPS (HttpSecure)

6
Internet Statistics
The World Wide Web Chapter 13
Source Used with permission of Matthew Gray of
the Massachusetts Institute of Technology
7
Internet Growth
The World Wide Web Chapter 13

• Web has been doubling in size every 3 to 6 year
  months
• From 130 sites in 6/1993 to more that 230.000
  sites in mid-1996
• and 27 million in early 2001

• Internet Backbones in the USA 1996

8
Architectural Solution
The World Wide Web Chapter 13

• Based on client and servers and wwwLibs
• - compact, portable library that can be built on
  to create Web-based applications such as clients,
  servers, databases, and Web Spiders

9
libWWW layers
The World Wide Web Chapter 13
Support a set of application functionalities for
writing applications
Support a set of network-protocol-aware modules,
like HTTP, FTP, TELNET
Provides the abstraction of stream of all data
transported
Provides standard interfaces to Web Applications
Portability layer that provide platform-independen
t function
10
Lessons learned from libWWW
The World Wide Web Chapter 13

• Formalized application programming interfaces
  (APIs) are required
• Functionality and the APIs that present it must
  be layered
• The library must support a dynamic, open-ended
  set of features
• Processes built on the software must be thread
  safe

11
An Early Client-Server Architecture using libWWW
The World Wide Web Chapter 13

• WWW Client
• External Viewer
• HTTP Client
• UI Manager, Cache Manager and more
• WWW Server
• CGI
• HTTP Server
• Stream Manager, Access Control and more

12
Common Gateway Interface - CGI
The World Wide Web Chapter 13

• CGI is one of the most important requirement
  driving the evolution of Web software
• CGI scripts allowed dynamic request information
  to be returned to clients
• The most common use of CGI were create dynamic
  HTML document and return it to users
• CGI allowed users put information into the web,
  in contrast to get operation that servers
  normally provide. E.g. add info on databases by
  filling out a form

13
How the WW Achieved Quality Goals
The World Wide Web Chapter 13
14
The Evolution of Web-Based E-Commerce
Architectures
The World Wide Web Chapter 13

• The new requirements
• High performance
• Customer will not tolerate the site simply
  refusing
• their requests
• High availability
• The Web Sites have to be available 24/7
• Scalability
• Possibility of growth to maintain acceptable
  levels of customer service.
• Security
• Adapt mechanisms for avoiding stealing or
  modifying data.
• Modifiability
• Ability for changes

Customer
15
A typical e-commerce system
The World Wide Web Chapter 13
16
E-Commerce Architecture achieving qualities
The World Wide Web Chapter 13

• Web Browsers claim for MODIFIBILITY
• HTTPS claims for SECURITY
• Proxy Servers claim for PERFORMANCE
• Reuters and Firewalls claim for SECURITY
• Load Balancing claims for SCALABILITY and
  AVAILABILTY

17
E-Commerce Architecture achieving qualities
The World Wide Web Chapter 13

• Web Servers claim for PERFORMANCE
• Databases claim for PERFORMANCE, SCALABILITY and
  AVAILABILITY
• Application Servers claim for PERFORMANCE,
  MODIFIABILITY and SCALABILITY

18
The Architecture Business Cycle Today
The World Wide Web Chapter 13

• Several types of organization provide the
  technical environment Service providers and Data
  providers
• A number of open-source projects have increased
• E.g. Apache Project
• Web-enable languages, particularly Java, are
  changing the way functionality is developed over
  the Web
• The emergence of the Web as a distributed
  development environment has given rise to several
  new organizations and products

19
References
The World Wide Web Chapter 13

• Bass L., Clements P. and Kazman R. Software
  Architecture in Practice. Second Edition, 2003.
• o mundo pode esperar