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Research and Advances

Specifying queries as relational expressions: the SQUARE data sublanguage

This paper presents a data sublanguage called SQUARE, intended for use in ad hoc, interactive problem solving by non-computer specialists. SQUARE is based on the relational model of data, and is shown to be relationally complete; however, it avoids the quantifiers and bound variables required by languages based on the relational calculus. Facilities for query, insertion, deletion, and update on tabular data bases are described. A syntax is given, and suggestions are made for alternative syntaxes, including a syntax based on English key words for users with limited mathematical background.
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Research and Advances

A vector space model for automatic indexing

In a document retrieval, or other pattern matching environment where stored entities (documents) are compared with each other or with incoming patterns (search requests), it appears that the best indexing (property) space is one where each entity lies as far away from the others as possible; in these circumstances the value of an indexing system may be expressible as a function of the density of the object space; in particular, retrieval performance may correlate inversely with space density. An approach based on space density computations is used to choose an optimum indexing vocabulary for a collection of documents. Typical evaluation results are shown, demonstating the usefulness of the model.
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Research and Advances

A genealogy of control structures

The issue of program control structures has had a history of heated controversy. To put this issue on a solid footing, this paper reviews numerous theoretical results on control structures and explores their practical implications. The classic result of Böhm and Jacopini on the theoretical completeness of if-then-else and while-do is discussed. Several recent ideas on control structures are then explored. These include a review of various other control structures, results on time/space limitations, and theorems relating the relative power of control structures under several notions of equivalence. In conclusion, the impact of theoretical results on the practicing programmer and the importance of one-in, one-out control structures as operational abstractions are discussed. It is argued further that there is insufficient evidence to warrant more than if-then-else, while-do, and their variants.
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Research and Advances

Merging with parallel processors

Consider two linearly ordered sets A, B, | A | = m, | B | = n, m ≤ n, and p, p ≤ m, parallel processors working synchronously. The paper presents an algorithm for merging A and B with the p parallel processors, which requires at most 2⌈log2(2m + 1)⌉ + ⌊3m/p⌋ + [m/p][log2(n/m)] steps. If n = 2&bgr;m (&bgr; an integer), the algorithm requires at most 2[log2(m + 1)] + [m/p](2 + &bgr;) steps. In the case where m and n are of the same order of magnitude, i.e. n = km with k being a constant, the algorithm requires 2[log2(m + 1)] + [m/p](3 + k) steps. These performances compare very favorably with the previous best parallel merging algorithm, Batcher's algorithm, which requires n/p + ((m + n)/2p)log2m steps in the general case and km/p + ((k + 1)/2)(m/p)log2m in the special case where n = km.
Research and Advances

Optimizing the performance of a relational algebra database interface

An approach for implementing a “smart” interface to support a relational view of data is proposed. The basic idea is to employ automatic programming techniques so that the interface analyzes and efficiently refines the high level query specification supplied by the user. A relational algebra interface, called SQUIRAL, which was designed using this approach, is described in detail. SQUIRAL seeks to minimize query response time and space utilization by: (1) performing global query optimization, (2) exploiting disjoint and pipelined concurrency, (3) coordinating sort orders in temporary relations, (4) employing directory analysis, and (5) maintaining locality in page references. Algorithms for implementing the operators of E. F. Codd's relational algebra are presented, and a methodology for composing them to optimize the performance of a particular user query is described.
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Research and Advances

CONVERT: a high level translation definition language for data conversion

This paper describes a high level and nonprocedural translation definition language, CONVERT, which provides very powerful and highly flexible data restructuring capabilities. Its design is based on the simple underlying concept of a form which enables the users to visualize the translation processes, and thus makes data translation a much simpler task. “CONVERT” has been chosen for conveying the purpose of the language and should not be confused with any other language or program bearing the same name.
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Research and Advances

Implementation of a structured English query language

The relational model of data, the XRM Relational Memory System, and the SEQUEL language have been covered in previous papers and are reviewed. SEQUEL is a relational data sublanguage intended for ad hoc interactive problem solving by non-computer specialists. A version of SEQUEL that has been implemented in a prototype interpreter is described. The interpreter is designed to minimize the data accessing operations required to respond to an arbitrary query. The optimization algorithms designed for this purpose are described.
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Research and Advances

A preliminary system for the design of DBTG data structures

The functional approach to database design is introduced. In this approach the goal of design is to derive a data structure which is capable of supporting a set of anticipated queries rather than a structure which “models the business” in some other way. An operational computer program is described which utilizes the functional approach to design data structures conforming to the Data Base Task Group specifications. The automatic programming technology utilized by this program, although typically used to generate procedure, is here used to generate declaratives.
Research and Advances

Multidimensional binary search trees used for associative searching

This paper develops the multidimensional binary search tree (or k-d tree, where k is the dimensionality of the search space) as a data structure for storage of information to be retrieved by associative searches. The k-d tree is defined and examples are given. It is shown to be quite efficient in its storage requirements. A significant advantage of this structure is that a single data structure can handle many types of queries very efficiently. Various utility algorithms are developed; their proven average running times in an n record file are: insertion, O(log n); deletion of the root, O(n(k-1)/k); deletion of a random node, O(log n); and optimization (guarantees logarithmic performance of searches), O(n log n). Search algorithms are given for partial match queries with t keys specified [proven maximum running time of O(n(k-t)/k)] and for nearest neighbor queries [empirically observed average running time of O(log n).] These performances far surpass the best currently known algorithms for these tasks. An algorithm is presented to handle any general intersection query. The main focus of this paper is theoretical. It is felt, however, that k-d trees could be quite useful in many applications, and examples of potential uses are given.
Research and Advances

