Such terms as ''web app'', ''front-end architecture'', ''Web 2.0'', and ''HTML5 apps'' have recently become trendy. Unfortunately these terms are often found in a misleading context which doesn't think about the full specificity of implementation and usage of web app architecture. Today we'll look for out more about the types of web application architecture in the light of the most recent web trends and key conditions that matter to software owners.

We'll outline 3 main forms of web architecture and discuss their advantages and drawbacks for three points of view: software owner, software contractor (developer) and person. There can be other styles but they basically drop to these three as their subtypes.

First we'll define a web application: it's a client-server application - you will find a browser (the client) and a web server. The logic of a web application is distributed among the server and the client, there is a channel for information exchange, and the info is stored mainly on the server. Further details depend on the architecture: different styles distribute the logic in various ways. It can be positioned on the server in addition to on the client side.

It's near to impossible to evaluate these very different architectures impartially. But we'll make an effort to, using several criteria of evaluation:

User:
Responsiveness/Usability. Updates of data on pages, switching between pages (response time). Such qualities of user interface as richness and intuitiveness used.
Linkability. Capability to save bookmarks and links to various sections of the website.
Offline work. Speaks for itself.

Developer:
Speed of development. Addition of new functional features, refactoring, parallelizing the development process between developers, layout designers, etc.
Performance. Maximum speed of response from the server with minimum usage of computation power.
Scalability. Capability to increase computation power or disc space under increases in levels of information and/or amount of users. In the event the allocated scalable system can be used, one must provide data consistence, availability and partition tolerance (CAP theorem). It's also worth noting that the case, once the number of features/screens of the client app is increased at the software owner's request, depends on the framework and implementation as opposed to the type of web architecture.
Testability. Possibility and easiness of automated unit testing.

Software owner:
Functional extendability. Adding functionality within minimal time and budget.
SEO. Users must be able to find the application through any internet search engine.
https://archicadteam.com/ . Expenses on app infrastructure - hardware, network infrastructure, maintenance staff.
Security. The software owner must be sure that both business data and information about users are kept secure. Because the main security criterion we'll consider the possibility of changes in functionality of app behavior on your client side, and all associated risks. Standard dangers are the same for the compared architectures. We usually do not consider security on the 'server-client' channel, because each one of these architectures are equally subjected to break-ins - this channel can be the same.
Conversion: site - mobile or desktop application. Possibility to publish the application form on mobile markets or even to make a desktop application out of it with minimal additional costs.

Some of these criteria might seem inaccurate, but the reason for the article is not to show what's good and what's bad. It's more of a detailed review that shows the possible options of preference.

Let's outline three main forms of web applications according to the roles performed by the server and your client browser.

Type 1: Server-side HTML

Probably the most widespread architecture. The server generates HTML-content and sends it to the client as a full-fledged HTML-page. Sometimes this architecture is named ''Web 1.0'', since it was the first to appear and currently dominates the web.

Responsiveness/Usability: 1/5. The least optimal value among these architectures. It's so because there is a great amount of data transferred between the server and the client. The user has to wait before whole page reloads, responding to trivial actions, for instance, when only a part of the page should be reloaded. UI templates on the client depend directly on the frameworks applied on the server. As a result of limitations of mobile internet and large sums of transferred data, this architecture is hardly applicable in the mobile segment. There are no means of sending instant data updates or changes in real time. If we consider the possibility of real-time updates via generation of ready chunks of content on the server side and updates of the client (through AJAX, WebSockets), plus design with partial changes of a page, we'll exceed this architecture.

Linkability: 5/5. The best of the three, since it is the easiest implementable. It's due to the fact that by default one URL receives particular HTML-content on the server.

SEO: 5/5. Rather easily implemented, similarly to the previous criterion - this content is known beforehand.
Speed of development: 5/5. This can be the oldest architecture, so it's possible to select any server language and framework for particular needs.

Scalability: 4/5. If we have a look at the generation of HTML, beneath the increasing load comes the moment when load balance will be needed. There's a much more complicated situation with scaling databases, but this task is the same for these three architectures.

Performance: 3/5. Tightly bound to responsiveness and scalability in terms of traffic, speed etc. Performance is relatively low because a big amount of data should be transferred, containing HTML, design, and business data. Therefore it's necessary to generate data for your page (not merely for the changed business data), and all of the accompanying information (such as design).

Testability: 4/5. The positive thing is that there surely is no need in special tools, which support JavaScript interpretation, to check the front-end, and the content is static.

Security: 4/5. The application behavior logic is on the server side. However, data are transferred overtly, so a protected channel may be needed (that is basically a story of any architecture that concerns the server). All of the security functionality is on the server side.

Conversion: site - mobile or desktop application: 0/5. Typically it's simply impossible. Rarely there's an exception (more of exotics): for instance, if the server is realized upon node.js, and you can find no large databases; or if one utilizes third-party web services for data acquisition (however, it is a more sophisticated variant of architecture). Thus you can wrap the application form in node-webkit or analogous means.