Samira Yousefi Blog

Cloud Computing

samira — Tue, 03 Apr 2012 14:08:45 +0000

Cloud computing is becoming one of the next industry buzz words. It joins the ranks of terms including:grid computing, utility computing, virtualization, clustering, etc. In a cloud computing system, there's a significant workload shift. Local computers no longer have to do all the heavy lifting when it comes to running applications. The network of computers that make up the cloud handles them instead. Hardware and software demands on the user's side decrease. The only thing the user's computer needs to be able to run is the cloud computing system's interface software, which can be as simple as a Web browser, and the cloud's network takes care of the rest.

There's a good chance you've already used some form of cloud computing. If you have an e-mail account with a Web-based e-mail service like Hotmail, Yahoo! Mail or Gmail, then you've had some experience with cloud computing. Instead of running an e-mail program on your computer, you log in to a Web e-mail account remotely. The software and storage for your account doesn't exist on your computer — it's on the service's computer cloud.

new features of ZendFramework 2

samira — Sat, 03 Mar 2012 17:56:58 +0000

Zend Framework 2 Highlights:

Simpler and easier to use components that incorporate the vast amount of feedback from developers using Zend Framework 1.x
Better modularity and code reuse, so developers can focus on core business logic rather than generic tasks
A redesigned Model-View-Controller architecture layer that introduces greater pattern consistency across all framework elements with support for event-driven development
Significantly improved performance
An entirely new Cloud Infrastructure component
Fully supports PHP 5.3 today, and has built in forward compatibility to allow users to take advantage of the new features offered in PHP 5.4

So… I hear there’s this new Zend Framework 2? You’ve seen the beta announcements, you’ve heard tantalizing features details – here are the answers to the questions you have about Zend Framework 2.

Q: A new Zend Framework release? Why?

Q: What new features will I find in Zend Framework 2?

A: Some highlights:

An entirely re-written event-driven MVC layer
Dependency injection support
A powerful module management system
An EventManager, for writing event-driven systems, as well as for creating cut points in your software for introducing cross-cutting concerns.
A new view layer, architected around analyzing the request and generating a suitable response, be it plain old HTML, or Atom feeds or JSON.

Q: What’s the release schedule for Zend Framework 2?

A: Zend Framework 2 Beta 3 is the current release. There will be a feature-complete beta in spring 2012. Official general availability is planned for summer 2012.

Q: Does this mean that Zend Framework 1 is about to be end-of-lifed?

A: Definitely not! We currently plan to fully support Zend Framework 1 until at least early 2014, including maintenance and security updates.

Q: I have an application built with Zend Framework 1 – will I be able to migrate it to the new version?

A: Absolutely. An important part of Zend Framework 2 is the migration layer that will allow ZF 1 code to run on the new ZF 2 engine, which will be made available once the ZF 2 APIs are finalized. With it, you will be able to add new ZF 2 code, and refactor existing code, at a controlled pace.

Q: I’m starting a new project – which version of Zend Framework should I use?

A: If the project will complete mid-2012 or later, start using Zend Framework 2! The current beta 3 is a great opportunity to begin acquainting yourself with the main features, and the feature-complete beta 4 and GA releases will follow quickly.

Q: What version of PHP is Zend Framework 2 based on?

A: Zend Framework 2 is based on PHP 5.3. We expect to add support for PHP 5.4 once it starts to be adopted by the PHP community.

Q: I’m convinced, where can I try out the latest beta release?

A: You can download the latest build from http://packages.zendframework.com. You can also get more information about the Zend Framework 2 project at http://framework.zend.com/zf2/.

process maker software

samira — Sun, 25 Dec 2011 18:57:20 +0000

download from here

ProcessMaker is open source business process management (BPM) application which is cost-effective and easy to use. Workflow software such as ProcessMaker can assist organizations large or small with designing, automating and deploying business processes of various types.

ProcessMaker features an extensive toolbox which provides the ability to easily create web forms and map out fully functioning workflows. The software is entirely web based and accessed through a web browser, making it easy to manage and coordinate processes through the entire organization including user groups and departments. ProcessMaker can also connect with other applications and systems such as ERP, business intelligence, CRM and document management.

Subject matter experts and business analysts choose ProcessMaker as their workflow software solution because they can accomplish more and communicate with their technical teams more efficiently. System administrators choose ProcessMaker because they don’t have to spend a lot of time programming and end users prefer ProcessMaker because it is very easy to use.

In addition to having one of the lowest overheads of any workflow software in the industry, ProcessMaker is extremely efficient and lightweight. ProcessMaker Enterprise clients can take advantage of a fully supported, high quality BPM suite with the additional benefit of it being open source. Customers on 5 continents, through 17 different languages and across a variety of industries including manufacturing, telecommunications, finance and government are using ProcessMaker workflow software.

What is BPMS?

samira — Thu, 15 Dec 2011 13:05:16 +0000

Business Process Management (BPM) refers to the closed loop, iterative management of business processes over their entire lifecycle. It includes designing, optimizing, documenting, communicating, deploying, evaluating, updating, and retiring processes. Well-managed companies have always had robust, but time-consuming, mechanisms for performing all of these functions.

In the past, these mechanisms usually involved the following:

Designing and documenting processes using paper or software applications like Visio and MS Word
Using specialized products like Crystal Ball to simulate processes before deploying them
Deploying processes by developing new applications and by customizing existing applications
Using specialized products to monitor the performance of processes, and to identify areas for Improvement

Why should organizations consider BPM?

Problem identification with BPM

Triaging solutions with BPM

Enables creation of new biz metrics from the web

Monitors configured metrics for SLA compliance

Sends notifications to users of the process

Empowers business people to make changes themselves

Enables business users to configure and deploy rule based solution themselves

track and executes business rules on behalf business users

Analyzing Problem with BPM

Optimizing with BPM

Gives business people ad-hocaccess to deep analytical power on process data

Ensure all data is available without IT Configuration

Removes Bottlenecks, Coast forecasting
Remodeling of the system

Biz users can change the processes as and when required

What are BPMS?

