COBOL-Its relationship with other American national standards

Transcription

1 COBOL-Its relationship with other American national standards by L. ARNOLD JOHNSON, PATRICK M. HOYT and GEORGE N. BAIRD Department of the Navy Washington, DC INTRODUCTION The standards which interface with COBOL can effect the degree of machine independence a COBOL program has. COBOL 74 1 provides the capability to process the standard coded character set defined by the American National Standard Code for Information Interchange (ASCII). 2 In that' regard, COBOL 74 relies on the ASCII Standard for defining the character codes and the collating sequence that are to be reflected by the program when processing that particular character code. Additionally, COBOL can specify that ASCII be recorded on external media such as punch cards 3 or magnetic tape 4 with magnetic tape labels. 5 If that data is to be used for information interchange, then the recording of the data should be in accordance with the respective media standards. The American National Standards which interface with COBOL must be properly defined and implemented on a computer system for a COBOL program to be independent of the computer system. In the process of validating COBOL compilers, we use these other American National Standards related to COBOL and have found that data cannot be easily transported between computer systems. ANSC X3 ROLE IN COBOL AND RELATED STANDARDS American National Standard Committee X3 through its three standing committees is responsible for the standardization of COBOL and other subjects related to systems, computer equipments, devices and media for information processing. 6 Three committees assist X3 in discharging its responsibilities concerning the administration, evaluation, allocation and scheduling of standards projects. The Standards Planning and Requirements Committee (SPARC) and the International Advisory Committee (lac) of X3 have staff responsibilities while the Standards Steering Committee (SSC) has line responsibilities. The lac is responsible for coordinating the work of ANSC X3 with respect to international organizations. The purpose of SPARC is to review the need for standards, make recommendations to X3 on the desirability of standards and determine that work of the technical committees is responsive to the original objective of the standardization project. The administrative arm of X3 is the Standards Steering Committee which monitors and coordinates the standards projects that are being developed by the project groups. Individual projects are. classified as being in one of three project groups, hardware, software or systems. The technical committees (established for each individual project) designated for the development and maintenance of American National Standards for COBOL, character codes, magnetic tape labels, and data representation are part of the software group. Technical committees for the standardization of physical media asso-. ciated with magnetic tape and punched cards are included in the hardware group. The basic objectives of the American National Standards Institute (ANSI) as well as its subordinate committees are the (1) promulgating of standards, (2) coordination of standards development, (3) establishment of standards, and (4) exchange of information. The underlying purpose of the COBOL standard is to "promote a high degree of machine independence in such programs in order to permit their use on a variety of automatic data processing systems."* Further, one of the criteria used by ANSC X3J4 (technical committee for COBOL standardization) for considering a COBOL element as a candidate in the 1974 COBOL standard was its compatibility with other standards. A philosophy similar to COBOL is reflected in the standards associated with magnetic tape, punched cards, magnetic tapes labels and standard coded character set in that these standards are concerned with a common format for informatio,n interchange between computer systems. Based on experiences noted later in this paper, there is a question as to whether COBOL and related standards, as yet are fully effective in providing information interchange. STANDARDS INTERFACING WITH COBOL There are five different American National Standards which may either directly or indirectly interface with American National Standard Programming Language COBOL, * See Paragraph 1.1, page 1-1 in Reference

