The Composite Data Model: A Unified Approach for Combining and Querying Multiple Data Models

In this paper, we combine the characteristics of three fundamental data models in order to represent their semantics in a common framework. These fundamental data models include the familiar concepts of modeling (1) object classes (or entities), their properties (attributes) and relationships between them, (2) multidimensional objects and attributes that can be summarized over the dimensions, and (3) hierarchical structures. This model, called the Composite Data Model, facilitates combinations of these three model structures to be represented jointly in a single schema, thus providing more expressive and natural queries over them. The main advantage of the composite data model (CDM), and a composite query language (CQL) over it, is that any combination of the three fundamental models can be represented jointly based on explicit semantics of each of the fundamental data models. This is unlike existing data models that represent each data model individually or obscure the semantics of additional features being modeled. In order to develop a query language over the combined schemas, we introduce a new concept, referred to as anchor, which is an object class that acts as the focus of the query. We provide in the query language path structures relative to the anchor that facilitate data navigation and data manipulation. We develop the syntax and semantics of the proposed language, and illustrate its expressive power through numerous query examples, and comparisons to three other query languages: OQL, SPARQL, and XQuery.