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David Evans cs.virginia/evans

David Evans cs.virginia/evans

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David Evans cs.virginia/evans

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  1. Class 29: Vocational Skills How to Build a Dynamic Web Site David Evans http://www.cs.virginia.edu/evans CS200: Computer Science University of Virginia Computer Science

  2. Vocational Skills Job listings atmonster.com (31 March 2004): SQL PHP HTML Scheme “more than 5000” $80-$400K 3570 posted in last 14 days 785 $40-$150K “more than 5000” $30-50K 203 in last 24 hours 0 $200K? CS 200 Spring 2004

  3. Today’s Aberrant Class • Covers topics primarily selected for their practical (not intellectual) value • Covers material found in “For Dummies” books (but we’ll cover it differently) • There is no “Computability Theory for Dummies”, “Complexity Theory for Dummies”, “Higher Order Procedures for Dummies”, “Recursive Definitions for Dummies”, etc. book CS 200 Spring 2004

  4. HyperText Transfer Protocol Server GET /cs200/index.html HTTP/1.0 <html> <head> … Contents of file Client (Browser) HTML – hypertext markup language Way of describing hypertext documents CS 200 Spring 2004

  5. HTML: HyperText Markup Language • Language for controlling presentation of web pages • Uses formatting tags • Enclosed between < and > • Not a powerful language (we will learn what this means more precisely next week) • no way to make procedures or jump CS 200 Spring 2004

  6. HTML Grammar Excerpt Document ::= <html>HeaderBody</html>Header ::= <head>HeadElements</head>HeadElements ::= HeadElementHeadElementsHeadElements ::=HeadElement ::= <title>Element</title> Body ::= <body>Elements</body>Elements ::= ElementElementsElements ::=Element ::= <p> Element </p>Make Element a paragraph.Element ::= <center> Element </center>Center Element horizontally on the page.Element ::= <b> Element </b>                          Display Element in bold.Element ::= Text What is a HTML interpreter? CS 200 Spring 2004

  7. Dynamic Web Sites • Programs that run on the client’s machine • Java, JavaScript, Flash, etc.: language must be supported by the client’s browser (so they are usually flaky and don’t work for most visitors) • Used (almost exclusively) to make annoying animations to make advertisements more noticeable • Programs that run on the web server • Can be written in any language, just need a way to connect the web server to the program • Program generates regular HTML – works for everyone • (Almost) Every useful web site does this CS 200 Spring 2004

  8. Dynamic Web Site Server GET /cs200/notes/presidents.php3 <html> <head> … Client (Web Browser) “HTML Interpreter” CS 200 Spring 2004

  9. Dynamic Web Site Client GET /cs200/notes/presidents.php3 File Server Read ~evans/public_html/cs200/notes/presidents.php3 Request Processor <html> <head><title>Presidents of the United States</title></head> <body> <h1>Presidents of the United States</h1> <p> <? $hostName = "dbm1.itc.virginia.edu"; $userName = "dee2b"; $password = "quist"; $dbName = "dee2b_presidents"; … CS 200 Spring 2004

  10. Processing a GET Request <html> <head><title>Presidents of the United States</title></head> <body> <h1>Presidents of the United States</h1> <p> <? $hostName = "dbm1.itc.virginia.edu"; $userName = "dee2b"; $password = "quist"; $dbName = "dee2b_presidents"; … • Regular HTML: • Send through to client • PHP Code: (inside <? … ?>) • Evaluate using PHP evaluator, send result to client to Client PHP Evaluator CS 200 Spring 2004

  11. PHP Code • A universal programming language • Everything you can compute in Scheme you can compute in PHP • Everything you can compute in PHP, you can compute in Scheme • Friday we will explain why more convincingly • Imperative Language • Designed to support a style of programming where most of the work is done using assignment CS 200 Spring 2004

  12. Learning New Languages • Syntax: Where the {, ;, $, etc. all go • If you can understand a BNF grammar, this is easy • Semantics: What does it mean • Learning the evaluation rules • Harder, but most programming languages have very similar evaluation rules • Style • What are the idioms and customs of experienced programmers in that language? • Takes many years to learn • Need it to be a “professional” PHP programmer, but not to make a useful program CS 200 Spring 2004

  13. PHP If Instruction ::= if (Expression) {Instructions} Evaluate Expression. If it evaluates to true, evaluate the Instructions. It is similar to (if Expression (begin Instructions)) Difference is what “true” means. In Scheme, it means anything that is not #f. In PHP it means anything that is not 0, the empty string, or a few other things. CS 200 Spring 2004

