4.6. Query processing and optimization

4.6.1. Introduction

In this section, we analyze how global (or multi-data stores) queries are processed. They are done partly by the data stores and partly by an external component (global query engine). This query engine can be centralized or distributed and needs statistics from the different data stores to perform efficient optimizations. Of course, the query processing only somewhat depends on the underlying global query language. We distinguish two categories: integrated query languages (based on an integrated global schema) and federated query languages (without a global schema). The first part of this section describes federated query language works [KOL 16, DUG 15] and the second part describes integrated query language works [SEL 17, BAJ 11, LIA 16, VIL 13, ZHU 11, DEW 13, LEF 14].

4.6.2. Federated query language approaches

CloudMdsQL, Querying heterogeneous Cloud data stores with a functional query language: Valduriez et al. [KOL 16...