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...

We describe the TIGUKAT objectbase management system that is under development at the Laboratory for Database Systems Research at the University of Alberta. TIGUKAT has a novel object model whose identifying characteristics include a purely behavioral semantics and a uniform approach to objects. Everything in the system, including types, classes, collections, behaviors, functions as well as meta-information, is a first-class object with well-defined behavior. In this way, the model abstracts everything, including traditional structural notions such as instance variables, method implementation and schema definition, into a uniform semantics of behaviors on objects. Our emphasis in this paper is on the object model, its implementation, the persistence model and the query language. We also (briefly) present other database management functions that are under development such as the query optimizer, the version control system and transaction manager.

This paper describes a new object-oriented model and query algebra that will be used as an input language for the query optimizers that are being built as a part of the EREQ project. The model adopts a uniform view of objects and values and separates syntactic, semantic, and implementation concerns. The algebra addresses issues of type-defined equality and duplicate elimination as well as extensions to bulk types other than sets. 1 Introduction Recently, a great deal of work has been done on the topic of object-oriented query algebras [27, 22, 11] and the modeling of bulk types [4, 25, 19]. These proposals as well as those of other researchers on the topic have explored some of the fundamental issues and provided the starting point for the work reported here. AQUA (A QUery Algebra) is the result of a joint effort among researchers who have participated in the design of previous algebras [26, 30, 31]. AQUA has been designed to address a number of detailed modeling issues that we beli...

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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...

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...

Data Types New base types can be added to the EXTRA data model via the EXTRA abstract data type facility. To add a new ADT, the person responsible for adding the type begins by writing (and debugging) the code for the type in the E programming language. E is an extension of C++ [Stro86] that was developed as part of the EXODUS project. E serves as the implementation language for access methods and operators for systems developed using EXODUS. It is also the target language for the query compiler, and (most importantly for our purposes here) the language in which base type extensions will be defined. E extends C++ with a number of features to aid programmers in data- 89 base system programming, including "dbclasses" for persistent storage, class generators for implementing "generic" classes and functions, iterators for use as a control abstraction in writing set operations, and built-in class generators for typed files and variable-length arrays [Rich87]. Suppose that we wanted to add...

Querying source code interactively for information is a critical task in reverse engineering of software. However, current source code query systems succeed in handling only small subsets of the wide range of queries possible on code, trading generality and expressive power for ease of implementation and practicality. We attribute this to the absence of clean formalisms for modeling and querying source code. In this paper, we present an algebraic framework (Source Code Algebra or SCA) for modeling and querying source code. The framework forms the basis of our query system for C source code. An analogy can be drawn with relational algebra, which forms the basis for relational databases. The benefits of using SCA include the integration of structural and flow information into a single source code data model, the ability to process high-level source code queries (command-line, graphical, relational, or pattern-based) by translating them into SCA expressions which can be evaluated using th...

Object-oriented computing is influencing many areas of computer science including software engineering, user interfaces, operating systems, programming languages and database systems. The appeal of object-orientation is attributed to its higher levels of abstraction for modeling real world concepts, its support for incremental development and its potential for interoperability. Despite many advances, object-oriented computing is still in its infancy and a universally acceptable definition of an object-oriented data model is virtually nonexistent, although some standardization efforts are underway. This report presents the TIGUKAT 1 object model definition that is the result of an investigation of object-oriented modeling features which are common among earlier proposals, along with some distinctive qualities that extend the power and expressibility of this model beyond others. The literature recognizes two perspectives of an object model: the structural view and the behavioral view. ...