Patterns of Enterprise Application Architecture

These days, I am reading the book "Patterns of Enterprise Application Architecture - Martin Fowler".

In the introduction of the book there are some definitions about the terms such as Patterns, Enterprise Applications, and Architecture etc. The features of Enterprise software, and how they differ from other types of software are described in detail.

After the introduction, there are two main sections. The Narratives, and Patterns. The first section is a short tutorial on developing enterprise applications. The next section, is a detailed reference to the patterns themselves.

At the moment, I finished reading the Introduction and willing to start reading the first section.

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How to create a new module for vtiger...

Recently, I had to create a new module for vtigerCRM for my client in current working place. I did search in many places including the official vtiger sites, but couldn’t find a better documentation for my purpose. The latest vtiger version at that time was 5.0.3. Because I had some experience doing lots of core modifications for this system, I did decide to read the source code and find how to add a new module. Finally, I could create a new module and started the project. So, I thought it will be a good thing to write some thing on my blog about this topic, so that others who want to do this thing can read. Given below is a brief description about how to create a new module for vtiger CRM 5.0.3. Source code of this example module is also available to Download.
Step 01: Creating the module directory and minimum required files.
Create a directory called “newModule” inside your vtiger modules directory, or any other name that you prefer. Now, module index file should be created. Create a…

De Morgan's Laws in Programming

Recently, while I was reviewing some codes, I saw there were some conditional statements that check for the same condition but written in different ways. Most of these statements were written with common sense without using any mathematical analysis, since those are too simple to go for a more formal approach. The two identical conditional statements that has been written in different ways are given below.

01)

if ($comment['deleted'] == '1' || $comment['approved'] == '0') {
                unset($conversationsArray[$key]);
} else {
               ++$count;
}

02)

if ($comment['deleted'] == '0' && $comment['approved'] == '1') {
               ++$count;
} else {
           unset($conversationsArray[$key]);
}

Obviously, the above lines say that the inverse of the first condition is equals to the second condition and vice versa. That is...

($comment['deleted'] == '1' || $comment['ap…

How to create a simple Web Crawler

Web crawlers are used to extract information from web sites for many purposes.

The simple example given here accepts an URL and exposes some functions to query the content of the page.

To check out the source code of this example : https://github.com/nadeeth/crawler

If you are going to make any improvements to this code, I recommend you to follow TDD and use the unit test class in the code.

Step 1 : Create the class, init function and required attributes In this example, xpath is used for querying the given web page. There is an attribute to hold the page url, and another to hold the xpath object of the loaded page.

The init() function initializes the xpath object for the page URL assigned to url attribute.

class Crawler { public $url = false; protected $xpath = false; public function init() { $xmlDoc = new DOMDocument(); @$xmlDoc->loadHTML(file_get_contents($this->url)); $this->xpath = new DOMXPath(@$xmlDoc); } } In the next two ste…

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