===== Topic =====
[[dido:public:ra:xapend:xapend.a_glossary:start| Return to Glossary ]]


A **Topic** is the most basic description of data that is to be published 
and/or subscribed to.  A topic connects a [[dido:public:ra:xapend:xapend.a_glossary:d:data_writer]] with a [[dido:public:ra:xapend:xapend.a_glossary:d:data_reader]], i.e., communication does not occur unless the 
topic published by a data writer matches a topic subscribed to by a data reader. Communication via topics is anonymous and transparent, i.e., publishers and subscribers need not be concerned with how topics are created or who is writing/reading them since the [[dido:public:ra:xapend:xapend.a_glossary:d:dds]] [[dido:public:ra:xapend:xapend.a_glossary:d:dcps |DCPS]] [[dido:public:ra:xapend:xapend.a_glossary:m:midware|middleware]] manages 
these issues.  In programming terms, a Topic is a [[dido:public:ra:xapend:xapend.a_glossary:c:class|Class]] and each [[dido:public:ra:xapend:xapend.a_glossary:i:instance|instance]] is a [[dido:public:ra:xapend:xapend.a_glossary:s:sample|Sample]]. Topic instances are associated with a [[dido:public:ra:xapend:xapend.a_glossary:k:key|key]] (similar to a packet [[dido:public:ra:xapend:xapend.a_glossary:i:id |ID]]), defined by [[dido:public:ra:xapend:xapend.b_stds:tech:omg:idl|IDL]] and a set of [[dido:public:ra:xapend:xapend.f_qos:start|Quality of Service parameters]].


Source: [[https://istkb.adlinktech.com/article/vortex-opensplice-dds-glossary/ | OpenSplice Glossary]]