Visual Programming Languages ICS 519 by wulinqing

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									             Visual Programming

                      ICS 519
                       Part 1

                     ICS Department
                      Sept. 15, 2002

Muhammed Al-Mulhem    Visual Languages   1

• Learning programming is a difficult task.
• Writing and testing a program is a difficult and
  time consuming task.
• The majority of computer users are non

• Programming languages are designed for
  professional programmers and computer

Muhammed Al-Mulhem   Visual Languages                2
• There are historical reasons for this lack of
  emphasis on human convenience in
  programming languages (Shu, 1988).

• The computer scientists, for the last fifty years,
  have concentrated on machine efficiency.

• Computing costs were high and human costs
  were relatively low.

• In the early years of computing, it was justifiable
  that efficiency took precedence over ease of
Muhammed Al-Mulhem   Visual Languages                   3
• With the decline in computing costs it is realized
  that it is the human resource that must be

• The challenge is to bring computer capabilities to
  people without special computer training.

• To meet the challenge a number of facilities have
  been introduced to ease the pain of programming
  and remembering commands.

• These facilities include icons, pointing devices,
  and menus.
Muhammed Al-Mulhem   Visual Languages                  4
• Programming languages have evolved over the last
  fifty years from first generation programming
  languages to fourth generation programming

• One characteristic of most of these languages is that
  they use one-dimensional and textual formats to
  represent programs.

• These formats are suitable for sequential machines
  but not for the multi-dimensional and visual human
  mind (Chang, 1986).

 Muhammed Al-Mulhem   Visual Languages             5
• Visual programming is an attempt to simplify
  programming and to make better use of the
  human mind's capabilities

• George Raeder states "... human mind is strongly
  visually oriented and that people acquire
  information at a significantly higher rate by
  discovering graphical relationships in complex
  pictures than by reading text. ... When we scan
  paragraph, headlines, and material in bold type
  to speed up text search, we are really acting in
  the pictorial mode to overcome this limitation"
  (Raeder, 1985).

Muhammed Al-Mulhem   Visual Languages            6
• Visual programming represents a conceptually
    revolutionary departure from the traditional one-
    dimensional and textual programming languages.
It is stimulated by the following premises:

1) Pictures are more powerful than words as a
  means of communication. They can convey more
  meaning in a more concise unit of expression.
2) Pictures aid understanding and remembering.

3) Pictures may provide an incentives for learning

Muhammed Al-Mulhem   Visual Languages                7
4) Pictures do not have language barriers. When
  properly designed, they are understood by
  people regardless of what language they speak.

Muhammed Al-Mulhem   Visual Languages              8
• Visual programming has gained momentum in
  recent years.

• The falling costs of graphics-related hardware
  and software has made it feasible to use pictures
  as a means of communicating with the

• Visual programming is a very young but growing

• There is no common agreement on the definition
  of visual programming.
Muhammed Al-Mulhem   Visual Languages             9
• Visual programming languages is a new

• There is no single formal definition for VPL. For
  this reason we will present a number of
  definitions that appear in the literature.

Muhammed Al-Mulhem     Visual Languages               10
1) Chang, 1987
• Visual programming languages, usually deals with
  objects that do not have an inherent visual
  representation. This includes traditional data
  types such as arrays, stacks, and queues and
  application data types such as forms, documents,
  and databases. Presenting these objects visually
  is helpful to the user.
• For the same reason, the languages themselves
  should be represented visually.
• In other words, both programming constructs and
  the rules to combine these constructs should be
  presented visually.

Muhammed Al-Mulhem   Visual Languages           11
2) Shu, 1988
• A visual programming language can be informally
  defined as a language which uses some visual
  representations ( in addition to or in place of
  words and numbers) to accomplish what would
  otherwise have to be written in a traditional one-
  dimensional programming language.
• Note that this definition imposes no restrictions
  on the type of data or information.
    – It is immaterial whether the object being operated on or
      being displayed to a user by a visual language is
      textual, numeric, pictorial, or even audio.
    – What is important is that the language itself must
      employ some meaningful visual expressions as a
      means of programming.
Muhammed Al-Mulhem      Visual Languages                     12
3) Tortora, 1990
• A visual language models an icon system. In the
  icon system, a program consists of a spatial
  arrangement of pictorial symbols ( elementary
  icons ).
• Note that, the spatial arrangement is the two-
  dimensional counterpart of the sequential
  statements in the traditional programming
    – In these languages, a program consists of a string in
      which terminals are concatenated.
    – Concatenation is the only construction rule, therefore it
      doesn‟t appear in the language grammar.

Muhammed Al-Mulhem       Visual Languages                     13
• In the case of visual languages, three
  construction rules are used to spatially arrange
    – Horizontal concatenation.
    – Vertical concatenation.
    – Spatial overlay.
• For this reason, there is a need to include both
  spatial operators and elementary icons in the
  vocabulary of terminal symbols of the visual
  language grammar.
• Elementary icons are partitioned into two
    – Object icons which identify objects.
    – Process icons which express computation.
Muhammed Al-Mulhem     Visual Languages              14
4) Al-Mulhem, 1993
• Visual programming languages is a language
  which uses a combination of text and meaningful
  graphical symbols to write programs. These
  graphical/textual symbols represent the following:
a) Data types such as numbers, characters,
  pictures, and sound.
b) Data structures such as arrays, records, and
c) Programming constructs such as iteration,
  selection, and conditional looping.
d) Rules to combine the programming constructs.

Muhammed Al-Mulhem   Visual Languages             15
5) Burnett (1999)
• Visual programming is programming in which
  more than one dimension is used to convey
• Examples of such additional dimensions are the
  use of multi-dimensional objects, the use of
  spatial relationships, or the use of the time
  dimension to specify “before-after” semantic
• Each potentially-significant multi-dimensional
  object or relationship is a token (just as in
  traditional textual programming languages each
  word is a token) and the collection of one or more
  such tokens is a visual expression.

