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Semiotics and Programming LanguagesH . Z e m a n e k

U n i v e r s i t y o f T e c h n o l o g y , Vienna, and I B M L a b o r a t o r y , Vienna

1 . A V e r y P r a g m a t i c I n t r o d u c t i o nIt is a very great pleasure for me to have been invitedto this conference and to speak in this opening session.

When I accepted the invitation, I was sure that somehistorical background probably prompted the choice ofthe organizers, as this conference and its title have somespecific relations to the t own of Vienna and to t he c ountr yof Austria, where I come from. Let me explain.

1.1 THE TERM "PRAGMATICS". P ragmatics is a wordwhich any Austrian would associate with the hist ory of the18th century. In 1713 the emperor Charles VI settled thelaw of succession for the dominions of the house of Habs-burg so that his only daughter, Maria Theresa, could fol-low him on the throne. She governed from 1740 to 1780,the most glorious period of the Austrian history. Those whowere in Vienna at the conference last Septe mber have seenthe many baroque buildings and interiors so characteristicof Vienna; most of them were built in the time of MariaTheresa.

The document issued by Charles VI has the name,"Pragmatic Sanction." This term comes from the Roma nRight, and stands for a decision of the state dealing with amat ter of some importan ce and given for some communit yand for a public cause. The word "pra gma tic" itself comesfrom t he Greek an d means act or affair or business.

In the form "pragmatism," this word became a philo-sophical term when the American logician Charles S.Peirce (1839-1914) [1] introduced this philosophical direc-tion around 1870 as "a method of logic determining themeaning of intellectual concepts, i.e., of those upon whichreasoning may hinge." As a philosophical method, prag-matism is something different from pragmatics, but thereis enough interconnection and from a pragmatist point ofview, one might say with Peirce that pragmatics is "theconsideration of practical bearings of a notion," the syn-tactics and semantics of which are settled.

The idea is, of course, considerably older and had al-ready appeared in th e anci ent Greek philosophy [2], whenTheophrastus, the chief disciple of Aristotle, spoke of "t hetwofold relation of speech: one to the hearers, to whom itsignifies something, the other to the things about whichit informs the hearers." For Theophrastus, poetics andrhetoric were "pragmatic" aspects.The distinction between syntactics, semantics and prag-matics was first made by the American philosopher CharlesMorri s (b. 1901) when he developed a science of signswhich he called semiotics and which he subdivided into

P r e s e n t e d a t a n A C M P r o g r a m m i n g L a n g u a g e s a n d P r a g -m a t i c s C o n f e r e n c e , S a n D i m a s , C a l i f o r n i a , A u g u s t 1 9 65 .

V o l u m e 9 / Number 3 / March, 1966

these three fields. The terms-syntactics, semantics andpragmatics--need very careful definition. Morris, andbefore him Neurath, had given warnings tha t "they mayengender pseudoproblems and produce ambiguities." Thewarnings soon turned out to be very justified and this iseven more true for the field of programming languages.

In Foundations of the The ory of Signs [3], Morris de-fined the three terms as follows:

pragmatics--the study of the relation of signs to in-terpreters;semantics--the study of the relations of signs to theobjects to which the signs are applicable;

syntactics--the study of the formM relations of signst o o n e a n o t h e r .

In his later book, Signs, Language, and Behavior [4],Morris refined his definitions:pragmatics--deals with the origin, uses and effects of

signs within the be havior in which they occur;semantics--deals with the signification of signs in all

modes of signifying;syntactics--deals with combination of signs without

regard for their specific significations or their rela-tion to the behavior in which they occur.1.2 Ti~ E WIENER KREIS. B oth Peirce and Morris

were essentially oriented towards behavior; they con-sidered the acting human being, and their results cannot,therefore, directly be applied to computers and their lan-guages. The necessary bridge between empiric behaviorismand logic was developed in Vienna in a relatively shortperiod immediately before the barbaric time when an un-fortunate political development disturbed and disruptedorder, moral and science in Europe and deleted Austriafrom its map. Almost all the people who worked on thissubject during that period left Austria or had to leave it;and when you now come to Vienna, you will hardly find atrace of the glorious time of Austrian philosophy.

In 1895, a chair for the philosophy of induc tive scienceswas instMled at the University of Vienna. The first pro-fessor was Ernst Mach (1838-1916), a forerunner of Ein-stein as a physicist and one of the most important posi-tivists as a philosopher; his name is now attached to theunit of aircraft speed. After Mach, the chair went toLudwig Boltzmann (1844-1906), who worked in the t heor yof heat and promoted the notion of entropy; in his read-ings on gas theory [5] you can find a chapter on the H-theorem, which you will easily recognize as the kernel ofC. E. Shannon's famous paper introducing informationtheory [6].In 1922, Moritz Schlick was appoint ed professor to this

C o m m u n i c a t i o n s o f t h e ACM 139

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c h a ir , a n d d u r i n g h i s t i m e - - u n t i l h e w a s n m r d e r e d b y ap s y c h o p a t h i n 1 9 3 6 - - a s h o r t b u t f r u it f u l a c ti v i t y la i d d o w nt h e g r o u n d f o r a p h i l o s o p h i c a l s c ho o l w h i c h s u b s e q u e n t l yb e c a m e o n e o f t h e m o s t i m p o r t a n t g u i d e l i n e s f o r t h ep h i l o s o p h y o f o u r p r o g r a m m i n g l a n g u a g e s. A r o u n d S c h l ic k .d u r i n g t h i s p e r io d , a n u m b e r o f h i s p u p i ls a n d o t h e rp e o p l e i n t e r e s t e d i n l og ic a n d l a n g u a g e f o r m e d a c i r c lel a t e r c a l le d t h e W i e n e r K r e i s [7 ] p r o m o t i n g a p h i l o s o p h y a n dp h i l o s o p h i c a l m e t h o d s w h i c h b e s t a r e d e s i g n a t e d b y t h et e r m l o g ic a l e m p i r i s m . S o m e n a m e s o f t h i s g r o u p a r e F r .W a i s m a n n , O t to N e u r a t h , H a n s F e ig l, B e la y o n J u h o s ,R u d o l f C a r n a p , V i c to r K r a f t , K a r l M e n g e r , K u r t G S d e l,a n d O s k a r M o r g e n s t e r n [ 9 , 1 0 , 1 1 , 1 2 ] .

