An execution engine, running on top of the client platform’s native OS, translates a platform-independent application language into platform-specific native operations.

An execution engine can be any of

• a Virtual Machine (VM) for portable compiled languages such as Java,

• an interpreter for text-based scripting languages such as JavaScript, and

• a managed Just-in-Time (JIT) compiler, such as used in Microsoft's .NET framework.

A foundation class library is a collection of reusable objects that tightly integrate with the underlying client execution runtime and provide functionality for building client applications.

An IIA client foundation class library generally includes client display components that support rich presentation capabilities such as multiple windows, drag and drop, resizable windows, customizable screen colors, and fonts.

IIA systems are inherently asynchronous.  HTTP's request-driven communication does not naturally allow an IIA to be highly responsive. The workarounds that address this problem each have their problems.

The centralized nature of server-integrated systems makes supporting complex data flows and multi-point communication straightforward.  In client-integrated systems the client must manage data flows.

IIAs retain and extend Web application deployment and provisioning. In both client- and server-integrated IIA systems, a provisioning server provides components to the client application.

In the client-integrated case, a provisioning server is dedicated for this purpose.

In the server-integrated case, the provisioning server is often an integrated component of the IIA presentation layer server.  The provisioning server can be either a standard HTTP Web server or a proprietary protocol-based provisioning server.  HTTP-based provisioning leverages existing, mature Web infrastructure, but is not as efficient for binary payloads and cannot support progressive downloading effectively.

Events in the outside world cannot be controlled, whether initiated by real-world actions, other system activity, or collaboration partners.  As a result, it is critical for IIAs to manage asynchronous messages and events effectively allowing actions to be triggered by notifications.  Since requests may arrive before previous requests are completed and may be of higher priority, requests must be handled in parallel.  Most client-integrated IIA systems rely on Internet Middleware solutions to deal with this.

One of the key capabilities provided by IIAs is enabling users to work together collaboratively.

In server-integrated IIA systems, the server provides collaboration using shared sessions.

In client-integrated IIA systems, where each client application is a self contained, independent network entity, a client must first discover collaboration partners on the network and establish connections among them by creating and maintaining shared sessions. Responsibility for shared sessions must be shared and distributed across the network.

Synchronizing data between IIAs presents some of the same challenges in coordinating distributed information as supporting collaboration does.  Both collaboration and data synchronization are more naturally supported in at least partially server-integrated systems.

Client-integrated systems run both restricted and unrestricted features in the client. Server-integrated systems run restricted features on the server. In both cases, authorization to use the restricted feature is requested from an external service.

In the server-integrated case, the authorization service might be an integrated service provided by the host application server or a service running on an external server, both of which are handled by existing middleware.

In the client-integrated case, the authorization service runs on an independent server.

IIA systems must manage clients remotely, as with any other active element in a network application.

In server-integrated systems, management logic can be integrated with the application server, as is supported in server management systems such as Java Management Extension.

In client-integrated systems, management logic must be developed and deployed as an independent network application, an added complexity for client-integrated systems.