Such terms as ”web app”, ”front-end architecture”, ”Web 2.0”, and ”HTML5 apps” have recently become trendy. Unfortunately these terms tend to be used in a misleading context which doesn’t think about the full specificity of implementation and usage of web app architecture. Today we’ll try to find out more about the forms of web application architecture in the light of the latest web trends and key issues that matter to software owners.

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

First we’ll define a web application: it’s a client-server application – there exists a browser (your 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 data is stored mainly on the server. Further details be determined by the architecture: different ones distribute the logic in various ways. It can be placed on the server as well as on the client side.

It’s near to impossible to evaluate these completely different architectures impartially. But we’ll try to, using several criteria of evaluation:

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

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 amounts of information and/or number of users. In case the allocated scalable system can be used, one must definitely provide data consistence, availability and partition tolerance (CAP theorem). It is also worth noting that the case, once the number of features/screens of your client app is increased at the program owner’s request, depends upon the framework and implementation rather than 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 in a position to find the application through any internet search engine.
Support. Expenses on app infrastructure – hardware, network infrastructure, maintenance staff.
Security. The software owner should be sure both business data and information regarding 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 will be the same for the compared architectures. We usually do not consider security on the ‘server-client’ channel, because all these architectures are equally subjected to break-ins – this channel can be the same.
Conversion: site – mobile or desktop application. Possibility to create the application form on mobile markets or even to make a desktop application out of it with minimal additional costs.

Fort Lauderdale architects of these criteria might seem inaccurate, but the reason for the article is not showing what’s good and what’s bad. It’s more of a detailed review that presents the possible options of choice.

Let’s outline three main types of web applications according to the roles performed by the server and the client browser.

Type 1: Server-side HTML

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 net.

Responsiveness/Usability: 1/5. The least optimal value among these architectures. It’s so since 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 needs to 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. You can find no means of sending instant data updates or changes instantly. If we consider the chance for 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 go beyond this architecture.

Linkability: 5/5. The best of the three, since it’s 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 – the content is known beforehand.
Speed of development: 5/5. This can be a oldest architecture, so it is possible to select any server language and framework for particular needs.

Scalability: 4/5. If we take a look at the generation of HTML, beneath the increasing load comes as soon as when load balance will undoubtedly be needed. There’s a a lot more complicated situation with scaling databases, but this task may be the same for these three architectures.

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

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

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

Conversion: site – mobile or desktop application: 0/5. In many instances 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 one can wrap the application form in node-webkit or analogous means.

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