Introduction to Networks

1. Introduction to Networks

2. Data Communications Network A collection of computer systems configured to share digital data and resources

3. Local Area Networks • LANs extend across limited geographical area • servers, terminals, etc.

4. Internetwork • collection of autonomous networks • The Internet • Network spanning the world • intranets • single organization (ie Malu)

5. The Internet • Developed by the US Dept of Defence in the 60’s as a link to the missile silos of North Dakota. • The network had to be: • Decentralized – no single, central, managing authority. • Loosely-coupled – can continue communication even if parts of the system fail since components are autonomous. • Redundant – the network contains many paths between any two components.

6. Internet Applications • e-mail • telnet • ftp (file transfer protocol) • World Wide Web

7. World Wide Web • created as a medium for disseminating scientific research • organized by Tim Berners-Lee in 1989 • hypertext system • Documents with built-in cross-referencing called “hyperlinks” • open system – since anyone may link into the web

8. Client/Server • CLIENT--(local) system requesting services • SERVER--(remote) system that receives and handles requests from many clients concurrently • P2P – a computer may be both a client and server, WinMX, Kazaa

9. Web as Client/Server App • Protocol--a set of rules that govern how an activity takes place • HTTP--(HyperText Transfer Protocol) specifies how Web clients and servers communicate • URL--(Uniform Resource Locator) addressing for Web resources • HTML--(HyperText Markup Language) defines content and display of Web pages

10. Anatomy of a URL

11. Search Engines What are you really searching? • Finding the web documents (Web “pages” or “sites”) you want can range from extremely easy to impossible. • This is due to the size of the Web - currently estimated at approx. 1 billion documents. • There is also no standard cataloging system in place. • When you are searching the Web you are not searching it directly. You are actually querying an intermediate database which will supply you with the URL’s of other pages. • How is this database built?

12. Researching on the Web The two main categories of search tools are: • Subject or Web directory --a search service organized as a topical hierarchy and compiled by (human) editors. (ie Yahoo, about.com, etc) • Search engine--search services whose databases are compiled by automated Web crawlers. (ie Google, Alta Vista, InfoSeek, etc.)

13. Search Engines • Search by keyword, trying to match exactly the words in the pages to those in the criteria set up by the user. • No browsing, no subject categories • Databases are compiled by "spiders" (computer-robot programs) with minimal human contact • Search-Engine size: from small and specialized to 90+ percent of the indexable Web • Good search engines: • Google, MSN Search, AltaVista, Lycos

14. Keyword Searching • A form of (automated) text matching • keyword--a word or phrase used as a text pattern for matching • hits--matches with text patterns • misses--fails to match some or all of the text pattern • false positives--hits that are not related to the desired topic (ie Ford cars not president)

15. Hybrid Search Services • metasearch engines--consult other search engines and directories and summarize query. • niche services--commercial services targeted at a specific audience or topic. • Kelly’s blue book for used cars • portals--gateway Web site with searching capabilities (ie Yahoo, Excite, NBCi.com)

16. Meta-Search Engines • Meta-Search Engines quickly and superficially search several individual search engines at once and return results compiled into a sometimes convenient format. • Examples of Meta-Search engines: Metacrawler, Inference Find, Ixquick • Problems with meta-search engines • only spend a short time in each database (cover only about 10%) • meta-searchers simply pass your search terms along • They omit some good, large search engines.

17. Choosing Effective Keywords • Five to ten keywords are better than one or two • Names of specific people and places help – capitalize • Only capitalize proper names (first letter only) • Include the name of an organization that may post the info’ you seek • Use specific nouns that are relevant to your topic • Include alternative spellings or abbreviations of important names • Play with variations on your query • Use truncation and wildcards (*) (ie colo*r) • If a keyword seems to mislead the search engine delete it • Put more important keywords first

18. Subject Directory • Is a hierarchically organized collection of categories and subcategories that can be browsed to locate specific information. • Are created and maintained by human editors who review and select sites for inclusion in their directories on the basis of previously determined selection criteria. • When browsing, always start at the top of the directory. • Usually you use subject trees for mainstream type data. • There are different types of subject directories; general directories, academic directories, commercial directories.

19. Search Tool Features • Phrase Searching is a feature you want in every search tool you choose. • Requires your terms all to appear in exactly the order you enter them. • Enclose the phrase in double quotations " " • Examples: • "affirmative action" , "world health organization" , "Bill Gates" • Boolean operators: • AND • The AND operator makes sure all the terms you request appear on the selected sites. If you type Java AND JavaSoft your search will return pages about the Web's programming language, not coffee. • Nearly the same effect comes with the + sign which forces all + terms to be in all documents retrieved. • I.e. +Java + JavaSoft

