ORION-2 is a commercially available, federated, object-oriented database management system designed and implemented at MCC. One major architectural innovation in ORION-2 is the coexistence of a shared databese and a number of private databases. The shared database is accessible to all authorized users of the system, while each private database is accessible to only the user who owns it. A distributed database system with a shared database and private databases for individual users is a natural architecture for data-intensive application environments on a network of workstations, notably computer-aided design and engineering systems. This paper discusses the benefits and limitations of such a system and explores the impact of such an architecture on the semantics and implementation of some of the key functions of a database system, notably queries, database schema, and versions. Although the issues are discussed in the context of an object-oriented data model, the results (at least significant portions thereof) are applicable to database systems supporting other data models.

Various architectural components of ORION-1 and ORION-1SX are described and a review of the current implementation is provided. The message handler receives all messages sent to the ORION system. The object subsystem provides high-level data management functions, including query optimization, schema management, long data management (including text search) and support for versionable objects, composite objects, and multimedia objects. The transaction management subsystem coordinates concurrent object accesses and provides recovery capabilities. The storage subsystem manages persistent storage of objects and controls the flow of objects between the secondary storage device and main memory buffers. In ORION-1, all subsystems reside in one computer. The ORION-1SX architecture is significantly different from ORION-1 in the management of shared data structures and distribution of these subsystems and their components.>

Domain analysis, a classical approach to the indentification of reusable software modules, relies on in-depth studies of existing systems, published algorithms, and structures to discern generic architectures for large classes of systems. An architecture is a template in which building-block modules can be plugged. Interfaces are standardized to make blocks interchangeable. The authors explain how domain analysis has led them to a building-blocks technology for file management systems (FMSs), and they describe their most recent prototype, an FMS synthesizer. The synthesizer enables a customized FMS to be assembled from prewritten components in minutes at virtually no cost.>

In object-oriented systems, an object may recursively reference any number of other objects. The references, however, do not capture any special relationships between objects. An important semantic relationship which may be superimposed on a reference is the IS-PART-OF relationship between a pair of objects. A set of objects related by the IS-PART-OF relationship is collectively called a composite object.

There are two major issues to address to achieve integration of an object-oriented programming system with a database system. One is the language issue: an object-oriented programming language must be augmented with semantic data modeling concepts to provide a robust set of data modeling concepts to allow modeling of entities for important real-world applications. Another is the computational-model issue: application programmers should be able to access and manipulate objects as though the objects are in an infinite virtual memory; in other words, they should not have to be aware of the existence of a database system in their computations with the data structures the programming language allows. This paper discusses these issues and presents the solutions which we have incorporated into the ORION object-oriented database system at MCC.

In this paper, we describe transaction management in ORION, an object-oriented database system. The application environments for which ORION is intended led us to implement the notions of sessions of transactions, and hypothetical transactions (transactions which always abort). The object-oriented data model which ORION implements complicates locking requirements. ORION supports a concurrency control mechanism based on extensions to the current theory of locking, and a transaction recovery mechanism based on conventional logging.

A DAG (direct acyclic graph) is an important data structure which requires efficient support in CAD (computer-aided design) databases. It typically arise from the design hierarchy, which describes complex designs in terms of subdesigns. A study is made of the properties of the three types of clustered sequences of nodes for hierarchies and DAGs, and algorithms are developed for generating the clustered sequences, retrieving the descendants of a given node, and inserting new nodes into existing clustered sequences of nodes which preserve their clustering properties. The performance of the clustering sequences is compared.>

A novel yet simple technology is presented that enables customized database management systems (DBMSs) to be developed rapidly. The authors are designing an extensible DBMS, called GENESIS, which is based on this theory. They give a detailed description of their first operational prototype. DBMS software components in GENESIS can be written in a few months. When all components for a target DBMS are present, writing the architecture specification of the DBMS and reconfiguring GENESIS takes a few hours and can be accomplished with negligible cost.>

In this paper, we elaborate on three major enhancements to the conventional object-oriented data model, namely, schema evolution, composite objects, and versions. Schema evolution is the ability to dynamically make changes to the class definitions and the structure of the class lattice. Composite objects are recursive collections of exclusive components that are treated as units of storage, retrieval, and integrity enforcement. Versions are variations of the same object that are related by the history of their derivation. These additional features are strongly motivated by data management requirements of object-oriented applications from the AI, CAD/CAM, and OIS (office information systems with multimedia documents) domains. An object-oriented data model, with these enhancements, has been incorporated into ORION, a prototype database system developed at MCC as a vehicle of research into object-oriented databases.

Many applications in such domains as computer-aided design require the capability to define, store and retrieve as a single unit a collection of related objects known as a composite object. A composite object explicitly captures and enforces the IS-PART-OF integrity constraint between child and parent pairs of objects in a hierarchical collection of objects. Further, it can be used as a unit of storage and retrieval to enhance the performance of a database system.

Presented in this paper is the data model for ORION, a prototype database system that adds persistence and sharability to objects created and manipulated in object-oriented applications. The ORION data model consolidates and modifies a number of major concepts found in many object-oriented systems, such as objects, classes, class lattice, methods, and inheritance. These concepts are reviewed and three major enhancements to the conventional object-oriented data model, namely, schema evolution, composite objects, and versions, are elaborated upon. Schema evolution is the ability to dynamically make changes to the class definitions and the structure of the class lattice. Composite objects are recursive collections of exclusive components that are treated as units of storage, retrieval, and integrity enforcement. Versions are variations of the same object that are related by the history of their derivation. These enhancements are strongly motivated by the data management requirements of the ORION applications from the domains of artificial intelligence, computer-aided design and manufacturing, and office information systems with multimedia documents.