2 1114 National Computer Conference, 1978 X The COBOL 74 Standard conveniently includes the language syntax which make these interfaces possible and thereby provides a common definition for the purpose of data interchange. American National Standard Code for Information Interchange (ASCII) is the common character code used for the interchange of data. Ideally, a standard data interchange on punched cards or magnetic tape is possible between computer systems when ASCII together with the appropriate American National Standards for punched cards or for recorded magnetic tape and magnetic tape labels are used. For data interchange as well as program interchange to be possible, a fundamental assumption is that each of the computer systems between which the data interchange is to occur must implement and support the applicable ADP standards. Until COBOL 74, there was no definition within the COBOL language which allowed for the designation of a program collating sequence or how data would be represented on external media. Without such a definition each implementor was permitted to use his own techniques regarding the character collating sequence used, recording of signed data on external media, and the character code used for external media. The facilities in COBOL 74 for defining the collating sequence, the character code and representation of signed data are the COBOL features associated with the PROGRAM COLLATING SEQUENCE clause, CODE SET clause, alphabet-name clause and SIGN SEPARATE clause. For the first time, it is possible for COBOL programs to read, process and produce data that is interchangeable in accordance with related ADP standards. COBOL 74 The COBOL language feature by which ASCII is written to or read from an external media is the CODE-SET clause plus an associated alphabet-name clause. The CODE-SET clause in an optional clause of the File Description Entry in a COBOL program. When it is present, this clause specifies the character code convention used on the external media. Any conversion that may be required of the code, as represented internally in the computer system, and the code as represented on the external media occurs during execution of either an input or output operation (a READ or WRITE statement). The construct of the CODE-SET clause is "CODE-SET IS alphabet-name." Alphabet-name is defined in the SPECIAL-NAMES paragraph and has the form: STANDARD-l ) NATIVE I h b t IS implementor-name a p a e -name literal 1 When the STANDARD-l phrase is specified, the character code or collating sequence identified is that defined by the American National Standard Code for Information Interchange, X Each character of the standard character set is associated with a corresponding character of the native character code. Note the COBOL Standard does not require that the computer system's architecture use ASCII, only that the computer system and associated COBOL compiler process the character code as if it were ASCII. The ASCII character code standard defines the bit configuration for representing characters in the standard data format. The value of numeric fields may be represented in either binary or decimal form depending on the equipment. If more than one type of numeric representation is available for a computer system, this selection may be specified through COBOL by use of the USAGE clause. The. two options of the USAGE clause are COMPUTATIONAL (binary) and DISPLAY (decimal). Therefore, in order to produce ASCII on an external media via COBOL, data descriptions for the file must be explicitly or implicitly defined as DISPLAY. Another factor which effects the ability to interchange data between systems is the representation of signed data. The positive or negative characteristic of a numeric value may have, as many possible representations. Signs may be represented as part of the bit configuration associated with the high order or low order position of the numeric value. Signs also may be represented as a separate character which may be either leading or trailing. Since the ASCII character code does not provide for signed data values, the sign characteristic of a numeric value must be carried as a separate character. This is defined through COBOL using the SIGN SEPARATE clause. Data is only interchangeable if the sequence of data is characteristic of the character code selected and the COBOL program processes it accordingly. This sequence is controlled within the COBOL program by use of the PRO GRAM COLLATING SEQUENCE IS alphabet-name clause located in the OBJECT-COMPUTER paragraph. The PROGRAM COLLATING SEQUENCE clause is optional, but if specified, the program uses the collating sequence defined by a corresponding alphabet-name clause. If the alphabet-name clause specifies the ASCII character code (alphabet-name option STANDARD-I) then all nonnumeric comparisons for any relation conditions during program execution should reflect the ASCII code collating sequence. AMERICAN NATIONAL STANDARD CODE FOR INFORMATION INTERCHANGE (ASCII) ASCII is the standard coded character set to.be used for information interchange among information processing systems. The ASCII Standard describes the code insofar as the bit arrangement or configuration relates to an associated graphic character. A minimum of 7 bits is used to represent an ASCII code character. The Standard does not define the means by which the code set is to be recorded in any physical medium but there is a bit relationship with the ASCII code to other standards such as the American National Standard Recorded Magnetic Tape for Information Interchange, X (1600 CPI, PE) and also X (800 CPI, NRZI). For COBOL to produce or recognize ASCII data, the language feature CODE-SET in combina-

