The support for creating objects was from era of PHP3 but there was only the limited support of OOPS. Originally OOPS support was only meant to provide grouping of both data and functions together. As the PHP popularity grew the OOPS need also grew.

There were many significant changes in PHP5. Earlier was a very little support of encapsulation, and was only limited to grouping of data and functions or I can say that all the implementation was visible outside the class. But in PHP5 the concept of private and protected member variables and methods was introduced. Now the data protection is also possible with PHP5. The public, private and protected provide the various access levels.

PHP5 provide support for the constructors and destructors via member functions __construct and __destruct(). Constructors are the member functions that are automatically called when the instance of class in created. The earlier version of PHP the constructors were with the same name as of the class name. This unified constructor scheme helps in encapsulation of overridden subclass constructors. PHP 5 introduces a destructor support similar to that of other object-oriented languages, such as C++. The destructor method will be called as soon as all references to a particular object are removed or when the object is explicitly destroyed.

In PHP5 provides the concept of abstract classes and interfaces. For an abstract class we cannot create an instance of a class. Only non-abstract classes can be instantiated. For a methods defined abstract, only the method’s signature can be defined not their implementation. Interface allows you to define certain methods, which a class must implement. In interface we provide only the signature of member functions but the definitions are provided in the class that implements interface. The class that provides the implementation of an interface must define all the methods of interface otherwise the error will rise.

Like other programming languages there is also the support for final and static keywords in PHP5.The final keyword does not allow class and the member functions to be further extended. The classes declared with final keyword cannot further extended. The member or method declared with static keyword can’t be accessed by the instance of object. Since static methods are callable without an instance of the object created, so $this is not available inside the method declared as static.

PHP5 has better error handling support. It provides exception model similar to that of other programming languages like java or C#. An exception can be thrown and caught. Code is surrounded by try block, to catch various exceptions. Each try must have at least one corresponding catch block. Normal execution (when no exception is thrown within the try block, or catch the matching exception thrown. ]]> http://just.askbirbals.com/?feed=rss2&p=16 http://just.askbirbals.com/?p=14 http://just.askbirbals.com/?p=14#comments Fri, 12 Dec 2008 22:34:19 +0000 atul http://just.askbirbals.com/?p=14 Today the Internet connectivity is increasing the day by day. Earlier the connectivity was limited only to the computers that were using same hardware and software technologies. But this limited functionality was insufficient to fulfill the ever-growing needs. So there was necessity of such kind of a system can allow inter platform communications, or I can say that the communications should be independent of the Operating Systems and Programming Languages. To address this issue the concept of web services was introduced.

A web service has list of methods and procedures that can be used by any of the applications irrespective of the programming languages, OS, hardware used to develop them. Any type of applications can access the functionality provided by the web service and such functionality is called web methods or web APIs.

A web service allows the communication via internet standards XML and HTTP.Thus I, can say that any computer that has an access to the internet can have access to the web service. Once the web service is deployed on the Internet it can be used by any of the clients using HTTP and XML. There can be a web service, which provide the details of any person based on its social security number. This service can be readily available to any clients who need to access it.

The fundamental requirements for a web service are listed as under.

• A common format for data representation so that the communication or data exchange should be platform agnostic.
• A standard specification for sending messages to web service and receiving responses from web services.
• A standard format to describe a web service.
• A standard for publishing and discovering web services enabling applications to access them.

The various requirements described above are based on the open standards such as XML, SOAP, WSDL and UDDI.