  14. PHP Example Assignment: (define i 1) or (set! i 1) $i is a variable (all variables start with $) $i = 1; $a = 1; $b = 1; while ($i <= 10) { print "Fibonacci $i = $b<br>"; $next = $a + $b; $a = $b; $b = $next; $i = $i + 1; } ; Instruction ::= while (Expression) {Instructions} As long as Expressionevaluates to true, keep doing Instructions. CS 200 Spring 2004

  15. Using a Database • HTTP is stateless • No history of information from previous requests • To do something useful, we probably need some state that changes as people visit the site • That’s what databases are for – store, manipulate, and retrieve data CS 200 Spring 2004

  16. <html> <head><title>Presidents of the United States</title></head> <body> <h1>Presidents of the United States</h1> <p> <? $hostName = "dbm1.itc.virginia.edu"; $userName = "dee2b"; $password = "quist"; $dbName = "dee2b_presidents"; … • Regular HTML: • Send through to client • PHP Code: (inside <? … ?>) • Evaluate using PHP evaluator, send result to client to Client PHP Evaluator Values SQL Command Database CS 200 Spring 2004

  17. SQL • Structured Query Language (SQL) • (Almost) all databases use it • Database is tables of fields containing values • All fields have a type (and may have other attributes like UNIQUE) CS 200 Spring 2004

  18. Demo http://www.cs.virginia.edu/csdb/ CS 200 Spring 2004

  19. SQL Commands • Create a table CREATE TABLE presidents ( number INT PRIMARY KEY, lastname VARCHAR(100), firstname VARCHAR(100), college VARCHAR(100), startdate DATE, enddate DATE ) ; primary key – used to uniquely select and entry in the table all fields must have a type int – integer varchar(n) – string of up to n characters presidents CS 200 Spring 2004

  20. SQL: Add Entry INSERT INTO presidents (number, lastname, firstname, college, startdate, enddate) VALUES(3, 'Jefferson', 'Thomas', 'William and Mary', '1801-03-04', '1809-03-03'); presidents CS 200 Spring 2004

  21. SQL: Select SelectQuery ::= SELECT fields FROM tablejoinClause [WHERE conditions] [ORDER BY field [DESC]] SELECT * FROM presidents; SELECT lastname FROM presidents; SELECT lastname, firstname FROM presidents ORDER BY lastname; SELECT lastname, firstname FROM presidents WHERE college=‘William and Mary’ ORDER BY lastname; CS 200 Spring 2004

  22. Nesting Selects • SELECT evaluates to a table, so of course, we can SELECT from that table SELECT lastname, firstname FROM (SELECT * FROM presidents WHERE college=‘William and Mary’) ORDER BY lastname; CS 200 Spring 2004

  23. SQL in PHP in HTML <html> <head><title>Presidents of the United States</title></head> <body> <h1>Presidents of the United States</h1> <p> <? $hostName = "dbm1.itc.virginia.edu"; $userName = "dee2b"; $password = "quist"; $dbName = "dee2b_presidents"; mysql_connect($hostName, $userName, $password) or exit("Unable to connect to host $hostName"); mysql_select_db($dbName) or exit("Database $dbName does not exist on $hostName"); $result = mysql_query("SELECT lastname, firstname FROM presidents WHERE college='William and Mary' ORDER BY lastname"); CS 200 Spring 2004

  24. $numrows = mysql_num_rows($result); $numcols = mysql_num_fields($result); print "<table border=0 cellpadding=5>"; print "<tr>"; for ($k = 0; $k < $numcols; $k = $k + 1) { print "<th>" . mysql_field_name ($result, $k) . "</th>"; } print "</tr>"; for ($i = 0; $i < $numrows; $i++) { // $i++ is short for $i = $i + 1 for ($j = 0; $j < $numcols; $j++) { print "<td>" . mysql_result ($result, $i, $j) . "</td>"; } print "</tr>"; } print "</table>"; mysql_close(); // Close the database connection ?> <p><hr> <a href="mailto:evans@cs.virginia.edu"><em>evans@cs.virginia.edu</em></a> </body></html> CS 200 Spring 2004

  25. The Resulting Page CS 200 Spring 2004

  26. Charge • Combining PHP, SQL and HTML is Very Powerful • Query can be a string generated by your program! • Based on user input and hyperlink clicks • Code can be generated based on what is in the database CS 200 Spring 2004