Importing will affect large amounts of data, and to be able to update existing data the binary patches must build up, maintain and use mappings from the structure and contents of one repository to another. It is thus worth spending time making sure you understand a little of what happens during import, especially if you want to repeatedly export and import models from one repository to another, called the source and target repositories here.

The target repository remembers from which source repositories imported instances have come, so if the same graphs are exported again later, the existing imported instances in the target repository are updated, rather than creating new ‘duplicate’ instances. Previously imported instances will thus be updated in the correct project automatically, if the source repository name given when exporting the previously imported patch was the same as for this patch. Exporters should thus take care to always use the same, unique name for the source repository when exporting.

Recognizing previously imported types to be updated is based on unique internal names, stored with each type, and is thus not dependent on the name given for the source repository when exporting. However, if there are instances of port types within type definitions, these instances are handled in the same way as other instance data and the behavior is therefore affected by the source repository name. When importing, you are expected to first open all the areas where types to be updated exist. If a type is imported that already exists in another, unopened project, MetaEdit+ will warn you and ask for permission to open that project.

Whilst updating types works between any repositories, updating instances works only in one direction: from the source (exporting) repository to the target (importing) repository or repositories. It is not possible to update the exported models in the source repository by importing the same models back from the target repository.

Similarly, if A exports to B, and B exports to C, it is not possible to update models in C by directly exporting from A. Instead, B must import the models from A, and then re-export them for C to import. In many situations, it would be better for A to export one patch at the start, which both B and C could import. Later, A could export the newer versions of the same models, and again both B and C could import that same patch.