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Research and Advances Feb 1 1964

Bounded context syntactic analysis

Certain phase structure grammars define languages in which the phrasehood and structure of a substring of a sentence may be determined by consideration of only a bounded context of the substring. It is possible to determine, for any specified bound on the number of contextual characters considered, whether a given grammar is such a bounded context grammar. Such grammars are free from syntactic ambiguity. Syntactic analysis of sentences in a bounded context language may be performed by a standard process and requires a number of operations proportional to the length of sentence analyzed. Bounded context grammars form models for most languages used in computer programming, and many methods of syntactic analysis, including analysis by operator precedence, are special cases of bounded context analysis.
Research and Advances Feb 1 1964

A general business-oriented language based on decision expressions

The structure of a digital computer programming language which covers a wide class of business and file processing applications is presented. Such a structure, based on identifying and incorporating into a compiler the aspects common to all processes of such class, permits writing extremely compact programs, even for comparatively complex applications, in terms of tables of control expressions which express only information characteristic of the particular application. Furthermore, local changes of a process (e.g. changes affecting only one of the output files involved) can be effected by local modifications in the program (e.g. modification of only one entry of the tables). This structure also allows for inexpensive preparation of loading-speed compilers which translate the source programs into efficient machine codes. The approach adopted here departs from conventional mechanical language design philosophies. It stresses the structural analysis of the class of processes to be represented in the languages, as opposed to emphasizing formal (i.e., contents-independent) syntactical definitions. It relies exclusively on nonprocedural representation of processes as sets (tables) of relations between data and results (there are no control statements such as GO TO, etc.), instead of using procedure descriptions (which are one-to-one translations of flowcharts). Here an invariant pattern of procedure is identified as characteristic of the class of all batch file processes.
Research and Advances Jan 1 1964

GIT—a heuristic program for testing pairs of directed line graphs for isomorphism

Given a pair of directed line graphs, the problem of ascertaining whether or not they are isomorphic is one for which no efficient algorithmic solution is known. Since a straightforward enumerative algorithm might require 40 years of running time on a very high speed computer in order to compare two 15-node graphs, a more sophisticated approach seems called for. The situation is similar to that prevailing in areas such as game-playing and theorem-proving, where practical algorithms are unknown (for the interesting cases), but where various practical though only partially successful techniques are available. GIT—Graph Isomorphism Tester—incorporates a variety of processes that attempt to narrow down the search for an isomorphism, or to demonstrate that none exists. No one scheme is relied upon exclusively for a solution, and the program is designed to avoid excessive computation along fruitless lines. GIT has been written in the COMIT language and successfully tested on the IBM 7090.
Research and Advances Jan 1 1964

Analysis of decay-type data

A comparative study has been made of a variety of numerical techniques for fitting experimental data of the decay type by forms involving the sums of exponentials. Statistical errors of the fitted parameters are also calculated. These methods have been applied to artificially-generated sets of data as well as to the results of experiments with radioactive tracers on both human and animal subjects. Results show that the values of the fitted parameters are very sensitive to variations in the fitting procedure. Therefore great care must be exercised in identifying such values with physical constants. Although the values of functions derived from these fitted parameters which can definitely be associated with physical entities are generally more stable under variations in the fitting techniques, error bounds can be so large that no great confidence can be placed even in them. It would therefore appear best to select a uniform technique both for running the experiments and for analyzing the data, and then to consider as significant only relative results between one subject and the next.
Research and Advances Oct 1 1963

Use of the disk file on stretch

The paper begins by briefly describing the Stretch (IBM 7030) computer with special emphasis given to the organization and operation of its input-output equipment. Physical characteristics of the two-disk system (4,194,304 72-bit words, 8 µsec-per-word transmission rate, etc.) are noted. Timing limitations due to arm motion and disk rotation are discussed. Applications of disk usage are discussed separately for problem programs and for systems programs such as compilers and the supervisory program. Approximately 260,000 words of disk storage are reserved for the storage of systems programs and the subroutine library. Problem programs, however, are not currently filed on the disk. Certain programming techniques are discussed for transmitting words between disk and core storage with minimum delaying and interruption of the arithmetic unit. Dumps on disk are considered for both recovery from computer malfunction and for mathematical or physical developments during the calculation.
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Research and Advances Oct 1 1963

Computation’s development critical to our society

The ACM's growth continues: we are now at 13,000 members; expenses also grow. Our professional membership does not spring from a uniformly trained group as in mathematics or physics or even economics. Instead, our increasing membership comes from what I might call intellectual adventures—pioneers in an over-organized society—who see great futures in computing at all levels of aspiration.
Research and Advances Oct 1 1963

A comparison of disks and tapes

The principal characteristics of current magnetic disks and tape units are summarized and compared. Some of the characteristics of disk files are illustrated in a sorting example and compared to a tapesort. The conclusion is presented that disk files are competitive to tapes in some important applications.
Research and Advances Oct 1 1963

DATA-DIAL: two-way communication with computers from ordinary dial telphones

An operating system is described which allows users to call up a remotely located computer from ordinary dial telephones. No special hardware or connections are required at the users' telephones. Input to the computer is through the telephone dial; output from the computer is in spoken form. Results of a test with telephones in the Boston area are reported.
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