Muhammed Al-Mulhem   Visual Languages             16
• Examples of visual expressions used in visual
  programming include diagrams, free-hand
  sketches, icons, or demonstrations of actions
  performed by graphical objects.
• When a programming language‟s (semantically-
  significant) syntax includes visual expressions,
  the programming language is a visual
  programming language (VPL).

Muhammed Al-Mulhem   Visual Languages                17
                     VPL Research
•   Directions of research in this area are:

1. Visual approaches to traditional programming
   languages (flowchart).

2. Visual approaches that deviated from traditional
   programming (programming by demonstration).

Muhammed Al-Mulhem      Visual Languages          18
             How good are they?

• Good for toy programs.

• Bad for realistically-sized programs.

Muhammed Al-Mulhem   Visual Languages     19
                More approaches
• Incorporating visual techniques into programming
• To support textual specification of GUI layout
• To support electronic forms of software
  engineering diagrams.
• To create/visualize relationships among data
• To visually combine textually-programmed units
  to build new programs.

Muhammed Al-Mulhem   Visual Languages           20
• Visual Basic (for BASIC)

• VisualWork (for SmallTalk)

• CASE tools that support visual specificatio of
  relationships among program modules, automatic
  code generation, …etc.

Muhammed Al-Mulhem    Visual Languages        21
Muhammed Al-Mulhem   Visual Languages   22
               More approaches
• Domain-specific visual programming systems
• Examples:
1. LabVIEW – programming laboratory data
2. AVS – programming Scientific Visualization
3. PhonePro – programming telephone and voice-
   mail behavior.
4. Cocoa – programming graphical simulations
   and games.

Muhammed Al-Mulhem   Visual Languages        23
                     What is next?
•   VPLs for general-purpose programming.

• This can be reached by:
1. Improving the ways VP can be used.
2. Improving domain-specific programming

Muhammed Al-Mulhem      Visual Languages    24
        Strategies used in VPLs
• Concrete: specify some aspect of semantics on a
  specific object or value.

• Direct: manipulate a specific object or value
  directly to specify semantics.

• Explicit: describe dataflow relationships by
  drawing directed edges among related variables.

• Immediate visual feedback: automatic display of
  effects of program edits.
Muhammed Al-Mulhem   Visual Languages               25
1. Pure visual programming

2. Hybrid (textual / visual) programming

3. Programming-by-example

4. Constraint-based programming

5. Form-based programming
Muhammed Al-Mulhem      Visual Languages   26
       Pure visual programming
• Programmer manipulate icons to create a
• A program is debugged and executed in the
  same visual environment.
• A program is compiled directly from its visual
• A program is never translated into intermediate
  text-based language.

• Examples: Prograph, VIPR, and PICT.
Muhammed Al-Mulhem   Visual Languages               27
            Hybrid (textual / visual)
• Two forms:
1. Systems in which programs are created visually
   and then translated into an underlying high-level
   textual languages.

•   Example: Rehearsal World – the user trains the
    system to solve a particular problem by
    manipulating graphical actors (icons) and then
    the system generates a Smalltalk program to
    implement the solution.

Muhammed Al-Mulhem   Visual Languages             28
                Hybrid (continue)
2. Systems which involve the use of graphical
    elements in a textual language.

•   Example: Work of Erwig et. al. – developing
    extensions to languages like C and C++ which
    allow programmers to mix their text code with
•   For instance, one can define a linked list data
    structure textually and then perform an
    operation like deletion of a node by drawing the
    steps in the process.
Muhammed Al-Mulhem   Visual Languages              29
      Programming by example
• Allowing the user to create and manipulate
  graphical objects with which to teach the system
  how to perform a particular task.

• Examples: Rehearsal World and Pygmalion

Muhammed Al-Mulhem   Visual Languages            30
 Constraint-oriented programming

• A programmer models physical objects as
  objects in the visual environment which are
  subject to constraints designed to mimic the
  behavior of natural laws, like gravity.

• Popular for simulation design.

• Examples: ThingLab, ARK

Muhammed Al-Mulhem   Visual Languages            31
      Form-based programming
• Borrowed their visualizations and programming
  metaphors from a spreadsheets.

• Represent programming as altering a group of
  interconnected cells over time and often allow the
  programmer to visualize the execution of a
  program as a sequence of different cell states
  which progress through time.

• Example: Forms/3
Muhammed Al-Mulhem   Visual Languages             32
                     VPL Orphans
• Algorithm animation systems
• Provides interactive graphical displays of
  executing programs

• Example: BALSA

• user-interface design systems
• Provided with many modern compilers.
• Example: Visual Basic, Visual C++

Muhammed Al-Mulhem     Visual Languages        33
• Based on work by Chang
• Definitions
• Icon (generalized icon): An object with the dual
  representation of:
    – logical part (the meaning)
    – Physical part (the image)
• iconic system: structured set of related
• iconic sentence (visual sentence):
  spatial arrangement of icons from iconic
Muhammed Al-Mulhem   Visual Languages            34
                     Theory (con.)
• visual language: set of iconic sentences
  constructed with given syntax and semantics

• syntactic analysis (spatial parsing): analysis of
  an iconic sentence to determine the underlying

• semantic analysis (spatial interpretation):
  analysis of an iconic sentence to determine the
  underlying meaning
Muhammed Al-Mulhem      Visual Languages            35
                     Theory (con.)
• A visual Language Models an Icon System.

• In the Icon System, a program (Visual Sentence)
  consists of a spatial arrangement of pictorial
  symbols (elementary icons).

