Schema Flexibility and Data Sharing in Multi-Tenant Databases

Software as a Service applications, operated by service providers and accessed via the internet, commonly implement multi-tenancy to leverage economy of scale. In this thesis, we present schema-mapping techniques for currently available database systems to allow for schema extensibility and schema evolution as needed by SaaS applications. As this schema flexibility has to be handled from outside the database systems, and thus degrades the database system to a dumb data repository, we present a prototype of a main-memory database system with native support for schema flexibility. Our prototype is based on FlexScheme, an integrated data model which captures aspects of schema extensibility and schema evolution. Furthermore, FlexScheme allows for sharing data across tenants where each tenant has its own shadow copy, that the tenant can modify. Novel approaches for data organization like XOR deltas further increase tenant packaging.