Showing papers on "Class (philosophy) published in 1988"

Unfounded sets and well-founded semantics for general logic programs

Abstract: A general logic program (abbreviated to “program” hereafter) is a set of rules that have both positive and negative subgoals. It is common to view a deductive database as a general logic program consisting of rules (IDB) sitting above elementary relations (EDB, facts). It is desirable to associate one Herbrand model with a program and think of that model as the “meaning of the program,” or its “declarative semantics.” Ideally, queries directed to the program would be answered in accordance with this model. We introduce unfounded sets and well-founded partial models, and define the well-founded semantics of a program to be its well-founded partial model. If the well-founded partial model is in fact a model, we call it the well-founded model, and say the program is “well-behaved”. We show that the class of well-behaved programs properly includes previously studied classes of “stratified” and “locally stratified” programs Gelfand and Lifschits have proposed a definition of “unique stable model” for general logic programs. We show that a program has a unique stable model if it has a well-founded model, in which case they are the same. We discuss why the converse is not true.

Attitudes and Contents

Abstract: G. F. Schueler's paper puts in a forceful way various reservations about my treatment of indirect contexts, on behalf of the position I have called "quasi-realism."1 His opposition is, I think, as complete as could be: it is not only that my treatment has been incomplete, which I happily concede, or that its formulation has been defective, which I am prepared to believe, but also that nothing like it could possibly succeed. That at least is the proper consequence of some of his views-on logical form, and on validity, and on the nature of commitment. For example, if to show that an inference has "the logical form" or "is an instance" of modus ponens involves taking it as "the realist picture" has it, then no attempt to explain it in other terms will be compatible with its having that form. Again, if validity is ("as it is used in logic") defined in terms of the impossibility of premises being true and conclusions false, then persons reluctant to apply truth and falsity to any of the elements of an inference will have to admit that the inference is not valid, as the term is used in logic. Third, if "talk of 'commitments' is problematic for the antirealist" then antirealism will make no headway by thinking of a more general class of commitments than those with representative or realistic truth conditions. Fortunately, none of these contentions seems to me correct. Since the survival of quasi-realism even in spirit demands their rebuttal, I shall start by considering them in turn. 1. It is not too clear what it is for an argument to have the logical form of modus ponens. If that is a remark about syntactical form, then obviously having that logical form is compatible with any number of deep and different semantics for the components. To show this compare "P. P->Q, so Q" with the implication taken as truth-functional, with the same seeming argument taken as some suppose the English take it: P->Q is the commitment of one who attributes a high probability to Q conditional upon P. Which is the true modus ponens? If we plump for either exclusively, we face the uncomfortable consequence that it becomes

Object class definition by generalization using upward inheritance

Abstract: The authors show how the process of object class definition by generalization can be incorporated into object-oriented systems. Traditional message handling, which is mainly based on downward property inheritance, is revised and extended to upward property inheritance, so that a maximum of reusability of code and data can be achieved. Different types of semantic relationships that may hold between a generalization class's subclasses and their attributes are identified. The different semantic relationships can then be utilized to produce different default treatments of messages and upward property propagation.

Name collision in multiple classification hierarchies

Abstract: Supporting multiple classification in object-oriented programming languages is the topic of discussion in this paper. Supporting multiple classification gives rise to one important question -- namely the question of inheritance of attributes with identical names from multiple paths in the classification hierarchy. The problem is to decide how these multiple classification paths are reflected in the class being denned. One of the conclusions in this paper is, that by choosing strict and simple inheritance rules, one is excluding some particular usages of multiple classification. This leads to the notion of attribute-resolution at class definition, which means that the programmer in some cases is forced or allowed to resolve the potential ambiguity of the inherited names. The concept of attribute-resolution is managed through the identification of two conceptually different utilizations of specialization (unification and intersection), and two different attribute properties (plural and singleton) to guide the attribute-resolution.

Name Collision in Multiple Classification Hierarchies

Abstract: Supporting multiple classification in object-oriented programming languages is the topic of discussion in this paper. Supporting multiple classification gives rise to one important question --- namely the question of inheritance of attributes with identical names from multiple paths in the classification hierarchy. The problem is to decide how these multiple classification paths are reflected in the class being defined. One of the conclusions in this paper is, that by choosing strict and simple inheritance rules, one is excluding some particular usages of multiple classification. This leads to the notion of attribute-resolution at class definition, which means that the programmer in some cases is forced or allowed to resolve the potential ambiguity of the inherited names. The concept of attribute-resolution is managed through the identification of two conceptually different utilizations of specialization (unification and intersection), and two different attribute properties (plural and singleton) to guide the attribute-resolution.