Business Process Management Systems (BPMS) are a new family of software systems that automate and simplify the task of managing business processes over the entire lifecycle. In the past, IT-enabled business processes were implemented within the boundaries of particular software applications (Examples include Customer Relationship Management systems and Supply Chain Management Systems) Even when processes required multiple applications to be coordinated, the locus of control would remain within a specific application, which would call on others as and when required. With a BPMS, the process management system specializes in orchestrating every business process, and will call on other applications for services, as required.

When to Implement Business Process Management Systems?

The key advantage of a BPMS is agility – processes can be created and managed with minimal changes to application code, and new processes can be rapidly and easily created. The other primary advantage is conservatism: Past investments in business logic and applications can be reused to create new, composite, processes.

Consider implementing a BPMS whenever:

Business processes need to be maintained in several versions, for different product categories or for different markets
Business processes need to be extremely mutable
There are opportunities that have been identified for existing applications to work with one another, but these include a huge element of custom code that cannot easily be moved into an ERP

In fact, any occasion where you are considering implementing a new process, or redefining an existing process, is an opportunity to consider moving to a new â€œprocess platformâ€.

Tangible returns from a BPM Implementation

Business organizations are using BPM for different reasons and in different forms. BPM has an overall impact on the business ecosystem resulting in cost savings across the processes inside business ecosystem.

BPM is a way of looking at and then controlling the processes that are present in an organization. It is an effective methodology to use in times of crisis to make certain that the processes are efficient and effective, as this will result in a better and more cost efficient organization.

This diagram from the AIIM BPM certificate program course shows the elements present in most BPM suites. The elements of design and monitoring are immediately recognizable as important elements, also in the technology.

The rules engine and process registry indicate descriptions of the lessons learned from the analysis and design that allows the system to automate the process. A simple example of such a rule for a web retailer could be that the third item you buy is half price. The combination of the rules engine and registry allows a BPM suite to be a flexible tool that helps control and manage the business processes. Rules should be easy to update and change to make certain that any feedback from the monitoring tools can be used to further improve the processes. This all leads to a continuous cycle of evaluating and improving the organization.

Don’t you just love buzz words and abbreviations? Abbreviations come in handy in many situations but often confuse people not experienced with business process management.

Some of the most common concepts/abbreviations you will see are the following:

BPM – Business Process Management
BPA – Business Process Analysis
BPMN – Business Process Modeling Language
EA – Enterprise Architecture
BPMS – Business Process Management Suite

BPM is an abbreviation for Business Process Management and refers to the management discipline where the approach is managing the processes. Often BPM is just an umbrella under which you handle various things regarding business processes. Usually when people talk about BPM they refer to AS-IS and TO-BE analysis of processes.

However, analysing your existing processes, documenting the analysis as AS-IS process diagrams and then designing the TO-BE processes is BPA –>Business Process Analysis (notice that BPA is also a part of BPM). Business Process Analysis (BPA) is about analysing the business needs and identify the business process requirements. In BPA the output is process analysis and business requirements – usually the output is captured in process diagrams drawn in modelling tools using for example BPMN as the modelling syntax.

BPMN (Business Process Modeling Notation) is simply a collection of graphical shapes you can use for drawing business process diagrams where the business process diagram is a sequence of business processes connected by control/message directions. Below is shown an example of a process drawn with the BPMN notation. The example is drawn in Microsoft Visio. If you want to draw BPMN diagrams in Visio a Visio BPMN Stencil can be found here (http://www.omg.org/bpmn/documents.htm)

The Visio Stencil contains BPMN figures as shown here:

Enterprise Architecture is a logical structure (architecture) of an enterprise. In enterprise architecture you design how the logical structure and often enterprise architecture is producing logical structural outputs of how the business structure should be – for example using UML structural diagrams such as Class diagrams and component diagrams. Usually enterprise architecture is produced using a modelling tool. In enterprise architecture you design how you business structure should be while in Business Process Analysis you analyse the “problem” and design the business processes”.

BPMS Business Process Management Suite is a suite of applications that can execute your designed business processes. BPMS is both a design-time and run-time environment. In a BPMS you will have a model-driven approach and you will be able to design and orchestrate your business processes and business rules and have them executed in run-time. BPMS is excellent for letting the business drive business changes and BPMS is excellent for workflows especially long workflows (more than 1 hour processing time).

To summarise, as you can see from the figure below the concepts are used for different purposes. When doing Business Process Analysis you are in a conceptual level designing how the processes should be outlined. When moving on to Enterprise Architecture you are on a logical level designing how the structure should be in order to support the conceptual design of business processes. Finally on implementation level you can manage and orchestrate how business processes and business rules are executed. However, please notice that there are some overlap between the various concepts – e.g. requirements are not just captured by one concept alone.

PHP techniques to save your time and effort

samira — Sat, 20 Aug 2011 15:07:19 +0000

1. How to Properly Create a Website Index Page

Creating your website index page is the first thing to do for every website that you create. I’ve actually created a post that will help you properly create a website index page.

2. Use the Request Global Array to Grab Data

There is actually no reason to use $_GET and $_POST arrays to grab values. $_REQUEST, is another global array that fetches you either a get or form request. Therefore, it’s most times more convenient to use something like this to parse data :

$action = isset($_REQUEST['action']) ? $_REQUEST['action'] : 0;

3. Debugging PHP is About var_dump

If you’re looking for php debugging techniques, i have to say that var_dump is most times the way to go about it. This command is all you need to echo php information. There shouldn’t really be many cases where you need anything more than dumping values in PHP, in order to debug your code.

4. PHP Handles The Code Logic, Smarty Handles The Presentation

I think i’ve said this many times before, but Smarty usage (or other template system), is critical for creating organized PHP code. Learn to use smarty as a template engine for your websites, it will pay off, i promise.

