General Overview of PhiloLogic4's Web Architecture

Very early in the development of PhiloLogic4, we decided to separate the core library (the C core and Python bindings) from the actual Web interface. While there is still a clear separation between the Web environment and the library code, the two are nevertheless interdependent, which is to say that one cannot function independently of the other (unless you intend to use the library functions on the command line...)

As such, the Web component of PhiloLogic4 was designed as a Web Application, and each database functions as its own individual Web App. This allows for greater flexibility and customization. With PhiloLogic4, we wanted the Web layer to be the only part of the code a database developer has to deal with. We even went so far as to offer configuration options that drastically change the behavior of our various utilities. Before I start diving into each individual component (in later posts), I wanted to give a general picture of the Web app, as well as an idea of its features and flexibility.

The application is at its core a Python WSGI app which handles (most) requests through a script that interprets queries and reroutes them to the relevant parts of the application. The results of requests are rendered in HTML thanks to the use of Mako, a powerful and easy-to-use template library. A description of the general layout of the Web App will give a better idea of how the PhiloLogic4 Web App functions.

There are four distinct sections (besides CSS and JS resources) inside the application:
  • The reports directory, which contains the major search reports which fetch data from the database by interfacing with the core library, and then return a specialized results report. These reports include concordance, KWIC (Key Word In Context), collocation, and time series. 
  • The functions directory, which contains all of the generic functions used by individual reports. These functions include parsing the query string, loading web configuration options, access control, etc. 
  • The scripts directory, which contains standalone CGI scripts that are called directly from Javascript code on the client side. These functions bypass the dispatcher and have a very specialized purpose, such as returning the total number of hits for any given query, or switching from a concordance display to a KWIC display.
The first three directories contain all that is necessary to return initial results to the client. The CGI scripts contained in /scripts provide additional functionality made possible by the use of Javascript in our Web Client. Significant work has been done to provide a dynamic and interactive Web interface, and this was made possible via heavy use of Javascript throughout the application, something which I'll describe in greater detail in another post.

Another design decision we made, somewhat late in the development process, was to rely on a CSS/JS framework for the layout of our HTML. We decided to use Bootstrap for its flexibility and responsiveness. As a result, PhiloLogic4 should work on any screen, be it phone, tablet or computer, although some functionality (such as KWIC reports) is hidden on smaller screens due to the limited space available.

Finally-- and I will go into much further detail in a separate post--we've designed a RESTful API that provides access to the full functionality of our web app. This is made possible by delaying for as long as possible the process of choosing to render search results as HTML or JSON. Basically, we expose the same results object to the HTML renderer (the Mako templates) that we do to any potential client. This design feature has allowed us to build a PhiloReader Android client application, focused on reading, by calling the relevant APIs needed for such functionality.

In my next post on the Web Application, I will go through the various configuration options available. 
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