In a large class of distributed systems, real-time availability of information is of utmost importance. Information generated from multiple sources must be distributed and made available to 'interested parties' taking into account Quality of Service (QoS) offerings by information-producers and requests by information-consumers. Especially in real-time and mission-critical systems, getting 'the right data at the right time at the right place’ is not a trivial task at all and up until recently, there were no standards nor COTS products that addressed this challenge in an integrated solution.
The Object Management Group OMG recognized this need for a Data Distribution Service (DDS) and organized members with vast experience in both the 'underlying' technologies (networking and information-management) as well as 'user-level' requirements (distributed, real-time and mission-critical system characteristics), to join forces and these members defined the OMG Data Distribution Service for Real-Time Systems standard. The OMG-DDS service specifies a coherent set of profiles that target real-time information-availability for domains ranging from small-scale embedded control systems up to large-scale enterprise information management systems. Each DDS-profile adds distinct capabilities that define the service-levels offered by DDS in order to realize this 'right data at the right time at the right place' paradigm:
- DCPS Minimum Profile: this Data Centric Publish Subscribe (DCPS) 'basic' profile utilizes the well-known publish/subscribe paradigm to implement highly efficient information-dissemination between multiple publishers and subscribers that share interest in so-called 'topics. Topics are the basic data-structures expressed in the OMG's IDL-language (allowing for automatic generation of typed 'Readers' and 'Writers' of those 'topics' for any mix of languages desired). This profile also includes the QoS framework that allows the middleware to 'match' requested and offered Quality of Service parameters (the minimum profile offering basic QoS attributes such as 'reliability', 'ordering' or 'urgency').
- DCPS Ownership Profile: this 'replication' profile offers support for replicated publishers of the same information by allowing a 'strength' to be expressed by each publisher so that only the 'highest-strength' information will be made available to interested parties.
- DCPS Content Subscription Profile: this 'content awareness' profile offers powerful features to express fine-grained interest in specific information content (content-filters). This profile also allows applications to specify projection-views and aggregation of data as well as dynamic queries for subscribed 'topics' by utilizing a subset of the well-known SQL language whilst preserving the real-time requirements for the information-access.
- DCPS Persistence Profile: this 'durability' profile offers transparent and fault-tolerant availability of 'non-volatile' data that may either represent persistent ‘settings’ (to be stored on mass-media throughout the distributed system)
