A Simple PHP Example
14.1 A Simple PHP Example
PHP is an open source general-purpose scripting language. The interpreter engine for PHP is written in the C programming language so it can be used on nearly all types of computers and operating systems. PHP usually comes installed with the UNIX operating system. For computer platforms with other operating systems such as Windows, Linux, or Mac OS, the PHP interpreter can be downloaded from: http://www.php.net. As with other scripting languages, PHP is particularly suited for manipulation of text pages, and in particular for manipulating dynamic HTML pages at the Web server computer. This is in contrast to JavaScript, which is down- loaded with the Web pages to execute on the client computer.
PHP has libraries of functions for accessing databases stored under various types of relational database systems such as Oracle, MySQL, SQLServer, and any system that supports the ODBC standard (see Chapter 13). Under the three-tier architecture (see Chapter 2), the DBMS would reside at the bottom-tier database server. PHP would run at the middle-tier Web server, where the PHP program commands would manipulate the HTML files to create the customized dynamic Web pages. The HTML is then sent to the client tier for display and interaction with the user.
Consider the example shown in Figure 14.1(a), which prompts a user to enter the first and last name and then prints a welcome message to that user. The line num- bers are not part of the program code; they are used below for explanation purposes only:
1. Suppose that the file containing PHP script in program segment P1 is stored in the following Internet location: http://www.myserver.com/example/
greeting.php. Then if a user types this address in the browser, the PHP inter- preter would start interpreting the code and produce the form shown in Figure 14.1(b). We will explain how that happens as we go over the lines in code segment P1.
2. Line 0 shows the PHP start tag <?php , which indicates to the PHP inter- preter engine that it should process all subsequent text lines until it encoun-
14.1 A Simple PHP Example 483
(a) //Program Segment P1: 0) <?php 1) // Printing a welcome message if the user submitted their name
// through the HTML form 2) if ($_POST['user_name']) { 3)
print("Welcome, ") ; 4)
print($_POST['user_name']); 5) } 6) else {
7) // Printing the form to enter the user name since no name has // been entered yet
8) print <<<_HTML_ 9)
<FORM method="post" action="$_SERVER['PHP_SELF']"> 10)
Enter your name: <input type="text" name="user_name"> 11)
<BR/> 12)
<INPUT type="submit" value="SUBMIT NAME"> 13)
Enter your name: Enter your name: John Smith SUBMIT NAME
SUBMIT NAME
(d)
Figure 14.1
(a) PHP program segment for entering a greeting, Welcome, John Smith
(b) Initial form displayed by PHP program segment, (c) User enters name John Smith, (d) Form prints welcome message for John Smith.
printed as is. This allows PHP code segments to be included within a larger HTML file. Only the sections in the file between <?php and ?> are processed by the PHP preprocessor.
3. Line 1 shows one way of posting comments in a PHP program on a single line started by // . Single-line comments can also be started with # , and end
at the end of the line in which they are entered. Multiple line comments start with /* and end with */ .
4. The auto-global predefined PHP variable $_POST (line 2) is an array that holds all the values entered through form parameters. Arrays in PHP are
dynamic arrays, with no fixed number of elements. They can be numerically
484 Chapter 14 Web Database Programming Using PHP
can be associative arrays whose indexes can be any string values. For example, an associative array indexed based on color can have the indexes {“red”, “blue”, “green”}. In this example, $_POST is associatively indexed by the name of the posted value user_name that is specified in the name attribute of the input tag on line 10. Thus $_POST['user_name'] will contain the value typed in by the user. We will discuss PHP arrays further in Section 14.2.2.
5. When the Web page at http://www.myserver.com/example/greeting.php is first opened, the if condition in line 2 will evaluate to false because there is
no value yet in $_POST['user_name'] . Hence, the PHP interpreter will process lines 6 through 15, which create the text for an HTML file that dis- plays the form shown in Figure 14.1(b). This is then displayed at the client side by the Web browser.
6. Line 8 shows one way of creating long text strings in an HTML file. We will discuss other ways to specify strings later in this section. All text between an
opening <<<_HTML_ and a closing _HTML_; is printed into the HTML file as is. The closing _HTML_; must be alone on a separate line. Thus, the text added to the HTML file sent to the client will be the text between lines 9 and
13. This includes HTML tags to create the form shown in Figure 14.1(b).
7. PHP variable names start with a $ sign and can include characters, num- bers, and the underscore character _ . The PHP auto-global (predefined)
variable $_SERVER (line 9) is an array that includes information about the local server. The element $_SERVER['PHP_SELF'] in the array is the path name of the PHP file currently being executed on the server. Thus, the action attribute of the form tag (line 9) instructs the PHP interpreter to reprocess the same file, once the form parameters are entered by the user.
8. Once the user types the name John Smith in the text box and clicks on the SUBMIT NAME button (Figure 14.1(c)), program segment P1 is
reprocessed. This time, $_POST['user_name'] will include the string "John Smith" , so lines 3 and 4 will now be placed in the HTML file sent to the client, which displays the message in Figure 14.1(d).