F o r o u r s u b j e c t , n o t a l l t h e a s p e c t s o f t h e l o g i c a l e m -p i r i s m a r e o f in t e r e s t. T h e e s s e n ti a l f a c t is t h a t l a n g u a g ew a s i n v e s t i g a t e d f r o m a l o g ic a l p o i n t o f v i e w s o t h a t t h ea b s t r a c t w o r l d o f c o m p u t i n g n m c h i n e r y w a s p r e - e s ta b -l i s h e d . T h e b e h a v i o r i s t i c v i e w o f P e i r c e a n d M o r r i s w a ss p e c i f ie d in t o a f o r m a l o r, a t l e a s t i n t o a n a b s t r a c t d i r e c -t i o n . T h e s p i r i t u s r e c t o r of t h i s d e v e l o p m e n t w a s L u d w i gW i t t g e n s t e i n ( 1 8 8 9 - 1 9 5 1 ), a p u p i l o f R u s s e ll . A s a m a t t e ro f f a c t , W i t t g e n s t e i n n e v e r b e l o n g e d t o t h e W i e n e r K r e i s ,b u t h i s Traclus Logico-Philosophicus [ 8 ], f i n i s h e d d u r i n g h i sm i l i t a r y s e r v ic e i n th e A u s t r i a n a r m y d u r i n g W o r l d W a r I ,i n f lu e n c e d t h e t h i n k i n g o f t h e g r o u p e n o r m o u s l y . W i t t g e n -s t e i n d i d no t i n v e n t t h e t r u t h t a b l e s , b u t h e c o n t r i b u t e de s s e n t i a l l y t o t h e i r e f f i c i e n t a p p l i c a t i o n ; h e c o n s i d e r e d a l lp h i l o s o p h y t o b e c r i t iq u e a n d l o g ic a l in v e s t i g a t i o n o f l a n -g n a g e. A n d n o b e t t e r m o t t o c o u ld h a v e b e e n c h o s e n fo rt h e A L GO L d o c u m e n t s t h a n t h e q u o t a t i o n o f h i s p ri n c i p le ,t o s p e a k c l e a r l y o r n o t t o s p e a k a t a l l.

W i t t g e n s t e i n i s a n o t h e r r e f e r en c e to m y c o u n t r y . H ew a s b o r n i n V i e n n a , h e w o r k e d i n V i e n n a , a n d h e w a s at e a c h e r i n e l e m e n t a r y s c h o o l s n e a r V i e n n a . H e l e f t, b y t h ew a y , a f a s c in a t i n g m o n u m e n t f o r h i m s e lf , a n a p a r t m e n th o u s e h e d e s i g n e d h i m s e lf , w h e r e m e m b e r s o f t h e f a m i l ys t i l l l ive .O f c o u rs e , t h e W i e n e r K r e i s w a s n o t t h e o n l y p o i n t i nt h e w o r l d w h e r e t h e r e l a t i o n b e t w e e n l a n g u a g e a n d l o g i cw a s s t u d i e d . T h e r e w a s a n e x c h a n g e o f i d e a s a ll o v e r t h ew o r l d - - w h i c h m a d e i t ea s ie r f o r i ts m e m b e r s w h e n t h e yh a d t o g o a b r o a d i n t h e l a t e t h i r t i e s . A n d t h e m o s t i m -p o r t a n t e x c h a n g e s o f t h e s e i d e a s w e r e t h e c o n f e r e n c e s o nt h e u n i f i c a t i o n o f s c i e n c e , t o w h i c h t h e W i e n e r K r e i s c o n -t r i b u t e d i n a n o u t s t a n d i n g m a n n e r . A n d w i t h th i s r e m a r kI t e r m i n a t e m y h i s t o r i c c o m m e n t s .

L e t m e n o w t u r n t o t h e a d v e n t o f t h e c o m p u t e r a n d t r yt o s h o w i n w h a t s e n s e t h e c o m p u t e r j u s t if i e d a n d a c t u a l i z e dt h e l o g i c a l i n v e s t i g a t i o n o f l a n g u a g e . A l r e a d y i n p r e -c o m p u t e r t im e w h e n m a t h e m a t i c i a n s l i k e T u r i n g , M a r k o v ,a n d G 5 d e l d e f in e d c o m p u t a b i l i t y a n d d e c i d a b i l i t y ( o r t h ec o n t r a r y ) , t h e y b a s e d t h e i r a r g u m e n t s o n s t r u c tu r e s w h i c hf o u n d t h e i r i m p l e m e n t a t i o n l a t e r in t h e c o m p u t e r . A n d i n am o r e g e n e r a l w a y o n e c a n s a y t h a t t h e p r o g r a m m i n g l a n -g u a g e s i m p l e m e n t i n a c o r r e s p o n d i n g s t e p t h e t h o u g h t s o ft h e W i e n e r K r e i s : w h a t i n t h e i r w r i t i n g s m a y h a v e a p -p e a r e d t o m a n y p h i l o s o p h e r s a s a k i n d o f a r b i t r a r y f o r -

m a l i z a t io n , l o o k s n o w q u i t e a p p r o p r i a t e a n d h a s b e c o m et h e g r o u n d f o r t h e h i g h e r a r t o f p r o g r a m m i n g , w h i c h w i llc o r o n a t e a l l k i n d s o f s c i e n t i f i c d o c t r i n e : b e c a u s e i t i s o n l yt h e c o m p u t e r w h i c h c a n d e s c r i b e a n d r e a l i z e sc i e nt if ics t r u c t u r e s i n a l l g e n e r a l i t y a n d w i t h o u t a n y i n t u i t i v ej u m p s . T h e c o m p u t e r c a n i n d e e d b e m a d e t o p r i n t c l ea r lyw h a t e v e r i t p r i n ts a n d n o t t o p r i n t w h a t c a n n o t b e p r i n t e d ,j u s t a s W i t t g e n s t e i n d e s i re d f o r p h i l o s o p h y a n d s c ie n c e .

