Cyril Dangerville

A blog is a website first and foremost, i.e. a blog is a bunch of webpages hosted on a HTTP (HyperText Transfer Protocol) server.
Footnote
{
HTTP is indeed the request/response protocol used between the client (typically your web browser) and the server to receive webpages for the end-user. (HTTP is an application-layer protocol.)
}

There are two HTTP servers that dominate the market: Apache (70%) and IIS (Internet Information Services).
Footnote
{
Apache is open source, lead by the Apache software foundation and sponsored by IBM. IIS is proprietary, edited by Microsoft.
}

To understand how blogs work, you need to understand the client-server model which is at the foundation of all Internet services. The most common version of it is the 3-tier client-server model. Below are figures about the 3 tier client-server architecture and the real version of it.

The client (browser) requests for the web page stored on the remote machine through the server software. The server locates this file, then...

• Case 1: the webpage is a static webpage (extension html, htm), which means it is created once and for all. The content does not change unless the webmaster (or anybody allowed to) deigns to change it. In this case, the server just sends it to the browser. The browser then interprets the the HTML (HyperText Markup Language) or XHTML (eXtensible HTML, that is to replace HTML) code of the page and displays this file on your machine.

• Case 2: the webpage is dynamic (extension php, asp,aspx, jsp, etc.). In this page, some code in a specific programming language is embedded in the webpage, and executed by the web/application server when the client requests the page.

Footnote
{
Different server side programming languages are available. These are the most popular: PHP (Hypertext Preprocessor, recursive acronym) which is open source, Java with JSP (Java Server Pages) from Sun Microsystems, ASP (Active Server Pages) and ASP.NET which is the last evolution of it, from Microsoft. ASP.NET is web development platform like JSP, but unlike JSP which only supports Java code, ASP.NET actually support different programming languages (C#, VBScript, J# and others).
}

The HTML code is generated and the result is sent to the client. Such pages usually contain some static HTML code and some specific tags that indicates the code within this tags is in another language, the appropriate module has to execute it and the HTML result has to be merged with the source page.
The contents of the dynamic page depend on the query passed to the program. In particular, the program may use the parameters in the query to query the database and retrieve the relevant information, and finally use it to build the HTML page.

Footnote
{
Three database/SQL server software prevail: MySQL (open source, very very popular), PostgreSQL (open source, enterprise-level, much more sophisticated than MySQL, therefore more complex), Oracle (proprietary, leader in the business world), for very large databases
}

Think of search engines for which you specify keywords on a web page. You request is sent to the server with the keywords in the query and the database is processed as a result.

• Case 3: this case is useful to understand the process. It is just a simpler version of case 2, where the client request is sent directly to a script (short program) – not a webpage - using a language like Perl, which script produces (prints) HTML code to be sent to the client. No tags here, but instructions executed in sequence.

Now that you have the client-server architecture in mind, there is one last point to explain before you understand how blogs work.
“Blogs differ from traditional web sites in that, rather than being composed of many individual pages connected by hyperlinks, they are composed of a few templates (usually Main Page, Archive Page, and Individual Article/Item Page), into which content is fed from a database.” (Wikipedia, Weblog, http://en.wikipedia.org/wiki/Weblog, retrieved 11/26/2005). Indeed, you have 3 dynamic pages at least in a blog site, to keep it simple (Main, Archive, Individual Article/Item). The form of the page follows the appropriate template and the content is build from a database of articles, the articles you have already submitted through the Individual Article Page, the page where you edit your article. When you submitted your article, a program is executed by the webpage (cf.CASE 2 above) and filled out a database with information about the article such as the date, the author, the title, etc. You notice on the main page that articles are displayed in reverse chronological order, which is very specific to weblogs. Again, this main page executes a code that fetches data about:
- you as an author because this is your blog, you want to see your articles
- the dates of the articles, to sort them out in the reverse chronological order
- some extra things, less significant.

You got the idea.

References:
1. www.webdevelopersnotes.com, The Client Server Architecture, 2005, http://www.webdevelopersnotes.com/basics/client_server_architecture.php3
2. See http://www.dcs.bbk.ac.uk/~mick/academic/networks/msc/programming/server.shtml for extra references.

See Alok’s former blog for extra information.