The main result proved in the paper is that on every recursive structure the intrinsically hyperarithmetical sets coincide with the relatively intrinsically hyperarithmetical sets. As a side eeect of the proof an eeective version of the Kueker's theorem on deenability by means of innnitary formulas is obtained. 1. Introduction One of the main achievements of the classical recursion theory is th...

We deene the counting classes #NC 1 , GapNC 1 , PNC 1 and C = NC 1. We prove that boolean circuits, algebraic circuits, programs over non-deterministic nite automata, and programs over constant integer matrices yield equivalent deenitions of the latter three classes. We investigate closure properties. We observe that #NC 1 #L, that PNC 1 L, and that C = NC 1 L. Then we exploit our nite automato...

In this paper, two interesting complexity classes, PP and P, are compared with PH, the polynomial-time hierarchy. It is shown that every set in PH is polynomial-time Turing reducible to a set in PP, and PH is included in BP. 0)P. As a consequence of the results, it follows that PP PH (or 03P___ PH) implies a collapse of PH. A stronger result is also shown: every set in PP(PH) is polynomial-time...

Several problems concerning superpolynomial size circuits and superpolynomial-time advice classes are investigated. First we consider the implications of NP (and other fundamental complexity classes) having circuits slightly bigger than polynomial. We prove that if such circuits exist, for example if NP has n logn size circuits, the exponential hierarchy collapses to the second level. Next we c...

We give characterizations of nondeterministic complexity classes such as NP and PSPACE and the classes in the polynomial time hierarchy in the two-person pebble game model [VT89]. These characterizations motivate the definitions of these classes using firstorder sentences extending the results in [Im82]. It is shown that the role-switches resource in the pebble games closely model the levels of...

Class hierarchy design is central to object-oriented software development. However, it is sometimes difficult for developers to anticipate all the implications of a design until implementation is underway. To support experimentation with different designs, we extend prior work on live development environments to allow run-time modification of the class hierarchy. The result is a more fluid obje...

A new conference key distribution scheme is proposed in this study for access control in a hierarchy. A group of users with a different security class can generate a common secret key over a public channel so that a secure electronic conference can be held. The security classes form a hierarchy such that users in a higher security class can obtain a secret session key with users in the same or ...

In this paper, we present a locking-based concurrency control scheme for object-oriented databases (OODBs). Our scheme deals with class hierarchy which is an important property in OODBs. The existing concurrency controls for a class hierarchy perform well only for specific environments. Our scheme is based on so called special classes and can be used for any applications with less locking overh...

The partitioning of related objects should be performed before clustering for an efficient access in object-oriented databases. In this paper, a partition of related objects in object-oriented databases is presented. All subclass nodes in a class inheritance hierarchy of a schema graph are condensed to a class node in the graph because the aggregation hierarchy has more influence on the partiti...

A degree of parallelism is an equivalence class of Scott-continuous functions which are relatively deenable each other with respect to the language PCF (a paradigmatic sequential language). We introduce an innnite (\bi-dimensional") hierarchy of degrees. This hierarchy is inspired by a representation of rst order continuous functions by means of a class of hypergraphs. We assume some familiarit...