1 . 3 S E M I O T I C S A N D O T H E R A S P E C T S O F L A N G U A G E . I h a v eb a s e d m y p a p e r o n s e m i o t i c s a n d i t s t h r e e d i m e n s i o n s . Is h o u l d i n s e r t a t t h i s p o i n t t h a t l a n g u a g e h a s m a n y a s p e c t sa n d t h a t p r a g m a t i e s , s e m a n t i c s a n d s y n t a c t i c s d o n o tn e c e s s a r i l y c o v e r a l l o f t h e m . O n e c a n , h o w e v e r , p r o j e c tm o s t a s p e c t s i n t o t h e t h r e e s e m i o t i c d i m e n s i o n s a n d t h e r es e e m s t o b e a s t r o n g t e n d e n c y t o d o s o t o d a y . L e t m e s a y af e w w o r d s o n t h e s e o t h e r a s p e c t s a n d t h e i r p r o j e c t i o n i n t osemi o t i c s .1.3.1 Formal i za t ion . M a n y p h i l o s o p h e r s s e e m t o c o n -s i d e r f o r m a l i s m a n d s y n t a c t i c s t o b e t h e s a m e , o r a t l e a s tf o r m a l i s m t o b e b u t i d e a l s y n t a c ti c s . N o n i t is c e r t a i n l yt r u e t h a t s y n t a x c a n b e t r e a t e d v e r y i n f o r m a l l y - - a n d h a sb e e n t r e a t e d v e r y i n f o r m a l l y f o r c e n t u r ie s . A n d i t is v e r yp o s s i b l e 4 o f o r m a l i z e s e m a n t i c s a s w e l l a s p r a g m a t i c s [1 7].I n d e e d , f r o m a p r o g r a m m i n g l a n g u a g e s p o i n t o f v i e w , w ew i l l h a v e t o i n s i s t t h a . t a l l t h e t h r e e s e m i o t i c d i m e n s i o n s o fo u r p r o d u c t s c a n b e a n d s h o u l d b e f o r m a l i z e d - - p r a g m a t i c sa t l e a s t o v e r a c e r t a i n r a n g e .

1.3.2 Object World, Object Language, and Metalanguage.O b j e c t w o r ld , o b j e c t la n g u a g e a n d m e t a l a n g u a g e a r e c o n -s i d e r e d b y m a n y p h i l o s o p h e r s t o b e s e m a n t i c l e v e l s ; t h eo b j e c t s o f t h e r e a l ( o r a n i n v e n t e d ) w o r l d a r e o f le v e l z e ro ,t h e i r n a m e s a r e o f l e v e l o n e , a n d t h e n a m e s o f t h e n a m e sa r e of l e v el t w o . A r b i t r a r i l y m a n y l e v e ls c a n b e c o n c e i v e da n d s o m e a u t h o r s th i n k t h a t t h e r e is n o e n d - - b u t t h a t o ns o m e p o i n t s w e w i ll e v e r h a v e t o s t e p b a c k t o o u r u l t i m a t em e t a l a n g u a g e , i . e ., to E n g l i s h . I f t h e i n v e s t i g a t i o n is b a s e do n t h e s e l e v e l s a s pr ima~/not ions , t h e s e m i o t ic d i m e n s i o n sc h a n g e c h a r a c t e r a n d d e f i n i t i o n : s y n t a c t i c s b e c o m e s r e l a -t i o n s w i t h i n o n e l e v e l , w h a t e v e r t h e l e v e l i s ; s e m a n t i c sb e c o m e s r e l a t i o n s b e t w e e n t w o a d j a c e n t l e v e l s ; a n d p r a g -m a t i c s p r e s u m a b l y b e c o m e s t h e r e l a t i o n s l e a d i n g o u t s i d eo f t h e l e v e l s c h e m e , w h a t e v e r " o u t s i d e " is .

A t t h i s p o i n t m a y I r e f e r a l a s t t i m e t o V i e n n a a n d r e -m i n d y o u o f th e I F I P C o n f er e n ce o n " F o r m a l L a n g u a g eD e s c r i p t io n L a n g u a g e s " h e l d i n V i e n n a in S e p t e m b e r ,1 9 64 . I n t h e p a p e r s o f t h a t c o n f e r e n c e th e d e s c r i p t i o n r el a -t i o n s h i p s o f p r o g r a m m i n g l a n g u a g e s a r e r e f le c t e d i n v e r ym a n y w a y s [1 3].1.3.3 De scriptive and Prescriptive Aspects. L a n g u a g et h e o r y i s a s w e l l a w a r e a s i s p r o g r a m m i n g p r a c t i c e t h a tl a n g u a g e s h a v e t h e t w o a s p e c t s o f d e s c r i p t i o n a n d p r e -s c r i p ti o n : o f c o g n i t i v e v . s i n s t r u m e n t a l c h a r a c t e r ; o fd e c l a r a t i o n a n d c o m m a n d ; o f d e a l i n g w i t h s t a t e s o r w i t ha c t io n s . S o m e p h i l o s o p h e r s c o n s i d e r t h e s e t w o a s p e c t s a sb e i n g o f p r a g m a t i c a l c h a r a c t e r , b u t i t i s t r u e t h a t b o t ha s p e c t s r u n t h r o u g h t h e w h o l e g a m u t f r o m s y n t a c t i c s t os e m a n t i c s t o p r a g m a t i c s a n d , e s p e ci M l y f r o m t h e p r o g r a m -

1 4 0 C o m m u n i c a t i o n s o f t h e A C M V o l u m e 9 / N u m b e r 3 / M a r c h , 1 96 6

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r u in g l a n g u a g e s p o i n t o f v i e w , t h e r e i s n o q u e s t i o n t h a tt h e s e t w o a s p e c t s h a v e t o b e t r e a t e d i n d e p e n d e n t l y o f t h es e m i o t i c tr i p l e . O n t h e o t h e r h a n d , I d o n o t b e l i e v e t h a t t h ed i s t i n c t i o n i s e s s e n ti a l . F o r a n y c o m m a n d i s t h e d e s c r i p t i o no f t h e w a n t e d s t a t e , a n d a n y d e s c r i p t i o n c a n b e u n d e r s t o o da s g u i d a n c e f o r c o n s t r u c t i o n . T h e u n d e r l y i n g r e a l - t i m ea s p e c t i s n o t i m p o r t a n t f o r l a n g u a g e c o n s i d e r a t i o n s a ss u c h .

