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Cobol | |
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COBOL is a Third-generation programming language, and one of the oldest programming languages still in active use. Its name is an acronym for COmmon Business-Oriented Language, defining its primary domain in business, finance, and administrative systems for companies and governments.
The COBOL 2002 standard includes support for object-oriented programming and other modern language features. History and specification COBOL was initially created in 1959 by The Short Range Committee, one of three committees proposed at a meeting held at the Pentagon on May 28 and 29, 1959, organized by Charles Phillips of the United States Department of Defense (exactly one year after the Zürich ALGOL 58 meeting).[2] The Short Range Committee was formed to recommend a short range approach to a common business language. It was made up of members representing six computer manufacturers and three government agencies. In particular, the six computer manufacturers were Burroughs Corporation, IBM, Minneapolis-Honeywell (Honeywell Labs), RCA, Sperry Rand, and Sylvania Electric Products. The three government agencies were the US Air Force, the David Taylor Model Basin, and the National Bureau of Standards (Now NIST). This committee was chaired by a member of the NBS. An Intermediate-Range Committee and a Long-Range Committee were proposed at the Pentagon meeting as well. However although the Intermediate Range Committee was formed, it was never operational; and the Long-Range Committee was never even formed. In the end a sub-committee of the Short Range Committee developed the specifications of the COBOL language. This sub-committee was made up of six individuals: William Selden and Gertrude Tierney of IBM Howard Bromberg and Howard Discount of RCA Vernon Reeves and Jean E. Sammet of Sylvania Electric Products This subcommittee completed the specifications for COBOL as the year of 1959 concluded. The specifications were to a great extent inspired by the FLOW-MATIC language invented by Grace Hopper, commonly referred to as "the mother of the COBOL language", and the IBM COMTRAN language invented by Bob Bemer. COBOL (Common Business Oriented Language) was one of the earliest high-level programming languages. It was developed in 1959 by a group of computer professionals called the Conference on Data Systems Languages (CODASYL). Since 1959 it has undergone several modifications and improvements. In an attempt to overcome the problem of incompatibility between different versions of COBOL, the American National Standards Institute (ANSI) developed a standard form of the language in 1968. This version was known as American National Standard (ANS) COBOL. In 1974, ANSI published a revised version of (ANS) COBOL, containing a number of features that were not in the 1968 version. In 1985, ANSI published still another revised version that had new features not in the 1974 standard. The language continues to evolve today. Object-oriented COBOL is a subset of COBOL 97, which is the fourth edition in the continuing evolution of ANSI/ISO standard COBOL. COBOL 97 includes conventional improvements as well as object-oriented features. Like the C++ programming language, object-oriented COBOL compilers are available even as the language moves toward standardization. History of COBOL standards The specifications approved by the full Short Range Committee were approved by the Executive Committee on January 3 1960, and sent to the government printing office, which edited and printed these specifications as Cobol 60. The American National Standards Institute (ANSI) has since produced several revisions of the COBOL standard, including COBOL-68 COBOL-74 COBOL-85 COBOL 2002 Defining features COBOL as defined in the original specification included a PICTURE clause for detailed field specification. It did not support local variables, recursion, dynamic memory allocation, or structured programming constructs. Support for some or all of these features has been added in later editions of the COBOL standard. COBOL has many reserved words (over 400), called keywords. The original COBOL specification supported self-modifying code via the infamous "ALTER X TO PROCEED TO Y" statement. This capability has since been removed. Legacy COBOL programs are in use globally in governmental and military agencies, in commercial enterprises, and on operating systems such as IBM's z/OS, Microsoft's Windows, and the POSIX families (Unix/Linux etc.). In 1997, the Gartner Group reported that 80% of the world's business ran on COBOL with 180 billion lines of code in existence and with an estimated 5 billion lines of new code annually. Near the end of the twentieth century the year 2000 problem was the focus of significant COBOL programming effort, sometimes by the same programmers who had designed the systems decades before. The particular level of effort required for COBOL code has been attributed both to the large amount of business-oriented COBOL, as COBOL is by design a business language and business applications use dates heavily, and to constructs of the COBOL language such as the PICTURE clause, which can be used to define fixed-length numeric fields, including two-digit fields for years. Hello, world IDENTIFICATION DIVISION. PROGRAM-ID. HELLO-WORLD. PROCEDURE DIVISION. PARAGRAPH-1. DISPLAY 'Hello, world.'