We examine the problem of type evolution in an objectoriented database environment. Type definitions are persistent objects in the database and as such may be modified and shared. The effeets of changing a type extend to objects of the type and to programs that use objeets of the type. We propese a solution to the problem through an extension of the semantic data model. A ehange in the interfaee defined by a type may result in errors when programs use new or old objects of the type. Through the use of an abstraction of the type over time, timestamping and error handling mechanisms provide support for the type designer in creating compatible versions of the type. The mechanisms are incorporated Into the behavior defined by the type and are inherited via the type-lattice. 1.

This paper describes the basic data model of an object-oriented database and the basic architecture of the system implementing it. In particular, a secondary storage segmentation scheme and a transaction-processing scheme are discussed. The segmentation scheme allows for arbitrary clustering of objects, including duplicates. The transaction scheme allows for many different sharing protocols ranging from those that enforce serializability to those that are nonserializable and require communication with the server only on demand. The interaction of these two features is described such that segment-level transfer and object-level locking is achieved.

We define an algebra which synthesizes relational query concepts with object-oriented databases. The algebra fully supports abstract data types and object identity while providing associative access to objects, including a unique join capability. The operations take an abstract view of objects and access typed collections of objects through the public interface defined for the type. The algebra supports access to relationships implied by the structure of the objects, as well as the definition and creation of new relationships between objects. The structure of the algebra and the abstract access to objects offer opportunities for query optimization. 1 Introduction Object-oriented databases are emerging in response to a requirement for more complete modelling of complex data in modern design and office environments. Such databases attempt to combine the modelling power of object-based programming models with traditional database concepts such as persistence, data sharing, cons...

data types can also define equality operations. Such operations are typespecific and will not be considered in this paper. Objects can be represented graphically, where nodes are objects or atomic values, arcs connect collection type objects to all objects that are members of the collection, and arcs connect non-collection type objects to the values of all properties of that object (similarly to [11] for example). Nodes representing atomic values are leaves and are labelled with the atomic value. Nodes representing non-atomic objects are labelled with an (artificial) object identifier as well as the object type. Types can be labelled symbolically, using ? for set types, !? for tuple types, and ffl for other abstract data types. In Figure 1 three set objects are represented graphically. Note that graphs b and c represent 3-equal set objects: C 2 and C 1 are 1-equal, making t 3 and t 5 2-equal (t 1 and t 4 are 1-equal, therefore 2-equal), thus S 2 and S 3 are 3-equal. Object S1 (graph a...

This paper compares two approaches to meeting the data handling requirements of Intermedia, a hypermedia sysfem developed at fhe institute for Research in information and Scholarship at Brown Universify. Intermedia, though wriffen using an object-oriented programming language, relies on a traditional relafional database management system for data storage and retrieval. We examine the ramifications of replacing the relational database with an object-oriented database. We begin by describing the important characteristics each database system. We then describe Intermedia and give an overview of its architecture and its dafa handling requirements. We explain why and how we used a relational database management system and the problems that we encountered with this system. We then present the design of art objectodenfed database schema for Intermedia and compare the relational and object-oriented dafabase management system approaches. 1. lNTRODUCTlON The Institute for Research in Information and

IRO-DB is an object-oriented federated database system to access multiple data sources from an ODMG compliant C++ inteqace. The system encompasses several components, including local database adapters to homogenize local data sources, a remote object access component to query and transfer collections of objects from site to site, ana ’ a mediator to de$ne integrated views, decompose ana’ optimize queries, and combine results. This paper gives an overview of the IRO-DB architecture and describes in detail the cost evaluator currently under elaboration for the next version of the distributed query optimizer. The cost model is composed of a set of mathematical formulas with coejficients to estimate the cost of the search operators. The coeficients are deduced from a calibrating objectoriented database composed of linked collections of objects. A tuning application is run on each local site to adjust the cost formulas and fix the coeficients. We report on the tuning of 02 and ObjectStore. We show that the estimation is quite accurate for path traversals with the 007 benchmark on top of ObjectStore. 1.

In this thesis we address the problem of providing efficient processing of queries in the extensible environment induced by object-oriented databases. We define a framework for query processing in an object-oriented database and develop designs for major components of this framework. The framework encompasses an object-oriented data model, an algebra to query over that model, transformation rules for the algebra, an internal representation for queries expressed in the algebra, a cost model for analyzing query expressions, and an architecture for an extensible query optimizer. The major contributions of this thesis are an algebra and transformation rules, a representation, and an architecture for extensible query optimization. We show how these components fit into the framework and interact with each other. The EQUAL query algebra presented in this thesis is the first query algebra for object-oriented database systems to be completely consistent with data abstraction, and one of the few...

Query optimizers for persistent object systems should be extensible to react to user-supplied abstract types. Current architectures support only a single, non-extensible technique for controlling the optimization process. We propose an alternative to the current extensible architectures that will support multiple optimizer control strategies and the addition of new control strategies. The optimizer consists of a collection of optimization regions, each of which can transform queries according to a particular control strategy, set of transformations and cost model. A global optimizer control coordinates the movement of a query between these regions. This architecture provides extensibility in the optimizer's repertoire of control strategies through the addition of new regions. In this paper we describe our approach and demonstrate its utility by following the optimizer as it works on an example query. The optimizer will move the query between three distinct regions. The different region...

In this paper we present how an open object-oriented database model can be used for modelling argumentative networks utilized by an authoring system in a hypermedia environment. The concepts of our open object-oriented data model are presented and an example of an argumentative schema represented as a hypermedia network is given. The paper shows how the concepts of the data model, especially the concept of metaclasses, can be employed in order to specify the semantics of the primitive constituents of an argumentative network and to tailor the data model for these specific needs.

An object-oriented database model can support features such as abstract data types, methods, encapsulation, subtyping (or inheritance), complex structures, and object identity. The processing of queries in such a model also entails support for these features. Query optimization will require new techniques for supporting the object-oriented features. Although many of the problems that must be solved by an object-oriented query optimizer are similar to problems solved by relational and extensible optimizers, there are also many problems that are unique to the object-oriented model. In this paper we explore some of the problems that are encountered when trying to optimize queries in an object-oriented database. We present these problems in the context of the modelling constructs which generate the problem. We also survey current approaches to solving some of these problems and discuss problems that are not addressed by these approaches. 1 Introduction We are interested in effi...