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Writing and Reading IntraMaps

It is most important to realise that when you write an IntraMapIntraMap to a ChannelChannel (§15.3), the transformation function which it uses is not stored with it. To do so is impossible, because the function has been compiled and loaded into memory ready for execution before AST gets to see it. However, AST does store the name associated with the transformation function and various details about the IntraMap itself.

This means that any program attempting to read the IntraMap (§15.4) cannot make use of it unless it also has independent access to the original transformation function. If it does not have access to this function, an error will occur at the point where the IntraMap is read and the associated error message will direct the user to the author of the transformation function for more information.

However, if the necessary transformation function is available, and has been registered before the read operation takes place, then AST is able to re-create the original IntraMap and will do so. Registration of the transformation function must, of course, use the same name (and, in fact, be identical in most particulars) as was used in the original program which wrote the data.

This means that a set of co-operating programs which all have access to the same set of transformation functions and register them in identical fashion (see §20.12 for how this can best be achieved) can freely exchange data that contain IntraMaps. The need to avoid exporting such data to unsuspecting third parties (§20.3) must, however, be re-iterated.