Before we can access data in a database, we need to create a connection to the database.
In PHP, this is done with the mysql_connect() function.
Syntax
mysql_connect(servername,username,password);
Example:
In the following example we store the connection in a variable ($con) for later use in the script. The "die" part will be executed if the connection fails:
Closing a Connection
Component Object Model (COM): The Component Object Model (COM) is a software architecture that allows applications to be built from binary software components. COM is the underlying architecture that forms the foundation for higher-level software services, like those provided by OLE. OLE services span various aspects of commonly needed system functionality, including compound documents, custom controls, inter application scripting, data transfer, and other software interactions.
Distributed COM (DCOM): Microsoft® Distributed COM (DCOM) extends the Component Object Model (COM) to support communication among objects on different computers—on a LAN, a WAN, or even the Internet. With DCOM, an application can be distributed at locations that make the most sense to customer and to the application.
Because DCOM is a seamless evolution of COM, the world's leading component technology, an organization can take advantage of existing investment in COM-based applications, components, tools, and knowledge to move into the world of standards-based distributed computing. As organization do so, DCOM handles low-level details of network protocols so organization can focus on real business: providing great solutions to customers.
Reference:
Parallel Processing, Semaphore, Microsoft .Net Framework, Microsoft .Net, E-commerce and Mobile Commerce
Parallel Processing: Parallel Processing is simultaneous use of more than one computer or processor to solve a problem. The processors may communicate in order to be able to cooperate in solving a problem or they may run completely independently, possibly under the control of another processor which distributes work to the others and collects results from them.
Semaphore: A semaphore is an integer counter associated with a thread wait queue. Two atomic operations are available on semaphores: P (or pass) and V (or free). The P operation decrements the counter, and blocks the thread if the counter has reached a negative value. The V operation increments the counter and wakes up a thread, if any, in the semaphore wait queue.
Microsoft .Net Framework: The Microsoft .NET Framework is a software component which can be added to the Microsoft Windows operating system. It provides a large body of pre-coded solutions to common program requirements, and manages the execution of programs written specifically for the framework. The .NET Framework is a key Microsoft offering, and is intended to be used by most new applications created for the Windows platform.
Microsoft .Net: Microsoft .Net is an umbrella term that applies to a collection of products and technologies from Microsoft. All have in common a dependence on the Microsoft .NET Framework, a component of the Windows operating system.
E-commerce: E-commerce (electronic-commerce) refers to business over the Internet. Web sites such as Amazon.com, Buy.com, and eBay are all e-commerce sites. The two major forms of e-commerce are Business-to-Consumer (B2C) and Business-to-Business (B2B). While companies like Amazon.com cater mostly to consumers, other companies provide goods and services exclusively to other businesses. The terms "e-business" and "e-tailing" are often used synonymously with e-commerce.
Mobile Commerce:
Reference:
Designing distributed systems
A distributed system is a collection of independent computers that appear to its users as a single coherent system.
Characteristics of distributed system
A distributed system is a collection of independent computers that are used jointly to perform a single task or to provide a single service.
Examples of distributed systems
Probably the simplest and most well known example of a distributed system is the collection of Web servers—or more precisely, servers implementing the HTTP protocol—that jointly provide the distributed database of hypertext and multimedia documents that we know as the World-Wide Web. Other examples include the computers of a local network that provide a uniform view of a distributed file system and the collection of computers on the Internet that implement the Domain Name Service (DNS).
Why do we use distributed systems?
The alternative to using a distributed system is to have a huge centralized system, such as a mainframe. For many applications there are a number of economic and technical reasons that make distributed systems much more attractive than their centralized counterparts.
Cost: Better price/performance as long as commodity hardware is used for the component computers.
Performance: By using the combined processing and storage capacity of many nodes, performance levels can be reached that are beyond the range of centralized machines.
Scalability: Resources such as processing and storage capacity can be increased incrementally.
Reliability: By having redundant components the impact of hardware and software faults on users can be reduced.
Inherent distribution: Some applications, such as email and the Web (where users are spread out over the whole world), are naturally distributed. This includes cases where users are geographically dispersed as well as when single resources (e.g., printers, data) need to be shared.
Reference:
Concurrency and transactions
Concurrent execution of user programs is essential for good database management system (DBMS) performance.
Because disk accesses are frequent, and relatively slow, it is important to keep the CPU humming by working on several user programs concurrently.