A f t e r t h i s h i g h l y p r a g m a t i c i n t r o d u c t i o n ( c o n t a i n i n g al o t o f r e l a t i o n s h i p b e t w e e n l a n g u a g e s a n d m y s e l f ) i t is t i m et o t u r n t o a m o r e s e m a n t i c s e c t i o n o n t h e s e m i o t i c s o f p r o -g r a m m i n g l a ng u a g es .2 . W h a t i s a L a n g u a g e ?

A s l o ng a s s o m e b o d y s p e a k s o n l y o n e l a n g u ag e , " w h a ti s a l a n g u a g e ? " i s n o t a r e a l q u e s t i o n f o r h im . L a n g u a g e i sw h a t h e s p e a k s . A s lo n g a s w e c o n s i d e r o n l y n a t u r a l l a n -g u a g e s , t h e n o t i o n o f a l a n g u a g e c a n b e d e s i g n a t e d b yn a m i n g s o m e o f t h e m , s a y E n g li s h , F r e n c h , a n d S p a n i s h .

B u t a s s o o n a s a r t i f i c i a l o r c o n s t r u c t e d l a n g u a g e s c o m ei n t o t h e g a m e , i t i s n o t a t a l l c l e a r w h e r e t o p u t l i m i ts . A l lk i n d s o f d o u b t f u l i n t e r m e d i a t e p r o d u c t s m a y o c c u r . I sm a c h i n e l a n g u a g e r e a l l y a l a n g u a g e o r i s i t m e r e l y a c o d e ?T h e f a c t t h a t t h e c a r r i e d i n f o r m a t i o n m a y b e t h e s a m ew h e t h e r d e s c r i b e d o r e xp r e s s e d i n E n g l i s h , i n F O R T R A N ,i n a f l o w c h a r t o r i n t h e 1 40 1 m a c h i n e l a n g u a g e d o e s n o tp r o v e a n y t h i n g f o r o u r p u r p o s e . F o r t r a n s l a t i o n m a y h a p -p e n b e t w e e n l a n g u a g e s , b u t i t m a y h a p p e n a l s o f r o ma n d t o l a n g u a g e s , t o a n d f r o m o t h e r m e a n s o f c o m -m u n i c a t i o n . A p p a r e n t l y s o m e t y p e s o f a r t i f i c i a l l a n g u a g e sa r e m u c h c l o s e r t o a n a t u r a l l a n g u a g e t h a n o t h e r t y p e s .B u t o n t h e o t h e r h a n d , t h e g e n e r a l t h e o r y o f l a n g u a g e si n s i s t s s t r o n g l y o n i n c l u d i n g all k i n d s o f l a n g u a g e , i .e .,e v e n g e s t u r e s a n d l o o k s . S o w e c a n n o t p o s s i b l y e x c l u d em o r e p r i m i t i v e s y s t e m s , w e c a n m e r e l y c l a s s i f y a n d s u b -d i v i d e t h e n o t i o n o f p r o g r a m m i n g l a n g u a g e s .I n a n a l o g y t o t h e d e f i n i t i o n o f n a t u r a l l a n g u a g e w e m a ys a y t h a t a p r o g r a m m i n g l a n g u a g e i s a s y s t e m o f c h a r a c t e rs t r i n g s w h i c h f o r m w o r d s , e xp r e s s i o n s , s e n t e n c e s a n dh i g h e r a g g r e g a t e s . T h e p u r p o s e i s t h e c o m m u n i c a t i o n o fp r o g r a m s b e t w e e n c o m p u t e r s , f r o m m a n t o c o m p u t e r s ,a n d a l s o f r o m m a n t o m a n . A n d f u r t h e r m o r e t h e e l a b o r a -t i o n o f p r o g r a m s i s a n i m p o r t a n t p u r p o s e b e c a u s e i t i s o n l yi n e xc e p t i o n a l c a s e s t h a t t h e f i r s t w r i t i n g i s t h e c o r r e c t a n df i n a l v e r s i o n . T h e l a n g u a g e i s t h e c a r r i e r a n d t h e i m p l e -m e n t a t i o n o f i d e a s ; s i n c e i t i s v e r y h a r d t o h a n d l e i d e a s i na n a b s t r a c t f o r m , t h e l a n g u a g e i s a n i m p o r t a n t i n s t r u m e n tf o r t h e e xp r e s s i o n , r e f i n e m e n t a n d p r e c i s i o n o f i d e a s . S o ap r o g r a m m i n g l a n g u a g e i s a l s o a m e a n s o f c o m n m n i c a t i o nb e t w e e n a h u m a n b e i n g a n d h i m s e l f .

I n t h e c a s e o f p r o g r a m m i n g l a n g u a g e s , t h e r e a l i za t i o n o ft h e f o r m u l a t e d i d e a s i n t h e i n f o r m a t i o n p r o c e s s i n g m a c h i n ei s - - i n a c e r t a i n s e n s e - - g u a r a n t e e d . T h i s i s a f a s c i n a t i n gp r o p e r t y : w r i t i n g t e xt s i n p r o g r a m m i n g l a n g u a g e s c a n n o to n l y b e a s c r e a t i v e a s p o e t r y , t h e c r e a t i o n s , m o r e t h a n i np o e t I T , b e l o n g t o t h e r e a l w o r l d a s s o o n a s r u n t h r o u g h t h em a c h i n e .