• Since XML (eXtensionable Markup Language) is considered as cross platform standard for transferring data over Internet because it is understand by any hardware and software. The XML also describes the data.
• In order to communicate there must be a common protocol to exchange the information. SOAP (Simple Object Access Protocol) is Microsoft implementation, responsible for transporting messages between network applications and includes protocols such as HTTP, HTTPS, SMTP and MIME. It uses the XML for information exchange. The messages received or returned by SOAP are called Request and Response envelopes. These are strictly based on XML and described in WSDL for that web service.
• WSDL (Web Services Description Language) describes, publicly available methods provided by the web service. The information it provides such as the name of methods, parameters passed to the web services and the values it returns. It is a standard for describing the web service methods. WSDL is a XML format that is used to describe web services.The following are the elements of WSDL.
  • definitions: This is the root element and has web service name and its target namespace.
  • types: This element defines the data types used by the web services. WSDL uses W3C XML Schema syntax to define data types.
  • message: This describes the request and response messages.
  • portType: It is most important element of web service. This defines the operations such as the input and output/Request and Response messages involved.
  • bindings: In bindings element we define the way messages are transported i.e. binding style and transport protocol.
  • documentation: It will provide the brief description of the service.
• UDDI (Universal Description, Discovery and Integration) provides a mechanism for clients to dynamically discover services available. When a service provider wants to make a web service publicly available it registers it in UDDI directory and provides WSDL for describing the web service.

HTTP is one of the most successful and widely used protocols on the Internet today. It is application-layer protocol used to transmit and receive hypertext pages. HTTP allows a client usually a web browser to send a simple request and receive response back from the server. Whenever you write a URL in address bar of you browser, your browser firstly contacts the web server, web server locates the requested page and sends the appropriate response. These requests and responses are issued in HTTP.

Each HTTP cycle has following steps:

Connection

The connection is established between a web browser and a web server. The connection is established via TCP/IP protocols over particular port generally port 80 is used. However, HTTP is not used to establish connection, it only defines the rules that specify how they communicate.

Request

The web browser sends a request to server, specifying the resource to retrieve. HTTP defines the set of rules for sending the request. Every HTTP request consists of Request-Line, Request-Headers and Message-Body. Sample HTTP request is shown below.

GET /index.htm HTTP/1.1

HOST: www.google.com

Accept: text/html, text/plain

User-Agent: Mozilla/4.0

Each HTTP request has request line and consists of request methods, URI, and HTTP version. After Request-Line, Request-Header starts and providing the characteristics associated with data returned.

Response

It is the response send by the web server to client. The server firstly locates the requested document and sends the appropriate response. However there is a format specified by HTTP to send the response from server. Every HTTP response consists of Status-Line, Response-Headers and Message-Body. Sample HTTP response is shown below.

HTTP/1.1 200 OK

Server: Apache/1.3.3.7

Date: Mon, 23 May 2005 22:38:34 GMT

Accept-Ranges: bytes

Content-Type: text/html

Content-Length: 512

Last-Modified: Tue, 18 Jan 2007 10:12:30 GMT

Connection: close

<html>

<head><title>hello world</title>

<meta http-equiv=”Content-type” content=”text/html; charset=ISO-8859-1″>

</head>

<body>

Hello world

</body>

</html>

The first line of the every HTTP response is called the Status-Line and consists of numeric status code returned along with reason phrase. It is the response returned associated with the HTTP request. After Status-Line, Response-Header starts and providing the characteristics associated with data returned.

Close

Finally connection is closed. After each request and response cycle the connection is closed. Each time the web browser makes request, new connection is established. There is no account for the previous requested resource on web server or I can say that there is no session maintained. This makes HTTP a stateless protocol.

People are always confused about the WEB 2.0, most people consider that it is a new technology - development platform, for developing the new generation websites. It is confusion in their mind, WEB 2.0 is only a concept discovered at a conference session between O’Reilly and MediaLive International in year 2004.

It is a successor to traditional WWW (Collection of static pages with limited functionality). Most of the technology components of WEB 2.0 have belong to early days of the Web. Web 2.0 is a strong combination of several technologies and aims to enhance creativity, information sharing, user interaction, and innovation, rich desktop experience, thus making the application usage faster and simpler.

The technology infrastructure that WEB 2.0 includes several techniques such content syndication, Rich Internet Application Techniques, Inter site Communication Techniques, Mashups, and rich Server softwares.

