Twenty years of object-relational mapping: A survey on patterns, solutions, and their implications on application design

Abstract

ContextAlmost twenty years after the first release of TopLink for Java, Object-Relational Mapping Solutions (ORMSs) are available at every popular development platform, providing useful tools for developers to deal with the impedance mismatch problem. However, no matter how ubiquitous these solutions are, this essential problem remains as challenging as ever. Different solutions, each with a particular vocabulary, are difficult to learn, and make the impedance problem looks deceptively simpler than it really is. ObjectiveThe objective of this paper is to identify, discuss, and organize the knowledge concerning ORMSs, helping designers towards making better informed decisions about designing and implementing their models, focusing at the static view of persistence mapping. MethodThis paper presents a survey with nine ORMSs, selected from the top ten development platforms in popularity. Each ORMS was assessed, by documentation review and experience, in relation to architectural and structural patterns, selected from literature, and its characteristics and implementation options, including platform specific particularities. ResultsWe found out that all studied ORMSs followed architectural and structural patterns in the literature, but often with distinct nomenclature, and some singularities. Many decisions, depending on how patterns are implemented and configured, affect how class models should be adapted, in order to create practical mappings to the database. ConclusionThis survey identified what structural patterns each ORMS followed, highlighting major structural decisions a designer must take, and its consequences, in order to turn analysis models into object oriented systems. It also offers a pattern based set of characteristics that developers can use as a baseline to make their own assessments of ORMSs.