P r o g r a m m i n g l a n g u a g e s a re a l w a y s c o n s t r u c te d l a ng u a g e s ( G o r n [ 1 4, 1 5] c al ls t h e m m e c h a n i c a l l a n g u a g e s , t ow h i c h o n e m i g h t o b j e c t t h a t c o n s t r u c t e d l a n g u a g e s a r em o r e t h a n m e c h a n i s m s i n s o f a r a s t h e y c a r r y o n t h e n o n -m e e h a n i e M c o n t e n t t h e p r o g r a m m e r h a s p u t i n t o t h e t e x t )P r o g r a m m i n g l a n g u a g e s h a v e t o b e a s f o r m a l a s p o s s i b l eT h e r e a s o n s f o r t h i s a r e o b v i o u s .

B u t l e t m e r e m i n d y o u t h a t " a r t i f ic i a l " a n d " f o r m a l "a r e n o t a t a l l i d e n t ic a l . T h e r e a r e c a s e s w h e r e o n l y o n e ot h e s e a s p e c t s a p p l i e s : t h e r e a r e i n f o r m a l a r t i f i c i a l l a ng u a g e s , j u s t a s t h e r e i s t h e f o r m a l i z a t i o n o f n a t u r a l l a ng u a g e s .

P e r i o d ic a l l y w e h e a r a r g u m e n t s t h a t n a t u r a l l a n g u a g e ss h o u l d b e u s e d i n p r o g r a m m i n g ; t h e b a s i c r e a s o n s f o r t h i sm a y b e t h e h i g h g e n e r a l i t y o f n a t u r a l l a n g u a g e s o n t h e o n ee x t r e m e a n d t h e e a s y a v a i l a b i l i ty o n t h e o t h e r ( " t h ec u s t o m e r d o e s n o t l i k e t o l e a r n t h e a r t i f i c i a l l a n g u a g e " )E i t h e r r e a s o n i s a m i s u n d e r s t a n d i n g o f t h e p u r p o s e . R u s -s e l l o n c e g a v e f o u r r e a s o n s f o r f o r m a l i z a t i o n w h i c h s t i la p p l y t o b o t h t h e o r y a n d p r a c t i c e : ( 1) s e c u r i t y o f o p e r at i o n is a ss u r e d , ( 2) t a c i t p r e - a s s u m p t i o n s a r e e x c l u d e d , ( 3)n o t i o n s a r e c l a r i fi e d , a n d ( 4) r e s o l v i n g s t r u c t u r e s c a n b ea p p l i e d t o m a n y o t h e r p r o b l e m s .

A n d h e h a s g i v e n f o u r o t h e r r e a s o n s f o r t h e a p p l i c a t i o no f a r t i fi c i a l l a n g u a g e s : ( 1) a b s t r a c t n o t i o n s a r e u s u a l l yd i f f e r e n t f r o m t h e c o m m o n o n e s , (2 ) t h e s y n t a x o f n a t u r a ll a n g u a g e s i s n o t e x a c t , ( 3 ) a m b i g u o u s w o r d s a r e e l i m i n a t e da n d ( 4) e x p r e s s i on s b e c o m e s h o r t e r .

I t m a y b e t r ue t h a t o u r ul t i m a t e m e t a l a n g u a g e m u s t bE n g l i s h - - I h a v e n o t s e e n a n y c o n v i n c in g p r o o f f o r th is t a t e m e n t - - b u t e v e n i f t h i s is r i g h t, i t w o u l d b e n o r e a s of o r u s in g E n g l i s h a s p r o g r a m m i n g l a n g u a g e o r a s f ir sm e t a l a n g u a g e . W e d o n o t w a n t t h e f u l l g e n e r a l i t y of n a t u r a l l a n g u a g e b e c a u s e w e w a n t t h e w r i t t e n p r o g r a m s t or e m a i n i n th e a r e a o u r s c ie n c e h a s a l r e a d y w o r k e d t h r o u g hA n d w e d o n o t w a n t t h e e a s y a p p l i c a t io n t h a t a n a t u r al a n g u a g e o f f er s b e c a u s e t h e u s e r w o u l d t h e n n o t r e f l e ce n o u g h o n w h a t h e i n s t r u c t s t h e m a c h i n e t o d o .3 . O n t h e S e m i o t ic s o f P r o g r a m m i n g L a n g u a g e s

L e t m e s t a r t w i t h t h e r e m a r k t h a t t h e t h r e e d i m e n s i o no f s e m i o t i c s a r e w a y s o f c o n s i d e r a t i o n o r k i n d s o f p o s i ti or a t h e r t h a n a b s o l u t e p r o p e r ti e s o f a l a n gu a g e . T h e b o r d el i n es b e t w e e n t h e t h r e e f i e ld s a r e v a g u e a n d c a n b e m o v ef o r w a r d a n d b a c k b y m o d i f y i n g d e t a i l s o f i n v e s t i g a t i o np r i n c i p l e s .

T h e r e i s a l w a y s p r a g m a t i c s b e c a u s e t h e r e i s a l w a y s a no b s e r v e r a n d b e c a u s e n o l a n g u a g e m a k e s s e n s e w i t h o ui n t e r p r e t a t i o n . T h e f i r s t r e d u c t i o n i s t o r e m o v e t h e p r a gm a t i c a l a s p e c t s i n o r d e r t o t a l k a b o u t s e m a n t i c s a n d s y nt a c ti c s . T h e r e i s a l w a y s s e m a n t i c s - - u n l e s s w e p l a y a m e a ni n g le s s g a m e w i t h c h a r a c t e r s : i n t h i s e a s e a lo n e w e w o u lh a v e s t r i c tl y s y n t a x . W e c a n c o n s i d e r a n d e v e n f o r m a l i zs e m a n t i c s i n d e p e n d e n t l y o f n o t a t i o n s o t h a t s e m a n t i c s ii s o la t e d a s s u c h; b u t t h e n w e h a v e t o a p p l y a m e t a l a n g u a gw h i c h i n i ts e l f w o u l d c a r r y s e m a n t i c s a n d s y n t a e t i c s . Sw e w i ll s c a r c e l y h a v e c l e a r a n d e a s y s i t u a t i o n s i n th e t h e o wo f p r o g r a m m i n g l a n g ua g e s .