• The spatial arrangement is the two-dimensional
  counterpart of the standard sequentialization in
  the construction of programs in the case of
  traditional programming languages.
Muhammed Al-Mulhem      Visual Languages             36
• In traditional languages, a program is expressed
  by a string in which terminals are concatenated.

• As this operation (concatenation) is the only
  construction rule, it does not appear explicitly in
  the vocabulary of the language grammar.

• In the case of visual languages, three
  construction rules are used to spatially arrange
    – Horizontal concatenation             &
    – Vertical concatenation               ^
    – Spatial overlay                      +

Muhammed Al-Mulhem      Visual Languages                37
• For this reason, there is a need to include the
  spatial operators and elementary icons in the
  vocabulary of terminals of the visual language

• The elementary icons are partitioned into:
    – object icons
    – process icons.
• Elementary object icons identify objects while
  process icons express computations.

• The meaning depends on the specific visual
  sentence in which it appears.
 Muhammed Al-Mulhem    Visual Languages             38
• Consider the following primitive icons from the
  Heidelberg icon set.

• the square denotes a character, and its
  interpretation is unique in the system.
• the arrow can be used to express insertion or
  moving operations in different visual sentences.

Muhammed Al-Mulhem   Visual Languages                39
• A Visual Language (VL) is specified by the triple

         » (ID, Go, B)


• ID is the icon dictionary
• Go is a context-free grammar
• B is a domain-specific knowledge base.

Muhammed Al-Mulhem       Visual Languages             40
            The icon dictionary ID
• It is a set of triples of the form

           » i = (il , ip , type(i))

• Each triple i describes a primitive icon where

    – il             is the icon name (logical part or meaning)

    – ip             is the icon sketch (physical part)
    – type(i)        is the icon type (process or object)
Muhammed Al-Mulhem           Visual Languages                     41
                 The grammar Go
• It is a context-free grammar (N, T, S, P).

•   N      is the set of nonterminals
•   T = Tl U Tsp
•   Tl = { il | i = ( il, ip, type(i))  ID}
•   Tsp = { &, ^, + }
•   S      is the start symbol of the grammar
•   P      is the set of productions of Go

Muhammed Al-Mulhem        Visual Languages      42
 • The grammar Go specifies how more complex
   icons can be constructed by spatially arranging
   elementary icons.

 • Usually, nonterminals in Go & the start symbol
   represent composite object icons.

 • Composite object icons can be derived in one or
   more steps starting from a given nonterminals, N,
   which is different from S.
 • In other words, composite object icons are
   obtained by spatial arrangement of elementary
   object icons only and are assumed to be of type
Muhammed Al-Mulhem   Visual Languages                43
• Visual Sentences contain at least one process icon.
• Visual Sentences have no type.
• Here, object icons denote both elementary object
  icons & composite object icons.
• It is easy to prove that all the icons involved in the
  icon system (elementary object, composite object,
  and visual sentences) are objects with dual
  representation of a logical and a physical part as

Muhammed Al-Mulhem   Visual Languages               44
• Elementary object --- by definition in ID.

• Composite object and visual sentences ---
    – The physical part is their image
    – The logical part (the meaning) can be derived from the
      meaning of the elementary objects occurring in them.

• The meaning of a visual sentence is expressed in
  terms of a conceptual tree, which represents an
  intermediate code for later execution.

Muhammed Al-Mulhem      Visual Languages                       45
                Conceptual Trees

• The meaning of a visual sentence is expressed in
  terms of a conceptual tree (CT), which represents
  an intermediate code for later execution.

• In CT notations a concept is denoted by [   ],
  and a relation is denoted by ( ).

Muhammed Al-Mulhem   Visual Languages              46
The concepts are expressed in the form

         [ OBJECT : object-name]
         [ EVENT : event-name]
• object-name represents the logical part
  (meaning) of an object icon (elementary icon or
  composite object icon)

• event-name are event names, i.e., procedure
  names, which accomplish the task expressed by
  the visual sentence
Muhammed Al-Mulhem   Visual Languages               47
• The following CTs are basic substructures
  occuring in all the CTs which represent the
  logical part of a visual sentence.

[EVENT: event-name]     (rel1)      [OBJECT: object-name1]
                        (rel2)      [OBJECT: object-name2] (1)

[EVENT: event-name]     (rel)       [OBJECT: object-name] (2)

[OBJECT: object-name]    (rel)      [OBJECT: object-name] (3)

The meanings of these CTs are as follows:
 Muhammed Al-Mulhem      Visual Languages                        48
• 1) A process icon has two object icons as
consider the following icon from the Heidelberg
  icon set

Muhammed Al-Mulhem   Visual Languages             49
• It is composed of the object icons

• Selected-string

• String

• and the process icon Up-arrow

Muhammed Al-Mulhem   Visual Languages   50
• Its meaning is expressed by the CT

[EVENT: replace]      (object)            [OBJECT: String]
                      (place)             [OBJECT: Selected-string]

 Muhammed Al-Mulhem    Visual Languages                          51
2) A process icon requires only one argument.


Muhammed Al-Mulhem   Visual Languages           52
• It is obtained by composing in spatial overlay:

• the object icon Selected-string

• and the process icon cross

Muhammed Al-Mulhem   Visual Languages               53
• Its meaning is described by the CT

[EVENT: delete]      (object)           [OBJECT: Selected-string]

Muhammed Al-Mulhem   Visual Languages                        54
3) Here we have two combined object icons. This
  is the case in which one of the two objects
  involved in the visual sentence represents a
  qualitative or quantitative specification of the
  other object.