5. When You Absolutely Need Global Values, Create a Config File

It is a bad practice to create global values for everything. There are limited cases where you would actually need to do so. Doing it for database tables or database connection information is a good idea, but do not use global variables throughout your PHP code. Moreover, it is always a better idea to keep your global variables at a single config.php file.

6. If NOT Defined, Access Denied !

If you’re creating your pages the correct way, there will absolutely no reason for anybody to access any other php page other than index.php or home.php. The idea is that once index.php is accessed, you utilize get variables in order to open the needed pages. Your index page should contain something like :

define('yourPage',1);

Then, your other pages should contain this :

if (!defined('yourPage')) die('Access Denied');

What this does, is preventing direct access to your other php pages. Therefore, any user who tries to access your other web pages, not through index.php, gets an “Access Denied” message.

7. Create a Database Class

If you’re doing database programming (pretty common in PHP), it would be a very good idea to create a database class to handle any database management functions. A good way to do it is by creating functions like :

public function dbExec($query)

{

$result = $this->db->exec($query);

if (PEAR::isError($result))

errorRedirect($result->getMessage(), true);

else

return $result;

}

This is an example function from an actual project i’m creating. This one just receives a query and executes it. It also handles any errors that may occur. You could also include sanitization code here, but i prefer to do it using a sanitization function like :

// checks if arguments given are integer values not less than 0 - has multiple arguments

function sanitizeInput()

{

$numargs = func_num_args();

$arg_list = func_get_args();

for ($i = 0; $i < $numargs; $i++) {

if (!is_numeric($arg_list[$i]) || $arg_list[$i] < 0)

errorRedirect("Unexpected variable value", true);

}

8. A php File Handles Input, a class.php File Handles Functionality

It is pretty important that you learn not to mess the code that retrieves user input and redirects it to any functions, with those actual functions. The idea is pretty simple. The php file gets any input that we need and then redirects execution to a function residing to the class file. For example, let’s suppose that a url is like “index.php?page=profile&action=display”. The profile.php file retrieves the url and gets that action is “display”. Then, using a simple switch, we execute the actual display function like :

require_once PROJECTROOT.'libs/messages.class.php';

$message = new Message();

switch ($action)

{

case 'display':

$message->display();

break;

...

Again, this is part of a project that i create. You see that i include the messages class and then initiate the switch check. $message is just an object that is used to call functions inside the class.

9. Know Your SQL and Always Sanitize

As i mentioned before, a database is 99% of times important for any php created website. Therefore, you need to know many things about how to use sql properly. Learn to combine tables and more advanced techniques. I promise there will be mysql tutorials soon in codercaste.com. Let me present you an example of a function that uses mySQL and sanitazes using the function seen on point #7 :

private function getSentMessages($id)

{

$this->util->sanitizeInput($id);

$pm_table = $GLOBALS['config']['privateMsg'];

$users = $GLOBALS['config']['users'];

$sql = "SELECT PM.*, USR.username as name_sender FROM $pm_table PM, $users USR

WHERE id_sender = '$id' AND sender_purge = FALSE AND USR.id = PM.id_receiver AND is_read = TRUE

ORDER BY date_sent DESC";

$result = $this->dbQueryAll($sql);

return $result;

}

At first, we sanitize the user input (the message id at this point, that is passed through a GET variable) and then we execute our sql command. Notice the usage of sql here. You need to learn how to use aliases and combine tables.

10. When You Need Just an Object, Use a Singleton Pattern

It happens pretty often in PHP that we just need a single object created one time and then used globally throughout our whole program. A good example of this is the smarty variable that has to be initialized once and then is used all over the place. A good way to do that is a Singleton pattern, where an object is just created once and for all. The way to do this is like :

function smartyObject()

{

if ($GLOBALS['config']['SmartyObj'] == 0)

{

$smarty = new SmartyGame();

$GLOBALS['config']['SmartyObj'] = $smarty;

}

else

$smarty = $GLOBALS['config']['SmartyObj'];

return $smarty;

}

Notice that we have a global smarty variable (initialized in config.php in example) and if it equals 0, we go about creating a new smarty object. If not, it means that the object is already created and we just need to return it.

Speeding Up Your Web Site

samira — Mon, 27 Jun 2011 14:35:17 +0000

Minimize HTTP Requests

tag: content

80% of the end-user response time is spent on the front-end. Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Reducing the number of components in turn reduces the number of HTTP requests required to render the page. This is the key to faster pages.

One way to reduce the number of components in the page is to simplify the page’s design. But is there a way to build pages with richer content while also achieving fast response times? Here are some techniques for reducing the number of HTTP requests, while still supporting rich page designs.

Combined files are a way to reduce the number of HTTP requests by combining all scripts into a single script, and similarly combining all CSS into a single stylesheet. Combining files is more challenging when the scripts and stylesheets vary from page to page, but making this part of your release process improves response times.

CSS Sprites are the preferred method for reducing the number of image requests. Combine your background images into a single image and use the CSS background-image and background-position properties to display the desired image segment.

Image maps combine multiple images into a single image. The overall size is about the same, but reducing the number of HTTP requests speeds up the page. Image maps only work if the images are contiguous in the page, such as a navigation bar. Defining the coordinates of image maps can be tedious and error prone. Using image maps for navigation is not accessible too, so it’s not recommended.

Inline images use the data: URL scheme to embed the image data in the actual page. This can increase the size of your HTML document. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages. Inline images are not yet supported across all major browsers.

Reducing the number of HTTP requests in your page is the place to start. This is the most important guideline for improving performance for first time visitors. As described in Tenni Theurer’s blog postBrowser Cache Usage – Exposed!, 40-60% of daily visitors to your site come in with an empty cache. Making your page fast for these first time visitors is key to a better user experience.

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Use a Content Delivery Network

tag: server

The user’s proximity to your web server has an impact on response times. Deploying your content across multiple, geographically dispersed servers will make your pages load faster from the user’s perspective. But where should you start?