A user’s program may carry out many operations on the data retrieved from the database, but the DBMS is only concerned about what data is read/write from/to the database.
A transaction is the DBMS abstract view of a user program: a sequence of reads and writes.
When multiple users access a database simultaneously, their data operations have to be coordinated in order to prevent incorrect results and to preserve the consistency of the shared data. This activity is called concurrency control and should provide each concurrent user with the illusion that he is referencing a dedicated database. The classical transaction concept defines a transaction as the unit of concurrency control, that is, the DBMS has to guarantee isolated execution for an entire transaction. This implies that its results as derived in a multi-programming environment should be the same as if obtained in a serial execution schedule. Other important transaction properties are atomicity, consistency, and durability. In a DBMS, the component responsible for achieving these properties is transaction management which includes concurrency control as a major function.
Concurrency control and recovery are among the most important functions provided by a DBMS.
Users do not need to worry about concurrency.
System automatically inserts lock/unlock requests and schedules actions of different Xacts in such a way as to ensure that the resulting execution is equivalent to executing the Xacts one after the other in an order.
Reference:
Internet Security
Security has become one of the primary concerns when an organization connects its private network to the Internet. Regardless of the business, an increasing number of users on private networks are demanding access to Internet services such as the World Wide Web (WWW), Internet mail, Telnet, and File Transfer Protocol (FTP). In addition, corporations want to offer WWW home pages and FTP servers for public access on the Internet. Network administrators have increasing concerns about the security of their networks when they expose their organization’s private data and networking infrastructure to Internet crackers. To provide the required level of protection, an organization needs a security policy to prevent unauthorized users from accessing resources on the private network and to protect against the unauthorized export of private information. Even if an organization is not connected to the Internet, it may still want to establish an internal security policy to manage user access to portions of the network and protect sensitive or secret information.
Internet Firewalls
An Internet firewall is a system or group of systems that enforces a security policy between an organization’s network and the Internet. The firewall determines which inside services may be accessed from the outside, which outsiders are permitted access to the permitted inside services, and which outside services may be accessed by insiders. For a firewall to be effective all traffic to and from the Internet must pass through the firewall, where it can be inspected. The firewall must permit only authorized traffic to pass, and the firewall itself must be immune to penetration. Unfortunately, a firewall system cannot offer any protection once an attacker has gotten through or around the firewall. It is important to note that an Internet firewall is not just a router, a bastion host, or a combination of devices that provides security for a network. The firewall is part of an overall security policy that creates a perimeter defense designed to protect the information resources of the organization. This security policy must include published security guidelines to inform users of their responsibilities; corporate policies defining network access, service access, local and remote user authentication, dial-in and dial-out, disk and data encryption, and virus protection measures; and employee training. All potential points of network attack must be protected with the same level of network security. Setting up an Internet firewall without a comprehensive security policy is like placing a steel door on a tent.
Benefits of an Internet Firewall
Internet firewalls manage access between the Internet and an organization’s private network
Without a firewall, each host system on the private network is exposed to attacks from other hosts on the Internet.
Internet firewalls allow the network administrator to define a centralized “choke point” that keeps unauthorized users such as hackers, crackers, vandals, and spies out of the protected network; prohibits potentially vulnerable services from entering or leaving the protected network; and provides protection from various types of routing attacks. An Internet firewall simplifies security management, since network security is consolidated on the firewall systems rather than being distributed to every host in the entire private network.
Reference:
Distributed Objects and CORBA
The term distributed objects, describes objects which reside in separate address spaces and methods of which can be subject of remote method calls (a remote call is issued in an address space separate to the address space where the target object resides). By convention, the code issuing the call is referred to as the client; the target object is referred to as the server object (or simply remote object); the set of methods which implements one of the server object’s interfaces is sometimes designated as a service that this object provides. Similarly, the process in which the server object is located is referred to as a server. (Orfali, Harkey and Edwards, Wiley Computer Publishing Group)
CORBA
CORBA stands for Common Object Request Broker Architecture, is the result of the work done by major actors of the hardware and software industry to set up a communication framework. The goal is to facilitate the development of distributed applications over a heterogeneous network. In a distributed environment, clients are talking to objects. The services that can be delivered to a client by an object are described in an interface. The means of communication are handled by an Object Request Broker (ORB). The idea behind CORBA is to provide an intermediary layer that handles access requests on data. It frees the developer from most of the portability issues. It enables the development of distributed objects. (Jon Siegel, Wiley Computer Publishing Group)
Distributed objects in CORBA
Basic principles
1. Request & response
In CORBA, a client issues a request to execute a method of an object implementation. There is no constraint imposed on the location of the client and the requested object implementation (remote object); they can share an address space, can be located in separate address spaces on the same node, or can be located on separate nodes. A server (process) can contain implementation of several objects or a single object, or even provide an implementation of one particular method only. However, typically, a multithreaded server encapsulates implementations of multiple objects.