Thinking processes, management routines and student perceptions of expert and novice physical education teachers

Abstract: E v e r t s o n , C. (19 8 9) T r a i n i n g t e a c h e r s in c l a s s r o o m m a n ­ age m e n t : An e x p e r i m e n t a l s t u d y in s e c o n d a r y school c 1 as s r o o m s . J o u r n a l of E d u c a t i o n a l R e s e a r c h , 7 9 , 91-

Clarification of two phase locking in concurrent transaction processing

Abstract: The authors propose a formal definition of the two-phase locking class derived from the semantic description of the two-phase locking protocol, and prove that this definition is equivalent to that given by C.H. Papadimitriou (1979). They present: (1) a precise definition of the two phase locking; (2) a clarification of the occurrence and the order of all events such as lock points, unlock points, read operations, and write operations of conflicting transactions; and (3) by relaxing some conditions in the given definition, the derivation of a new class called restricted-non-two-phase locking (RN2PL), which is a superset of the class two-phase locking (2PL) but a subset of the class D-serializable (DSR) given by Papadimitriou. >

A Chess Analogy: Teaching the Role of Animals in Ecosystems

Abstract: Information only has meaning within a context, and outside its context, information may be of little use. Context supports information and provides a framework that makes it useful. For teaching to be effective then, both information and context need to be communicated. This is not always easy, and often we take context for granted and just teach basic information. In this paper I describe a teaching exercise I use to demonstrate the importance of context in studying the ecology of animals. The exercise uses the game of chess to examine the relationship between information and context and, secondarily, as an analogy with ecology. Students in the class are divided into two groups, those who know how to play chess ("experts") and those who have never played ("non-players"). Sometimes a third group is formed of those students who have been introduced to the game but do not feel they confidently know how to play ("novices"). Students decide for themselves which group they belong in, but it is important that no "experts" are included with the "novices" or "nonplayers." Each group is given a set of chess pieces and is physically separated from the other groups so there is

Discussion: Ghiselin and Mayr on species

Abstract: think." But, as she says, things do not come to us with their label on them. "The argument that for some purposes Homo sapiens ... is a class, for some purposes an individual, depending on one's point of view, does not mean that entities in the world change as we move between individual and class. Rather the argument means that Homo sapiens has many real properties" (Heise, 1981). If we look at some properties we think of it as an individual. But if we look at others we think of it rather as a class. "In each case the judgment is based on what we take to be real properties, but they do not all work to give us a single concept by means of which we unite the plural entities" (Heise, 1981). As a matter of fact, such an instrumental approach is often adopted also by Ghiselin. He prefers, for example, the pragmatic ecological criterion of the species definition, "'a reproductive community of populations ... that occupies a specific niche in nature", over Simpson's theoretical definition of a species as an evolutionary lineage (Ghiselin, 1987, p. 139). The reason seems to be that this latter, more "objective" definition, leads at once to difficulties: A lineage is said to evolve "with its own unitary role and tendencies." But what are these "roles"? And, do asexual organisms form a lineage? To summarize, in the framework of the theory of evolution through natural selection species are individuals, and individuals are contextdependent regulative entities.

Decidability of the problem of semantic equivalence of words in the class of syntax-directed translations

Abstract: The models of the application domains of these systems usually have a multilevel description. The upper-level language constructs provide a substantive description of the model, whereas lower-level language constructs constitute a standard description of the model with different degrees of detail. The orientation of the system toward standard structures necessitates the construction of a mapping that associates to each string in the upper-level language its semantic equivalent in one of the lower-level languages. This problem is solved by invoking both exact language definition tools and semantics definition methods.

One-directional recursive formulas

Abstract: We show a general and uniform planning mechanism for one-directional recursive formulas, which can map an arbitrary query of that class to a compiled formula. We also give the syntactic and the semantic definitions of one-directional recursive formulas. The syntactic definition is given from the graph model, and the semantic definition is from the query evaluation point of view. It is shown that two definitions are equivalent.

Summary Data Analysis and Expert Systems: Generating Rules from Data

Abstract: The combined viewpoints of Data Analysis and Artificial Intelligence are helpful in approaching certain problems with reviewed efficiency; for example, an easily compre­ hensible description of clusters may be provided by a conjunctive representation of variables in clustering; and in the techniques of learning from examples, a reduction of the order of an algorithm complexity may be obtained by hierarchical methods. In order to work in an area dealing with "symbolic data", new tools of formalization are needed. For example, these symbolic data demand an extension of classical rectan­ gular array of Data Analysis: case may contain an interval or several values instead of a single value as usual, and objects are not necessarily defined by the same variables. Three algorithms are based on that knowledge representation. The first one gen­ erates clustering characterized by conjunctions of events. The second and the third generate rules that can be used in the knowledge base of an expert system: they use logical operators and counting procedures simultaneously. The purpose is to produce rules defining membership for objects belonging to a class of examples, and rules for the class of counterexamples, with discriminant and covering criteria. One of these al­ gorithms requires the "non overlapping rules" constraint; the other does not have that constraint and its complexity may be improved by a data analysis method. They are presented with computer programs and examples on marketing data sets.