Transcript Design methods for Internet based Information systems

Ontwerpmethoden voor
Internet gebaseerde Informatie
Systemen
Design methods for Internet
based Information Systems
Design Methods for IIS
Prof. Dr. O. De Troyer
1
1. Evolution of the Web
Design Methods for IIS
Prof. Dr. O. De Troyer
2
1.1 Before the web
– 1945 Vannevar Bush
• He found that it was increasingly difficult to keep in
touch with the growing literature
He designed the memex:
• A futuristic information and retrieval system
• A massive quantity of photocopies of documented
information + links between different parts of documents
– Mid-1960s: Ted Nelson
Hypertext: term for non-linear text structure
– Mid-1980’s: first hypertext systems (HyperCard)
• Also hypermedia
Design Methods for IIS
Prof. Dr. O. De Troyer
3
1.2 The Internet
– 1969: ARPA network
• Connects 4 universities in the USA
– 1981: every 20 days a new host computer
– 1982: TCP/IP
– 1987: more than 10.000 host computers
– 1994: 3 million host computers
• Use
– 1973 : sending messages using ARPANet - E-mail
– 1979: first newsgroups
Design Methods for IIS
Prof. Dr. O. De Troyer
4
• 1989: Tim Berners-Lee and Robert Cailliau
• Simplification of the use of Internet
• To solve the information-sharing problem
• 1990: term World Wide Web
• Early web
• Built for a research environment
• Little need for presentation, security or
programming facilities
Design Methods for IIS
Prof. Dr. O. De Troyer
5
1.3 The first generation
• 1993 Mosaic
– Simple: text with few graphics
– Few pages
– No screen layout control, such as background
colour, tables, …
– Usually built by system administrator or
programmer
– No or little money to do this
– Web sites only for the pioneers
Design Methods for IIS
Prof. Dr. O. De Troyer
6
First generation web technology
Client side
Server side
GIF images
HTTP Server
CGI Programs
Database
Design Methods for IIS
Older IS
Prof. Dr. O. De Troyer
HTML
Forms
Helper Applications
• Audio
• Video
• Multimedia
7
1.4 The second generation
• 1994: Mosaic Netscape
– New HTML features for improved layout:
• centering, text flow around graphics, backgrounds
– Graphic designers came in the picture
– Sites more about appearances than about
functionality or a well-defined purpose
Design Methods for IIS
Prof. Dr. O. De Troyer
8
Second generation web technology
Client side
Server side
GIF & JPEG images
HTTP Server
Server API Programs
HTML + Netscape extensions
Forms
CGI Programs
Database
Helper Applications
• Audio
• Video
• Multimedia
Media Server
Cookies
Design Methods for IIS
Prof. Dr. O. De Troyer
9
1.5 The third generation
• Netscape Navigator and Internet Explorer
– Even more layout facilities:
• Proprietary HTML tags
• Frames, style sheets, ...
– Animation, video
– Sites significantly more complex
– Many new technologies:
• Java, JavaScript, ActiveX, …
– E-commerce
– Need for team-based approach to web site
construction
Design Methods for IIS
Prof. Dr. O. De Troyer
10
Third generation web technology
Client side
Server side
HTTP Server
Server API Programs
Plug-Ins
GIF & JPEG
images
Active X
Controls
HTML + Netscape extensions
Forms
JavaScript/VBScript
CGI Programs
Database
Java
Applets
Media Server
Cookies
Design Methods for IIS
Prof. Dr. O. De Troyer
11
• Web sites becomes more like programs and less
like static documents
– Not only
• Presentation
• Organisation
• Content
– But also
• Program logic
All these issues are all mixed up:
• HTML for presentation
• Java for animation
• Text in images
Design Methods for IIS
Prof. Dr. O. De Troyer
12
• Web site crisis is rapidly developing, because
–
–
–
–
Increase of complexity
Ad hoc methodology used
Current web culture
Builders not always schooled
• Not in basic programming techniques
• Not in classical design techniques
– interface design
– graphical design
• Not in communication skills
• Need for Web Engineering discipline
Design Methods for IIS
Prof. Dr. O. De Troyer
13
2. Web Engineering principles
Design Methods for IIS
Prof. Dr. O. De Troyer
14
2.1 Why the web is different
• Visual aspects are much more important than in
classical software
• Still very document-oriented
• More content-driven
• The need for continual change
Design Methods for IIS
Prof. Dr. O. De Troyer
15
• More aggressive release demands
– Planning must be different
• Many sites are driven by marketing goals
• Public web site have to compete for user attention
• Internet is highly unpredictable and has specific needs
• Web technology is constantly changing
• Web development tools are not yet mature
• Little experience with web engineering in general
Design Methods for IIS
Prof. Dr. O. De Troyer
16
2.2 Major web site types
• Internet sites
– Public
– No knowledge about the environment or the users
• Intranet sites
– For internal use within an organisation
– Good knowledge about the environment
• Extranet sites
– For a unique community, usually between
organisations
– Some knowledge about the environment
Design Methods for IIS
Prof. Dr. O. De Troyer
17
2. 3 Complexity of web sites
• Static web sites
– Collection of static documents tied together with
links
• Static web sites with form-based interactivity
– Limited interactivity via fill-in forms
• Web sites with dynamic data access
– Front end for a database
Design Methods for IIS
Prof. Dr. O. De Troyer
18
• Dynamically generated web sites
– Dynamically created documents, content usually
from a database
– The resulting pages may be static
• Web-based software applications
– Applications with web interface
– Facilitate business processes
• Active/Adaptive web sites
– navigation may influence the content of a page on
the fly
