1. 1 CS 502: Computing Methods for Digital Libraries Lecture 22 Web browsers

2. 2 Administration Final examination May 19, 2000 1:00 - 2:30pm Phillips 219 5 or 6 questions on whole course Traditional 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.

3. 3 Administration Discussion class, Wednesday April 19 One class only, from 7:30 to 8:30 p.m.

4. 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. 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. 6 Web user interface: basic Web servers Web browser Static pages from server, using http get All interaction requires communication with server http get (URL) file + MIME type

7. 7 Separation of type from presentation Information to be displayed Presentation software Display MIME type

8. 8 Rendering Web browser file + MIME type Rendering software Rendering and display may be: built into browser plug-in helper application

9. 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. 10 Basic extensibility in web browsers Browsers are highly extensible Data types: built-in -- html, gif, jpeg helper applications plug-ins Protocols HTTP, WAIS, Gopher, FTP, etc. proxies

11. 11 Web user interface: CGI script Non-web systems CGI Scripts Web servers Web browser http post

12. 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. 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. 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 Java Script html

15. 15 Mobile code: Java Applet Any server Web servers Web browser Any executable code can run on client Client can connect to any server Security model restricts some applications Applets

16. 16 Levels of usability interface design functional design data and metadata computer systems and networks conceptual model

17. 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. 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. 19 Extensibility Data types Protocols Executable code XML and style sheets Gaps State Security architecture Functional design

20. 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. 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. 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. 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