As a first step to implementing geographically dispersed content, don’t attempt to redesign your web application to work in a distributed architecture. Depending on the application, changing the architecture could include daunting tasks such as synchronizing session state and replicating database transactions across server locations. Attempts to reduce the distance between users and your content could be delayed by, or never pass, this application architecture step.

Remember that 80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc. This is the Performance Golden Rule. Rather than starting with the difficult task of redesigning your application architecture, it’s better to first disperse your static content. This not only achieves a bigger reduction in response times, but it’s easier thanks to content delivery networks.

A content delivery network (CDN) is a collection of web servers distributed across multiple locations to deliver content more efficiently to users. The server selected for delivering content to a specific user is typically based on a measure of network proximity. For example, the server with the fewest network hops or the server with the quickest response time is chosen.

Some large Internet companies own their own CDN, but it’s cost-effective to use a CDN service provider, such as Akamai Technologies, EdgeCast, or level3. For start-up companies and private web sites, the cost of a CDN service can be prohibitive, but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times. At Yahoo!, properties that moved static content off their application web servers to a CDN (both 3rd party as mentioned above as well as Yahoo’s own CDN) improved end-user response times by 20% or more. Switching to a CDN is a relatively easy code change that will dramatically improve the speed of your web site.

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Add an Expires or a Cache-Control Header

tag: server

There are two aspects to this rule:

For static components: implement “Never expire” policy by setting far future Expires header
For dynamic components: use an appropriate Cache-Control header to help the browser with conditional requests

Web page designs are getting richer and richer, which means more scripts, stylesheets, images, and Flash in the page. A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable. This avoids unnecessary HTTP requests on subsequent page views. Expires headers are most often used with images, but they should be used onall components including scripts, stylesheets, and Flash components.

Browsers (and proxies) use a cache to reduce the number and size of HTTP requests, making web pages load faster. A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached. This is a far future Expires header, telling the browser that this response won’t be stale until April 15, 2010.

      Expires: Thu, 15 Apr 2010 20:00:00 GMT

If your server is Apache, use the ExpiresDefault directive to set an expiration date relative to the current date. This example of the ExpiresDefault directive sets the Expires date 10 years out from the time of the request.

      ExpiresDefault "access plus 10 years"

Keep in mind, if you use a far future Expires header you have to change the component’s filename whenever the component changes. At Yahoo! we often make this step part of the build process: a version number is embedded in the component’s filename, for example, yahoo_2.0.6.js.

Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser’s cache is empty. Therefore the impact of this performance improvement depends on how often users hit your pages with a primed cache. (A “primed cache” already contains all of the components in the page.) We measured this at Yahoo! and found the number of page views with a primed cache is 75-85%. By using a far future Expires header, you increase the number of components that are cached by the browser and re-used on subsequent page views without sending a single byte over the user’s Internet connection.

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Gzip Components

tag: server

The time it takes to transfer an HTTP request and response across the network can be significantly reduced by decisions made by front-end engineers. It’s true that the end-user’s bandwidth speed, Internet service provider, proximity to peering exchange points, etc. are beyond the control of the development team. But there are other variables that affect response times. Compression reduces response times by reducing the size of the HTTP response.

Starting with HTTP/1.1, web clients indicate support for compression with the Accept-Encoding header in the HTTP request.

      Accept-Encoding: gzip, deflate

If the web server sees this header in the request, it may compress the response using one of the methods listed by the client. The web server notifies the web client of this via the Content-Encoding header in the response.

      Content-Encoding: gzip

Gzip is the most popular and effective compression method at this time. It was developed by the GNU project and standardized by RFC 1952. The only other compression format you’re likely to see is deflate, but it’s less effective and less popular.

Gzipping generally reduces the response size by about 70%. Approximately 90% of today’s Internet traffic travels through browsers that claim to support gzip. If you use Apache, the module configuring gzip depends on your version: Apache 1.3 uses mod_gzip while Apache 2.x uses mod_deflate.

There are known issues with browsers and proxies that may cause a mismatch in what the browser expects and what it receives with regard to compressed content. Fortunately, these edge cases are dwindling as the use of older browsers drops off. The Apache modules help out by adding appropriate Vary response headers automatically.

Servers choose what to gzip based on file type, but are typically too limited in what they decide to compress. Most web sites gzip their HTML documents. It’s also worthwhile to gzip your scripts and stylesheets, but many web sites miss this opportunity. In fact, it’s worthwhile to compress any text response including XML and JSON. Image and PDF files should not be gzipped because they are already compressed. Trying to gzip them not only wastes CPU but can potentially increase file sizes.

Gzipping as many file types as possible is an easy way to reduce page weight and accelerate the user experience.

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Put Stylesheets at the Top

tag: css

While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages appear to be loading faster. This is because putting stylesheets in the HEAD allows the page to render progressively.

Front-end engineers that care about performance want a page to load progressively; that is, we want the browser to display whatever content it has as soon as possible. This is especially important for pages with a lot of content and for users on slower Internet connections. The importance of giving users visual feedback, such as progress indicators, has been well researched and documented. In our case the HTML page is the progress indicator! When the browser loads the page progressively the header, the navigation bar, the logo at the top, etc. all serve as visual feedback for the user who is waiting for the page. This improves the overall user experience.

The problem with putting stylesheets near the bottom of the document is that it prohibits progressive rendering in many browsers, including Internet Explorer. These browsers block rendering to avoid having to redraw elements of the page if their styles change. The user is stuck viewing a blank white page.

The HTML specification clearly states that stylesheets are to be included in the HEAD of the page: “Unlike A, [LINK] may only appear in the HEAD section of a document, although it may appear any number of times.” Neither of the alternatives, the blank white screen or flash of unstyled content, are worth the risk. The optimal solution is to follow the HTML specification and load your stylesheets in the document HEAD.

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Put Scripts at the Bottom

tag: javascript

The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specificationsuggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won’t start any other downloads, even on different hostnames.

In some situations it’s not easy to move scripts to the bottom. If, for example, the script usesdocument.write to insert part of the page’s content, it can’t be moved lower in the page. There might also be scoping issues. In many cases, there are ways to workaround these situations.

