DDS — Attributes_on_a_topic_description

Attributes_on_a_topic_description Issue [Boeing SOSCOE] ? Some use-cases need more control on association of DataReader and DataWriters beyond the control offered by means of the Topic ? For example, SOSCOE may need to add a layer on top of the DDS API to offer additional customized services to the applications that sit on top. These services may include the propagation of identity-certificates, security, dynamic selection of the “best” DataWriter to use for a given Topic, etc. ? These mechanisms would like to benefit from the propagation of Topics and QoS that DDS offers and extend that mechanism with additional information that can then be used by the SOSCOE layer to provide these additional services. ? However the matching that DDS offers is performed only on the topic name. It would be useful to have a more extensible mechanism to allow matching on other application-defined attributes. ? These attributes are an expansion of the topic_name that appears in the TopicDescription. In addition to the string (topic_name) we could have a set of attribute-name/value pairs that could then be used to match the writers with readers. In a sense the topic_name would be a singular, mandatory attribute used for matching but they could be others. ? These attributes are not mutable. ? SOSCOE has created a provider property class that allows applications to have attributes with typed values; it becomes a triplet (name, type, value). Currently the “type” only supports simple types, but the intent is to extend it to well-known structured types. ? For example, the Topic “weather data” would describe a general topic but there may be an attribute that describes the region (e.g. “North America”) and the subscriber can specify they want weather-data but only over “North America” Proposal [Boeing SOSCOE] ? One approach would be to add a set of “name-value” attributes to the TopicDescription. Matching would be done not only on the topic-name but also on the remaining attributes. In a sense, the topic name is just one of the attributes that must be matched between the Topic that is published and that which is subscribed.

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