David Rozenshtein

Windows on the world

We discuss the philosophy, history and theory of window functions. Window functions (sometimes called connections) are a means to treat a relational database as a semantic whole, rather than as an arbitrary collection of relations. Simply stated, a window function maps a database state and a relation scheme to a relation over the scheme. Window functions are the basis for all existing universal scheme interfaces. We present an assumption inherent in universal scheme interfaces, the unique role assumption.Window functions have evolved along two paths, giving rise to computational definitions and weak instance definitions. We examine several examples of each type of window function, with special attention to the association-object window function of PIQUE. We then look at properties we feel a reasonable window function should satisfy, notably the containment condition and faithfulness. We also define implicit objects, which are relation schemes that a window function treats in a special manner, and which are useful for describing the behavior of window functions.

A software development environment for law-governed systems

This paper describes a software development environment based on a new approach for managing large-scale evolving systems. Under this approach, the conventional notion of a <italic>system</italic> is augmented with a new component called the <italic>law of the system</italic>, which is an <italic>explicit</italic> and <italic>strictly enforced</italic> set of rules about the operation of the system, about its evolution, and about the evolution of the law itself. The resulting combination is called a <italic>law-governed system.</italic>

A law-based approach to object-oriented programming

The central idea behind this paper is that the discipline governing the exchange of messages between objects should be specifiable by the programmer in the form of an explicit law of the system . We show how, starting from a very primitive foundation, which presumes neither encapsulation nor inheritance, one can establish various forms of both, as well as other useful disciplines, simply by means of appropriate laws.

PIQUE: A relational query language without relations

Abstract Relational database systems have gone far towards providing users with physical data independence. To use a relational database, users need not know the physical storage structures of relations, and are protected from changes in these structures. However, a user must still navigate among relations. In other words, if the information needed to answer a question spans several relations, he must explicitly specify how these relations are to be combined. Physical data independence is not enough. A user should also be afforded some degree of structural data independence. More specifically, he should be able to pose queries without having to explicitly navigate among relations in the database. Instead, the system should do the navigation for him. We consider universal scheme interfaces as a means for automatic database navigation, and introduce the concept of a generator as central to such navigation. We describe a particular generator based on the semantic notions of reducible and irreducible facts, and present PIQUE, an attribute-based query language designed to work with this generator. PIQUE is a concise, yet powerful, language with natural semantics. A distinguishing feature of PIQUE is that tuple variables in queries are bound implicitly and that the logical connectives “and”, “or,” and “not” can affect the binding, and, therefore, take on “semantic overtones.” Furthermore, the semantic interpretation PIQUE gives to these connectives is more natural than the one given by most other query languages. In the Appendix, we present PIQUEs formal syntax and semantics, along with the proof that PIQUE is relationally complete.

Configuration management by consensus: an application of law-governed systems

It is self-evident that if one wants to model and control the cooperative process of software development, one must provide for cooperative decision making. In particular, one should be able to base the decision on whether and how to carry out a given operation on the consensus of several, possibly independent, agents. It is important to emphasize that this is not just a matter of computing the conjunction of some set of conditions. One must also provide a mechanism for establishing any desired consensus structure, which would specify who is allowed to state which kinds of concerns regarding this operation, and what the relationship among these concerns should be. In this paper we propose a general framework for such decision making by consensus, which is based on the concept of law-governed software development. As a concrete application domain in which to illustrate this framework, we consider here the issue of configuration binding.

Representing Roles in Universal Scheme Interfaces

Users of a relational database must explicitly navigate between relations in order to establish a connection among a set of attributes spanning several relation schemes. While a universal scheme interface to a relational database provides users with automatic navigation, it usually imposes on the database a unique role assumption. This assumption requires every attribute name to represent a unique role in the database, so that connections among sets of attributes are unambiguous.

Controlling the use and evolution of database systems: A Prolog-based approach

Abstract:This paper presents a model that provides a single comprehensive mechanism to control the use, operation, and evolution of database systems. This model unifies several concepts generally considered to be quite distinct. In particular, it minimizes the formal distinction between the users of the database, the programs embedded in it, and even the administrators and the programmers maintaining it. Furthermore, under this model, the concepts of subschema and of program module are replaced with a single concept of frame, which serves as the locus of power and of activity in the system. Moreover, the proposed control mechanism is closed, in the sense that the process of establishing controls is itself controllable by the same mechanism. This can be used to formalize and enforce a variety of managerial policies about the use and evolution of database systems.

System = program + users + law

This paper is based on a new approach for dealing with large scale software systems. This approach is based on the concept of a <italic>Law-Governed System</italic>, which is a triple >program, users, law< where the <italic>law</italic> is an <italic>explicit</italic> and <italic>strictly enforced</italic> set of rules about the structure and operation of the program, and about the evolution of the entire system. We describe Darwin, a skeleton of a programming environment that supports our notion of law-governed systems. Darwin is based on the <italic>object-oriented</italic> programming paradigm and uses <italic>logic programming</italic> to express and enforce the law.

A controllable Prolog database system

This paper presents a model that provides a single comprehensive mechanism to control the use, operation and evolution of database systems. This model unifies several concepts generally considered to be quite distinct. In particular, it minimizes the formal distinction between the users of the database, the programs embedded in it and even the administrators and the programmers maintaining it. Furthermore, under this model, the concepts of subschema and of program module are replaced with a single concept of frame, which serves as the locus of power and of activity in the system. Moreover, the proposed control mechanism is closed, in the sense that the process of establishing controls is itself controllable by the same mechanism. This can be used to formalize and control managerial policies about the use and evolution of database systems.

Representing roles in universal scheme interfaces

In universal scheme interfaces to relational databases, an attribute name must represent a unique role in the database, so that the connection among a set of attributes is unambiguous. A drawback to this requirement is that several attributes can represent the same underlying class of of entities, but the relationship among those attributes is not captured in the database scheme. As our method for relating attributes uses natural joins, some semantically meaningful.