Architecture Overview

DeepaMehta features an OSGi-based modular architecture that shares features with an service-oriented architecture (SOA). Each module's service can be consumed as an OSGi service. At the same time DeepaMehta can publish a module's service as a RESTful web service without requiring the module developer to do extra coding.

In a distributed (client-server) DeepaMehta setup the OSGi container runs at the server-side. Clients access the server via HTTP.

A central part of DeepaMehta is its plugin development framework. A DeepaMehta plugin is an OSGi bundle. However the DeepaMehta plugin developer must not know about the OSGi intrinsics. Instead she can rely on the facilities and conventions rooted in the DeepaMehta Core and its high-level API.

DeepaMehta Core

Features of the DeepaMehta Core:

• The DeepaMehta Core mediates between the DeepaMehta plugins and the underlying OSGi environment. In particular the DeepaMehta Core ...
  • registers the plugin's service as an OSGi service.
  • additionally publishes the plugin's service as a RESTful web service via OSGi's HTTP service.
  • publishes the plugin's web resources (images, scripts, CSS) via OSGi's HTTP service.
  • tracks the plugin services the plugin want to consume.

• The DeepaMehta Core Service provides transactional access to the DeepaMehta database. There are high-level methods for dealing with the basic DeepaMehta application objects (Topics, Associations, Topic Types, Association Types) and complex composite structures. The DeepaMehta Core Service also provides basic query (including fulltext) and traversal capabilities.

Every DeepaMehta plugin has access to the DeepaMehta Core Service. External applications can access the DeepaMehta Core Service as a RESTful web service (via HTTP).

• DeepaMehta Core Events are fired in particular situations, e.g. before and after a topic is created in the database. By implementing event listeners DeepaMehta plugins can react upon these events.

• The Migration Manager ensures the database model and content is compatible with the installed plugins. It does so by running database migrations when a plugin is installed or updated.

• Defining a DB-agnostic low-level service provider interface for the storage layer. By implementing this interface developers can deploy any database system as the DeepaMehta storage.

The DeepaMehta Core is an OSGi bundle.

DeepaMehta Plugins

A DeepaMehta plugin can have several parts:

• A data model. The data model is a collection of domain-specific topic types and/or association types.

• Server-side logic. Server-side logic comes in form of a) event handlers, and/or b) service methods. Server-side logic is written in Java.

• Client-side logic. Client-side logic runs inside the DeepaMehta Webclient. Client-side logic comes in form of a) event handlers, b) custom renderers, and/or c) public API methods. Client-side logic is written in JavaScript??.

Each of these parts is optional. Which parts a plugin provides depends on its purpose.

DeepaMehta Webclient

Storage Implementation

The default storage implementation embeds Neo4j. Neo4j is accessed via its native Java API.