. STOP RUN. Criticism Critics have argued that COBOL's syntax serves mainly to increase the size of programs, at the expense of developing the thinking process needed for software development. In his letter to an editor in 1975 titled "How do we tell truths that might hurt?", computer scientist and Turing Award recipient Edsger Dijkstra remarked that "The use of COBOL cripples the mind; its teaching should, therefore, be regarded as a criminal offense". COBOL 85 was not compatible with earlier versions, resulting in the "cesarean birth of COBOL 85". Joseph T. Brophy, CIO, Travelers Insurance, spearheaded an effort to inform users of COBOL of the heavy reprogramming costs of implementing the new standard. As a result the ANSI COBOL Committee received more than 3,200 letters from the public, mostly negative, requiring the committee to make changes.(The COBOL 85 Example Book) Older versions of COBOL lack local variables and so cannot truly support structured programming. Others criticize the ad hoc incorporation of features on a language that was meant to be a short term solution to interoperability in 1959. Coupled with the perceived archaic syntax, they argue that it tries to fill a niche for which better tools have already been designed and developed. Defense Advocates claim that typically those who criticize the language have never been COBOL programmers and often misrepresent it. Critic Edsger Dijkstra was also positively impressed by Michael A. Jackson's ideas about "Structured Programming" in COBOL (Jackson Structured Programming). The COBOL specification has also been revised over the years to incorporate developments in computing theory and practice . As with any language, COBOL code can be made more verbose than necessary. For example the COBOL code for one of the roots X = (-B + (B ^ 2 - (4 * A * C)) ^ (1/2)) / (2 * A) of the quadratic equation ax2 + bx + c = 0 can be written, using the "compute" verb, as: COMPUTE X = (-B + (B ** 2 - (4 * A * C)) **.5) / (2 * A) The same formula could also be written less concisely as: MULTIPLY B BY B GIVING B-SQUARED. MULTIPLY 4 BY A GIVING FOUR-A. MULTIPLY FOUR-A BY C GIVING FOUR-A-C. SUBTRACT FOUR-A-C FROM B-SQUARED GIVING RESULT-1. COMPUTE RESULT-2 = RESULT-1 ** .5. SUBTRACT B FROM RESULT-2 GIVING NUMERATOR. MULTIPLY 2 BY A GIVING DENOMINATOR. DIVIDE NUMERATOR BY DENOMINATOR GIVING X. Which form to use is a matter of style. In some cases the less concise form may be easier to read. For example: ADD YEARS TO AGE. MULTIPLY PRICE BY QUANTITY GIVING COST. SUBTRACT DISCOUNT FROM COST GIVING FINAL-COST. Newer versions of COBOL support local variables via embedded programs (scope-delimited by the keywords PROGRAM-ID and END-PROGRAM). Variables declared within the embedded program are invisible outside its scope. In older versions of COBOL local variables may be hidden by using sub-programs, which must be invoked (via the keyword CALL). The calling program will not have access to the variables declared and manipulated by the sub-program. This technique could result in an unwieldy mass of sub-programs, particularly if those are not well documented. Another point to be made is that COBOL was one of the earliest high-level programming languages that allowed for fairly long identifiers (identifiers may to be up to 30 characters long), whereas other languages at the time were limited to short identifiers (e.g., FORTRAN compilers typically limited identifiers to six characters). Supporting longer identifiers allows programmers to use more descriptive names, and to reduce the risk that the same name is accidentally used in more than one context. Aphorisms and humor about COBOL It has been said of languages like C, C++, and Java that the only way to modify legacy code is to rewrite it - write once and write once again; or write once and throw away. On the other hand, it has been said of COBOL that there actually is one original COBOL program, and it has only been copied and modified millions of times. The name "ADD 1 TO COBOL GIVING COBOL" has been suggested for a hypothetical object-oriented dialect of COBOL, as a play on the name C++. While this is meant to suggest that COBOL is inherently verbose, the form given is more verbose than COBOL actually requires. COBOL allows adding a value or variable into another variable in the form ADD YEARS TO AGE. The values of the two variables are added together and the result placed into the variable after TO, if no GIVING is present. So the succinct form would be "ADD 1 TO COBOL". This is verbose when compared to "++" the increment operator in several programming languages, but much more English like. Another suggested name is "POSTINCREMENT COBOL BY 1", which not only reflects the verbose nature of COBOL statements, but also highlights the tendency for COBOL features to require their own dedicated reserved keywords (standard COBOL employs over 400 reserved words), this example being the case for a hypothetical new POSTINCREMENT operator. COBOL 2002 and object-oriented COBOL The COBOL2002 standard supports Unicode, XML generation and parsing, calling conventions to/from non-COBOL languages such as C, and support for execution within framework environments such as Microsoft's .NET and Java (including COBOL instantiated as EJBs). However, no vendor has yet produced a completely conforming compiler. original - http://en.wikipedia.org/wiki/COBOL |
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