![]() We will go into this in more detail when we talk about the Lifecycle to detect an event such as a flight landing or a chocolate lotįinishing. ![]() Instances allow you to model the behavior ![]() Requires less memory, and the instances do not need to be discovered the wayĭataWriters and DataReaders discover each other. Using instances to represent unique flights That’s over a thousand flights per day! The problem withĪ one- Topic-per-flight system is that it uses more memory than necessary,Īnd it takes more time for discovery. So why use instances at all?Ĭreating a new instance is lighter-weight than creating a new DataWriter/ DataReader/ Topic.įor example, if you’re representing airline flights, you could create a newĭataWriter, DataReader, and Topic each time a new flight takes off. You’re alreadyĭividing up your data into multiple Topics. Not every data model requires that you use instances. To specify one or more key fields, annotate them with in the IDL file. Vehicle identification number (VIN) of the carĬhocolate lot being processed in a factoryĬhocolate lot identifier likely an incrementing number that rolls over “tempering-machine-1” or “FirstFloorSensor1” Unique identifier of that sensor, such as: Sensor sending data, such as an individual temperature sensor Table 4.2 Examples of Instances and Keys in Distributed Systems ¶ Instance See other examples of keys, instances, and samples in the following table. Samples would be the updated locations of each flight “instance.” Traffic control system, the key fields might be the airline name and flight number. Long as they uniquely identify the object you are representing. A key can be composed of multiple fields in your data as Is a unique identifier of something within your data. A key in DDS is similar to a primary key in a database-it When you need to represent multiple objects within a DDS Topic, you use a Publish samples of data for several different objects, such as flights or sensors.Ĭonnext DDS uses “instances” to represent these real-world objects. ![]() A DataWriter, for example, publishes samples Introduction to Keys and Instances ¶ Prerequisites ![]()
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