2. Remote reference
Remote references are called Object References and the target of an Object Reference must be an object that supports the CORBA::Object IDL interface (such objects are called CORBA objects).
3. IDL Interface
CORBA specifies the CORBA IDL Language and its mapping to several programming languages (e.g., C++, Java, and Smalltalk). The IDL language provides means for interface definitions; there are no constructs related to object implementation (object state definitions have been proposed recently by OMG).
4. Proxy: local representative
Using the Broker Pattern terminology, the client-side proxy code is called IDL stub; the server-side proxy code is referred to as IDL skeleton. However, in CORBA, the concept "proxy" is used to denote an object created on the client side which contains the IDL stub plus provides some other functionality, e.g. support for dynamic invocation.
Reference:
An important aspect of creating Web Forms pages for user input is to be able to check that the information users enter is valid.
Functionality: Workshop 10 is CSU Registration Form - PHP program that grants an easy-to-use but powerful way to check for errors and, if necessary, display messages to the user.
When the user submits a form to the server, PHP code is invoked to review the user's input.
If an error has occurred in any of the input controls, the page itself is set to an invalid state (validation failed) and user is redirected back to the form page with displayed error messages.
If validation passed, user’s registration details specified on form processing page are invoked. Thus, this program doesn't change HTML forms behavior except it always redirects user to the form page until user enters fully valid data.
This program converts decimal value to binary value, and vice-versa.
Functionality: This program asks user to enter valid value in binary or decimal input box.
The validations are as follows:
Binary Input Box:
* The binary input box should not be left blank for the purpose of decimal conversion.
* User can not enter decimal value or any character value in binary input box. User need to enter only binary number that is made of 0s and 1s.
Decimal Input Box:
* The decimal input box should not be left blank for the purpose of binary conversion.
* User can not enter any character value in decimal input box.
This program validates submitted value at Server Side. If user submits invalid value then the program will display error message in Red color. This is possible because of Server Side validation script.
Conditional statements are used to perform different actions based on different conditions.
The if statement is used to execute some code only if a specified condition is true.
Syntax:
if (condition) code to be executed if condition is true;
Functionality: This program asks user to input temperature. This program converts temperature from Celsius to Fahrenheit and vice-versa.
Two radio buttons have been provided for selection. They are 1. Convert temperature from Celsius to Fahrenheit and 2. Convert temperature from Fahrenheit to Celsius.
This workshop demonstrates how to use PHP forms. Forms are a special component which allows site visitors to supply information on another web page or server.
AJAX: Asynchronous JavaScript and XML (AJAX) have been used to display tool tip for text box. Whenever user places a cursor in any of the three text boxes, program will display a corresponding tool tip message. Web server might be some where in
Functionality: This program asks user to input his name, birth year and favorite color. JavaScript validation has been used to validate the input values. Finally, this program calculates user's age and display the text - name and age in user's favorite color.
The meaning of a while statement is simple. It tells PHP to execute the nested statement(s) repeatedly, as long as the while expression evaluates to TRUE. The value of the expression is checked each time at the beginning of the loop, so even if this value changes during the execution of the nested statement(s), execution will not stop until the end of the iteration (each time PHP runs the statements in the loop is one iteration). Sometimes, if the while expression evaluates to FALSE from the very beginning, the nested statement(s) won't even be run once. We can group multiple statements within the same while loop by surrounding a group of statements with curly braces.
Syntax:
Functionality: Workshop 6 program asks user to input a number. A JavaScript validation has been used to validate the numerical value. Then program prints Table using PHP while loop.
Elevator Pitch
Here is Elevator Pitch for Assignment 2.
CORBA stands for Common Object Request Broker Architecture. CORBA is an industry standard developed by The Object Management Group to support distributed objects programming. CORBA is just a specification for creating and using distributed objects; CORBA is not a programming language.