The object "name” identifies the object "file"


                                          File name

Muhammed Al-Mulhem   Visual Languages                 55
The meaning is

[OBJECT: file]       (identifier)            [OBJECT: name]

Muhammed Al-Mulhem        Visual Languages                    56
• Complex structures can be obtained by
  composing the basic substructures as shown
                                   
                                   
                                   

       1               2                        3

This visual sentence could mean: append file1 to
  file2 and copy the result into file3

 Muhammed Al-Mulhem        Visual Languages                 57
• The sentence could be decomposed into two

                            
                            
                            

                     1                      2
                                          
                                          
                                          

                      2                                      3
Muhammed Al-Mulhem           Visual Languages                      58
 • These subsentences are described, respectively, by
   the following CTs

 [EVENT: append]      (object)          [OBJECT: file1]
                      (place)           [OBJECT: file2]

 [EVENT: copy]        (source)                  [OBJECT: file2]
                      (destination)             [OBJECT: file3]

Muhammed Al-Mulhem   Visual Languages                       59
The whole visual sentence is described by

[EVENT: copy]        (destination)      [OBJECT: file3]
                     (source)           [EVENT: append]
                     (object)           [OBJECT: file1]
                     (object)           [OBJECT: file2]

Muhammed Al-Mulhem   Visual Languages               60
         The Knowledge Base B
• The Knowledge Base B contains domain-specific
  information necessary for constructing the
  meaning of a given visual sentence.

• It contains information regarding
         »   Event names
         »   Conceptual relations
         »   Names of the resulting objects
         »   References to the resulting objects.

Muhammed Al-Mulhem         Visual Languages         61
It is structured in the following seven tables:
1) EVENT-NAME [proc-name, obj-name1, obj-name2, op1, op2]
  This table returns the name of the event (procedure) to be
  associated to the process icon proc-name when the objects
  obj-name1, obj-name2 are spatially arranged (via op1, op2) to

2)LEFT-REL [proc-name, obj-name1, obj-name2, op1, op2]
3)RIGHT-REL [proc-name, obj-name1, obj-name2, op1, op2]

  These two tables hold the conceptual relations existing
  between EVENT-NAME [Proc-name, obj-name, obj-name2,
  op1, op2] and obj-name1 or obj-name2 respectively.
     Muhammed Al-Mulhem   Visual Languages            62
4)RESULT-NAME [Proc-name, obj-name1, obj-name2, op1, op2]
  This table returns the name of the object resulting from the
  execution of the event.
  EVENT-NAME [Proc-name, obj-name1, obj-name2, op1, op2].
  With arguments obj-name1 and obj-name2.

5)RESULT-REF [Proc-name, obj-name1, obj-name2, op1, op2].
  This table returns a reference to the object representing the

       Muhammed Al-Mulhem   Visual Languages            63
The following two tables take into account cases in
 which object icons are composed (composite object

6) RELATION [obj-name1, obj-name2, op].
  This returns the conceptual relation existing between obj-
  name1 and obj-name2 when they are spatially combined by
  means of the operator op.

7)RESULT-OBJECT [obj-name1, obj-name2, op].
  This returns the name of the object resulting by the spatial
  combination (via op) of obj-name1 and obj-name2.
  In the previous tables, obj-namei refer to the logical part of
  the icons.
     Muhammed Al-Mulhem    Visual Languages                64
• Besides domain-specific relations the tables can also
  contain three special relations:

<new> :This relation means that the combination
             obj-name1 op obj-name2
       gives rise to a new object, different from obj-name1
       and obj-name2.

<null>:This relation means that the combination
      obj-name1 op obj-name2
      generates an object that has the same logical part
      of the obj-name1 or obj-name2.
      In other words, it points out that no additional
      information is derived from such a combination.
     Muhammed Al-Mulhem   Visual Languages                65
 <l-obj> , <r-obj>:

    These two relations mean that the combination

    obj-name1 op1 proc-name op2 obj-name2

    generates an object that has the same reference
    of the icon whose name is obj-name1 or obj-
    name2 respectively.

Muhammed Al-Mulhem    Visual Languages              66
                                               
                                               
                                               

                file2                                          file3


                          Op1=&                        Op2=&            Obj-name2

Muhammed Al-Mulhem                Visual Languages                              67
Table 1: returns the name of the event “copy”

Table 2, 3:


[EVENT: copy]        (source)               [OBJECT: file2]
                     (destination)          [OBJECT: file3]


Muhammed Al-Mulhem   Visual Languages                    68
Table 4:           Return file 3

Table 5:           Return a reference (pointer) file3

Table 6:

[OBJECT: file]            (identifier)              [OBJECT: file3]

                               returns this

Table 7:           Return the name of the resulting object in 6

     Muhammed Al-Mulhem              Visual Languages                 69
         The Attribute Grammar
• An attribute grammar consists of a semantics
  rules for synthesizing the meaning of a visual

• AG consists of an underlying context-free
  grammar where
  i) each nonterminal in the context-free grammar
  has associated two attribute sets, namely,
  synthesized and inherited attributes.

Muhammed Al-Mulhem   Visual Languages               70
  ii) each production has associated a set of
      semantics rules, used to determine the values of
      the attributes of the nonterminals depending on
      the values of the attributes of the remaining
      nonterminals appearing in the same production.

  • The initial nonterminal has only synthesized
    attributes, and one of them is designated to hold
    the meaning of the derivation tree.

Muhammed Al-Mulhem   Visual Languages              71
The production rules in Go are of the following form:
  a)    X         t         tT
  b)    X         Y          where type (X) = type (Y)
  c)    X         M op L | L op M | M1 op M2
  d)    X         M1 op1 L op2 M2

• type (L) = PROCESS
• type (M) = type (M1) = type (M2) = OBJECT.
• op, op1, op2 = nonterminals for spatial operators ( &, * , +)

    Muhammed Al-Mulhem     Visual Languages              72
• The type for a given nonterminal X is determined as

   X         t       be a derivation in Go and t       T*

   Then              type (X) = spatial operator if t    Tsp
                     type (X) = type (t) otherwise.

