Dynamic workflow schema evolution based on workflow type versioning and workflow migration

An important yet open problem in workflow management is the evolution of workflow schemas, i.e., the creation, deletion and modification of workflow types in such a way that the schema remains correct. This problem is aggravated when instances of modified workflow types are active at the time of modification because any workflow instance has to conform to the definition of its type. The paper presents a framework for dynamic workflow schema evolution that is based on workflow type versioning and workflow migration. Workflow types can be versioned, and a new version can be derived from an existing one by applying modification operations. Workflow type versions allow us to handle active instances in an elegant way whenever a schema is modified. If possible, an affected workflow instance is migrated to the new version of its type. Otherwise, it continues to execute under its old type. We introduce correctness criteria that must be met by workflow schemas and workflow schema modification operations. We also define under which conditions the migration of workflow instances to new workflow type versions is allowed.