As part of the Adaptive Sensor Fusion (ASF) program sponsored by AFRL, AIT has developed a software architecture that is useful in developing distributed systems. This eXtensible Distributed Architecture (XDA) was developed to address problems encountered when creating distributed systems by building capabilites for:

• System Evolution
• A globally accessible data object model
• Minimal coupling between components
• Efficient messaging architecture
• An abstracted transport level
• Incremental deployment of object model updates
• Database query capabilities defined at the object level

A fundamental design feature of the XDA architecture is the separation between a high-level domain definition (for example a terrain visualization data model) and low-level persistence and inter-process communication details. XDA is based on the capability to build sophisticated, flexible, high-level models of the problem domain whose implementation is accomplished in terms of a fixed low-level object model called the Generic Transport Object (GTO) model.

"Model-on-a-Model" Architecture Facilitates System Evolution

The figure above illustrates the "model-on-a-model" architecture of XDA. The runtime classes conform to a flexible "evolveable" domain definition. At runtime we have objects that are instances of entities. A set of related entities forms an "ontology." Persistence and transport utilize a fixed generic object model called the Generic Transport Format. Ontologies can be modified and can evolve without requiring modifications of the transport model. Generic Transport Objects carry both data and structure information. The containment hierarchy and the physical layout of the attributes of a class are retained when an instance of the class is converted to a GTO. Thus, the attribute layout and the containment information can be saved if an object-oriented database is used for persistence. This structure information combined with the ontology-based semantics can be used, for example, to implement efficient object-oriented queries.

For more information, please download the documentation located in the releases section.