• The set of inherited attributes is empty for each
  nonterminal in Go.

Muhammed Al-Mulhem          Visual Languages                 73
• The set of synthesized attributes associated to each
  nonterminal X is defined as follows.
• For a given non-terminal X

1. if type (X) = OBJECT :
   NAME (X) is the name of the object icon represented by X.
   CG(X) is the CT associated to the subtree rooted in X.
   REF(X) is the reference number. The reference number is
   an index associated with each elementary object icon
   occurring in a visual sentence. It allows one to distinguish
   between different occurrences of the same elementary
   object icon in a visual sentence.

    Muhammed Al-Mulhem   Visual Languages                74
2. if type (X) = PROCESS:
  NAME(X) is the name of the process icon
  represented by X.

3. if type (X) : "spatial operator" :
   OP(X) is the spatial operator derived from X.

   Muhammed Al-Mulhem   Visual Languages           75
• The semantic rules associated with the four production
  rules are:
a) X         t

a1) If t = icon-id
    ( icon-id, icon-sk, type( i ) )  ID      and
    type ( i ) = OBJECT (i.e. t is a terminal for an elementary icon).
        NAME(X)               icon-id
        REF (X)               ref-set
        CG (X)                [OBJECT : NAME(X), REF(X)]

  Muhammed Al-Mulhem      Visual Languages                    76
a2) If t = icon-id
         ( icon-id, icon-sk, type( i ) )           ID   and
         type ( i ) = PROCESS

         NAME(X)           t

a3)    If t  {&, L , +}
         OP(X)       t

      Muhammed Al-Mulhem       Visual Languages                 77
b) X        Y
b1)  If     type (Y) = OBJECT
     NAME(X)            NAME (Y)
     REF (X)            REF (Y)
     CG (X)             CG (Y)
b2)  If    type (Y) = PROCESS
     NAME(X)            NAME (Y)
b3)    If Y            op         and          op    {&, L , +}
       OP(X)            OP(Y)

  Muhammed Al-Mulhem        Visual Languages                 78
c) X          M op L
c1) If type (M) = OBJECT and type (L) = PROCESS

 NAME(X)                RESULT-NAME [NAME(L),
                        NAME (M), „null-obj‟, op(op), „null-op‟]

 REF(X)                 SET-REF (L, M, „null-obj‟, op, „null-op‟)

 CG (X)                 SELECTIVE-MERGE (L, M, „null-obj‟, op,

   Muhammed Al-Mulhem       Visual Languages                79
c2) If type (M) = PROCESS              and     type (L) = OBJECT

 NAME (X)               RESULT-NAME [NAME(M), „null-obj‟,
                            NAME(L), „null-op‟, OP(op)]

 REF(X)                 SET-REF (M, „null-obj‟, L, „null-op‟ , op)

 CG (X)                 SELECTIVE-MERGE (M, „null-obj‟, L,
                        „null-op‟, op)

   Muhammed Al-Mulhem       Visual Languages                80
c3) If type (M) = type (L) = OBJECT


        NAME (X)              RESULT-OBJECT [NAME (M),
                              NAME(L), OP(op)]

        REF(X)                REF (M) U REF (L)

        CG (X)                LINK (X, M, L, op)

 Muhammed Al-Mulhem   Visual Languages             81
d) X                M1 op1       L op2 M2

If type (L) = PROCESS           and
   type (M1) = type (M2) = OBJECT


 NAME (X)                   RESULT-NAME [NAME (L), NAME(M1),
                            NAME (M2), OP(op1), OP (op2)]

 REF(X)                     SET-REF (L, M1, M2, op1, op2)

 CG (X)                     SELECTIVE-MERGE (L, M1, M2, op1, op2)
       Muhammed Al-Mulhem        Visual Languages           82
• Semantic rules c and d make use of the following
Procedure LINK (X, M1, M2, op)
  rel         RELATION [NAME(M1), NAME (M2), OP(op)]
  case rel of
  <new> : if NAME (X)  ID then
               - add the new composite object NAME(X) to ID
               - return [OBJECT: NAME (X), REF(X)]
  <null> : return CG(M1)
  else :          return APPEND (CG(M1), CG(M2), rel)
  end case
end LINK
    Muhammed Al-Mulhem   Visual Languages             83
Procedure SELECTIVE-MERGE (L, M1, M2, op1, op2)
  C             [EVENT:EVENT-NAME [NAME(L),
                NAME(M1), NAME(M2), OP(op1), OP(op2)]
  if OP(op1) = „null-op‟       then G1       C
  else rel1        LEFT-REL [NAME(L), NAME(M1),
                   NAME (M2), OP(op1), OP(op2)]
        G1        APPEND (C, CG(M1), rel1)
  if OP(op2) = „null-op‟       then G2       C
  else rel2              RIGHT-REL [NAME(L), NAME(M1),
                         NAME (M2), OP(op1), OP(op2)]
        G2               APPEND (C, CG(M2), rel2)
  return HEADER-MERGE (G1, G2)

     Muhammed Al-Mulhem    Visual Languages              84
Procedure SET-REF (L, M1, M2, op1, op2)
  ref      RESULT-REF [NAME(L), NAME(M1),
                NAME (M2), OP(op1), OP(op2)]

  case ref of
      <l-obj> :       return REF(M1)
      <r-obj> :       return REF(M2)
      <new-obj>:      return NEXT-REF( )
  end case

 Muhammed Al-Mulhem    Visual Languages    85
                       The Icon Interpreter:
         • The system diagram of the icon interpreter is as

                               G0             ID             B
Sentencce S

     Pattern                   Syntax                  of the         Meaning of S
     Analysis                  Analysis                Logical part   CG

         Pattern String of S
                                      Parse Tree of S
         Muhammed Al-Mulhem         Visual Languages                    86
• The module ”Pattern Analysis" transforms the
  visual sentence into pattern string .

