modelant publishes the UML 1.3 metamodel component that allows program load, manipulation and export of of UML 1.3 models, together with an operation to compare UML 1.3 models.
See the dedicated plugin documentation
Load a UML 1.3 model
ModelRepository repository;
ModelFactory modelFactory;
org.omg.uml13.Uml13Package model;
repository = ModelRepositoryFactory.construct(workDirectory);
modelFactory = repository.loadMetamodel("UML13");
model = modelFactory.instantiate("model name");
repository.readIntoExtent(model, "model file path" );
Use the org.omg.uml13.Uml13Package interface to navigate the model and retrieve the model elements.