An alternative suggestion that often comes up is to use deferred scripts. The DEFER attribute indicates that the script does not contain document.write, and is a clue to browsers that they can continue rendering. Unfortunately, Firefox doesn’t support the DEFER attribute. In Internet Explorer, the script may be deferred, but not as much as desired. If a script can be deferred, it can also be moved to the bottom of the page. That will make your web pages load faster.

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Avoid CSS Expressions

tag: css

CSS expressions are a powerful (and dangerous) way to set CSS properties dynamically. They were supported in Internet Explorer starting with version 5, but were deprecated starting with IE8. As an example, the background color could be set to alternate every hour using CSS expressions:

      background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );

As shown here, the expression method accepts a JavaScript expression. The CSS property is set to the result of evaluating the JavaScript expression. The expression method is ignored by other browsers, so it is useful for setting properties in Internet Explorer needed to create a consistent experience across browsers.

The problem with expressions is that they are evaluated more frequently than most people expect. Not only are they evaluated when the page is rendered and resized, but also when the page is scrolled and even when the user moves the mouse over the page. Adding a counter to the CSS expression allows us to keep track of when and how often a CSS expression is evaluated. Moving the mouse around the page can easily generate more than 10,000 evaluations.

One way to reduce the number of times your CSS expression is evaluated is to use one-time expressions, where the first time the expression is evaluated it sets the style property to an explicit value, which replaces the CSS expression. If the style property must be set dynamically throughout the life of the page, using event handlers instead of CSS expressions is an alternative approach. If you must use CSS expressions, remember that they may be evaluated thousands of times and could affect the performance of your page.

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Make JavaScript and CSS External

tag: javascript, css

Many of these performance rules deal with how external components are managed. However, before these considerations arise you should ask a more basic question: Should JavaScript and CSS be contained in external files, or inlined in the page itself?

Using external files in the real world generally produces faster pages because the JavaScript and CSS files are cached by the browser. JavaScript and CSS that are inlined in HTML documents get downloaded every time the HTML document is requested. This reduces the number of HTTP requests that are needed, but increases the size of the HTML document. On the other hand, if the JavaScript and CSS are in external files cached by the browser, the size of the HTML document is reduced without increasing the number of HTTP requests.

The key factor, then, is the frequency with which external JavaScript and CSS components are cached relative to the number of HTML documents requested. This factor, although difficult to quantify, can be gauged using various metrics. If users on your site have multiple page views per session and many of your pages re-use the same scripts and stylesheets, there is a greater potential benefit from cached external files.

Many web sites fall in the middle of these metrics. For these sites, the best solution generally is to deploy the JavaScript and CSS as external files. The only exception where inlining is preferable is with home pages, such as Yahoo!’s front page and My Yahoo!. Home pages that have few (perhaps only one) page view per session may find that inlining JavaScript and CSS results in faster end-user response times.

For front pages that are typically the first of many page views, there are techniques that leverage the reduction of HTTP requests that inlining provides, as well as the caching benefits achieved through using external files. One such technique is to inline JavaScript and CSS in the front page, but dynamically download the external files after the page has finished loading. Subsequent pages would reference the external files that should already be in the browser’s cache.

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Reduce DNS Lookups

tag: content

The Domain Name System (DNS) maps hostnames to IP addresses, just as phonebooks map people’s names to their phone numbers. When you type www.yahoo.com into your browser, a DNS resolver contacted by the browser returns that server’s IP address. DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname. The browser can’t download anything from this hostname until the DNS lookup is completed.

DNS lookups are cached for better performance. This caching can occur on a special caching server, maintained by the user’s ISP or local area network, but there is also caching that occurs on the individual user’s computer. The DNS information remains in the operating system’s DNS cache (the “DNS Client service” on Microsoft Windows). Most browsers have their own caches, separate from the operating system’s cache. As long as the browser keeps a DNS record in its own cache, it doesn’t bother the operating system with a request for the record.

Internet Explorer caches DNS lookups for 30 minutes by default, as specified by the DnsCacheTimeoutregistry setting. Firefox caches DNS lookups for 1 minute, controlled by thenetwork.dnsCacheExpiration configuration setting. (Fasterfox changes this to 1 hour.)

When the client’s DNS cache is empty (for both the browser and the operating system), the number of DNS lookups is equal to the number of unique hostnames in the web page. This includes the hostnames used in the page’s URL, images, script files, stylesheets, Flash objects, etc. Reducing the number of unique hostnames reduces the number of DNS lookups.

Reducing the number of unique hostnames has the potential to reduce the amount of parallel downloading that takes place in the page. Avoiding DNS lookups cuts response times, but reducing parallel downloads may increase response times. My guideline is to split these components across at least two but no more than four hostnames. This results in a good compromise between reducing DNS lookups and allowing a high degree of parallel downloads.

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Minify JavaScript and CSS

tag: javascript, css

Minification is the practice of removing unnecessary characters from code to reduce its size thereby improving load times. When code is minified all comments are removed, as well as unneeded white space characters (space, newline, and tab). In the case of JavaScript, this improves response time performance because the size of the downloaded file is reduced. Two popular tools for minifying JavaScript code areJSMin and YUI Compressor. The YUI compressor can also minify CSS.

Obfuscation is an alternative optimization that can be applied to source code. It’s more complex than minification and thus more likely to generate bugs as a result of the obfuscation step itself. In a survey of ten top U.S. web sites, minification achieved a 21% size reduction versus 25% for obfuscation. Although obfuscation has a higher size reduction, minifying JavaScript is less risky.

In addition to minifying external scripts and styles, inlined


An alternative in PHP would be to create a function called insertScript.
      
