On top of database technologies on diverse data models, the concept of polystore has been studied for unified management of heterogeneous data. However, the design of multi-model query languages, which are the major interface of polystores, is an important yet challenging task. There are still drawbacks in the existing multi-model query languages, including limited expressiveness of query representation and fixed data models.
To address these problems, this paper presents the Equivalently Combinations of Query Languages (ECQL) as a holistic representation of multi-model queries. This paper firstly makes fundamental abstractions of the query results of different data models, and then designs a new multi-model query language that combines the query languages of different data models based on these abstractions. We explain the expressiveness of ECQL that it supports both single-model query functionalities and cross-model queries. The evaluation results between ECQL and existing multi-model query languages on polystore benchmarks show the succinctness of ECQL. We also demonstrate the extensibility of ECQL that it can be integrated with new type of query languages.