The CORBA architecture is based on the object model. This model is derived from the abstract core object model defined by the OMG in the Object Management Architecture Guide
The model is abstract in the sense that it is not directly realized by any particular technology; this allows applications to be built in a standard manner using basic building blocks such as objects. Therefore, a CORBA-based system is a collection of objects that isolates the clients from the servers by a well-defined encapsulating interface. It is important to note that CORBA objects differ from typical programming objects in three ways:
• CORBA objects can run on any platform.
• CORBA objects can be located anywhere on the network.
• CORBA objects can be written in any language that has IDL mapping.
Electronic commerce, commonly known as e-commerce , consists of the buying and selling of products or services over electronic systems such as Internet and other computer networks. The amount of trade conducted electronically has grown rapidly since the spread of Internet. A wide variety of commerce is conducted in this way, encouraging and drawing on innovations in electronic funds transfer, supply chain management, Internet marketing, online transaction processing, electronic data interchange (EDI), inventory management systems, and automated data collection systems. Modern electronic commerce typically uses the World Wide Web at least at some point in the transaction's lifecycle, although it can encompass a wider range of technologies such as e-mail as well.
PHP is a server-side HTML integrated scripting language, which is used for designing dynamic web pages. PHP is mainly used in world-class operating system, such as, UNIX, LINUX and also in Windows. In the true sense, PHP is the perfect combination of practical programming rules and object oriented programming (OOPs). Since PHP uses desktop applications and command line interface, it is considered to be the best traditional server side scripting language.
Most of the well-known database connections, such as, Oracle, My SQL, ODBC and SQL get support from PHP programming. So, it is indeed a good choice for the freelance programmers to use PHP development for creating their dynamic e-commerce websites.
$_ENV and $_SERVER. Most scripts, which use these variables, only use one or two at a time. The following script accesses 2 different _SERVER variables.
Test Code
Arrays can also be created using a key/value pair combination. These are often referred to as associative arrays or hashes. In a hash each value is associated with a unique key. Unlike list arrays that use a number as an index value, associative arrays use any value. The easiest way to comprehend how a hash works is to think of it as a table. In the following table the state name serves to role as key and the city is the value.
| State (key) | City (value) |
| | |
| NSW | |
| | |
| | |
| | |
An array is an ordered collection of values. Each value can be referenced individually using its position in the array. The first element of an array is in position 0 and the second element is in position 1. Creating arrays in PHP can be done in multiple ways, though the following example is one of the simplest.
$cities = array('Beijing', 'Oaxaca', 'Habana', 'Jakarta');
For example, to access the third element of the $cities array use $cities[2].
The Workshop 2 introduces some variables to our PHP script. Variables in PHP begin with the $ symbol. PHP uses arrays and variables to store different values. Variables begin with a $ followed by characters, digits, and underscores. Variable names are case sensitive and are assigned with the '=' operator. Variables are incredibly useful. For example, you may need to keep track of information submitted via a web form or perform calculations on data and store the results.
Here's a simple example:
The first PHP example will print "Hello World" in the browser window.
The PHP statement:
print("Hello World");
displays the message "Hello World" in the browser window. Here PHP statement is embedded into HTML documents and PHP statement appears between symbols.
The PHP print function displays the value or string within parentheses in the browser window.
Several important things to note about PHP scripts:
XML: eXtensible Markup Language
What is XML?
XML as Internet standard
The major goals of the language are as follows.
XML at work
Building block of XML
Elements and tags
Attributes
PCDATA
CDATA
What is XSLT?
XSLT as a programming language
XSLT summary
Hypertext Markup Language
JavaScript has been popular for including
Java Virtual Machine at work
The rise of the application servers
Microsoft .NET
Advantages of Microsoft .NET
A database server is a computer program that provides database services to other computer programs or computers, as defined by the client-server model. The term may also refer to a computer dedicated to running such a program. Database management systems frequently provide database server functionality, and some DBMSs (e.g., MySQL) rely exclusively on the client-server model for database access.
Such a server is accessed either through a "front end" running on the user’s computer which displays requested data or the back end which runs on the server and handles tasks such as data analysis and storage.
In a master-slave model, database master servers are central and primary locations of data while database slave servers are synchronized backups of the master acting as proxies.
