Orthogonally Persistent Object Systems1

Persistent Application Systems (PASs) are of increasing social and economic importance. They have the potential to be long-lived, concurrently accessed and consist of large bodies of data and programs. Typical examples of PASs are CAD/CAM systems, office automation, CASE tools, software engineering environments and patient-care support systems in hospitals. Orthogonally persistent object systems are intended to provide improved support for the design, construction, maintenance and operation of PASs. The persistence abstraction allows the creation and manipulation of data in a manner that is independent of its lifetime thereby integrating the database view of information with the programming language view. This yields a number of advantages in terms of orthogonal design and programmer productivity which are beneficial for PASs. Design principles have been proposed for persistent systems. By following these principles, languages that provide persistence as a basic abstraction have been developed. In this paper the motivation for orthogonal persistence is reviewed along with the above mentioned design principles. The concepts for integrating programming languages and databases through the persistence abstraction and their benefits are given. The technology to support persistence, the achievements and future directions of persistence research are then discussed. 1 Introduction This paper presents a broad review of current research and achievements in orthogonally persistent object systems. It provides an advanced tutorial for those commencing research or advanced study in persistence, databases or database programming languages and a survey of the persistent language community's contribution to this growing research area. A particular goal is to summarise the existing achievements and to identify the current research issues. Orthogonally persistent object systems support a uniform treatment of objects irrespective of their types by allowing values of all types to have whatever longevity is required. The motive for establishing this uniform treatment is presented first. Subsequent sections of the paper present definitions, integration concepts, technology to support persistence and achievements. The penultimate section suggests some of the crucial areas of further research. Table 1 identifies the major topics covered. The aim of persistent programming is to support the activity of applications' construction for long-lived, concurrently accessed and potentially large bodies of data and programs; referred to here as Persistent Applications Systems (PASs). They are designated persistent application systems because the application often outlives its individual components and even its implementation technology. Typical examples of such PASs are: CAD/CAM systems, office automation, CASE tools, software, integrated hospital administration and medical systems, large …