MySQL and Requirements Session 4 INFM 718N Web-Enabled Databases

Agenda Database normalization Access and MySQL Requirements analysis (if we have time) PHP-MySQL integration

Database Server-side Programming Interchange Language Client-side Programming Web Browser Client Hardware Server Hardware (PC, Unix) (MySQL) (PHP) (HTML, XML) (JavaScript) (IE, Firefox) (PC) Business rules Interaction Design Interface Design Relational normalization Structured programming Software patterns Object-oriented design Functional decomposition

An E-R Example studentteam implement-role member-of project creates manage-role php-projectajax-project d 1 1 M M 1 1 human client needs 1M

Making Tables from E-R Diagrams Pick a primary key for each entity Build the tables –One per entity –Plus one per M:M relationship –Choose terse but memorable table and field names Check for parsimonious representation –Relational “normalization” –Redundant storage of computable values Implement using a DBMS

Extended ER Diagram (Access)

Goals of “Normalization” Save space –Save each fact only once More rapid updates –Every fact only needs to be updated once More rapid search –Finding something once is good enough Avoid inconsistency –Changing data once changes it everywhere

Normalization 1NF: Single-valued indivisible (atomic) attributes –Split “Doug Oard” to two attributes as (“Doug”, “Oard”) –Model M:M implement-role relationship with a table 2NF: Attributes depend on complete primary key –(id, impl-role, name)->(id, name)+(id, impl-role) 3NF: Attributes depend directly on primary key –(id, addr, city, state, zip)->(id, addr, zip)+(zip, city, state) 4NF: Divide independent M:M tables –(id, role, courses) -> (id, role) + (id, courses) 5NF: Don’t enumerate derivable combinations

Normalized Table Structure Persons: id, fname, lname, userid, password Contacts: id, ctype, cstring Ctlabels: ctype, string Students: id, team, mrole Iroles: id, irole Rlabels: role, string Projects: team, client, pstring

Referential Integrity “Foreign key” values must exist in another table –If not, those records cannot be joined Checked when data added to this table –MySQL “Error 150” Triggers when data deleted/changed in other table –Specify SET NULL, RESTRICT or CASCADE

Getting started with MySQL “root” creates database, grants permissions –By you on WAMP (mysql –u root –p) –By Charles Goldman on OTAL –CREATE DATABASE team1; –GRANT SELECT, INSERT, UPDATE, DELETE, INDEX, ALTER, CREATE, DROP ON team1.* TO IDENTIFIED BY ‘bar’; –FLUSH PRIVILEGES; Start mysql –Start->Run->cmd for WAMP, ssh for OTAL –mysql –u foo –p bar [you can cd to your playspace first, but you don’t need to] Connect to your database –USE team1;

Some Useful MySQL Commands Looking around –SHOW DATABASES; –SHOW TABLES; –DESCRIBE tablename; –SELECT * FROM tablename; Optimization –SHOW TABLE STATUS \G; OPTIMIZE TABLE tablename; –EXPLAIN ; ALTER TABLE tablename ADD INDEX fieldname;

Creating Tables CREATE TABLE contacts ( ckeyMEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT, idMEDIUMINT UNSIGNED NOT NULL, ctypeSMALLINT UNSIGNED NOT NULL, cstringVARCHAR(40) NOT NULL, FOREIGN KEY (id) REFERENCES persons(id) ON DELETE CASCADE, FOREIGN KEY (ctype) REFERENCES ctlabels(ctype) ON DELETE RESTRICT, PRIMARY KEY (ckey) ) ENGINE=INNODB;  To delete: DROP TABLE contacts;

Populating Tables INSERT INTO ctlabels (string) VALUES ('primary '), ('alternate '), ('home phone'), ('cell phone'), ('work phone'), ('AOL IM'), ('Yahoo Chat'), ('MSN Messenger'), (‘other’);  To empty a table: DELETE FROM ctlabels;

The SQL SELECT Command SELECT (“projection”) chooses columns –Based on their label WHERE (“restriction”) chooses rows –Based on their contents e.g. department ID = “HIST” These can be specified together –SELECT Student ID, Dept WHERE Dept = “History”

WHERE Clause Each SELECT contains a single WHERE Numeric comparison, =, <>, … e.g., grade<80 Boolean operations –e.g., Name = “John” AND Dept <> “HIST”

