Shared Variables: Difference between revisions

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'''Shared Variables''' are a feature of the programming language [[APL (programming language)|APL]] language which allowed mainframeallows APL programs to communicate with other facilitiesrunning on a computer, which could include external files, DBMS, or other users. Shared Variables were first introduced byone [[InternationalProcessor Business Machines Corporation(computing)|IBMprocessor]] in their APL.SV program product in 1973 and continue to beshare availableinformation todaywith inanother IBMprocessor.<ref andname="ency">{{cite Dyalog APL for Linux and Windows.book

|title=Encyclopedia of Microcomputers |volume=1

|year=1987

|editor1= Allen Kent |editor2=James G. Williams

|isbn=0824727002

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

|pages=206–207

|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

|issue= 4

|year=1973

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

|access-date=2017-12-11

|title=The Design of APL

|author1=A.D. Falkoff

|author2=K.E. Iverson

|pages= 324–334

|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

|access-date=2017-12-11

|title=Shared Variable Principles

|work=Dyalog APL 15.0 Help

|date=2017-07-14}}</ref> for the operating systems [[Linux]] and [[Microsoft Windows|Windows]].

==Origin==

The Shared Variable facility is roughly analagous to a Windows out-of-process server today.

When APL\360 was first introduced in 1968, there were no built-in means by which a user could importdirectly access data from outside of the APL system. Thus, Somestarting ofin the timesharing vendors began offering an external file system at the time1969, however IBM's approachdeveloped wasthe toshared supply a more genericvariable facility whereby an external process could be used by an APL program.<ref name="design"/> Following APL.SV, the IBM VS APL and APL2 program products also supported shared variables, as well asdid the [[IBM 5100]] line of computers.

Shared Variable Processors were available to allow APL access to the following:<br />

* Standard operating system files (TSIO)<br />

* [[Time Sharing Option|TSO]] (TSO) and [[Conversational Monitor System|CMS]] (CMS) command processors (AP100)<br />

* VSAPL Stack Processor (AP101)<br />

* VSAPL Session Manager (AP102)<br />

* CMS Native Files (AP110)<br />

* CMS and TSO Native Files (AP111)<br />

* APL2 Data File Processor (AP121)<ref>{{cite book

[[Virtual storage access method|VSAM]] Files (AP123)<br />

|url=https://archive.org/stream/tutorialonapl200jaya#page/30/mode/2up/search/shared+variable

Full Screen Display Manager (AP124)<br />

|accessdate=2017-12-11

[[IBM Graphical Data Display Manager (GDDM)]] (AP126)<br />

|title=A tutorial on APL2

[[IBM DB2]] (AP127)<br />

|author=Toke Jayachandran

|year=1987

}}</ref>

* [[Virtual storage access method|VSAM]] (VSAM) Files (AP123)<br />

* Full Screen Display Manager (AP124)<br />

[[* IBM [[Graphical Data Display Manager]] (GDDM)]] (AP126)<br />

* [[IBM DB2Db2]] (AP127)<br />

==Subsequent uses==

In the early 1980s, I. P. Sharp Associates, which offered a highly modified version of IBM APL\360, introduced Shared Variables in their product offering. 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, or NSVP, allowed programs from one mainframe site to access another. NSVP predates the widespread usage of the Internet by five years.

In the early 1980s, [[I. P. Sharp Associates]], which offered a highlyrich modifiedand version of IBMadvanced APL\360, introduced Shared Variables in their product offering. 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, or (NSVP,) allowed programs from one mainframe site to access another.<ref>{{cite NSVP predates the widespread usage of the Internet by five years.web

With the advent of more powerful personal computing, the exodus of the APL community to Microsoft Windows was inevitable. Although Shared Variables are still a feature of IBM APL2 for Linux and Windows, other APL vendors chose to embrace Microsoft COM and ActiveX as a means to provide services from external programs. Dyalog APL supported Shared Variables as an interface to Microsoft Direct Data Exchange (DDE), however today that interface has been largely supplanted by COM, ActiveX, and .Net.

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

|access-date=2017-12-11

|title=Network Shared Variable Processor

|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 Z80]] based hardware, later the original IBM PC, and as 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), 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 functions, 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==

{{Reflist}}

{{APL programming language}}

[[Category:APL programming language family]]

[[Category:IBM software]]