The notion of class is ubiquitous in computer science and is central in many formalisms for the representation of structured knowledge used both in knowledge representation and in databases. In this paper we study the basic issues underlying such representation formalisms and single out both their common characteristics and their distinguishing features. Such investigation leads us to propose a unifying framework in which we are able to capture the fundamental aspects of several representation languages used in different contexts. The proposed formalism is expressed in the style of description logics, which have been introduced in knowledge representation as a means to provide a semantically well-founded basis for the structural aspects of knowledge representation systems. The description logic considered in this paper is a subset of first order logic with nice computational characteristics. It is quite expressive and features a novel combination of constructs that has not been studied before. The distinguishing constructs are number restrictions, which generalize existence and functional dependencies, inverse roles, which allow one to refer to the inverse of a relationship, and possibly cyclic assertions, which are necessary for capturing real world

Although the mathematical foundations of relational databases are very well established, the state of affairs for object-oriented databases is much less satisfactory. We propose a semantic foundation for object-oriented databases based on a simple logic of change called rewriting logic, and a language called MaudeLog that is based on that logic. Some key advantages of our approach include its logical nature, its simplicity without any need for higher-order features, the fact that dynamic aspects are directly addressed, the rigorous integration of user-definable algebraic data types within the framework, the existence of initial models, and the integration of query, update, and programming aspects within a single declarative language. 1 Introduction Although the mathematical foundations of relational databases are very well established, the state of affairs for object-oriented databases is much less satisfactory. This is unfortunate, because object-oriented databases seem to have impor...

We consider evaluation strategies for database queries expressed in three functional query languages: the complex value algebra, the simply typed lambda calculus, and method schemas. Each of these query languages derives its expressive power from a different primitive: the complex value algebra from the powerset operator, the simply typed lambda calculus from list iteration, and method schemas from recursion. We show that "natural" evaluation strategies for these primitives may lead to very inefficient space usage, but that with some simple optimizations many queries can be evaluated with little or no space overhead. In particular, we show: (1) In the complex value algebra, all expressions with set nesting depth at most 2 can be evaluated in pspace, and this set of expressions is sufficient to express all queries in the polynomial hierarchy; (2) In the simply typed lambda calculus with equality and constants, all query terms of order at most 5 (where "query term" is a syntactic condition on types) can be evaluated in pspace, and this set of terms expresses exactly the pspace queries; (3) There exists a set of second-order method schemas (with no simple syntactic characterization) that can be evaluated in pspace, and this set of schemas is sufficient to express all pspace queries.

An iterator is proposed that allows to apply sequences of update operations in a set-oriented way with deterministic semantics. Because the mechanism is independent of a particular model, it can be used in the relational and in object-oriented ones. Thus, the deterministic semantics of embedded SQL cursors, and of triggers that are applied after (set-oriented) SQL updates can be checked. Furthermore, the iterator can be used to apply object-oriented methods, which are usually update sequences defined on a single object, also to sets in a deterministic way. It turns out that the criteria that guarantee determinism are also used in semantic or multi-level concurrency control. 1 Introduction The paper deals with the general problem of defining update languages that are comparable in expressive power to typical query languages. When designing such an update language, one should pursue the following objectives: ffl genericity: update operations should be applicable to all types of objects...

Business Artifacts are the core entities used by businesses to record information pertinent to their operations. Business operational models are representations of the processing of business artifacts. Traditional process modeling approaches focus on the actions taken to achieve a certain goal (verb-centric). Business artifact-centric modeling starts by identifying what is acted upon (noun-centric), and constructs business operational models by identifying the tasks/actions that business actors execute to add business value. In this paper, we identify important classes of properties on artifact-centric operational models. In particular, we focus on persistence, uniqueness and arrival properties. To enable a static analysis of these properties, we propose a formal model for artifact-centric operational models. We show that the formal model guarantees persistence and uniqueness. We prove that, while checking an arrival property is undecidable in general, under a restricted version of the formalism, an arrival property can be checked in EXPTIME. 1

We study a mechanism that supports the migration of objects from one class of an OODB to another, thereby enabling us to model the same object playing different roles throughout its lifetime. Object migration may introduce typing conflicts due to the different typing constraints imposed by the classes. We present a coercion-like adaptation process that automatically resolves these conflicts. The process combines re-classification of objects and modification of attributes. We study the computational complexity of the problem, and show that the adaptation process can be performed efficiently in databases with covariant schemas. 1 Introduction Two of the dogmas of object-oriented databases are that objects have existence independent of their value (the principle of object identity) and that objects are grouped into classes that capture their commonalities. But there is a logical next step that has not been studied in depth yet: why not let objects retain their identity, not only when th...

Databases provide one of the main concrete scenarios for finitemodel theory within computer science. This paper presents an informal overview of database theory aimed at finite-model theorists, emphasizing the specificity of the database area. It is argued that the area of databases is a rich source of questions and vitality for finite-model theory.

. An evolution language is composed of an instance update language, a schema update language, and a mechanism to combine them. We present a formal evolution language for object-oriented database management systems. This language allows to write programs to update simultaneously both the schema and the instance. Static checking of these programs insures that the resulting database is consistent. We propose an autonomous instance update language, based on an adequate specific query language and a pure instance update language. The main features of the query language are a formal type inference system including disjunctive types, and the decidability of the satisfiability problem, despite a negation operator. The pure instance update language allows objects migration, and objects and references creation and deletion; its semantics is declarative, and an algorithm to compute it is presented. We propose an evolution mechanism for combining this instance update language with a...

Object-oriented databases have brought major improvements in data modeling by introducing notions such as inheritance or methods. Extensions in many directions are now considered with introductions of many concepts such as versions, views or roles. These features bring the risk of creating monster data models with a number of incompatible appendixes. We do not propose here any new extension or any novel concept. We show more modestly that many of these features can be formally and (we believe) cleanly combined in a coherent manner. 1 Introduction We propose an extension of IQL [AK89], therefore the name 1 IQL(2), to encompass many new extensions to the core OODB models that have been considered separately in the past. The model is based on two not novel concepts: (i) contexts that are used to parameterized class and relation names; and (ii) views to define intensional data. This brings two kinds of ubiquity to objects, i.e., the same object may belong really or virtually to several ...

: Object-oriented databases enforce behavioral schema consistency rules to guarantee type safety, i.e., that no run-time type error can occur. When the schema must evolve, some schema updates may violate these rules. In order to maintain behavioral schema consistency, traditional solutions require significant changes to the types, the type hierarchy and the code of existing methods. Such operations are very expensive in a database context. To ease schema evolution, we propose to support exceptions to the behavioral consistency rules without sacrificing type safety. The basic idea is to detect unsafe statements in a method code at compile-time and check them at run-time. The run-time check is performed by a specific clause that is automatically inserted around unsafe statements. This check clause warns the programmer of the safety problem and lets him provide exception-handling code. Schema updates can therefore be performed with only minor changes to the code of methods. Key-words: Ob...