How Does DDS Work ?
HOW DOES DDS WORK ?
HIGH LEVEL DATA-CENTRIC INTERFACES REPLACE MESSAGE-CENTRIC PROGRAMMING
The main goal of DDS is to share the right data at the right place at the right time , even between timedecoupled publishers and consumers . DDS implements global data space by carefully replicating relevant portions of the logically shared dataspace .
THE RIGHT DATA
Not all data needs to be everywhere . Middleware should only deliver the data that consumers really need . Interest-based filtering can apply to both content and data rates . With proper implementation , DDS saves bandwidth and processing power , and minimizes overall application complexity .
As a data-centric solution , DDS can understand the schema of the shared data . This allows it to filter on content , age and / or lifecycle to provide applications with only the data they need . For example , you can send only boiler temperatures over 300 ( content filter ) with at most ten updates per second ( rate ). This efficient approach can often save 90 % of the data communications overhead in many systems .
THE RIGHT PLACE
Data must be available where it is needed , to facilitate self-forming systems . DDS distributes and maintains data so it is readily available .
DDS dynamically discovers publishers and subscribers , the data types they want to share , and the related Quality-of-Service ( QoS ). Following a successful match , DDS enforces timely distribution according to the QoS . It implements a QoS-enforced logical channel for each data stream between each publishersubscriber pair . A DDS subscriber can be sure that its peer publisher is actually alive and that any data produced will be delivered . This greatly simplifies application development and error handling .
THE RIGHT TIME
Real-time systems interact with the real world . Data must be available on time — the right data too late is a failure . Data differ in priority , reliability , timing , and other non-functional properties . DDS balances utilization of scarce resources to distribute data at the right time .
DDS middleware uses logical QoS policies , as set by the applications at runtime , to balance efficiency and determinism . The QoS contracts ensure these timing relationships . For example , if a subscriber requires an update every 10ms and its matched publisher does not deliver , the system declares an error , enabling remedial action . QoS policies cover many characteristics , including urgency , importance , reliability , persistence , and liveliness .
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