• The visual sentence

• is represented by the pattern string
             (char & char & char) + cross

 Muhammed Al-Mulhem   Visual Languages           87
• The icon interpreter is logically divided into two phases:

1. The syntax analysis is accomplished by a parsing
   algorithm for context-free grammars.

2. Constructing the meaning of the given visual sentence by
   evaluating the attributes of the nonterminal on the root of
   the parse tree using the ATTRIBUTE_EVALUATOR

• The attribute evaluation is accomplished by means of a
  postorder visit of the parse tree t of the visual sentence S

    Muhammed Al-Mulhem   Visual Languages               88
  if X is a nonterminal in Go
       then /* let p be the production applied to the
       node X in t, and let 1, ..., np be the indices of
       nonterminals in the right-hand side of p*/
       for j = 1 to np do
               call ATTRIBUTE-EVALUATOR (jth
                             nonterminal son of X in t)
       end for
       apply the semantic rules associated to p so as
       to evaluate the attributes of X

   Muhammed Al-Mulhem    Visual Languages                  89
• This example shows an iconic command
  language for simple operating system.

• The set of elementary icons ID and the grammar
  G0, are shown in the following slides.

Muhammed Al-Mulhem   Visual Languages          90
Muhammed Al-Mulhem   Visual Languages   91
Muhammed Al-Mulhem   Visual Languages   92
• The knowledge base B is given next.

• Each entry in the tables, which constitute the
  knowledge base, contains five items, which
  correspond, from top to bottom, to the tables:
     –   EVENT_NAME
     –   LEFT_REL
     –   RIGHT_REL
     –   RESULT_NAME
     –   RESULT_REF

Muhammed Al-Mulhem     Visual Languages            93
Muhammed Al-Mulhem   Visual Languages   94
• Consider the following visual sentence:

                                 
                                 
                                 

• Whose corresponding pattern string is
[FILE,1] & PLUS & [FILE,2] & ARROW&[FILE,3]

• The parse tree for this sentence is shown next.
 Muhammed Al-Mulhem   Visual Languages                    95
Muhammed Al-Mulhem   Visual Languages   96
• The construction of the conceptual tree is given in
  the next table. At level 1, the resulting conceptual
  tree is given by:

[EVENT: copy]        (destination)      [OBJECT: file3]
                     (source)           [EVENT: append]
                     (object)           [OBJECT: file1]
                     (object)           [OBJECT: file2]

Muhammed Al-Mulhem   Visual Languages                97
               Examples of VPLs
•   Prograph (1989) – Dataflow programming
•   DataLab (1990) – Programming by example
•   Form/3 (1994) – Form-based programming
•   Clarity (2001) – Functional programming

Muhammed Al-Mulhem   Visual Languages         98
• The Prograph language is an iconic language.
• Program is drawings.
• Prograph interpreter and compiler execute those
• Prograph is object-oriented
• Prograph supports dataflow specification of
  program execution

Muhammed Al-Mulhem    Visual Languages          99
                     Simple program
• A simple Prograph code
  which sorts, possibly in
  parallel, three database
  indices and updates the

Muhammed Al-Mulhem       Visual Languages   100
               Paragraph‟s icons
• Prograph uses a set of icons:
• classes are represented by hexagons,
• data elements by triangles,
• pieces of code by rectangles with a small picture
  of data flow code inside, and
• inheritance by lines or downward pointing arrows.

Muhammed Al-Mulhem   Visual Languages            101
Muhammed Al-Mulhem   Visual Languages   102
                     More Icons
• The representations can then be combined and
  used in a variety of language elements.

• For example, initialization methods - which are
  associated with an individual class - are depicted
  as hexagonally shaped icons with a small picture
  of data flow code inside.

Muhammed Al-Mulhem     Visual Languages            103
                     Icon (C0nt.)
• Triangles represent instance variables in a class‟
  Data Window to show that they‟re data.

• Hexagons drawn with edges and interiors similar
  to the instance variable triangles represent class
  variables. This associates them with the class as
  a whole while also associating them with data.

• Next Figure shows three more complex
  representations: initialization methods , instance
  variables, and class variables.

Muhammed Al-Mulhem     Visual Languages                104
                     Icon (Cont.)

Muhammed Al-Mulhem     Visual Languages   105
• The Prograph language is object-oriented.
• Class-based,
• Single inheritance (a subclass can only inherit
  from one parent),
• Dynamic typing
• With garbage collection mechanism based on
  reference counting.

Muhammed Al-Mulhem       Visual Languages           106
• The programmer can design and implement new
• He can visually specifying:
   – the new class‟ inheritance,
   – additional instance or class variables,
   – modified default values for inherited instance
     or class variables,
   – and new or overridden methods.

Muhammed Al-Mulhem   Visual Languages             107
• Polymorphism allows each object to respond to a
  method call with its own method appropriate to its
• Binding of a polymorphic operation to a method
  in a particular class happens at run-time, and
  depends upon the class of the object.
• The syntax for this „message send‟ is one of the
  more unusual aspects of Prograph‟s syntax.
• The concept of „message sending‟ per se is not
  used in Prograph.

Muhammed Al-Mulhem   Visual Languages             108
•   Rather, the idea of an annotation on the name
    of an operation is used. There are four cases:

1. No annotation means that the operation is not

2. „/‟ denotes that the operation is polymorphic and
   is to be resolved by method lookup starting with
   the class of the object flowing into the operation
   on its first input
Muhammed Al-Mulhem    Visual Languages               109
               Annotation (Cont.)
3. „//‟ denotes that the operation is polymorphic
   and is to be resolved by method lookup starting
   with the class in which this method is defined.