V o l u m e 9 / N u m b e r 3 / M a r c h , 1966 C o m m u n i c a t i o n s o f t h e A C M 1 4

7/29/2019 Semiotics of Programming Languages

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T o d i s t i n g u i s h s y n t a c t i c s a n d s e m a n t i c s w e h a v e t os e p a r a t e f o r m a n d m e a n i n g . B u t t h i s i s a p a r t i c u l a r p r o b -l e m i n i n f o r m a t i o n p r o c e s s in g b e c a u s e o f it s m a t h e m a t i c a ln a t u r e . N o w h e r e e l se h a v e f o r m a n d m e a n i n g b e e n i n t e r -f a c e d s o i n te n s i v e l y . A s a m a t t e r o f f a c t , f o r m a l i z a t i o n i sn o t h i n g m o r e t h a n p a c k i n g a s m u c h m e a n i n g a s p o s s i b l ei n t o d e f i n e d f o r m s . T o a c e r t a i n d e g r e e t h i s is d o n e a l r e a d yi n n a t u r a l l a n g u a g e s . T h e p l u r a l , f o r i n s t a n c e , i s a s y n -t a c t i c a l f o r m c o n n e c t e d t o a c l e a r ly e s t a b li s h e d m e a n i n g .I n o u r c o n s t r u c t e d l a n g u a g e s w e d o t h e s a m e i n a m u c hm o r e e l a b o r a t e d f a s h i o n . T h e s y n t a c t i c e l e m e n t s o f c o n -s t r u c t e d l a n g u ag e s c a r r y a n i m p o r t a n t p o r t i o n o f m e an i n g .P r a g m a t i c a l ly , t h i s i s v e r y i m p o r t a n t b e c a u s e t h e h u m a nb e i n g w h e n r e a d i n g h a s a k i n d o f m e a n i n g - a s s i g n m e n tm e c h a n i s m r u n n i n g w h i c h p r o d u c e s m a n y e r ro r s if t h ea r t i f i c ia l l y a ss i g n e d m e a n i n g i s d i f f e r e n t f r o m t h e u s u a l ,t h e n a t u r a l o n e .

I n n u m e r i c a l a n a l y s i s , s t il l t h e f i r s t f i e ld o f a p p l i c a t i o n ,t h e m e a n i n g o f a n e x p r e s s i o n c a n b e c o n s i d e r e d i n t w od i f f e r e n t w a y s . O n e p o s s i b i l i t y is t h e o n e w e l e a r n i n t h eu s u a l m a t h e m a t i c a l e d u c a t i o n . A s e c o n d v e r s i o n of t h i sm e a n i n g , h o w e v e r , i s b u i l t i n t o t h e m a c h i n e d u r i n g t h ed e s i g n o f h a r d w a r e o r s o f t w a r e , a n d i t is n o t a t a ll u n w i s et o d e fi n e t h e m e a n i n g b y t h e i m p l e m e n t e d f o r m o f a m a t h e -m a t i c a l n o t i o n . T h e s e t w o k i n d s o f d e f i n i t i o n o f m e a n i n gc e r t a i n l y o v e r l a p n i c e ly b u t t h e r e i s n o d o u b t t h a t t h e r ea r e d i s c r e p a n c i e s ( a s w e l l a s t h e r e a r e , b y t h e w a y , b e -t w e e n m a t h e m a t i c i a n s o f d i ff e r e n t s c h o o ls ) .

T h e r e i s a p o s i t i v e f e e d b a c k f r o m m a c h i n e r y t o p h i l o s -o p h y a n d s o m e o f t h e d i s c r e p a n c ie s w il l b e o v e r c o m e s i m p l yb y t h e f a c t t h a t t h e t h e o r y s o m e d a y w i ll a c c e p t th em a c h i n e - c o v e r e d n o t i o n . I f i t i s p h i l o s o p h i c a l l y c o r r e c tt h a t m e a n i n g i s p r i m a r i l y a m a t t e r o f v e r i f ic a t i o n , t h e ns u c h a d e v e l o p m e n t i s p e r f e c t l y s o u n d . T h e r e i s n o b e t t e rv e r i f ie r t h a n a c o m p u t e r . B u t t h i s d e v e l o p m e n t i n te n s if i esa l s o t h e t e n d e n c y t o r e d u c e s e m a n t i c s t o s y n t a c t i c s a n d i tb e c o m e s h a r d e r t o f in d o r d e s c r ib e t h e b o r d e r l i n e b e t w e e nt h e t w o .

T h e d i s t i n c t i o n b e t w e e n s e m a n t i c s a n d p r a g m a t i c s i s ,o f c o u rs e , a ls o t o u c h e d b y t h i s e v o l u t i o n . S i n c e p r o g r a m -m i n t l a n g u a g e s a r e a c o m m u n i c a t io n l in k b e t w e e n m a na n d m a c h i n e , w e h a v e t w o k i n d s o f u s e r s : a n a r t if ic i a l o n ea n d a n a t u r a l o n e ; a m e c h a n i z e d o n e a n d a n i ll o g ic a l o n e.T h e f i r st is f u ll y a lg o r i t h m i c a n d c a r r ie s o u t w h a t t h e t e x tm e a n s t o h i m , w h i l e t h e s e c o n d h a s n o t i o n s , o p i n i o n s a n df e el in g s . C l e a r l y b o t h k i n d s c a n a p p e a r i n t h e s a m e m a n - -h e m a y r e a c t e i t h e r w a y d e p e n d i n g o n h is m o m e n t a r y i n-t e n t i o n .

S o w e h a v e t w o k i n d s o f p r a g m a t ie s , t h e h u m a n p r a g -m a t i c s a n d t h e m e c h a n i c a l p r a g m a t i c s , a p p l y i n g a t e r m o fS . G o r n [1 5, 1 6 ]. T o il l u s t r a t e t h e t w o k i n d s : t o t h e f i r s tk i n d w o u l d b e l o n g a n i n v e s t i g a t i o n t o f i n d o u t w h y a e e r -t a i n a u d i e n c e m a y b r e a k o u t i n t o l a u g h t e r w h e n t h e n a m eo f a c e r t a in p r o g r a m m i n g l a n g u a g e i s p r o n o u n c e d , a n d t ot h e s e c o n d , t o f i n d o u t h o w m u c h o f a c e r t a i n p r o g r a m m i n gl a n g u a g e r e f le c t s a c e r t a i n f a m i l y o f c o m p u t e r s .

