In data-centric communications, the applications participating in the communication need to share a common view of the types of data being passed around.
Within different programming languages there are several ‘primitive’ data types that all users of that language naturally share (integers, floating point numbers, characters, booleans, etc.). However, in any non-trivial software system, specialized data types are constructed out of the language primitives. So the data to be shared between applications in the communication system could be structurally simple, using the primitive language types mentioned above, or it could be more complicated, using, for example, C and C++ structs, like this:
struct Time {
long year;
short day;
short hour;
short minute;
short second;
};
struct StockPrice {
float price;
Time timeStamp;
};
Within a set of applications using DCPS, the different applications do not automatically know the structure of the data being sent, nor do they necessarily interpret it in the same way (if, for instance, they use different operating systems, were written with different languages, or were compiled with different compilers). There must be a way to share not only the data, but also information about how the data is structured.
In DCPS, data definitions are shared among applications using OMG IDL, a language-independent means of describing data. For more information on data types and IDL, see Data Types and DDS Data Samples.
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