Schema Evolution

Schema Evolution and Data Migration for JSON Databases, Graph Databases and XML Documents

While the design of databases in different data models is a very well researched area of computer science, methods and languages for evolution are not yet available everywhere. Therefore, this topic has been the focus of our research for decades. In particular, we concentrate on methods for non-relational data models (XML, JSON, Graph) and develop evolution languages and implement tools for this task. 

An evolution on these data models isalways a co-evolution of schema and data (since the schema, if it exists at all) can be stored separately from the data. For this reason, all approaches must also translate the evolution operations defined for the schema level into data migration operations. The following figure shows this schematically. 

(Figure from Uta Störl, Meike Klettke, Stefanie Scherzinger: NoSQL Schema Evolution and Data Migration: State-of-the-Art and Opportunities. Tutorial at EDBT 2020)

In NoSQL databases without an explicitly available schema, a schema extraction algorithm is required in the overall procedure; we have also developed procedures for this, which are described here. 

• Evolution of JSON databases: Further information on the results of the DFG project NoSQL Schema Evolution and Big Data Migration at Scale can be found here.   
• Evolution of Graph databases: Our ongoing work in this field can be found here. 

References

• Uta Störl, Meike Klettke, Stefanie Scherzinger: NoSQL Schema Evolution and Data Migration: State-of-the-Art and Opportunities. EDBT 2020: 655-658
• Mark Lukas Möller, Meike Klettke, Andrea Hillenbrand, Uta Störl: Query Rewriting for Continuously Evolving NoSQL Databases. Article, ER2019 conference, Brazil, 2019, (pdf)
• Meike Klettke, Uta Störl, Manuel Shenavai, Stefanie Scherzinger: NoSQL Schema Evolution and Big Data Migration at Scale, 4th Scalable Cloud Data Management Workshop (SCDM) @ IEEE Big Data Conference, Washington, D.C., USA, December 2016, (pdf)
• Stefanie Scherzinger, Meike Klettke, and Uta Störl: Managing Schema Evolution in NoSQL Data Store, The 14th International Symposium on Database Programming Languages DBPL@VLDB, Italy, 2013
• Meike Klettke: Conceptual XML Schema Evolution - the CoDEX Approach for Design and Redesign. (pdf) BTW Workshops 2007: 53-63
• Meike Klettke: Modellierung, Bewertung und Evolution von XML-Dokumentkollektionen. Habilitationsschrift, Universität Rostock, Fakultät für Informatik und Elektrotechnik, eingereicht am 09.09.2006, verteidigt am 19.09.2007, Probevorlesung am 06.12.2007