B u t o n e c o u ld g o e v en f u r t h e r a n d u n d e r s t a n d w a g -m a t i c s a s t h e r e l a t i o n b e t w e e n c h a r a c t e r s a n d i n t e r p r e t e r1 4 2 C o m m u n i c a t i o n s o f t h e A CM

i n s u c h a w a y t h a t t h e i n t e r p r e t e r i s t h e c o m p i l e r in g e n e r a l.E v e r y a s p e c t o f t h e l a n g u a g e i n r e l a t i o n t o t h e c o m p i l e r i st h e n o f p r a g m a t i c n a t u r e . S . G o r n , i n h is p a p e r t o t h e c o n -f e r e n c e i n J e r u s a l e m a y e a r a g o [ 1 6 ] h a s e x t e n s i v e l yt r e a t e d m e c h a n i c a l p r a g m a t i c s i n w h a t h e c al ls a m b i g u -o u s l y s t r a t i f i e d l a n g u a g e s y s t e m s a n d I c a n o n l y r e g r e tt h a t t h is p a p e r h a s n o t y e t a p p e a r e d i n p r i n t s o t h a t i tc o u l d h a v e s e r v e d a s o n e o f t h e b a c k g r o u n d p a p e r s f o r th i sc o n f e r e n c e .4 . P r a g m a t i e s o f P r o g r a m m i n g L a n g u a g e s

I t i s t h e p u r p o s e o f t h i s c o n f e r e n c e t o t r e a t t h e w a g -m a t i c s o f p r o g r a m m i n g l a n g u a g e s . I d o n o t h a v e t o g o i n t od e t a i ls i n t h is i n t r o d u c t o r y p a p e r . I s h a l l r e s t r i c t m y s e l f t ot h e m e n t i o n o f a f e w s u b j e c t s w h i c h m a y o u t l i n e t h e g e n -e r a l p i c t u r e o f t h i s f ie l d .

I f t h e g e n e r a l r e l a t i o n s h i p b e t w e e n l a n g u a g e a n d c o m -p i l er is in c l u d e d , t h e f u l l p r o b l e m o f h o w t o t r a n s l a t e p r o -g r a m m i n g l a n g u a g e s i n t o m a c h i n e la n g u a g e s b e l o n g s to t h es u b j e c t . A n d c e r t a i n l y t h e c o n s i d e r a t i o n o f e f f ic i e n c y o f t h ei n v o l v e d p r o c e ss e s is a p a r t o f p r a g m a t i c s .I f w e r e s t r i c t t h e n o t i o n o f p r a g m a t i c s t o k i n d s o f i n d i-v i d u a l r e l a t io n s h i p s , t h e n w e f ir s t h a v e t h e q u e s t i o n : w h a td o d i f f e r e n t t r a n s l a t i n g p r i n c i p l e s a n d w h a t d o d i f f e r e n tc o m p i l e r s d o t o t h e l a n g u a g e ? H o w d o t h e y i n f lu e n c e t h em a c h i n e ( l a n g u a g e ) p r o g r a m s a n d t h e r e s u l t s? W h a t i s t h er e l a t i o n b e t w e e n l a n g u a g e a n d o p e r a t i n g s y s t e m s ? H o wm u c h s h o u ld la n g u a g e a n d o p e r a t i n g s y s t e m b e m a t c h e da n d h o w f a r s h o u l d t h e y i n f lu e n c e e a c h o t h e r ?

T h e n w e h a v e t h e p r o b l em s o f t h e d e p e n d e n c e o f p r o -g r a m m i n g l a n g u a g e s o n t h e m a c h i n e , a s w e l l a s t h e f e e d -b a c k f r o m p r o g r a m m i n g l a n g u a ge s t o h a r d w a r e . I n t h ei d ea l e a se t h e c o m p l e t e s y s te m , p r o g r a m m i n g l a n g u a g e - -m a c h i n e l a n g u a g e - - c o m p u t e r h a r d w a r e , s h o u l d b e c o n -c e i v e d a t o n c e , w h i c h i n d i c a t e s h o w m u c h p r a g m a t i c d e -v e l o p m e n t w e s t i ll h a v e b e f o r e us .

F i n a l l y , t h e r e a r e t h e r e l a t i o n s b e t w e e n p r o g r a m m i n gl a n g u a g e s a n d t h e i r a p p l i c a t i o n f i e ld s w h i c h d e f i n i t e lyb e l o n g t o p r a g m a t i c s . H e r e w e a r e v e r y f a r f r o m a n yf o rm M t r e a t m e n t .

T h e r e l a t io n b e t w e e n p r o g r a m m i n g l a n g u a g e s a n d t h eh u m a n b e i n g is t h e l a s t b u t c e r t a i n l y n o t t h e l e a s t d o m a i no f p r a g m a t i e s . R e a d i n g , l e a r n i n g a n d t e a c h i n g o f p r o g r a m -m i n g l a n g u a g e s a r e p s y c h o l o g i c a l p r o b l e m s o n w h i c h t h es u cc e ss o f a p r o g r a m m i n g l a n g u a g e m a y d e p e n d m u c hm o r e t h a n o n M 1 i t s t e eh n i e M p r o p e r t i e s .