4. „//‟ plus super annotation means that the
   operation is polymorphic and resolves by
   method lookup starting with the superclass of
   the class in which this method is defined.
• In Prograph there is no SELF construct (or a
   „this‟ construct, to use the C++ terminology).

Muhammed Al-Mulhem   Visual Languages               110
• Prograph has an almost completely iconic
  syntax, and this iconic syntax is the only
  representation of Prograph code.

• Next Figure shows a small code fragment typical
  of the Prograph language.

• There is no textual equivalent of a piece of a
  Prograph program - the Prograph interpreter and
  compiler translate directly from this graphical
  syntax into code.

Muhammed Al-Mulhem   Visual Languages           111

Muhammed Al-Mulhem   Visual Languages   112
• Next Figure shows most of the lexicon of the
  language (icons).
• The inputs and outputs to an operation are
  specified by small circles at the top and bottom,
  respectively, of the icons.
• The number of inputs and outputs - the
  operation‟s arity - is enforced only at run-time.
• In addition, there are a variety of annotations that
  can be applied to the inputs and outputs, or to the
  operation as a whole to implement looping or
  control flow.
Muhammed Al-Mulhem   Visual Languages               113
Muhammed Al-Mulhem   Visual Languages   114
                     Spaghetti Code
• Visual languages like Prograph sometimes suffer
  from the spaghetti code problem: there are so
  many lines running all over that the code for any
  meaningful piece of work actually ends up
  looking like spaghetti.

• Prograph deals with this issue by enabling the
  programmer to „iconify‟ any portion of any piece
  of code at any time during the development

Muhammed Al-Mulhem       Visual Languages            115
• This iconified code is called a „local‟.
• Effectively, locals are nested pieces of code.

• There is no limit to the level of nesting possible
  with locals, and there is no execution penalty to
  their use.

• In addition, locals can be named and this
  naming, if done well, can provide a useful
  documentation for the code.
Muhammed Al-Mulhem   Visual Languages                  116
• Next Figure is a code to build a dialog box
  containing a scrolling list of the installed fonts
  without the use of Prograph locals to factor the

Muhammed Al-Mulhem   Visual Languages                  117
Muhammed Al-Mulhem   Visual Languages   118
                     Same Example
• Next Figure is the same code with the use of
  Prograph locals to factor the code.

Muhammed Al-Mulhem      Visual Languages         119
Muhammed Al-Mulhem   Visual Languages   120
                     Local (Cont.)
• Note that long names, often containing
  punctuation or other special characters can be
  used for the names of locals.

• The proper use of locals can dramatically
  improve the comprehensibility of a piece of code.

• The one negative aspect of their use is the so-
  called “rat hole” phenomena - every piece of
  code in its own rat hole. This can sometimes
  make finding code difficult.

Muhammed Al-Mulhem      Visual Languages            121
• Three of the most interesting aspects of the
  Prograph syntax are:

    – list annotation,
    – injects, and
    – control annotation.

Muhammed Al-Mulhem   Visual Languages            122
                     List Annotation
• Any elementary operation can be made to loop
  by list annotating any of its inputs.
• When this is done, the operation is invoked
  multiple times - one time for each element of the
  list that is passed on this input.
• Thus, list annotation on an input causes the
  compiler to construct a loop for the programmer.
  Since this annotation can be made on a local as
  well as a primitive operation, this looping
  construct is quite powerful.

Muhammed Al-Mulhem       Visual Languages         123
          List Annotation (Cont.)
• In addition, list annotation can be done on a

• On an output terminal, list annotation causes the
  system to put together all the outputs at this
  terminal for every iteration of the operation and to
  pass as the „final‟ output of the terminal this
  collection of results as an output list.

Muhammed Al-Mulhem   Visual Languages               124
          List Annotation (Cont.)
• List annotation, then, enables the programmer to
  easily make an operation into a loop that either
  breaks down a list into its component elements
  and runs that operation on the elements, or to
  builds up a list from the multiple executions of an
• An individual operation can have any number of
  its inputs or outputs with list annotations.

Muhammed Al-Mulhem   Visual Languages               125
          List Annotation (Cont.)
• Next Figure shows several examples of list
  annotation, an efficient mechanism for iterating
  over a list.

• The operation will automatically be called
  repeatedly for each element of a list, or its
  outputs will be packaged together into a list.

Muhammed Al-Mulhem   Visual Languages                126
Muhammed Al-Mulhem   Visual Languages   127
Muhammed Al-Mulhem   Visual Languages   128
Muhammed Al-Mulhem   Visual Languages   129
• Inject lets you pass a name at run-time for an
  input which expects a function.
• This is similar to Smalltalk‟s perform, procedure
  variables in Pascal or function pointers in C.
• Suppose, for example, that you want to
  implement a function FooMe that takes two
  arguments: a list of objects, and a reference to a
  method to be applied to each of those objects.

Muhammed Al-Mulhem   Visual Languages              130
                            Inject (Cont.)
• In Object Pascal pseudo-code, this function might look
  something like this:

Function FooMe(theList: TList; Procedure DoThis(object: TObject));
{ Iterates through the list of objects applying the DoThis procedure }

       Muhammed Al-Mulhem       Visual Languages                     131
• Next Figure shows a Prograph implementation of

• Note that just the name - as a string - of the
  method to be applied to each object is passed to

• This string is turned into a method invocation by
  the inject.