3 COBOL 1115 tion with the STANDARD-1 option of the alphabet-name clause is required. The binary bit pattern of the character code gives a collating sequence position for each character in the code. For an implementation to support the ASCII standard, the computer system must be capable of not only accepting and producing ASCII, but also must be able to process ASCII coded data in the proper collating sequence. AMERICAN NATIONAL STANDARD HOLLERITH PUNCHED CARD CODE X The Hollerith Punched Card Code Standard specified 256 Hole-pattern in twelve-row punched cards. These Hole-patterns are assigned to the 128 characters of 7-bit ASCII and to 128 additional characters for use in 8-bit coded systems. This standard relates these punched Hole-patterns to a particular bit pattern in an 8-bit data system. An example of such a system noted in this standard is the American National Standard Recorded Magnetic Tape for Information Interchange (800 CPI, NRZI), X3.22-l973. In addition to relating Hole-patterns to a particular bit construct, the code table presented in this standard also associates a graphic character to that particular position within the table. Columns 0-7 of the table correspond to the bit pattern and associated graphic character of that defined in the ASCII standard. The standard does not specify a card sorting sequence; however, when we consider the bit patterns of any two ASCII characters there is a well-defined sequence relationship. Since the CODE-SET clause gives COBOL the capability to specify the character code convention used to represent data on the external media (such as punched cards) a relationship does exist through the ASCII character code standard for a COBOL program to accept, process, and create data on punched cards in accordance with X AMERICAN NATIONAL STANDARD MAGNETIC TAPE LABELS FOR INFORMATION INTERCHANGE, X3.27-l976 The magnetic tape label standard gives specifications for the recording of magnetically recorded labels on magnetic tapes used for information interchange. Rather than specify how the labels of the tape are to be processed or the data bit structure on the tape, this Standard identifies the information and the structure of tape labels that are recorded on tape. As such, the tape label standard is applicable to either 7 track or 9 track magnetic tape. The standard makes note of the fact that the physical recording size of labels may be larger than the required 80 characters subject to hardware constraints. These 80-character records are grouped together based on their respective locations on tape related to beginning of tape volume, beginning of file, end of the file and end of tape volume. A tape mark, both before and after the file data, separates a label record group from the file data. Each label record is uniquely recognized by the first four characters in that record. A record group may have one or more records depending on the implementation and an agreement between the data interchange parties. For a single volume tape all label records are optional except for label records identified as VOL1, HDRI and EOFI which respectively define the beginning of the volume or tape, header label for beginning of each data file, and label record immediately following the data file. An illustration follows: VOL1----HDR1---*File Data*t EOF1----** The tape label standard identifies the information and the data category (numeric or alphanumeric) that is to be stored in each field of the label record. ASCII is mentioned by the standard as a character code which can be used; however, the standard is applicable to any code structure. Certain fields of the label records are designated as optional by the standard. These optional fields may be recognized and processed or may be ignored at the option of the implementor. COBOL includes provisions for specifying labels for data files through the LABEL RECORD STANDARD clause of the File Description Entry. However, COBOL 74 does not describe the format, structure, or content of file labels. It states only that file labels will be present when the clause is specified. If an implementation claims support of the tape label standard for use with COBOL, then the implementor should be expected to accept and process ANS tape labels on input, process those tape labels and create ANS tape labels on output, both in accordance with the ~agnetic tape label standard, X3.27-l976. AMERICAN NATIONAL STANDARD RECORDED MAGNETIC TAPE FOR INFORMATION INTERCHANGE (800 CPI, NRZI), X3.22-l973 AND (1600 CPI, PE), X3.39-l973 The standards X3.22-l973 and X for recorded magnetic tape provide specifications for the format andrecording of half inch, 9-track magnetic tape to be used for information interchange with systems and associated equipment utilizing the ASCII code, X3.4-l976. These standards define the physical requirements for magnetic tape and the bit pattern for the recording of information on 9-track tape. Seven of the nine tracks are used for data; one track is used for character parity; and one track is treated as a bit of higher order than ASCII bits (shall be a zero bit). Each of the tracks used for the recording of data are assigned a particular bit identification which corresponds to the bit assignment used by the ASCII character code standard. COBOL 74 does not reference the recorded magnetic tape standards; however, it includes COBOL syntax and general rules governing the semantics for the COBOL statements which apply specifically to.the treatment of files on magnetic teach "'" represents a tape mark.

