14430828
An Extension of "Representative Instances and &#947;-Acyclic Relational Schemes"
Let R be a γ-acyclic relational scheme, and let F be the set of functional dependencies (FD's) embodied in R. Given an existence constrained database r over R, it was shown in [1] that it is possible to connect tuples from different relations in r and construct a universal instance L, possibly containing null values δ, such that the total projection of L onto R yields exactly the set r. Moreover, conditions were given which guarantee that this L would satisfy the functional dependency with nulls (NFD) counterparts of FD's, in F. The purpose of this note is to generalize the latter result and show that under the same conditions, L actually satisfies NFD counterparts of FD's in the closure F+ of F.
45139817
Alternative methods for the reconstruction of trees from their traversals
It is well-known that given the inorder traversal of a binary tree's nodes, along with either one of its preorder or postorder traversals, the original binary tree can be reconstructed using a recursive algorithm. In this short note we provide a short, elegent, iterative solution to this classical problem.
17317346
Representative instances and γ-acyclic relational schemes
In this paper, we study under what conditions will a pairwise inconsistent relational database ≪R,r≫ have a universal/representative instance L. If R is γ-acyclic and r satisfies all existence constraints, then it is possible to construct a universal instance L, using unmarked nulls, whose total projections onto R yield exactly the relations in r. We show that L would actually be a representative instance under a set of functional dependencies if R satisfies the additional mild condition: for any functional dependency X → A where A is a single attribute, whenever XA is contained in two relation schemes R and R' of R, it follows that R ∩R' is a relation scheme of R, having X as one of its keys.
13942242
A Scheme of Parallel Processing for MIMD Systems
This paper presents a recognition procedure for parallel tasks in the user program written in a conventional programming language. To establish our program model, it describes the parallelism of the program in tenns of a process flow graph in which the relationships among processes are of predecessors and successors. And finally it presents a parallel processing scheme which realizes automatically the recognition of parallel tasks and schedules these tasks for parallel execution.
24298643
Translation of entity-relationship diagrams into relational structures
Abstract An entity-relationship diagram (ERD) is considered to have two conceptual domains: its upper and lower conceptual domains. The semantic properties intrinsic in the upper conceptual domain were studied recently by Lien. In this paper, we discuss the properties inherent in the lower conceptual domain. We show that the latter contains a significant portion of the semantic information of an ERD and helps determine its data representation power. We develop the notions of fundamental functional dependencies (FDs) which can be readily recognized for the lower conceptual domain of an ERD, and regular ERDs which are ERDs such that all the FDs present among their attributes can be derived from their fundamental FDs. Then we give conditions under which a large number of ERDs are equivalent to their underlying relational structures.
120699
Enhancements to the Voting Algorithm
There are several consistency control algorithms for managing replicated files in the face of network partitioning due to site or communication link failures. In this paper, we consider the popular voting scheme along with three enhancements: voting with a primary site, dynamic voting, and dynamic voting with linearly ordered copiee. We develop a stochastic model which compares the file availabilities afforded by each of these schemes. We show that in this model dynamic voting with linearly ordered copies provides the greatest availability.
12121717
ADAM: a testbed for exploring the use of data mining in intrusion detection
Intrusion detection systems have traditionally been based on the characterization of an attack and the tracking of the activity on the system to see if it matches that characterization. Recently, new intrusion detection systems based on data mining are making their appearance in the field. This paper describes the design and experiences with the ADAM (Audit Data Analysis and Mining) system, which we use as a testbed to study how useful data mining techniques can be in intrusion detection.
16984957
Multilevel Secure Transaction Processing: Status and Prospects
Since 1990, transaction processing in multilevel secure database management systems (DBMSs) has been receiving a great deal of attention from the database research community. Transaction processing in these systems requires modification of conventional scheduling algorithms and commit protocols. These modifications are necessary because preserving the usual transaction properties when transactions are executing at different security levels often conflicts with the enforcement of the security policy. Considerable effort has been devoted to the development of efficient, secure algorithms for the major types of secure DBMS architectures: kernelized, replicated, and distributed. An additional problem that arises uniquely in multilevel secure DBMSs is that of secure, correct execution when data at multiple security levels must be written within one transaction. Significant progress has been made in a number of these areas, and a few of the techniques have been incorporated into commercial trusted DBMS products. However, there are many open problems remain to be explored. This paper reviews the achievements to date in transaction processing for multilevel secure DBMSs. The paper provides an overview of transaction processing needs and solutions in conventional DBMSs as background, explains the constraints introduced by multilevel security, and then describes the results of research in multilevel secure transaction processing. Research results and limitations in concurrency control, multilevel transaction management, and secure commit protocols are summarized. Finally, important new areas are identified for secure transaction processing research.
21166100
A note on estimating the cardinality of the projection of a database relation
The paper by Ahad et al. [1] derives an analytical expression to estimate the cardinality of the projection of a database relation. In this note, we propose to show that this expression is in error even when all the parameters are assumed to be constant. We derive the correct formula for this expression.
32784248
Measuring the effect of commutative transactions on distributed database performance
Abstract In this paper, we consider algorithms that permit every site in a partitioned system to perform new updates. Because this may result in independent updates to items in different partitions, conflicts among transactions are bound to occur. Commutative transactions can be used to reduce the number of these conflicts. We develop a probabilistic model to estimate the possible reduction in conflicts if we incorporate this notion of commutativity. Our results show that the additional efforts to recognize this commutativity are not beneficial unless the number of transactions that commute with each other is significantly large.
14141298
A consensus glossary of temporal database concepts
This document contains definitions of a wide range of concepts specific to and widely used within temporal databases. In addition to providing definitions, the document also includes separate explanations of many of the defined concepts. Two sets of criteria are included. First, all included concepts were required to satisfy four relevance criteria, and, second, the naming of the concepts was resolved using a set of evaluation criteria. The concepts are grouped into three categories: concepts of general database interest, of temporal database interest, and of specialized interest. This document is a digest of a full version of the glossary1. In addition to the material included here, the full version includes substantial discussions of the naming of the concepts.The consensus effort that lead to this glossary was initiated in Early 1992. Earlier status documents appeared in March 1993 and December 1992 and included terms proposed after an initial glossary appeared in SIGMOD Record in September 1992. The present glossary subsumes all the previous documents. It was most recently discussed at the "ARPA/NSF International Workshop on an Infrastructure for Temporal Databases," in Arlington, TX, June 1993, and is recommended by a significant part of the temporal database community. The glossary meets a need for creating a higher degree of consensus on the definition and naming of temporal database concepts.