Optimal balancing of I/O requests to disks

Determining a policy for efficient allocation and utilization of a set of disk drives with differing operational characteristics is examined using analytical techniques. Using standard queueing theory, each disk drive is characterized by a queueing model with service time of a disk drive represented by the probability density function of the sum of two uniform distributions. Total response time of the set of disk models is then minimized under varying load conditions. The results indicate that faster devices should have higher utilization factors and that the number of different device types utilized tends to decrease with decreasing load. Specific examples using 2314 and 3330 combinations are examined.
Research and Advances

The digital simulation of river plankton population dynamics

This paper deals with the development of a mathematical model for and the digital simulation in Fortran IV of phytoplankton and zooplankton population densities in a river using previously developed rate expressions. In order to study the relationships between the ecological mechanisms involved, the simulation parameters were varied illustrating the response of the ecosystem to different conditions, including those corresponding to certain types of chemical and thermal pollution. As an investigation of the accuracy of the simulation methods, a simulation of the actual population dynamics of Asterionella in the Columbia River was made based on approximations of conditions in that river. Although not totally accurate, the simulation was found to predict the general annual pattern of plankton growth fairly well and, specifically, revealed the importance of the annual velocity cycle in determining such patterns. In addition, the study demonstrates the usefulness of digital simulations in the examinations of certain aquatic ecosystems, as well as in environmental planning involving such examinations.
Research and Advances

Multiprocessing compactifying garbage collection

Algorithms for a multiprocessing compactifying garbage collector are presented and discussed. The simple case of two processors, one performing LISP-like list operations and the other performing garbage collection continuously, is thoroughly examined. The necessary capabilities of each processor are defined, as well as interprocessor communication and interlocks. Complete procedures for garbage collection and for standard list processing primitives are presented and thoroughly explained. Particular attention is given to the problems of marking and relocating list cells while another processor may be operating on them. The primary aim throughout is to allow the list processor to run unimpeded while the other processor reclaims list storage The more complex case involving several list processors and one or more garbage collection processors are also briefly discussed.
Research and Advances

Mechanical program analysis

One means of analyzing program performance is by deriving closed-form expressions for their execution behavior. This paper discusses the mechanization of such analysis, and describes a system, Metric, which is able to analyze simple Lisp programs and produce, for example, closed-form expressions for their running time expressed in terms of size of input. This paper presents the reasons for mechanizing program analysis, describes the operation of Metric, explains its implementation, and discusses its limitations.
Research and Advances

Combining decision rules in a decision table

The techniques for minimizing logic circuits are applied to the simplification of decision tables by the combining of decision rules. This method is logically equivalent to the Quine-McCluskey method for finding prime implicants. If some of the decision rules implied in the ELSE Rule occur with low frequency, then the ELSE Rule can be used to further simplify the decision table. Several objectives merit consideration in optimizing a decision table: reducing machine execution time; reducing preprocessing time; reducing required machine memory; reducing the number of decision rules. (This often improves the clarity of the decision table to a human reader.) It will be shown that objectives (3) and (4) can be furthered with the above methods. Objective (1) is also attained if overspecified decision rules are not combined. Objective (2) must be compared against the potential benefits of objectives (1), (3), and (4) in deciding whether to use the above methods.
Research and Advances

Consecutive storage of relevant records with redundancy

This paper studies the properties of a new class of file organizations (CRWR) where records relevant to every query are stored in consecutive storage locations but the organizations contain redundancy. Some theorems which provide tools for reducing redundancy in CRWR organizations have been also developed. Redundancies obtained by the application of these theorems are compared with that of query-inverted file organizations. Some CRWR organizations with minimum redundancy have also been developed for queries which specify sets of keys.
Research and Advances

On the external storage fragmentation produced by first-fit and best-fit allocation strategies

Published comparisons of the external fragmentation produced by first-fit and best-fit memory allocation have not been consistent. Through simulation, a series of experiments were performed in order to obtain better data on the relative performance of first-fit and best-fit and a better understanding of the reasons underlying observed differences. The time-memory-product efficiencies of first-fit and best-fit were generally within 1 to 3 percent of each other. Except for small populations, the size of the request population had little effect on allocation efficiency. For exponential and hyperexponential distributions of requests, first-fit outperformed best-fit; but for normal and uniform distributions, and for exponential distributions distorted in various ways, best-fit out-performed first-fit. It is hypothesized that when first-fit outperforms best-fit, it does so because first-fit, by preferentially allocating toward one end of memory, encourages large blocks to grow at the other end. Sufficient contiguous space is thereby more likely to be available for relatively large requests. Results of simulation experiments supported this hypothesis and showed that the relative performance of first-fit and best-fit depends on the frequency of requests that are large compared to the average request. When the coefficient of variation of the request distribution is greater than or approximately equal to unity, first-fit outperformed best-fit.

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