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David Evans http://www.cs.virginia.edu/evans
Class 29: Vocational Skills How to Build a Dynamic Web Site CS200: Computer Science University of Virginia Computer Science David Evans
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Menu Building a Dynamic Web Site SQL PHP HTML LISP Scheme
Job listings at monster.com: ~ $80-250K 215 ~$65K ~$40K 9 4 April 2003 CS 200 Spring 2003
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Today’s Aberrant Class
Covers topics primarily selected for their practical (not intellectual) value Covers material found in “for dummies” books 4 April 2003 CS 200 Spring 2003
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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 4 April 2003 CS 200 Spring 2003
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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 4 April 2003 CS 200 Spring 2003
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HTML Grammar Excerpt What is a HTML interpreter?
Document ::= <html> Header Body </html> Header ::= <head> HeadElements </head> HeadElements ::= HeadElement HeadElements HeadElements ::= HeadElement ::= <title> Element </title> Body ::= <body> Elements </body> Elements ::= Element Elements Elements ::= 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? 4 April 2003 CS 200 Spring 2003
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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 4 April 2003 CS 200 Spring 2003
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Dynamic Web Site Server GET /cs200/notes/presidents.php3 <html>
<head> … Client (Web Browser) “HTML Interpreter” 4 April 2003 CS 200 Spring 2003
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Dynamic Web Site Request Processor 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"; … 4 April 2003 CS 200 Spring 2003
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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 4 April 2003 CS 200 Spring 2003
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PHP Code A universal programming language Imperative Language
Everything you can do in Scheme you can do in PHP Everything you can do in PHP, you can do in Scheme Imperative Language Designed to support a style of programming where most of the work is done using assignment 4 April 2003 CS 200 Spring 2003
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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 4 April 2003 CS 200 Spring 2003
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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. 4 April 2003 CS 200 Spring 2003
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PHP Example Assignment: (define i 1) or (set! i 1) $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 Expression evaluates to true, keep doing Instructions. 4 April 2003 CS 200 Spring 2003
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Using a Database Web requests are 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 4 April 2003 CS 200 Spring 2003
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Database to Client PHP Evaluator SQL Command Regular 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 4 April 2003 CS 200 Spring 2003
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SQL Structured Query Language (SQL)
(Almost) all databases use it Database is tables of fields containing values number lastname firstname college 1 Washington George 2 Adams John Harvard 3 Jefferson Thomas William and Mary 4 April 2003 CS 200 Spring 2003
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SQL Commands Create a table presidents 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 number lastname firstname college startdate enddate 4 April 2003 CS 200 Spring 2003
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SQL: Add Entry insert into presidents (number, lastname, firstname, college, startdate, enddate) values (3, 'Jefferson', 'Thomas', 'William and Mary', ' ', ' '); presidents number lastname firstname college startdate enddate 3 Jefferson Thomas William and Mary 4 April 2003 CS 200 Spring 2003
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SQL: Select SelectQuery ::= SELECT fields FROM table joinClause
[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; 4 April 2003 CS 200 Spring 2003
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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; 4 April 2003 CS 200 Spring 2003
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Problem Set 8 Due last day of class
Either a presentation/demo (your site works) Report (your site doesn’t work) Do something interesting enough you will keep it going after the class If your team has a project listed on the PS8 handout, you already have a good topic If not, by 5:00PM Monday you need to: Either convince me the idea you sent earlier is interesting enough Or, think of a new, more exciting idea 4 April 2003 CS 200 Spring 2003
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Cracking the Cracker Barrel
4 April 2003 CS 200 Spring 2003
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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"); $result = mysql_query("SELECT lastname, firstname FROM presidents WHERE college='William and Mary' ORDER BY lastname"); 4 April 2003 CS 200 Spring 2003
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$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 "</table>"; mysql_close(); // Close the database connection ?> <p><hr> <a </body></html> 4 April 2003 CS 200 Spring 2003
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The Resulting Page 4 April 2003 CS 200 Spring 2003
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This is Powerful Just change the query to get a new page
Query can be a string generated by your program! Based on user input and hyperlink clicks See the example site $result = mysql_query("SELECT lastname, firstname FROM presidents WHERE college='William and Mary' ORDER BY lastname"); 4 April 2003 CS 200 Spring 2003
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Charge PS8: Out Today Some teams have project idea already (if it is listed with your team) Other teams need to think of a better idea (or convince me the idea you sent already is exciting enough that you will want to keep using it after class ends) Design Reviews: sign up Wednesday Due 28 April (last day of class) Either get it working enough to demo or turn in a written report 4 April 2003 CS 200 Spring 2003
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