Connecting PHP to MySQL On WAMP: $dbc=mysql_connect (‘localhost’, ‘userid’, ‘password’); On OTAL: $dbc=mysql_connect(‘:/export/software/otal/mysql/run/mysqld.sock’, ‘userid’, ‘password’);

Using PHP with (X)HTML Forms ”, size=30 /> Yes No if (isset($_POST[“submitted”])) { echo “Your address is $ .”; } else { echo “Error: page reached without proper form submission!”; }

<?php # Script mysql_connect.php // Set the database access information as constants. DEFINE ('DB_USER', 'tester'); DEFINE ('DB_PASSWORD', 'tester'); DEFINE ('DB_HOST', 'localhost'); DEFINE ('DB_NAME', 'sitename'); // Make the connection. $dbc (DB_HOST, DB_USER, DB_PASSWORD) OR die ('Could not connect to MySQL: '. mysql_error() ); // Select the (DB_NAME) OR die ('Could not select the database: '. mysql_error() ); // Create a function for escaping the data. function escape_data ($data) { // Address Magic Quotes. if (ini_get('magic_quotes_gpc')) { $data = stripslashes($data); } // Check for mysql_real_escape_string() support. if (function_exists('mysql_real_escape_string')) { global $dbc; // Need the connection. $data = mysql_real_escape_string (trim($data), $dbc); } else { $data = mysql_escape_string (trim($data)); } // Return the escaped value. return $data; } // End of function. ?>

<?php # Script login.php (7th version after Scripts 9.1, 9.3, 9.6, & 9.14) // Send NOTHING to the Web browser prior to the session_start() line! // Check if the form has been submitted. if (isset($_POST['submitted'])) { require_once ('../mysql_connect.php'); // Connect to the db. $errors = array(); // Initialize error array. // Check for an address. if (empty($_POST[' '])) { $errors[] = 'You forgot to enter your address.'; } else { $e = escape_data($_POST[' ']); } // Check for a password. if (empty($_POST['password'])) { $errors[] = 'You forgot to enter your password.'; } else { $p = escape_data($_POST['password']); }

if (empty($errors)) { // If everything's OK. /* Retrieve the user_id and first_name for that /password combination. */ $query = "SELECT user_id, first_name FROM users WHERE ='$e' AND password=SHA('$p')"; $result ($query); // Run the query. $row = mysql_fetch_array ($result, MYSQL_NUM); // Return a record, if applicable. if ($row) { // A record was pulled from the database. // Set the session data & redirect. session_name ('YourVisitID'); session_start(); $_SESSION['user_id'] = $row[0]; $_SESSION['first_name'] = $row[1]; $_SESSION['agent'] = md5($_SERVER['HTTP_USER_AGENT']); // Redirect the user to the loggedin.php page. // Start defining the URL. $url = ' $_SERVER['HTTP_HOST']. dirname($_SERVER['PHP_SELF']); // Check for a trailing slash. if ((substr($url, -1) == '/') OR (substr($url, -1) == '\\') ) { $url = substr ($url, 0, -1); // Chop off the slash. } // Add the page. $url.= '/loggedin.php'; header("Location: $url"); exit(); // Quit the script. } else { // No record matched the query. $errors[] = 'The address and password entered do not match those on file.'; // Public message. $errors[] = mysql_error(). ' Query: '. $query; // Debugging message. } } // End of if (empty($errors)) IF. mysql_close(); // Close the database connection. } else { // Form has not been submitted. $errors = NULL; } // End of the main Submit conditional.

// Begin the page now. $page_title = 'Login'; include ('./includes/header.html'); if (!empty($errors)) { // Print any error messages. echo ' Error! The following error(s) occurred: '; foreach ($errors as $msg) { // Print each error. echo " - $msg \n"; } echo ' Please try again. '; } // Create the form. ?> Login Address: Password: <?php include ('./includes/footer.html'); ?>

Arrays in PHP A set of key-element pairs $days = array(“Jan”->31, “Feb”=>28, …); $months = explode(“/”, “Jan/Feb/Mar/…/Dec”); $_POST Each element is accessed by the key –{$days[“Jan”]} –$months[0]; Arrays and loops work naturally together

Thinking about Arrays Naturally encodes an order among elements –$days = rksort($days); Natural data structure to use with a loop –Do the same thing to different data PHP unifies arrays and hashtables –Elements may be different types

