Structured documents (e.g., SGML) can benefit a lot from database support and more specifically from object-oriented database (OODB) management systems. This paper describes a natural mapping from SGML documents into OODB's and a formal extension of two OODB query languages (one SQL-like and the other calculus) in order to deal with SGML document retrieval. Although motivated by structured documents, the extensions of query languages that we present are general and useful for a variety of other OODB applications. A key element is the introduction of paths as first class citizens. The new features allow to query data (and to some extent schema) without exact knowledge of the schema in a simple and homogeneous fashion. 1 Introduction Structured documents are central to a wide class of applications such as software engineering, libraries, technical documentation, etc. They are often stored in file systems and document access tools are somewhat limited. We believe that (object-oriented) d...

Many declarative query languages for object-oriented databases allow nested subqueries. This paper contains the first (to our knowledge) proposal to optimize them. A two-phase approach is used to optimize nested queries in the object-oriented context. The first phase---called dependency-based optimization---transforms queries at the query language level in order to treat common subexpressions and independent subqueries more efficiently. The transformed queries are translated to nested algebraic expressions. These entail nested loop evaluation which may be very inefficient. Hence, the second phase unnests nested algebraic expressions to allow for more efficient evaluation. 1 Introduction Many declarative query languages for object-oriented database management systems have been proposed in the last few years (e.g. [3, 5, 2, 18, 14]). To express complex conditions, access nested structure, or produce nested results, an essential feature found in these languages is the nesting of q...

Spatial data types or algebras for database systems should (1) be fully general, that is, closed under set operations, (2) have formally defined semantics, (3) be defined in terms of finite representations available in computers, (4) offer facilities to enforce geometric consistency of related spatial objects, and (5) be in-dependent of a particular DBMS data model, but cooperate with any. We present an algebra that uses realms as geometric domains underlying spatial data types. A realm, as a general database concept, is a finite, dynamic, user-defined structure underlying one or more system data types. Problems of numerical robustness and topological correctness are solved within and below the realm layer so that spatial algebras defined above a realm have very nice algebraic properties. Realms also interact with a DMBS to enforce geometric consistency on object creation or up-date. The ROSE algebra is defined on top of realms and offers general types to represent point, line, and region features, together with a comprehensive set of operations. It is described within a polymorphic type system and interacts with a DMBS data model and query language through an abstract object model interface. An example integration of ROSE into the object-oriented data model 02 and its query language is presented.

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Many declarative query languages for object-oriented (oo) databases allow nested subqueries. This paper contains a complete classification of oo nested queries and appropriate unnesting optimization strategies based on algebraic rewriting. We adapt some known relational techniques and introduce new ones that use and are concerned with features specific to object-oriented queries. In particular, we introduce two new and powerful grouping operators which will form the basis for our unnesting techniques.

This paper develops a query language for sequence databases, such as genome databases and text databases. The language, called SequenceDatalog, extends classical Datalog with interpreted function symbols for manipulating sequences. It has both a clear operational and declarative semantics, based on a new notion called the extended active domain of a database. The extended domain contains all the sequences in the database and all their subsequences. This idea leads to a clear distinction between safe and unsafe recursion over sequences: safe recursion stays inside the extended active domain, while unsafe recursion does not. By carefully limiting the amountof unsafe recursion, the paper develops a safe and expressive subset of Sequence Datalog. As part of the development, a new type of transducer is introduced, called a generalized sequence transducer. Unsafe recursion is allowed only within these generalized transducers. Generalized transducers extend ordinary transducers by allowing them to invoke other transducers as "subroutines." Generalized transducers can be implemented in Sequence Datalog in a straightforward way. Moreover, their introduction into the language leads to simple conditions that guarantee safety and finiteness. This paper develops two such conditions. The first condition expresses exactly the class of ptime sequence functions; and the second expresses exactly the class of elementary sequence functions.

This paper addresses the problem of defining views that span several objectbases. Views are expressed in terms of an object algebra. We are interested in the degrees of coupling and in the degrees of integrity maintained through multi-objectbase views. A key issue is the problem of global object identity. Each local system has its private object identifiers (OIDs) to represent objects. Globally, however, we need other mechanisms to uniquely refer to objects. We propose a technique that is based on the definition of (updatable) views: Queries to other objectbases are used as a referencing mechanism. The mechanism is useful as a formal basis for (partial or complete) schema integration in multi-objectbase systems. 1 INTRODUCTION Object-orientation is supposed to offer advantages in the context of multi-database systems. The advanced modeling capabilities of object models provide generalizations and the possibility to include computations (in the form of methods) in schema definitions. T...

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...

We survey the fundamental problems of designing general purpose, descriptive query languages for object-oriented database systems. Structural aspects of object models are investigated and their implications on the query language capabilities are analyzed and summarized as requirements that should be met by a `good' object-oriented query language. The type system of an OODB model has to distinguish atomic types (such as basic data types -- numbers, strings, -- or abstract object types) and constructed types (such as sets and tuples). Each of the type constructors should be supported by an adequate set of generic access and manipulation operators. The query language should allow orthogonal combination of operators according to the nesting structure of type constructors, the model should be closed against its operators, and the language should be adequate. The latter criterion ensures, for instance, that queries can be expressed that return objects instead of just data about objects ("object preservation"). Several recent proposals for query languages are evaluated against these criteria.

In this paper, we study the implementation of a spatial relational-like query language for geographic applications in an object-oriented environment. A prototype has been developed on top of the object-oriented database system O 2 . We report on our design choices, describe the current status of implementation and conclude on the suitability of the object-oriented approach and more specifically of the O 2 system for developing such applications. 1 Introduction Data intensive geographic applications such as cartography, urban planning and natural resource management are built using Geographic Information Systems (GIS). GISs are database systems that allow the manipulation, storage and retrieval of geographic data and the display of data in the form of maps. Conventional database management systems (DBMS) do not address correctly the needs of geographic applications: the underlying data models, query languages and access methods were designed to deal with simple data types such as integ...