 
In addition to preventing the same script from being inserted multiple times, this function could handle other issues with scripts, such as dependency checking and adding version numbers to script filenames to support far future Expires headers.
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Configure ETags
tag: server
Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser’s cache matches the one on the origin server. (An “entity” is another word a “component”: images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date. An ETag is a string that uniquely identifies a specific version of a component. The only format constraints are that the string be quoted. The origin server specifies the component’s ETag using the ETag response header.
      HTTP/1.1 200 OK
      Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
      ETag: "10c24bc-4ab-457e1c1f"
      Content-Length: 12195
 
Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.
      GET /i/yahoo.gif HTTP/1.1
      Host: us.yimg.com
      If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
      If-None-Match: "10c24bc-4ab-457e1c1f"
      HTTP/1.1 304 Not Modified
 
The problem with ETags is that they typically are constructed using attributes that make them unique to a specific server hosting a site. ETags won’t match when a browser gets the original component from one server and later tries to validate that component on a different server, a situation that is all too common on Web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.
The ETag format for Apache 1.3 and 2.x is inode-size-timestamp. Although a given file may reside in the same directory across multiple servers, and have the same file size, permissions, timestamp, etc., its inode is different from one server to the next.
IIS 5.0 and 6.0 have a similar issue with ETags. The format for ETags on IIS isFiletimestamp:ChangeNumber. A ChangeNumber is a counter used to track configuration changes to IIS. It’s unlikely that the ChangeNumber is the same across all IIS servers behind a web site.
The end result is ETags generated by Apache and IIS for the exact same component won’t match from one server to another. If the ETags don’t match, the user doesn’t receive the small, fast 304 response that ETags were designed for; instead, they’ll get a normal 200 response along with all the data for the component. If you host your web site on just one server, this isn’t a problem. But if you have multiple servers hosting your web site, and you’re using Apache or IIS with the default ETag configuration, your users are getting slower pages, your servers have a higher load, you’re consuming greater bandwidth, and proxies aren’t caching your content efficiently. Even if your components have a far future Expiresheader, a conditional GET request is still made whenever the user hits Reload or Refresh.
If you’re not taking advantage of the flexible validation model that ETags provide, it’s better to just remove the ETag altogether. The Last-Modified header validates based on the component’s timestamp. And removing the ETag reduces the size of the HTTP headers in both the response and subsequent requests. This Microsoft Support article describes how to remove ETags. In Apache, this is done by simply adding the following line to your Apache configuration file:
      FileETag none
 
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Make Ajax Cacheable
tag: content
One of the cited benefits of Ajax is that it provides instantaneous feedback to the user because it requests information asynchronously from the backend web server. However, using Ajax is no guarantee that the user won’t be twiddling his thumbs waiting for those asynchronous JavaScript and XML responses to return. In many applications, whether or not the user is kept waiting depends on how Ajax is used. For example, in a web-based email client the user will be kept waiting for the results of an Ajax request to find all the email messages that match their search criteria. It’s important to remember that “asynchronous” does not imply “instantaneous”.
To improve performance, it’s important to optimize these Ajax responses. The most important way to improve the performance of Ajax is to make the responses cacheable, as discussed in Add an Expires or a Cache-Control Header. Some of the other rules also apply to Ajax:

Gzip Components
Reduce DNS Lookups
Minify JavaScript
Avoid Redirects
Configure ETags

 
 
Let’s look at an example. A Web 2.0 email client might use Ajax to download the user’s address book for autocompletion. If the user hasn’t modified her address book since the last time she used the email web app, the previous address book response could be read from cache if that Ajax response was made cacheable with a future Expires or Cache-Control header. The browser must be informed when to use a previously cached address book response versus requesting a new one. This could be done by adding a timestamp to the address book Ajax URL indicating the last time the user modified her address book, for example, &t=1190241612. If the address book hasn’t been modified since the last download, the timestamp will be the same and the address book will be read from the browser’s cache eliminating an extra HTTP roundtrip. If the user has modified her address book, the timestamp ensures the new URL doesn’t match the cached response, and the browser will request the updated address book entries.
Even though your Ajax responses are created dynamically, and might only be applicable to a single user, they can still be cached. Doing so will make your Web 2.0 apps faster.
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Flush the Buffer Early
tag: server
When users request a page, it can take anywhere from 200 to 500ms for the backend server to stitch together the HTML page. During this time, the browser is idle as it waits for the data to arrive. In PHP you have the function flush(). It allows you to send your partially ready HTML response to the browser so that the browser can start fetching components while your backend is busy with the rest of the HTML page. The benefit is mainly seen on busy backends or light frontends.
A good place to consider flushing is right after the HEAD because the HTML for the head is usually easier to produce and it allows you to include any CSS and JavaScript files for the browser to start fetching in parallel while the backend is still processing.
Example:
      ... 
    
    
    
      ... 
 
Yahoo! search pioneered research and real user testing to prove the benefits of using this technique.
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Use GET for AJAX Requests
tag: server
The Yahoo! Mail team found that when using XMLHttpRequest, POST is implemented in the browsers as a two-step process: sending the headers first, then sending data. So it’s best to use GET, which only takes one TCP packet to send (unless you have a lot of cookies). The maximum URL length in IE is 2K, so if you send more than 2K data you might not be able to use GET.
An interesting side affect is that POST without actually posting any data behaves like GET. Based on theHTTP specs, GET is meant for retrieving information, so it makes sense (semantically) to use GET when you’re only requesting data, as opposed to sending data to be stored server-side.
 
