A model for compound type changes encountered in schema evolution

Abstract

Schema evolution is a problem that is faced by long-lived data. When a schema changes, existing persistent data can become inaccessible unless the database system provides mechanisms to access data created with previous versions of the schema. Most existing systems that support schema evolution focus on changes local to individual types within the schema, thereby limiting the changes that the database maintainer can perform. We have developed a model of type changes incorporating changes local to individual types as well as compound changes involving multiple types. The model describes both type changes and their impact on data by defining derivation rules to initialize new data based on the existing data. The derivation rules can describe local and nonlocal changes to types to capture the intent of a large class of type change operations. We have built a system called Tess (Type Evolution Software System) that uses this model to recognize type changes by comparing schemas and then produces a transformer that can update data in a database to correspond to a newer version of the schema.

A formal model for temporal schema versioning in object-oriented databases

“…A completely different approach is taken in [39], where algorithms were devised to analyse complex type changes by comparing two schema versions and accordingly derive transformation rules that can applied to propagate the changes to extant objects.…”

Software diversity: state of the art and perspectives

“…When modeling variability among diverse systems and managing the evolution of these systems, techniques for handling and expressing differences between models are helpful, e.g., model comparison [72,73], delta models [73,71], and change operators [146,109]. Despite its importance, comparably few publications discuss product line evolution, e.g., [36,62,162,212].…”

Integrated Model-Based Software Development, Data Access, and Data Migration

“…Input to the generator is a declarative definition of an object-relational mapping. The successor of OTGen is the Tess [17] system. The Tess generator also takes into account an existing old schema so that it can generate an initial schema mapping itself.…”