1. Computer apparatus with a storage medium for managing configurations of programming models, comprising: a user workspace respective to a user, the user workspace holding a programming model configuration specified by the user, the configuration being formed of one or more model elements; and one or more change-flow hierarchies defining, for each user workspace, flow of changes to the model elements; wherein the change-flow hierarchies define default source projects and target projects of accept operations issued from the user workspaces; wherein the change-flow hierarchies define default source projects and target projects of deliver operations; further comprising an intermediate workspace between the user workspace and a subject project, the user workspace deferring acceptance of the subject project checkpoint by delivering a change-set to the intermediate workspace instead of delivering a configuration to the project; wherein the change-flow hierarchies employ indications of primary change flow and supplementary change flow; wherein primary change flow is defined such that accept and deliver operations issued from one workspace apply changes to a release or a project within the change-flow hierarchy; and supplementary change flow can be defined to ensure that a workspace sees changes made by other workspaces which its change-flow hierarchy or in another hierarchy.