Showing papers on "Class (philosophy) published in 1982"

Horn clauses and database dependencies

Abstract: Certain first-order sentences, called "dependencies," about relations in a database are defined and studied. These dependencies seem to include all prewously defined dependencies as special cases A new concept is mtroduced, called "faithfulness (with respect to direct product)," which enables powerful results to be proved about the existence of "Armstrong relations" in the presence of these new dependencies. (An Armstrong relaUon is a relation that obeys precisely those dependencies that are the logical consequences of a given set of dependencies.) Results are also obtained about characterizing the class of projections of those relations that obey a given set of dependencies.

Classes and Cladists

Abstract: Beatty, J. (Department of the History of Science, Harvard University, Cambridge, Massachusetts 02138) 1982. Classes and cladists. Syst. Zool., 31:25-34.-Disillusions concerning evolutionary theorizing have forced a split among cladists. The disillusioned group of "pattern" cladists seeks an evolutionarily neutral brand of cladistics. But pattern cladistics is not, after all, evolutionarily neutral. Rather, it is at odds with evolutionary theorizing. [Classes; cladistics; evolution; phylogenetics; Popper.] Hull (1976, 1978) has argued that if species are interpreted as classes, as is traditional, then a little problem arisesnamely, species cannot evolve. But according to our best accounts, they do. Thus there is an inconsistency in our understanding of species. In Section 1, I reformulate the difficulty in order to reemphasize the problem. My ultimate purpose, however, is to discuss the differences between two ever more distinguishable groups of cladists in terms of the difficulty that this problem poses for each. In Section 2, I discuss the background to the widening split between phylogenetic and pattern cladists. Finally, in Section 3, I argue that pattern cladism has conceptual drawbacks that stem from the problem outlined in Section 1. 1. Evolutionary Theory vs. a School of Systematics 1.1The sort of interpretation of species that Hull finds most objectionable from the viewpoint of evolutionary biology is one according to which a species name is defined in terms of the set of properties operationally employed to recognize and distinguish members of that.species from other species. Thus, we recognize and distinguish polar bears (Ursus maritimus) from brown bears (Ursus arctos) by, among other traits, their white coats. Consequently, we might include the differentiating property "white coat" in the definition of "Ursus maritimus." We would also include the other properties that distinguish maritimus from other species of Ursus, as well as those properties that distinguish Ursus from other genera of its family, and the properties that distinguish its family from other families of its order, and so on. To say that species so designated are "classes" is just to say that they are collections of objects that share the defining properties of the species name. Two kinds of classes, hence two kinds of class interpretations of species, are commonly distinguished (e.g., Beckner, 1959, Chapter 5; Caplan, 1980). The name of an "Aristotelian class" is defined in terms of properties that are collectively necessary and sufficient for membership in the group. Members of a "cluster class," on the other hand, need only satisfy most of the defining properties of the class name. So any defining property of the name of an Aristotelian class is present in 100% of the members of that class, while any defining property of a cluster class is present in a high proportion of members of the class. One can imagine still other sorts of class interpretations of species. For example, the defining properties of a species name need not be the usual sorts of properties operationally used to recognize and distinguish members of different species. They might instead be relational properties like interbreeding and ancestor-descendant relations specified with regard to model members of the group. Alternative class interpretations like the latter can be worked out. But it is the interpretation in terms of the usual recognition properties that is at issue in Hull's work and in the recent division

Two-Way Counter Machines and Diophantine Equations

Abstract: Let Q be the class of deterministic two-way one-counter machines accepting only bounded languages. Each machine in Q has the property that in every accepting computation, the counter makes at most a fixed number of reversals. We show that the emptiness problem for Q is decidable. When the counter is unrestricted or when the machine is provided with two reversal-bounded counters, the emptiness problem becomes undecidable. The decidability of the emptiness problem for Q is useful in proving the solvability of some numbertheoretic problems. It can also be used to prove that the language L = {u1iu2i2|i≥0} cannot be accepted by any machine in Q (u1 and u2 are distinct symbols). The proof technique is new in that it does not employ the usual "pumping", "counting", or "diagonal" argument. Note that L can be accepted by a deterministic two-way machine with two counters, each of which makes exactly one reversal.

On the definition of likelihood in abstract spaces

Abstract: The aim of this work is to give a rigorous definition of likelihood without any reference to the peculiarities of Euclidean spaces, and is thus applicable to a larger class of problems with a more complex result space. Here we intend to offer the simplest possible discussion of the ideas on which likelihood methods are based, with some remarks about their links to some classical measure-theoretical concepts, such as Radon—Nikodym derivatives. Since the definition of likelihood relies on the topological structure of the result space, it is necessary to point out the connections that it has with the measure-theoretical one, mostly caused by the fact that singletons, i.e. the actual observable results, are usually measure-zero sets.

The Effect of Two Methods of Instruction on Parent Child Interaction.

Abstract: The purpose of this study was to compare two methods of instruction in the teaching of parent-child interaction skills. By comparing a highly structured method and a less structured method of instruction, data were compiled in order to determine the manner in which interaction skills could be most effectively taught to parents of threeand four-year old children. The study was conducted in six parishes within Louisiana: Ascension, Lafourche, Livingston, Plaquemines, Pointe Coupee and Ouachita. Forty-five subjects in the study were volunteers who were recruited for parent-child inter­ action classes by the Extension Home Economist in each parish. The Extension Home Economist served as the teacher and re­ ceived detailed instruction on conducting classes according to a prescribed format for each of the two instructional approaches being compared. The study was performed in a two year period beginning in the summer of 1980 and ending in the summer of 1982. The first method of instruction involved a highly structured approach which utilized video taped demonstra­ tions, written materials, role play, group discussion and nine weekly class meetings in teaching parents methods to interact with their preschool aged children. Nine toys designed for use by parents in teaching children concepts

A Framework for data structurest

Abstract: In this paper we outline a framework for data structures in the spirit of the Vienna Definition Language but extended to the most general class of objects, namely arbitrary directed rooted graphs in which the information asociated with each node is either empty or elementrary or an object in the general class. Since many data structures cannot be modelled by tree structures in a natural way, such a generalisation to graphs is desirable. Furthermore, the concept of hierarchy in which a node may serve for a arbitrary complex substructure supports a structured view of complex data objects.