A l a n g u a g e i s a s o c i a l t o o l ; t h i s i s a p r a g m a t i c t r u t hw h i c h w e m u s t a l s o t a k e i n t o a c c o u n t w h e n w e w i s h ap r o g r a m m i n g l a n g u a g e t o b e c o m e r e a l ly a language. F o r ,t h e b e s t l o g ic a l s y s t e m i s e s s e n t i al l y n o t a l a n g u a g e a s l o n ga s i t is o n t h e d e s k o f i t s i n v e n t o r . A r e a l l a n g u a g e i sc h a r a c t e r i z e d b y t h e p r a c t i c a l u s e w i t h i n a c e r t a i n g r o u po f p e o p l e. T h e r e a r e p r o g r a m m i n g l a n g u a g e m i n o r i t ie sw i t h p r o b l e m s s i m i l a r to t h e c a s e o f n a t u r a l l a n g u a g e s .A n d t h e r e a r e t h e b ig p r o g r a m m i n g n a t i o n s - - a n d a ll t h a tm a k e s a n i m p o r t a n t p r a g m a t i c p r o b l e m .

M a n - m a c h i n e c o m m u n i c a t i o n i s t h e n e x t b i g d e v e l o p -m e n t w h i c h c o m p u t i n g c a n e x p e c t . H e r e w e h a v e a w a g -

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mat ic problem which wi l l s t rongly inf luence coming pro-gram m ing languages . No t on ly wi ll co nversa t iona l fea -t u r e s be essential, there may even be a trend back from alltoo sophisticated language systems to the simple pointingwith a light-pen. Pointing has always been one of thesafest ways to convey information.

We come back to Wittgenstein and his principle ofspeaking clearly or not speaking at all. Since we know t hatit is the computer which we can make speak arbitrarilyclearly, we possibly should try to let the computer speakmore and more and to restrict the human user in thepractical situation to point at YES or NO, or some moreequally simple choices, while the co mpute r talks. This maysound like science fiction today, but it could really be truethat one day this will become the central application ofpragmatics around the computer.

REFERENCES1. PEIRCE, C. S. Collected Papers Harvard Press, Cambridge,Mass. Vol. 1-6 , 1931-1935.Philosophical Writings. (J. Buchler, Ed.). Routledgeand Kegan Paul, London, 1940; or Dover Publications, NewYork, 1955; 368 pp.2. BOCttENSKI, I. M. A History of Formal Logic. U. of NotreDame Press, Notre Dame, Indiana, 1961; pp. 99-100.3. MORRIS, C. Foundations of the theory of signs. In Interna-tional Encyclopedia of Unified Science, Vol. 1, No. 2, Uni-versity of Chicago Press, Chicago, 1938.4. - - . Signs , Language, and Behavior. G. Braziller, New York,1955.

5. BOLTZMANN, L. Vorlesungen ueber Gastheorie, 1. Theil,Paragraph 6. Mathematische Bedeutung der Groesse H,J. A. Barth , Leipzig, 1895, pp. 38-42.6 SHANNON,C. E. A mathematical theory of communication.Bell System Tech. J. 27 (1948), 379-433; 623-656.7. KRAFT, V. Der Wiener Kreis. Springer Verlag, Vienna, 1950.8 WITTGENSTEIN, L. Tractatus Logico-Philosophicus. FirstPrint in German, 1921; in English: Routledge and KeganPaul, London, 1922.9. SCHLICK,M. Gesammelte Aufsaetze. Gerold and Co., Vienna,1938.10. FEIGI~,H. Logical empirism. InTwentie th Century Philosophy(D. D. Runes, Ed.), Philosophical Library, New York, 1943,pp. 373-416.11. CARNAP,R. The Logical Syntax of Language. First print inGerman, 1934; in English: Harcourt Brace and Co., NewYork, 1937.12. - - . Introduction to Semantics Harvard University Press,Cambridge, Mass., 1942.13. Formal Language Description Languages (T. B. Steel, Jr., Ed.).Proc. of the IF IP Working Conf., Vienna, 1964; North Hol-land, Amsterdam 1966.14. GORN, S. Somebasic terminology connected with mechanicallanguages and their processors Comm. ACM 4 (1961), 336-339.15. -- . Mechanical pragmatics: a time motion study of a mini-

ature mechanical linguistic system. Comm. ACM 5 (1962),576-589.1 6 . - - . Semiotic relationships in ambiguously stratified lan-guage systems. Presented at the Internat. Colloq. for Al-gebraic Linguistics and Automata Theory, Jerusalem, 1964.17. MARTIN,R.M. Towards a Systematic Pragmatics--Studies inLogics. Nor th Holland, Amsterdam, 1959.

Programming Semantics for M ultiprogrammedComputations

Jack B . Dennis and Ear l C . Van HornM a s s a c h u s e t ts n s t i tu t e o f T e c h n o l o g y , C a m b r i d g e , M a s s a c h u s e t ts

The semantics are defined for a number of meta-instructionswhich perform operations essential to the wri ting of programsin multip rogra mm ed computer sy stems. Th ese meta-instructionsrelate to paral lel processing, protection of separate computa-t ions, program debu gging, and the sharing among users ofmemory segments and other computing objects, the names ofwhich are hierarchical ly structured. The language sophistica-t ion contemplated is midw ay b etw een an assembly languag ean d an ad v an ced a l g ebr a i c l an g u ag e .

Presented at an ACM Programming Languages and PragmaticsConference, San Dimas, California, August 1965.Work reported herein was supported by Project MAC, an MITresearch program sponsored by the Advanced Research ProjectsAgency, Department of Defense, under Office of Naval ResearchContract Number Nonr-4102(01). Reproduction in whole or inpart is permitted for any purpose of the United States Govern-mentV o l u m e 9 / Number 3 / March, 1966

I n t r o d u c t i o nAn increasing percentage of computation activity will

be carried out by multiprogrammed computer systems.Such systems are characterized by the application of com-putation resources (processing capacity, main memory,file storage, peripheral equipment) to many separate butconcurrently operating computations.

We can cite three quite different examples of multipro-grammed computer systems to illustrate their diversity ofapplication. The American Airlines SABRE passengerrecord system couples ticketing agents at dispersed officesto a central dat a file [1]. The c omput er sup port systems ofNASA provide real time control and mon itoring of mann edspace flights [2]. The Pro ject MAC time-sharing systempermits research workers closer interaction with the powersof auto matic compu tatio n [3]. Althou gh these are all on-line systems, multiprogramming techniques have also been

C o m m u n i c a t i o n s o f t h e A C M 1 4 3