Using the uni-level description (ULD) to support data-model interoperability

We describe a framework called the Uni-Level Description (ULD) for accurately representing information from a broad range of data models. The ULD extends previous meta-data-model approaches by: (a) providing uniform representation and access to data model, schema, and data, and (b) supporting data models with non-traditional schema arrangements, including those that allow optional and multiple levels of schema. Because the ULD is a flat, first-order representation, we show how Datalog over the ULD can provide a flexible mechanism to query, extract, and transform information from data sources that exhibit various types of structural heterogeneity.