Functions in PHP Declaration function multiply($a, $b=3){return $a*$b;} Invoking a method $b = multiply($b, 7); All variables in a function have only local scope Unless declared as global in the function

Why Modularity? Limit complexity –Extent –Interaction –Abstraction Minimize duplication

What are Requirements? Attributes –Appearance –Concepts (represented by data) Behavior –What it does –How you control it –How you observe the results

Who Sets the Requirements? People who need the task done (customers) People that will operate the system (users) People who use the system’s outputs People who provide the system’s inputs Whoever pays for it (requirements commissioner)

The Requirements Interview Focus the discussion on the task –Look for entities that are mentioned Discuss the system’s most important effects –Displays, reports, data storage –Learn where the system’s inputs come from –People, stored data, devices, … Note any data that is mentioned –Try to understand the structure of the data Shoot for the big picture, not every detail

First Things First Functionality Content Usability Security/Stability

Backup Slides

A Denormalized “Flat File”

A Normalized Relational Database Student Table Department TableCourse Table Enrollment Table

Example of Join Student TableDepartment Table “Joined” Table

Project New Table SELECT Student ID, Department

Restrict New Table WHERE Department ID = “HIST”

Sources of Complexity Syntax –Learn to read past the syntax to see the ideas –Copy working examples to get the same effect Interaction of data and control structures –Structured programming Modularity

Some Things to Pay Attention To Syntax How layout helps reading How variables are named How strings are used How input is obtained How output is created Structured Programming How things are nested How arrays are used Modular Programming Functional decomposition How functions are invoked How arguments work How scope is managed How errors are handled How results are passed

Programming Skills Hierarchy Reusing code [run the book’s programs] Understanding patterns [read the book] Applying patterns [modify programs] Coding without patterns [programming] Recognizing new patterns

Best Practices Design before you build Focus your learning Program defensively Limit complexity Debug syntax from the top down

Rapid Prototyping + Waterfall Update Requirements Choose Functionality Build Prototype Initial Requirements Write Specification Create Software Write Test Plan

Focus Your Learning Find examples that work –Tutorials, articles, examples Cut them down to focus on what you need –Easiest to learn with throwaway programs Once it works, include it in your program –If it fails, you have a working example to look at

Defensive Programming Goal of software is to create desired output Programs transform input into output –Some inputs may yield undesired output Methods should enforce input assumptions –Guards against the user and the programmer! Everything should be done inside methods

Limiting Complexity Single errors are usually easy to fix –So avoid introducing multiple errors Start with something that works –Start with an existing program if possible –If starting from scratch, start small Add one new feature –Preferably isolated in its own method

Types of Errors Syntax errors –Detected at compile time Run time exceptions –Cause system-detected failures at run time Logic errors –Cause unanticipated behavior (detected by you!) Design errors –Fail to meet the need (detected by stakeholders)

Debugging Syntax Errors Focus on the first error message –Fix one thing at a time The line number is where it was detected –It may have been caused much earlier Understand the cause of “warnings” –They may give a clue about later errors If all else fails, comment out large code regions –If it compiles, the error is in the commented part

Run Time Exceptions Occur when you try to do the impossible –Use a null variable, divide by zero, … The cause is almost never where the error is –Why is the variable null? Exceptions often indicate a logic error –Find why it happened, not just a quick fix!

Debugging Run-Time Exceptions Run the program to get a stack trace –Where was this function called from? Print variable values before the failure Reason backwards to find the cause –Why do they have these values? If necessary, print some values further back

Logic Errors Evidenced by inappropriate behavior Can’t be automatically detected –“Inappropriate” is subjective Sometimes very hard to detect –Sometimes dependent on user behavior –Sometimes (apparently) random Cause can be hard to pin down

Debugging Logic Errors First, look where the bad data was created If that fails, print variables at key locations –if (DEBUG) echo “\$foobar = $foobar”; Examine output for unexpected patterns Once found, proceed as for run time errors –define (“DEBUG”, FALSE); to clean the output

Three Big Ideas Functional decomposition –Outside-in design High-level languages –Structured programming, object-oriented design Patterns –Design patterns, standard algorithms, code reuse

One-Minute Paper What was the muddiest point in today’s class? Be brief! No names!