Date post: | 19-Dec-2015 |
Category: |
Documents |
View: | 213 times |
Download: | 0 times |
2
Administration
Final examination
May 19, 20001:00 - 2:30pm Phillips 219
5 or 6 questions on whole courseTraditional closed book examination
There will be a make up examination near the beginning of the examination period. Please send me email if you might wish to take it.
4
User interface needs for digital libraries
• Users have wide variety of computers, systems, network connections.
• Digital library materials encompass every known data type.
• Users range from experienced to unskilled.
• Digital libraries have complex needs for authentication and authorization.
• Protocols may be stateless or stateful.
• Federations include both state-of-the-art and legacy systems.
• Persistent naming is important to digital libraries.
5
Cost of user interfaces
Programming and maintaining a user interface is very expensive if it must support many types of computer and versions of operating systems.
Therefore, most digital libraries use web browsers for the user interface.
• If a function fits well with the web browser conceptual model, it is easy to implement.
• If a function does not fit well with the web browser conceptual model, it is hard to implement.
6
Web user interface: basic
Web serversWeb browser
• Static pages from server, using http get
• All interaction requires communication with server
http get (URL)
file + MIME type
7
Separation of type from presentation
Information to be displayed
Presentation software
Display
MIME type
8
Rendering
Web browser
file + MIME typeRendering software
Rendering and display may be:
• built into browser
• plug-in
• helper application
9
Basic web browser
Good• Runs on all computers• Supports wide range of data types
Bad• Stateless • Data checking requires interaction with host• No accommodation for legacy systems• Rendering varies according to local software
10
Basic extensibility in web browsers
Browsers are highly extensible
• Data types:
built-in -- html, gif, jpeghelper applications plug-ins
• ProtocolsHTTP, WAIS, Gopher, FTP, etc.proxies
12
CGI scripts
CGI scripts:
• Interface to non-web systems
• Can configure pages
• Can validate information
but ...
• Server interaction is constrained by web protocols
• CGI requires all interactions to be via server
13
The web and legacy systems
The web is a legacy system. New systems must find ways to interface with it. This is a problem for new technology,
• Stateful protocols, e.g., Z39.50
• URNs
CGI scripts enable web browsers to act as interfaces to non-web systems.
• Interface new system (web) to legacy system
• Interface new system to legacy system (web)
14
Mobile code: JavaScript
Web servers
Web browser
• Mobile code (e.g., JavaScript) can validate information as typed
• Some interactions are local
• Server interaction constrained by web protocols
JavaScript
html
15
Mobile code: Java Applet
Any server
Web serversWeb browser
• Any executable code can run on client
• Client can connect to any server
• Security model restricts some applications
Applets
16
Levels of usability
interface design
functional design
data and metadata
computer systems and networks
conceptual model
17
Interface design
Clickable links plus mobile code
• Easy for users to learn and use• Certain categories of error are avoided• Enables context-sensitive help
Major difficulty is structure of large sets of choices
• Scrolling menus (e.g., states of USA)• Hierarchical• Associated control panels• Menus plus command line
Users prefer broad and shallow to deep menu systems
18
Interface design
Conventions are growing over the years
• www.... for home page
• scroll bars, buttons, help systems, sliders
• terminology
Good for users, good for designers
19
Extensibility
• Data types
• Protocols
• Executable code
• XML and style sheets
Gaps
• State
• Security architecture
Functional design
20
Data and metadata
Identifiers
• URLs are very powerful
• Digital libraries need URNs
XML
• Provides a framework for metadata
• Namespaces and RDF -- open question
No support for structural metadata
21
Computer systems and networks
• Personal computer cycles are there to be used
• Any network transfer involves delay
• Shared systems have unpredictable performance
• Data validation often requires access to shared data
• Mobile code poses security risks
22
Computer systems and networks
Caching and mirroring: effective in digital library systems where digital objects change relatively slowly with time.
• Mirroring of web sites for performance and reliability
• Caching servers (e.g., Google cache, domain name system)
• Caching on user's computer
• Service bureau for world wide performance (e.g., Digital Island)
Parallelism:
• Display page while downloading
• Parallel streams of data
23
The importance of design
Good support for users is more than a cosmetic flourish
• Elegant design, appropriate functionality, & responsive system: => a measurable difference to effectiveness
• If a system is hard to use: => users may fail to find important results, or mis-interpret what they do find=> user may give up in disgust
A computer system is only as good as the interface it provides to its users