4 1116 National Computer Conference, 1978 tape. Within COBOL 74, Sequential 1-0 module statements such as the CLOSE REEL, CLOSE WITH NO REWIND, OPEN WITH NO REWIND and OPEN REVERSED are used to specify the actions for files stored on tape or analogous sequential media. Also the general rules associated with the READ and WRITE verbs define the actions to be taken when an end of reel is recognized during a read or write. USING COBOL WITH RELATED STANDARDS Programs written in compliance with the 1974 COBOL Standard language specification do not necessarily accept or produce data files that comply with the other data processing standards on many systems. Part of our work, here at the Federal COBOL Compiler Testing Service, involves the validation of COBOL compilers with respect to FederalStandard COBOL s (ANS, X COBOL). Because we are continuously implementing the COBOL Compiler Validation System (CCVS)9 on different computer systems, the underlying purposes for which standards are developed are of vital importance to our operations. More importantly, we test COBOL compilers and as part of those tests we validate the compiler's capability to read, process and write ASCII in accordance with the 1974 COBOL Standard. Briefly stated, the 1974 CCVS consists of some 250 COBOL programs which collectively test a COBOL compiler's conformance to COBOL 74 language syntax and semantics. That part of the CCVS used to validate the compiler's ASCII capability consist of three COBOL programs, an ASCII-encoded punched card deck, and an ASCII-encoded magnetic tape. The ASCII validation requires three steps. In the first step, the first of the three-program set produces an ASCII-encoded magnetic tape and punched card file. The two remaining COBOL programs read and check the files produced by the first COBOL program. For the second step, the two programs which read and check the ASCII-encoded files are again executed. However, for this run they use as inputs an ASCII-encoded tape file and punched card file produced on another computer system. The purpose of this run is to validate that the compiler/ computer system being tested is capable of processing ASCII (represented both on magnetic tape and punched cards) that was produced by another computer system in accordance with the appropriate American National Standards. The final step is to take the magnetic tape and punched card file produced during the validation to a different computer system for further checking. The purpose of this latter step is to determine whether the compiler/computer system being tested can also produce ASCII (represented both on magnetic tape and punched cards) which is capable of being processed on another computer system. Since COBOL 74 is not definitive regarding labels that are used for magnetic tape, the labels used for the ASCII portion of the compiler validation are dependent on the system under test. If the system under test supports the ANSI tape label standard, then tape labels conforming to ANS X are placed on the magnetic tapes. If the system under test does not support ANSI tape labels then the magnetic. tapes for the validation were supplied without tape labels. To recognize a system under test as being in full support of COBOL and associated data related standards, the system is expected to do the following: (1) Compile and execute the audit routines (CCVS programs) that conform to the 1974 COBOL Standard (ANS X ) without requiring any modifications to the source code, (2) Pass all the semantic tests made by the audit routines as reflected in the execution report of each audit routine, (3) Accept ASCII-encoded (ANS X ) data files from tape and punched cards that conform to the Magnetic Tape Standard (ANS X and ANSI X ) and Hollerith Punched Card Code Standard (ANS X ) respectively, (4) Produce ASCII -encod~d data files on tape and punched cards that conform to the same standards noted in 3 above, and (5) Accept and produce magnetic tapes containing magnetic tape labels that conform to Magnetic Tape Label Standard (ANS X ). Very few of the compiler/computer systems validated to date were successful in meeting all of the above criteria. The type of problems that were found follow: (0 Date recording formats unacceptable. One system tested resulted in an end of file condition occurring after processing the first record of a 50 record tape file. Another system could not read either a labeled or an unlabeled magnetic tape. However, this same system, for some unexplained reason, was able to create a tape that, when read on another computer system, proved to be correct according to applicable standards. (2) Data code not read or recorded correctly. One system tested produced records on tape which included an additional character located in the first character position of each record thus causing the contents of the record to be offset by one character. Another system did not provide proper character translation of all ASCII characters when reading punched cards. (3) Incompatible Tape labels. Some systems tested simply did not support ANSI tape labels while others required the presence of optional labels HDR2 and EOF2. (4) Non-standard COBOL syntax. One system tested required that the nonstandard clause "RECORDING MODE IS STANDARD-ASCII" be added to the SE LECT Entry for all tape files. (The CODE-SET clause in the File Description Entry should have accomplished this function). One system, oddly enough,

5 COBOL 1117 could properly read and write ASCII on punched cards only when the CODE-SET clause was removed from the program. A number of special considerations were necessary in order to process ASCII. Some implementations required that specific hardware models of magnetic tape and card readers/punches be used. Others required that specific options be invoked through the job control language, and still others required particular system generation parameters be used when the operating system is generated. IMPACT OF COBOL 74 REVISION WITH REGARD TO OTHER STANDARDS In looking to the future to see how the revision to COBOL 74 might affect the interfaces of COBOL with related standards, it appears that there will be little or no impact. In a sense this is unfortunate because the COBOL standard could give more guidance as to the type of file labels that are to be used. The only feature for defining file labels within COBOL is via the LABEL RECORD STANDARD clause, which in COBOL 74 merely requires that labels will be present and conform to the implementor's label specifications. The difficulty most often found in transporting magnetic tape files between computer systems, next to improper implementation of standards related to COBOL, was the tape label. Many COBOL compiler/computer systems tested did not support ANSI magnetic tape labels. If the COBOL interface mechanisms for ANSI magnetic tape labels were similar in detail to the interfaces now present for ASCII, COBOL would have a direct link to another American National Standard. CONCLUSION One thing became quite apparent while testing the interfaces to ASCII and other standards related to COBOL. Even when strict adherence to American National Standards is maintained, COBOL programs and associated data files are not easily interchangeable among computer systems. This, in part, is due to improper implementation of ADP Standards by the parties involved in the interchange. Another factor is that the goals and objectives of X3 do not emphasize the compatibility of related standards or encourage interaction of related standards. REFERENCES 1. American National Standard Programming Language COBOL, X , American National Standards Institute Incorporated, New York, American National Standard Code for Information Interchange, X , American National Standards Institute Incorporated, New York, American National Standard Hollerith Punched Card Code, X , American National Standards Institute Incorporated, New York, American National Standard Recorded Magnetic Tape for Information Interchange (800 CPl, NRZI), X , American National Standards Institute Incorporated, New York, American National Standard Magnetic Tape Labels for Information Interchange, X , American National Standards Institute Incorporated, New York, Hill, MaIjorie F., The World ofedp Standards, Control Data Corporation, Tech Memo TM4, American National Standard Recorded Magnetic Tape for Information Interchange (1600 CPl, Phase Encoded), X , American National Standards Institute Incorporated, New York, Federal Information Processing Standards, Publication 21-1 COBOL, U. S. Government Printing Office, Washington, D.C., CCVS Users Guide Version 3.0, available from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, Virginia 22151

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