As we can see from this example, the PHP program can create two different HTML commands depending on whether the user just started or whether they had already submitted their name through the form. In general, a PHP program can create numerous variations of HTML text in an HTML file at the server depending on the particular conditional paths taken in the program. Hence, the HTML sent to the client will be different depending on the interaction with the user. This is one way in which PHP is used to create dynamic Web pages.
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» Fundamentals_of_Database_Systems,_6th_Edition
» Characteristics of the Database Approach
» Advantages of Using the DBMS Approach
» A Brief History of Database Applications
» Schemas, Instances, and Database State
» The Three-Schema Architecture
» The Database System Environment
» Centralized and Client/Server Architectures for DBMSs
» Classification of Database Management Systems
» Domains, Attributes, Tuples, and Relations
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» SQL Data Definition and Data Types
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» Discussion and Summary of SQL Queries
» Specifying General Constraints as Assertions in SQL
» Introduction to Triggers in SQL
» Specification of Views in SQL
» View Implementation, View Update, and Inline Views
» Schema Change Statements in SQL
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» The UNION, INTERSECTION, and MINUS Operations
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» Examples of Queries in Relational Algebra
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» ER Diagrams, Naming Conventions, and Design Issues
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» A Sample UNIVERSITY EER Schema, Design Choices, and Formal Definitions
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» The Role of Information Systems
» The Database Design and Implementation Process
» Use of UML Diagrams as an Aid to Database Design Specification 6
» Rational Rose: A UML-Based Design Tool
» Automated Database Design Tools
» Introduction to Object-Oriented Concepts and Features
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» Database Programming: Techniques
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» Retrieving Multiple Tuples with Embedded SQL Using Cursors
» Specifying Queries at Runtime Using Dynamic SQL
» SQLJ: Embedding SQL Commands in Java
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» Database Programming with SQL/CLI Using C
» JDBC: SQL Function Calls for Java Programming
» Database Stored Procedures and SQL/PSM
» PHP Variables, Data Types, and Programming Constructs
» Overview of PHP Database Programming
» Imparting Clear Semantics to Attributes in Relations
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» General Definitions of Second and Third Normal Forms
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» Inference Rules for Functional Dependencies
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» Dependency-Preserving and Nonadditive (Lossless) Join Decomposition into 3NF Schemas
» Problems with NULL Values and Dangling Tuples
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» Other Primary File Organizations
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» Types of Single-Level Ordered Indexes
» Some General Issues Concerning Indexing
» Algorithms for External Sorting
» Implementing the SELECT Operation
» Implementing the JOIN Operation
» Algorithms for PROJECT and Set
» Notation for Query Trees and Query Graphs
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» Catalog Information Used in Cost Functions
» Examples of Cost Functions for SELECT
» Examples of Cost Functions for JOIN
» Example to Illustrate Cost-Based Query Optimization
» Factors That Influence Physical Database Design
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» An Overview of Database Tuning in Relational Systems
» Transactions, Database Items, Read and Write Operations, and DBMS Buffers
» Why Concurrency Control Is Needed
» Transaction and System Concepts
» Desirable Properties of Transactions
» Serial, Nonserial, and Conflict-Serializable Schedules
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» Introduction to Database Security Issues 1
» Discretionary Access Control Based on Granting and Revoking Privileges
» Mandatory Access Control and Role-Based Access Control for Multilevel Security
» Introduction to Statistical Database Security
» Introduction to Flow Control
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» Distributed Database Concepts 1
» Types of Distributed Database Systems
» Distributed Database Architectures
» Data Replication and Allocation
» Example of Fragmentation, Allocation, and Replication
» Query Processing and Optimization in Distributed Databases
» Overview of Transaction Management in Distributed Databases
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» Current Trends in Distributed Databases
» Distributed Databases in Oracle 13
» Generalized Model for Active Databases and Oracle Triggers
» Design and Implementation Issues for Active Databases
» Examples of Statement-Level Active Rules
» Time Representation, Calendars, and Time Dimensions
» Incorporating Time in Relational Databases Using Tuple Versioning
» Incorporating Time in Object-Oriented Databases Using Attribute Versioning
» Temporal Querying Constructs and the TSQL2 Language
» Spatial Database Concepts 24
» Multimedia Database Concepts
» Clausal Form and Horn Clauses
» Datalog Programs and Their Safety
» Evaluation of Nonrecursive Datalog Queries
» Introduction to Information Retrieval
» Types of Queries in IR Systems
» Evaluation Measures of Search Relevance
» Web Analysis and Its Relationship to Information Retrieval
» Analyzing the Link Structure of Web Pages
» Approaches to Web Content Analysis
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» Data Mining as a Part of the Knowledge
» Goals of Data Mining and Knowledge Discovery
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» Market-Basket Model, Support, and Confidence
» Frequent-Pattern (FP) Tree and FP-Growth Algorithm
» Other Types of Association Rules
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» Commercial Data Mining Tools
» Data Modeling for Data Warehouses
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» Grouping, Aggregation, and Database Modification in QBE
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