If I understand your question correct, you would like to know if history kind and history depth QoS policies apply to an instance. In that case the answer is yes; each instance has its own history. This means specifying a history depth of 5 means that each instance has a history depth of 5.
Can you elaborate a bit more about what you mean with 'sequence numbers'? I don't understand where you are referring to.
Thanks. I would know if for two or more instances the Cache to store data is unique. The sequence numbers are the RTPS submessage elements associated for each RTPS message. My question is born because I'm simulating DDS middleware with a tool (OMNeT++) and I have to know the real structure of classes Thanks
> I would know if for two or more instances the Cache to store data is unique.
Yes, each instance has its own history. Data for one instance cannot overwrite data for another instance.
> The sequence numbers are the RTPS submessage elements associated for each RTPS message.
In RTPS, sequence numbers are assigned by RTPS Writers. This means a sequence number is unique per Writer.
The DDS API does not provide handles to gain access to that sequence number. This is logical since DDS specifies an API plus the according behaviour, not an underlying wire format to transport data. A product can be perfectly compliant with the DDS specification without using RTPS.
> I have to know the real structure of classes
DDS is an open standard managed by the Object Management Group (OMG). The DDS specification prescribes all structures and can be downloaded from the OMG website.