One very big reason for runtime binding is licensing. If an application includes subroutines from another vendor and they are hard linked, users of the software may be required to purchase the subroutine package. It gets even more complicated when open source software is used. The GNU GPL makes the new product a derivative product, covered by the same license and requiring it to become open source (if it is distributed outside the developing company).
Dennis Roach GHG Corporation Lockheed Martin Mission Services Facilities Design and Operations Contract NASA/JSC Address: 2100 Space Park Drive LM-15-4BH Houston, Texas 77058 Mail: P.O. Box 58487 Mail Code H4C Houston, Texas 77258 Phone: Voice: (281)336-5027 Cell: (713)591-1059 Fax: (281)336-5410 E-Mail: dennis.ro...@lmco.com All opinions expressed by me are mine and may not agree with my employer or any person, company, or thing, living or dead, on or near this or any other planet, moon, asteroid, or other spatial object, natural or manufactured, since the beginning of time. -----Original Message----- From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of john gilmore Sent: Tuesday, July 14, 2009 5:03 PM To: IBM-MAIN@bama.ua.edu Subject: Re: complexity I have propagated this thread name, but it is a dubious one: computational complexity is the standard name for an important computer-science topic that has nothing much to do with the content of this thread. Still, what Chris Craddock had to say about what I shall call binding times was of great interest. Decisions about the resolution of from where and/or when an external entry is to be invoked or a table is to be loaded may be taken at different times. These actions may, that is, be bound o at programming time, o at compile time, o at linkage time, or, finally, o at execution time. In PL/I, but not in C or its sequelae, one can use generic function references like x = sqrt(y) ; delegating to a compiler the responsibility to choose an appropriate entry, one consonant with the data types of x and y. However this is managed, execution-time binding of a sqrt routine is something to be avoided. Or again, one can write a division-method hashing routine that always uses the divisor/modulus m=29 (a convenient small prime), or instead one can make m an execution-time formal parameter of the hashing routine. (The option of making the decision which of a set of hashing routines, one each for m=2,3,5,7,11,13,..., an execution-time one is unattractive.) In recent years late binding times have come to be more and more heavily used. Sometimes this is appropriate because the maintenance/replacement cycles of invoker and invoked are very different. A CICS application that uses DB2 may not, for example, wish to commit itself at linkage time to the use of a particular version and modification level of DB2; and the dynamic invocation of a DB2 interface routine by alias provides one mechanism for avoiding the need to do so. Interestingly, however, the original IBM OS/360 linkage editor accepted load mules it had created on one occasion as inputs for modification on another; and the z/OS binder still does so. For reasons that I have never understood--There is no neurosurgery involved--these facilities have been used only by coloro che sanno. They are perceived to be too difficult for mandolinisti to master, and heroic measures are taken to avoid their use. Thus, while incompetence is not the only rationale for the use of DLLs and the like, it is the chief one. There are legitimate uses of late binding times, but two things about them must be understood: o deferring binding times incurs additional overheads and it incurs them repeatedly, and o doing so gives scope for more errors, not, in my experience, fewer of them. Generic preferences for early or late binding times are thus always unhelpful. These things said, Chris Craddock's projection of what the future holds is prescient, all but certainly correct. I wish I were as sanguine as he is about the consequences. Most homegrown systems are ugly, badly designed and badly implemented; and, while some acquired systems are radically better, many are not. Poor programming, inferior system design, and the like are things that we have tacitly agreed not to talk much about; instead we embrace, more or less briefly, and then discard a succession of shibboleths, each, like its predecessor, touted as a simple global remedy for all of our problems. There is little to be done about this; but we should all be familiar with Forster's story, 'The day the machine stopped'. John Gilmore Ashland, MA 01721-1817 USA _________________________________________________________________ Windows Live(tm): Keep your life in sync. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_BR_life_in_synch_062009 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html that has nothing much to do with the content of this thread. Still, what Chris Craddock had to say about what I shall call binding times was of great interest. Decisions about the resolution of from where and/or when an external entry is to be invoked or a table is to be loaded may be taken at different times. These actions may, that is, be bound o at programming time, o at compile time, o at linkage time, or, finally, o at execution time. In PL/I, but not in C or its sequelae, one can use generic function references like x = sqrt(y) ; delegating to a compiler the responsibility to choose an appropriate entry, one consonant with the data types of x and y. However this is managed, execution-time binding of a sqrt routine is something to be avoided. Or again, one can write a division-method hashing routine that always uses the divisor/modulus m=29 (a convenient small prime), or instead one can make m an execution-time formal parameter of the hashing routine. (The option of making the decision which of a set of hashing routines, one each for m=2,3,5,7,11,13,..., an execution-time one is unattractive.) In recent years late binding times have come to be more and more heavily used. Sometimes this is appropriate because the maintenance/replacement cycles of invoker and invoked are very different. A CICS application that uses DB2 may not, for example, wish ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