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Post-load Components
tag: content
You can take a closer look at your page and ask yourself: “What’s absolutely required in order to render the page initially?”. The rest of the content and components can wait.
JavaScript is an ideal candidate for splitting before and after the onload event. For example if you have JavaScript code and libraries that do drag and drop and animations, those can wait, because dragging elements on the page comes after the initial rendering. Other places to look for candidates for post-loading include hidden content (content that appears after a user action) and images below the fold.
Tools to help you out in your effort: YUI Image Loader allows you to delay images below the fold and theYUI Get utility is an easy way to include JS and CSS on the fly. For an example in the wild take a look atYahoo! Home Page with Firebug’s Net Panel turned on.
It’s good when the performance goals are inline with other web development best practices. In this case, the idea of progressive enhancement tells us that JavaScript, when supported, can improve the user experience but you have to make sure the page works even without JavaScript. So after you’ve made sure the page works fine, you can enhance it with some post-loaded scripts that give you more bells and whistles such as drag and drop and animations.
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Preload Components
tag: content
Preload may look like the opposite of post-load, but it actually has a different goal. By preloading components you can take advantage of the time the browser is idle and request components (like images, styles and scripts) you’ll need in the future. This way when the user visits the next page, you could have most of the components already in the cache and your page will load much faster for the user.
There are actually several types of preloading:

Unconditional preload – as soon as onload fires, you go ahead and fetch some extra components. Check google.com for an example of how a sprite image is requested onload. This sprite image is not needed on the google.com homepage, but it is needed on the consecutive search result page.
Conditional preload – based on a user action you make an educated guess where the user is headed next and preload accordingly. On search.yahoo.com you can see how some extra components are requested after you start typing in the input box.
Anticipated preload – preload in advance before launching a redesign. It often happens after a redesign that you hear: “The new site is cool, but it’s slower than before”. Part of the problem could be that the users were visiting your old site with a full cache, but the new one is always an empty cache experience. You can mitigate this side effect by preloading some components before you even launched the redesign. Your old site can use the time the browser is idle and request images and scripts that will be used by the new site

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Reduce the Number of DOM Elements
tag: content
A complex page means more bytes to download and it also means slower DOM access in JavaScript. It makes a difference if you loop through 500 or 5000 DOM elements on the page when you want to add an event handler for example.
A high number of DOM elements can be a symptom that there’s something that should be improved with the markup of the page without necessarily removing content. Are you using nested tables for layout purposes? Are you throwing in more 
s only to fix layout issues? Maybe there’s a better and more semantically correct way to do your markup.
A great help with layouts are the YUI CSS utilities: grids.css can help you with the overall layout, fonts.css and reset.css can help you strip away the browser’s defaults formatting. This is a chance to start fresh and think about your markup, for example use 
s only when it makes sense semantically, and not because it renders a new line.
The number of DOM elements is easy to test, just type in Firebug’s console:

document.getElementsByTagName('*').length
And how many DOM elements are too many? Check other similar pages that have good markup. For example the Yahoo! Home Page is a pretty busy page and still under 700 elements (HTML tags).
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Split Components Across Domains
tag: content
Splitting components allows you to maximize parallel downloads. Make sure you’re using not more than 2-4 domains because of the DNS lookup penalty. For example, you can host your HTML and dynamic content on www.example.org and split static components between static1.example.org andstatic2.example.org
For more information check “Maximizing Parallel Downloads in the Carpool Lane” by Tenni Theurer and Patty Chi.
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Minimize the Number of iframes
tag: content
Iframes allow an HTML document to be inserted in the parent document. It’s important to understand how iframes work so they can be used effectively.
 pros:

Helps with slow third-party content like badges and ads
Security sandbox
Download scripts in parallel

 cons:

Costly even if blank
Blocks page onload
Non-semantic

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No 404s
tag: content
HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found) is totally unnecessary and will slow down the user experience without any benefit.
Some sites have helpful 404s “Did you mean X?”, which is great for the user experience but also wastes server resources (like database, etc). Particularly bad is when the link to an external JavaScript is wrong and the result is a 404. First, this download will block parallel downloads. Next the browser may try to parse the 404 response body as if it were JavaScript code, trying to find something usable in it.
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Reduce Cookie Size
tag: cookie
HTTP cookies are used for a variety of reasons such as authentication and personalization. Information about cookies is exchanged in the HTTP headers between web servers and browsers. It’s important to keep the size of cookies as low as possible to minimize the impact on the user’s response time.
For more information check “When the Cookie Crumbles” by Tenni Theurer and Patty Chi. The take-home of this research:
 

Eliminate unnecessary cookies
Keep cookie sizes as low as possible to minimize the impact on the user response time
Be mindful of setting cookies at the appropriate domain level so other sub-domains are not affected
Set an Expires date appropriately. An earlier Expires date or none removes the cookie sooner, improving the user response time

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Use Cookie-free Domains for Components
tag: cookie
When the browser makes a request for a static image and sends cookies together with the request, the server doesn’t have any use for those cookies. So they only create network traffic for no good reason. You should make sure static components are requested with cookie-free requests. Create a subdomain and host all your static components there.
If your domain is www.example.org, you can host your static components onstatic.example.org. However, if you’ve already set cookies on the top-level domain example.orgas opposed to www.example.org, then all the requests to static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com, Amazon uses images-amazon.com and so on.
Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache the components that are requested with cookies. On a related note, if you wonder if you should use example.org or www.example.org for your home page, consider the cookie impact. Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it’s best to use the www subdomain and write the cookies to that subdomain.
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Minimize DOM Access
tag: javascript
Accessing DOM elements with JavaScript is slow so in order to have a more responsive page, you should:

Cache references to accessed elements
Update nodes “offline” and then add them to the tree
Avoid fixing layout with JavaScript

For more information check the YUI theatre’s “High Performance Ajax Applications” by Julien Lecomte.
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Develop Smart Event Handlers
tag: javascript
Sometimes pages feel less responsive because of too many event handlers attached to different elements of the DOM tree which are then executed too often. That’s why using event delegation is a good approach. If you have 10 buttons inside a div, attach only one event handler to the div wrapper, instead of one handler for each button. Events bubble up so you’ll be able to catch the event and figure out which button it originated from.
You also don’t need to wait for the onload event in order to start doing something with the DOM tree. Often all you need is the element you want to access to be available in the tree. You don’t have to wait for all images to be downloaded. DOMContentLoaded is the event you might consider using instead of onload, but until it’s available in all browsers, you can use the YUI Event utility, which has anonAvailable method.
For more information check the YUI theatre’s “High Performance Ajax Applications” by Julien Lecomte.
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Choose  over @import
tag: css
One of the previous best practices states that CSS should be at the top in order to allow for progressive rendering.
In IE @import behaves the same as using  at the bottom of the page, so it’s best not to use it.
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Avoid Filters
tag: css
The IE-proprietary AlphaImageLoader filter aims to fix a problem with semi-transparent true color PNGs in IE versions < 7. The problem with this filter is that it blocks rendering and freezes the browser while the image is being downloaded. It also increases memory consumption and is applied per element, not per image, so the problem is multiplied.
The best approach is to avoid AlphaImageLoader completely and use gracefully degrading PNG8 instead, which are fine in IE. If you absolutely need AlphaImageLoader, use the underscore hack_filter as to not penalize your IE7+ users.
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Optimize Images
tag: images
After a designer is done with creating the images for your web page, there are still some things you can try before you FTP those images to your web server.