Some examples of Database servers are Oracle, DB2, Informix, Ingres, SQL Server. Every server uses its own query logic and structure. The SQL query language is more or less same in all the database servers.
Reference: Eustace, K. (2004). Lecture 3: Database Servers [PowerPoint slides]. Retrieved from Charles Sturt University, Melbourne Study Centre
Client Server Architecture
The client-server characteristic describes the relationship of cooperating programs in an application. The server component provides a function or service to one or many clients, which initiate requests for such services.
Functions such as email exchange, web access and database access, are built on the client-server model. For example, a web browser is a client program running on a user's computer that may access information stored on a web server on the Internet. Users accessing banking services from their computer use a web browser client to send a request to a web server at a bank. That program may in turn forward the request to its own database client program that sends a request to a database server at another bank computer to retrieve the account information. The balance is returned to the bank database client, which in turn serves it back to the web browser client displaying the results to the user.
Client Server Diagram
The client-server model has become one of the central ideas of network computing. Many business applications being written today use the client-server model. So do the Internet's main application protocols, such as HTTP, SMTP, Telnet, and DNS. In marketing, the term has been used to distinguish distributed computing by smaller dispersed computers from the "monolithic" centralized computing of mainframe computers. But this distinction has largely disappeared as mainframes and their applications have also turned to the client-server model and become part of network computing.
Each instance of the client software can send data requests to one or more connected servers. In turn, the servers can accept these requests, process them, and return the requested information to the client. Although this concept can be applied for a variety of reasons to many different kinds of applications, the architecture remains fundamentally the same.
The most basic type of client-server architecture employs only two types of hosts: clients and servers. This type of architecture is sometimes referred to as two-tier. It allows devices to share files and resources. The two tier architecture means that the client acts as one tier and application in combination with server acts as another tier.
The interaction between client and server is often described using sequence diagrams. Sequence diagrams are standardized in the Unified Modeling Language.
Specific types of clients include web browsers, email clients, and online chat clients.
Specific types of servers include web servers, ftp servers, application servers, database servers, name servers, mail servers, file servers, print servers, and terminal servers. Most web services are also types of servers.
Reference: Eustace, K. (2005). Lecture 2: Clients, servers and distributed paradigms [PowerPoint slides]. Retrieved from Charles Sturt University, Melbourne Study Centre
E-commerce, distributed applications and the Internet
Introduction
In the first week we examine the type of system which is described by the umbrella term ‘e-commerce’. A number of typical application areas are examined including retailing using the internet, supply chain management and online auctions. We look at some of the underlying technologies used to implement e-commerce applications, for example web technology. We also look at some of the problems which are encountered when developing distributed e-commerce systems, for example problems in ensuring that a system is kept secure from criminal activity. It concludes with an examination of a typical retailing system, how some of the technologies fit together and business models used in the internet.
Distributed Systems
There is no doubt that there is great demand for large-scale distributed applications. Indeed, tremendously expensive special-purpose distributed systems have been deployed and today are used extensively in the banking, airline, and telecommunication industries. The major barrier to supporting these, and even richer, applications on the Internet is the difficulty of designing, building, testing, and maintaining distributed applications using the tools that comprise the state-of-the-art today.
The guiding principles of distributed multi-tiered architectures like J2EE and .net / Windows DNA are Web computing; faster time to market; true interoperability; Scalability, reduced complexity; language, tool, and hardware independence; and lower cost of ownership.
The life cycle of a distributed application can typically be viewed as having four phases:
It is a collection of experiences and best practices that have been taken from real-world development engagements, providing development teams with access to shared experiences and a proven, repeatable process. The Distributed Application Development Process encompasses modern design principles and proven practices to facilitate the development task and provide developers with a blueprint for building robust and correct distributed applications.
E-Commerce and Internet
There are a number of ways in which companies can make money from the internet. Probably the best known way of making money is by selling some commodity; this could be a non-IT commodity such as a CD or item of clothing or it could be some piece of application software, a font, a browser plug-in or an operating system. Other forms of revenue rising are:
Such applications have changed the face of retailing, for example the fast communication of the internet has made bulk buying sites feasible and popular and has given rise to a number of novel commercial models.
Reference: Eustace, K. (2004). Lecture 1: E-Commerce, distributed applications and the internet [PowerPoint slides]. Retrieved from Charles Sturt University, Melbourne Study Centre