20. Search Tools Features - cont. • OR • Use OR to return pages that contain either of two terms. For example, Microsoft OR Netscape • Best to us parenthesis with OR ie (Microsoft OR Netscape) • NOT • Use NOT to ensure that certain words won't appear in your search selections. Modems NOT internal. • BOOLEAN AND NOT helps narrow searches: • "biomedical engineering" AND cancer AND NOT "Department of" AND NOT "School of" • - gives the same result • +"biomedical engineering" +cancer -"Department of" -"School of“ • Always capitalize logical and Boolean operators

21. Search Tools Features - cont. Parentheses Organize your searches even further by using parentheses. NOT Malaspina AND Cooke will return pages with Cooke in them; NOT (Malaspina AND Cooke) will avoid pages with both names. Put most important keywords first in the search string. Italian (vineyards or vines) Always check your search engine for Boolean requirements. AND NOT vs ANDNOT … etc Field, Title, Domain, and Host searching

22. Subject-Specific Databases • Subject-Specific Databases are databases devoted to a single subject, created by researchers, experts, government agencies, and/or other individuals with a specialized interest or accumulated info’ on a subject. • Examples: • ERIC Clearinghouses • Expedia (travel) • Kelley Blue Book • MySimon (comparison shopping) • SportSearch • WebMD

23. E-Commerce • E-Commerce is rapidly emerging as an essential business strategy • Being driven by customer expectations from traditional business model • E-Commerce has the following components • Web interface on the client side • backend databases on the server side • scripts to enable the interaction of these two

24. Client-Side Scripting in E-Commerce • Resides on the client machine (downloaded with the Web interface) • Creates client interactivity • Collects data from the user • Does preliminary analysis and validation on user-supplied data • Sends validated data to the server

25. Server-Side Scripting in E-Commerce • Resides on the server • Accepts data from the client • Uses that data to • search backend databases • write to databases • initiate credit card processes, etc. • Returns response data to the client

26. Client-Side Processing with HTML • Web pages are cross-platform documents; they may be viewed on any computer provided it has an appropriate browser installed. • Web pages have become the default standard for creating and publishing documents electronically. • WWW documents are written in the language HTML in which HTML = Hypertext Markup Language

27. Web Document Characteristics • They are constructed to be resolution independent. • May contain text, sounds, images, graphics and video clips. • Are hypertext documents in that they contain electronic links to other web published information. • HTML is designed to implement these characteristics.

28. HTML Characteristics • Read Pages 92 – 101 Digital Domain • HTML allows us to define separately both the content and presentation of a document. • Once the document has been defined in HTML it is stored on a web server. When a client browser accesses the server and requests this document it is transferred to the client browser. The client browser then interprets the structure and displays it. The user of course may set browser preferences.

29. HTML document • HTML documents consist of marked-up plain (or unformatted) text, with special embedded markings to tell the browser how the text is to be displayed. • HTML code is just plain text with markup codes (called tags) interspersed in it. • The HTML code is saved as a plaintext file with “.html” or “.htm” extension to indicate the file type.

30. HTML document • paired tags <tag_id>content affected by tag</tag_id> • standalone tags <tag_id>content after the tag • Metatags are special descriptions stored in the HTML file which among other things help search engines build their databases.

31. HTML Document Structure <!DOCTYPE> <html> <head> <title>description of the page</title> <meta name=“metaname” content=“metacontent”> other head elements… </head> <body> body elements go here </body> </html>

32. Web Publishing Applications • General editor e.g. Notepad • tag editors • help with editing HTML code • e.g., CoffeeCup • HTML generators (editors) • WYSIWYG design views • e.g., Macromedia Dreamweaver, FrontPage

33. Client-Side Processing and DHTML • Dynamic HTML (DHTML) is • a collection of technologies to make client-side interactions better and more interactive • is a bit of a misnomer – it is not an extension of HTML • DHTML is not standardized • different browser companies compete with their own DHTML features • as long as the “browser wars” persist, DHTML is unlikely to be standardized • Two important components of DHTML • CSS (cascading style sheets) • client-side scripting

34. Cascading Style Sheets (CSS) • Define styles for formatting and displaying information • provides for better Web site internal consistency • makes Web site style modifications much easier • Three types of CSS • inline • embedded • external • applied with precedence: inline->embedded->external

35. Client-Side Scripting and Forms • Scripting works hand-in-hand with HTML forms • HTML forms have built-in mechanisms for soliciting and collecting user data • Forms are a part of standard HTML • Client-side scripts are used to take action on the data collected before sending it to the server • Such scripts are invoked using the onSubmit event handler • Other events could be onMouseOver, OnClick…

36. Server-Side Scripting • Accepts data from client • Often written in • CGI (Common Gateway Interface) • actually an interface rather than a scripting language • can be written in a number of different scripting languages • PHP: HyperText Preprocessor • ASP (Active Server Pages – Microsoft)

37. Java Programming • Java is an object-oriented full-purpose (as opposed to scripting only) programming language • Java is noted for its excellent cross-platform capability • Java applets are small Java programs designed specially for the Web to be downloaded and run on a client machine.