• The Rich Internet Applications techniques produce the rich desktop experience, making the web pages more interactive and responsive. Web page can update alter the content of web page without reloading or refreshing. RIAs also provide dynamic effects and animations on web page making it more and more eye catching. Several technologies are evolved such as Style Sheets, DMTML, AJAX, Adobe Flash, Flex, Java, ActiveX, Silverlight providing rich user-experience in browser-based applications.
• Inter site Communication is the most important feature of WEB 2.0. It involves use of web apis (web services) and make the application highly distributed. SOAP and REST are most popular and common approaches to achieve.
• Mashup are the web applications that integrate the content from multiple resources at a single location. Web Services (API), public interfaces, RSS feeds are used to fetch content from different resources. Importing the photos from FLICKER using SOAP based API is meshup example.
• XML and RSS Content Syndication is an important WEB 2.0 feature. It uses XML to present site content in different formats such as RSS, RDF, and Atom. With RSS usage users not only hyper-link to page but subscribes to it, with notification occurs every time the content changes.

Conclusion

WEB 2.0 has revolutionized World Wide Web, making applications more interactive easy to use, simpler and stylish. The differing but complementary approaches provide Web 2.0 with information-storage, creation, and dissemination capabilities that go beyond what the public formerly expected of websites and its going to be a new experience altogether.

MySQL is the world’s most popular open source relational database management system. It is widely used web applications due to fast performance, high reliability and scaliblity, cost-effectiveness. Several powerful and smart features make MySQL the ultimate choice for web applications.

MySQL is especially designed to support indexing and Full-text searching. Indexes are created on specific fields of a table and MySQL stores the records sorted based on the index fields created. Below I mention some of the features that makes it popular for web apps where mining of data is required from huge datastores.

• Full-text searching is ideal for extremely large databases that contain thousands or even millions of rows. Computations are performed faster and rows can be ranked based on search relevance, which is returned as a decimal number by MySQL.
• Noise words and any words that are 3 characters or less in length such as the, and, etc are removed from the search query. This means that more accurate results are returned. If you searched for “as the people”, then the noise words “the” and “as” will automatically be removed from your query.
• In addition to simple searches, full-text searches can also be performed in Boolean mode. Boolean mode allows searches based on and/or criteria, such as “%2Bperson %2BMitchell”, which would only return all records that contained the words person AND Mitchell. We will look at Boolean searches later in this article.
• The query is case-insensitive, meaning that “cat” is ranked the same as “Cat”, “CAT” and “cAT”.

A unique storage-engine architecture data managing capabilities with different performance and scaliblity features. Some of the popular storage engines are MyISAM, InnoDB, Memory, NDB. Developers can choose from multiple storage engines each table, according to the requirements.

• MyISAM is a disk based storage engine. Aiming for very low overhead, it does not support transactions. MyISAM is default storage engine of MySQL.
• InnoDB is also disk based, supports ACID transactional capabilities. It has strong referential integrity. InnoDB requires more disk space than MyISAM to store its data, and this increased overhead is compensated by more aggressive use of memory caching, in order to attain high speeds.
• Memory (formerly called “HEAP”) is a storage engine that utilizes only RAM. The tables are memory-based and very fast.
• NDB, the MySQL Cluster Storage engine, connects to a cluster of nodes, offering high availability through redundancy, high performance through fragmentation (partitioning) of data across multiple node groups, and excellent scalability through the combination of these two. NDB uses main-memory only, with logging to disk.

MySQL has exceptional high performance query engine that can easily handle ever-increasing volume of users, transactions and data. Further data insertion is also very fast . All these make it suitable for high-traffic web sites.

MySQL uses features like main memory tables, B-tree and hash indexes, and compressed archive tables that reduce storage requirements by up to eighty-percent make MySQL a strong standout for both web and business intelligence applications.

MySQL has many Plug-in libraries, so it can support nearly every application. All the major programming languages including PHP, Java, Perl, Python, .NET, and C etc has MySQL Plug-in libraries to access MySQL databases. But MySQL’s popularity is closely tied to PHP,Perl and Python.