You can check the GIFs and see if they are using a palette size corresponding to the number of colors in the image. Using imagemagick it’s easy to check using

identify -verbose image.gif

When you see an image useing 4 colors and a 256 color “slots” in the palette, there is room for improvement.
Try converting GIFs to PNGs and see if there is a saving. More often than not, there is. Developers often hesitate to use PNGs due to the limited support in browsers, but this is now a thing of the past. The only real problem is alpha-transparency in true color PNGs, but then again, GIFs are not true color and don’t support variable transparency either. So anything a GIF can do, a palette PNG (PNG8) can do too (except for animations). This simple imagemagick command results in totally safe-to-use PNGs:

convert image.gif image.png

“All we are saying is: Give PiNG a Chance!”
Run pngcrush (or any other PNG optimizer tool) on all your PNGs. Example:

pngcrush image.png -rem alla -reduce -brute result.png
Run jpegtran on all your JPEGs. This tool does lossless JPEG operations such as rotation and can also be used to optimize and remove comments and other useless information (such as EXIF information) from your images.

jpegtran -copy none -optimize -perfect src.jpg dest.jpg

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Optimize CSS Sprites
tag: images

Arranging the images in the sprite horizontally as opposed to vertically usually results in a smaller file size.
Combining similar colors in a sprite helps you keep the color count low, ideally under 256 colors so to fit in a PNG8.
“Be mobile-friendly” and don’t leave big gaps between the images in a sprite. This doesn’t affect the file size as much but requires less memory for the user agent to decompress the image into a pixel map. 100×100 image is 10 thousand pixels, where 1000×1000 is 1 million pixels

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Don’t Scale Images in HTML
tag: images
Don’t use a bigger image than you need just because you can set the width and height in HTML. If you need



then your image (mycat.jpg) should be 100x100px rather than a scaled down 500x500px image.
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Make favicon.ico Small and Cacheable
tag: images
The favicon.ico is an image that stays in the root of your server. It’s a necessary evil because even if you don’t care about it the browser will still request it, so it’s better not to respond with a 404 Not Found. Also since it’s on the same server, cookies are sent every time it’s requested. This image also interferes with the download sequence, for example in IE when you request extra components in the onload, the favicon will be downloaded before these extra components.
So to mitigate the drawbacks of having a favicon.ico make sure:

It’s small, preferably under 1K.
Set Expires header with what you feel comfortable (since you cannot rename it if you decide to change it). You can probably safely set the Expires header a few months in the future. You can check the last modified date of your current favicon.ico to make an informed decision.

Imagemagick can help you create small favicons
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Keep Components under 25K
tag: mobile
This restriction is related to the fact that iPhone won’t cache components bigger than 25K. Note that this is the uncompressed size. This is where minification is important because gzip alone may not be sufficient.
For more information check “Performance Research, Part 5: iPhone Cacheability – Making it Stick” by Wayne Shea and Tenni Theurer.
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Pack Components into a Multipart Document
tag: mobile
Packing components into a multipart document is like an email with attachments, it helps you fetch several components with one HTTP request (remember: HTTP requests are expensive). When you use this technique, first check if the user agent supports it (iPhone does not).
Avoid Empty Image src
tag: server
Image with empty string src attribute occurs more than one will expect. It appears in two form:

straight HTML



JavaScript

var img = new Image();

img.src = “”;


 
Both forms cause the same effect: browser makes another request to your server.

Internet Explorer makes a request to the directory in which the page is located.
Safari and Chrome make a request to the actual page itself.
Firefox 3 and earlier versions behave the same as Safari and Chrome, but version 3.5 addressed this issue[bug 444931] and no longer sends a request.
Opera does not do anything when an empty image src is encountered.

 
 
Why is this behavior bad?

Cripple your servers by sending a large amount of unexpected traffic, especially for pages that get millions of page views per day.
Waste server computing cycles generating a page that will never be viewed.
Possibly corrupt user data. If you are tracking state in the request, either by cookies or in another way, you have the possibility of destroying data. Even though the image request does not return an image, all of the headers are read and accepted by the browser, including all cookies. While the rest of the response is thrown away, the damage may already be done.

 
 
The root cause of this behavior is the way that URI resolution is performed in browsers. This behavior is defined in RFC 3986 – Uniform Resource Identifiers. When an empty string is encountered as a URI, it is considered a relative URI and is resolved according to the algorithm defined in section 5.2. This specific example, an empty string, is listed in section 5.4. Firefox, Safari, and Chrome are all resolving an empty string correctly per the specification, while Internet Explorer is resolving it incorrectly, apparently in line with an earlier version of the specification, RFC 2396 – Uniform Resource Identifiers (this was obsoleted by RFC 3986). So technically, the browsers are doing what they are supposed to do to resolve relative URIs. The problem is that in this context, the empty string is clearly unintentional.
HTML5 adds to the description of the  tag’s src attribute to instruct browsers not to make an additional request in section 4.8.2:
The src attribute must be present, and must contain a valid URL referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted. If the base URI of the element is the same as the document’s address, then the src attribute’s value must not be the empty string.
Hopefully, browsers will not have this problem in the future. Unfortunately, there is no such clause for