Design Methods for IIS
Prof. Dr. O. De Troyer
19
2.4 Design principles
• Correctness
– Functional, presentation, content
• E.g. broken links, scripts that don’t work, incomplete navigation
– Correct from user point of view
– Difficult because of the technology
• Different browser environments
• Usable
– Too much emphasis on look-and-feel can hinder efficiency
and confuse the user
– Lost in hyperspace syndrome
Design Methods for IIS
Prof. Dr. O. De Troyer
20
• Testable
– Compatibility issues
• Maintainable
– Easy to make changes
• Portable
– Easy to move from server to another server
• Used applications should be portable
• Links must be relative and content well-organised
– Important for replication or mirroring
Design Methods for IIS
Prof. Dr. O. De Troyer
21
• Reusable
– Database, scripts and content should be reusable
Robust and reliable
– Is intertwined with the physical medium of the Web
• Efficient
– Not only determined by the implementation
– Also by the server and network
Design Methods for IIS
Prof. Dr. O. De Troyer
22
• Readable
– of the source files
– Adequate comments, meaningful names, use of
white space and formatting
• Well documented
– Design documents, change history, project history
Design Methods for IIS
Prof. Dr. O. De Troyer
23
2.5 Current practices
• Many failures
– “Under construction” for ever
– Abandoned sites
• Wildly varying budgets:
– Almost free up to millions of dollars
– Also for the same project differences by a factor 10
– Budgets are too low because of the perceived ease of
development
– Budgets are too high because of the perceived value
– Lack of experience
Design Methods for IIS
Prof. Dr. O. De Troyer
24
• Ad hoc approach to develop web sites
– Typically: implement - test - release
– Planning is often limited to a few brief meetings
• Amount of time spent is negligible compared to
implementation
– No analysis or design
• Most web tools encourage design-on-the-fly
First decoration, then functionality
Ad hoc development does not work for classical
software, it also does not work for the Web !
Design Methods for IIS
Prof. Dr. O. De Troyer
25
3. The medium of the Web
Design Methods for IIS
Prof. Dr. O. De Troyer
26
3.1 Networked Communication
• Based on client/server model
– Client : browser
– Server: web server
– Network: Internet or private network within an
organisation
Design Methods for IIS
Prof. Dr. O. De Troyer
27
Design Methods for IIS
Prof. Dr. O. De Troyer
28
•
•
•
•
•
•
Browser requests pages from web server
Interchange is handled by HTTP
Actual data transmission is handled by TCP/IP
Addressing of requested objects is by URL
URLs rely on Domain name services
Resulting information is transmitted with a
MIME (Multiple purpose Internet Mail Extension) content-type
indicator
Design Methods for IIS
Prof. Dr. O. De Troyer
29
3.2 Client Side Considerations
• Performance affected by
– Client hardware
•
•
•
•
•
•
System speed
Memory
Monitor resolution
Colour support (thousands, millions, 256, 16, gray-scale)
Disk Speed
Network Adapter
– Client software
• Operating system
• Browser
Design Methods for IIS
Prof. Dr. O. De Troyer
30
• Browsers
– Many differences between
• Browsers
• Versions of browsers
• Browsers on different systems (PC, Mac, Unix)
• Display
–
–
–
–
May vary greatly
Colours may vary between displays
Available fonts may vary between systems
Display of font varies (Windows fonts are larger than their Mac
counterparts)
Design Methods for IIS
Prof. Dr. O. De Troyer
31
Design Methods for IIS
Prof. Dr. O. De Troyer
32
• Usually no control over the end user’s system
• Approaches to this
– Assume minimal software and hardware
requirement to ensure correct functioning
– Force user to do self evaluation (e.g. buttons
for different versions)
– Is asking for trouble
» Users may not know their system
» Users may make mistakes
Design Methods for IIS
Prof. Dr. O. De Troyer
33
– User profiling
• Characterising the user during analysis
• At run time: technology should be used to detect
conformance to the profile
– Look into the USER_AGENT header in the HTTP request
contains information about
» Browser
» Operating system
» Potentially the platform
» The character set accepted
– JavaScript may be used to find various display properties
Design Methods for IIS
Prof. Dr. O. De Troyer
34
3.3 Network Considerations
• Network difficult or impossible to control
• Aspects of network performance:
– Bandwidth
• Maximum about of data that can be transmitted during a
given unit of time
– Low-bandwidth: 14 kilobits per second
– High-bandwidth: 2 megabits per second
• Modem vs. local network
– Latency
• The amount of time needed for a single data packet to
travel the entire link that connects two systems.
Design Methods for IIS
Prof. Dr. O. De Troyer
35
• Dependant on the (network) distance
Use of mirror sites
• Network distance is different from physical distance
– The more interchange points the better
• Latency may increase due to delays introduced by
network equipment
– Network utilization
• Amount of traffic on the network has an impact on the
available bandwidth
Design Methods for IIS
Prof. Dr. O. De Troyer
36
3.4 Server Side Considerations
• As web developer most control over the server
• Performance affected by
– Server network connection
– Server hardware
– Server software
• Web server
• Middleware
• Database
Design Methods for IIS
Prof. Dr. O. De Troyer
37
• Server hardware
– In principle any type of machine
Important
– Fast disk access
– Memory to support simultaneous requests
– In case of a lot of server-side programming or
database access
• Processor and memory
Design Methods for IIS
Prof. Dr. O. De Troyer
38