Mike makes a valid point in that the “server request” has been there all along — the flip side of which of course is “so why do we only consider what gets served to the client?”… because without that fourth layer you’ve got static-only sites.

Anyway, it’s achieved my target: stirring up a debate. Whether the consensus is with me or against me matters less to me than whether I’ve made people think…

However, now I come to think about it I think I would express it slightly differently…

Data (Layer 0 - database and optional hence zero) -> [translate] -> Logic (Layer 1 - all the server response including dynamic coding, if present, but could just be provide plain html etc.) -> [transmit] -> Structure (Layer 2 - yer (X)HTML stuff) -> [transform] -> Style (Layer 3 - CSS, etc.)

Of course the chain could work backwards.

I never really considered JavaScript a ‘behaviour’ layer it mearly implements some client-side stuff already there or in the case of AJAX is a mechanism for handling the server request other than the ‘normal’ browser-triggered HTML related requests.

In relation to this discussion I have been working on the following layer principal for several years.

Database(Layer1) –> Code Layer(Layer2) –> Design layer(Layer3) –> CSS(Layer4)

The database layer could refer to calls to Oracle function, stored procedures or HTML templated SQL.

Code layer refers to your application code eg.. PHP, Java or ASP.

Design layer refers to your HTML layer or template.

And of course CSS is well straight forward.

In a lot of cases it’s obvious that this layout approach is not adhered to. This is an obvious disaster when working on enterprise level websites that take the following approach.

Database Layer(layer 1) –> Code, design and CSS layer(layer 2)

This is not necessarily the fault of the company or it’s web team but rather in many instances it can be attributed to the CMS they have integrated that does not even meet the basic requirements of W3C compliance let alone developing an adequate layered approach.

Regards
zeroanarchy

I would have to say now that the fourth layer was there all along and not form input triggered/dependent. It’s the HTTP request and that’s where it all begins.

I am involved both in building back-ends of a site in PHP - consuming/processing data from a variety of sources (databases, web services, etc) - as well as the front-end product (HTML), ‘presentation’ layer (CSS) and ‘behaviour’ layer (Javascript). The three-tier referred to in web-standards refers to this front-end but I work in an environment that employs a different three-tier system distinguishing between the data itself, business logic (the processing and delivery of data) and presentation (the consumption and presentation of data). As someone involved in placing these data sources online, all my work is - in the broader scheme of things - considered to be presentational.
Your fourth ‘process’ layer provides a useful interface between the back-end and front-end of the web but isn’t the process a server-sided/back-end thang and therefore part of a different model than the traditional three-layer model which I see as aimed primarily at the front-end of the web. This is not to say I think it isn’t important we adopt standards across the back-end of web development nor that many (most?) of us wear both hats in the jobs that we do. Rather, what takes place in PHP (or whatever your back-end of choice) stays in PHP. The products of that process may be dependent on the user, particularly with form processing, but this process takes place independently of the user and irrespective of whatever device(s) they use to view and interact with a website.

although many people fall into the mindset of just thinking “behavioural = javascript”

I have always struggled with the idea of Javascript as behavioural. Are we talking about the behaviour of the user or the content? Javascript, in my opinion, is there to add value and a richer experience to a website but that experience still has to be made available without that layer - just as a site still has to be available with CSS disabled or on a device that doesn’t support styling. In this case behaviour has to be functional and therefore becomes an essential means of navigating and interacting with the content - it is not an optional layer draped over the top.

It’s all enough to make my head spin a bit…