What is the Justice Reference Architecture and how do I use it?

The Justice Reference Architecture (JRA) consists of two principle sets of information:  a reference architecture that defines standard terminology and concepts for understanding a service-oriented approach to information sharing, and a set of documents that evolve JRA concepts into guidelines about how to design and implement information exchanges.
The JRA is a deliverable of the Global Infrastructure/Standards Working Group (GISWG).
The JRA is based on the OASIS Reference Model for Service-Oriented Architecture (SOA-RM).  The SOA-RM provides vendor-neutral, standard definitions of concepts involved in information exchange and system integration.  (Actually, the SOA-RM is sufficiently general to support exchange between and integration among non-computer entities, but the JRA applies the concepts only to system integration.)
They key innovation of the JRA is to introduce the concept of a service between two systems:  one that has a capability (called a "provider system"), and another ("consumer system") that needs to use that capability to achieve some business objective.  The capability can be simply providing information, or it can be a complex workflow or business process.  The service that sits between these two systems is defined by a formal model that documents clearly and specifically what the service does, as well as what information is needed to interact with the service.  In the JRA, the information model of the service is formed from NIEM- and GJXDM-conformant components.
The JRA also includes concepts that support the interaction between consumer systems and services, such as:  repositories to store and search service descriptions, infrastructure elements necessary to transmit information between systems, and technical standards for inter-system communication (called "service interaction profiles").
Specific guidelines currently under development include:  service interaction profiles for web services, MQ, file transfers, and ebXML; guidelines for modeling/describing services; guidelines for infrastructure capabilities; and guidelines for the identification of services.  GISWG is also developing guidelines for the management and governance of a service-oriented architecture.
Finally, the JRA will include a set of "reference services" that represent typical, common services that exist in justice.
There are two key use cases for the JRA.
The first use case involves an actor whose responsibility is to establish an architecture-that is, a set of standards and infrastructure capability requirements-for a justice information sharing initiative.  Often (but not always) this actor will be an architect or chief information officer, or equivalent.  The actor uses the JRA as a starting point for standardizing the terminology used to describe and understand information sharing in his/her enterprise.  The JRA will also provide baseline technical standards for the design and implementation of services, which the actor can modify as necessary to suit local business requirements.
The second use case involves separate jurisdictions using the set of "reference services" to establish interoperability between those jurisdictions.