Shared Variables: Difference between revisions

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'''Shared Variables''' are a feature of the programming language [[APL (programming language)|APL]] which allows APL programs running on one [[Processor (computing)|processor]] to share information with another processor.<ref name="ency">{{cite book

|title=Encyclopedia of Microcomputers: Volume |volume=1

|year=1987

|editorseditor1= Allen Kent, |editor2=James G. Williams

|isbn=0824727002

|chapter-url=https://books.google.com/books?id=F-Y0wdIIucgC&pg=PA206&lpg=PA206

|pages=206-207206–207

|chapter=APL for Microcomputers}}</ref> Although originally developed for [[mainframe computer]]s, Shared Variables were also used in [[personal computer]] implementations of APL.<ref name="ency"/> Shared Variables could be used to control [[peripheral device]]s, or to communicate with external files, [[database]] management systems, or other users.<ref name="ency"/> Shared Variables were first introduced by International Business Machines Corporation ([[IBM]]) in their APL.SV [[software]] product in 1973,<ref name="design">{{cite journal

|journal=IBM Journal of Research and Development

|volume= 17

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|year=1973

|url=http://www.jsoftware.com/papers/APLDesign1.htm

|accessdateaccess-date=2017-12-11

|title=The Design of APL

|author1=A.D. Falkoff

|author2=K.E. Iverson

|pages= 324–334

}}</ref> and are still available as of 2017, in APLs from IBM and Dyalog,<ref name="dya15">{{cite web

|doi=10.1147/rd.174.0324

|url-access=subscription

}}</ref> and are still available {{as of |2017|lc=y}}, in APLs from IBM and Dyalog,<ref name="dya15">{{cite web

|url=http://help.dyalog.com/15.0/Content/InterfaceGuide/Shared%20Variables/Shared%20Variable%20Principles.htm

|accessdateaccess-date=2017-12-11

|title=Shared Variable Principles

|work=Dyalog APL 15.0 Help

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==Origin==

When APL\360 was first introduced in 1968, there were no built-in means by which a user could directly access data from outside of the APL system. AccordinglyThus, in beginningstarting in 1969, IBM developed the shared variable facility.<ref name="design"/> Following APL.SV, the IBM VS APL and APL2 program products also supported shared variables, as did the [[IBM 5100]] line of computers.

Shared Variable Processors were available to allow APL access to the following:

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* Full Screen Display Manager (AP124)

* IBM [[Graphical Data Display Manager]] (GDDM) (AP126)

* [[IBM DB2Db2]] (AP127)

==Subsequent uses==

In the early 1980s, [[I. P. Sharp Associates]], which offered a rich and advanced APL, introduced Shared Variables in their product. Many of the Shared Variable Processors available for IBM products were also written for Sharp APL, notably TSIO (called PJAM), AP124, AP126, and AP127. Further, as I. P. Sharp also offered [[IPSANET]] which allowed in-house clients of SHARP APL to be connected to the network, a Network Shared Variable Processor (NSVP) allowed programs from one mainframe site to access another.<ref>{{cite web

|url=http://rogerdmoore.ca/INF/87QQPotyok4.htm

|accessdateaccess-date=2017-12-11

|title=NETWORKNetwork SHAREDShared VARIABLEVariable PROCESSORProcessor

|author=Richard L. Potyok

|year=1988}}</ref> NSVP predates the widespread use of the Internet by five years.

Shared Variables were one technique used by APL implementors and vendors to increase the richness of the APL language, doing so without changing the core implementation. With the advent of more powerful personal computing, the exodus of the APL user community to smaller computers was inevitable. APL was first available on [[Intel 8008]], [[Intel 8080|8080]], and Zilog [[Zilog Z80]] based hardware, later the original IBM PC, and todayas of 2015, on the 32- and 64-bit Linux and Windows workstations. Although Dyalog APL included an implementation of shared variables for communication with the now-deprecated Microsoft Windows [[Dynamic Data Exchange]] (DDE), it is interesting to note that only IBM continued to use Shared Variables as a means to supply new features to their versions of the APL2 language for non-mainframe computers.{{citation needed|date=December 2017}}

Nearly all other APL vendors chose to implement new functionalityfunctions, such as access to [[Linux]] and Windows native features, [[graphical user interface]]s, presentation graphics, database management system interfaces, and so on, more directly in their respective versions of the APL language.{{citation needed|date=December 2017}} In modern non-IBM APL implementations, the Shared Variable interface has been largely supplanted by [[Component Object Model]] (COM), [[ActiveX]], and [[.NET Framework]].

==References==

{{reflistReflist}}

{{APL programming language}}

[[Category:APL programming language family]]