Muhammed Al-Mulhem   Visual Languages                 132
Muhammed Al-Mulhem   Visual Languages   133
                     Inject (Cont.)
• The Prograph representation of inject - a
  nameless operation with one terminal
  descending into the operation‟s icon - is a
  particularly well-designed graphic representation
  for this programming concept.
• When properly used, inject can result in
  extremely powerful and compact Prograph
  implementations of complex functions.
• However, when used improperly, it can result in
  code that is very difficult to read or debug, like
  the computed GOTO of FORTRAN.
Muhammed Al-Mulhem      Visual Languages           134
                     Control Flow
• Control flow is a combination of annotations on
  operations and a case structure.
• A Prograph method can consist of a number of
  mutually exclusive cases. These cases are
  somewhat similar to the cases in a Pascal CASE
  statement or a C switch expression.
• The main difference is that unlike Pascal or C,
  the code to determine which case will be
  executed is inside the case, not outside it.

Muhammed Al-Mulhem     Visual Languages         135
• Suppose that we want to implement a small
  function that has one integer input, and
• if that input is between 1 and 10, the value of the
  function is computed one way;
• if it is between 11 and 100, another way, and
• if it is anything else, yet a third way.
• In Pascal-like pseudo-code, this function would
  look something like this:

Muhammed Al-Mulhem   Visual Languages               136
Function Foo( i: Integer): Integer;
  Case i of
       1..10: Foo := Calculation_A(i);
       11..100: Foo := Calculation_B(i);
       OtherwiseFoo := Calculation_C(i);
  End; {Case}
End; {Foo}

Muhammed Al-Mulhem   Visual Languages      137
             Control Flow (Cont.)
• The implementation of Foo in Prograph would
  also involve three cases, as shown in the next
• The control annotations are the small boxes on
  the right of the match primitives at the top of the
  first two cases. (Note that the window titles show
  the total number of cases in a method, and which
  case this window is, as in “2:3” the second of
  three cases.)

Muhammed Al-Mulhem   Visual Languages              138
Muhammed Al-Mulhem   Visual Languages   139
             Control Flow (Cont.)
• In this simple example, the same annotation - a
  check mark in an otherwise empty rectangle - is
• The semantics of this annotation are: “If this
  operation succeeds, then go to the next case.”
  The check mark is the iconic representation of
  success, and the empty rectangle represents the
  „go to the next case‟ notion. If the check mark
  were replaced by an „x‟, then the semantics
  would have been: “If this operation fails, then go
  to the next case”.
Muhammed Al-Mulhem   Visual Languages              140
             Control Flow (Cont.)
• In addition to the otherwise empty rectangle,
  there are four other possibilities, and the five
  different semantics of control annotations are
  shown together in the next Figure.
• It is a run-time error and a compile-time warning
  to have a next-case control annotation in a
  location where it cannot execute, for example, in
  the last case of a method.

Muhammed Al-Mulhem   Visual Languages             141
Muhammed Al-Mulhem   Visual Languages   142
Muhammed Al-Mulhem   Visual Languages   143
Muhammed Al-Mulhem   Visual Languages   144
Muhammed Al-Mulhem   Visual Languages   145
Muhammed Al-Mulhem   Visual Languages   146
Muhammed Al-Mulhem   Visual Languages   147
Muhammed Al-Mulhem   Visual Languages   148
Muhammed Al-Mulhem   Visual Languages   149
Muhammed Al-Mulhem   Visual Languages   150
Classification of Visual Programming
  • Looking at the recent work reported in the
    literature, we see visual programming
    progressing in number of directions.

  1) Visual Environments for different applications.
  2) Visual Languages.
  3) Theory of Visual Languages.

  Muhammed Al-Mulhem   Visual Languages                151
         1) Visualization of Data
• Typically, the information or data is stored internally
  in traditional databases, but expressed in graphical
  form and presented to the user in a special

• Users can traverse the graphical surface or zoom
  into it to obtain greater detail with a joystick or a
  pointing device.

Muhammed Al-Mulhem   Visual Languages                152
     Visualization of Data (Cont.)
• The user can use the mouse to answer many
  questions without the need of a keyboard.

• These systems are devoted primarily to using
  “direct manipulation” as a means of information
  retrieval, using a graphical view of a database for
  visualization of the information retrieved.

Muhammed Al-Mulhem   Visual Languages              153
• A visual environment can be built for the retrieval
  of information from a database of ships.

• Each ship will be represented by an icon.

• Icon shape, color and size represent type, status,
  and size of the ship.

Muhammed Al-Mulhem   Visual Languages               154
    2) Visualization of Programs
• The goal of this is to provide programmers and
  users with an understanding of :
   –   What the program can do
   –   How they work
   –   Why they work
   –   What are the effects

Muhammed Al-Mulhem      Visual Languages           155
This is beneficial for
• beginners learning to program.

• professionals dealing with various aspects of
  programming tasks:
   –   Designing,
   –   Debugging,
   –   Testing, and
   –   Modification.

Muhammed Al-Mulhem     Visual Languages           156

• BALSA ( Brown Algorithm Simulator and
  Animator ) developed by Sedgewick and his
  colleages in Brown University. [ Sedgwick, 1983 ]
• It enables users :
    – to control the speed of an animated algorithm
    – to decide which view to look at.
    – to specify the input data to be processed.

Muhammed Al-Mulhem      Visual Languages              157
• BALSA include the following animated
• Mathematical algorithms such as
   – Euclid‟s GCD algorithm.
   – Random numbers.
   – Curve fitting.

• Sorting algorithms such as
   –   Insertion sort.
   –   Quick sort.
   –   Merge sort.
   –   External sort.

Muhammed Al-Mulhem       Visual Languages   158
• Searching algorithms such as
    –   Sequential search.
    –   Balanced trees.
    –   Hashing.
    –   Radix searching.

• Selecting an icon from the iconic table with a
  mouse causes a 10 - 15 minute dynamic
  simulation of the selected topic to be run, with
  pauses at key images, after which the user can
  interact with the algorithms and images.

Muhammed Al-Mulhem       Visual Languages            159
Muhammed Al-Mulhem   Visual Languages   160
3) Visualization of Software Design
  • It is very important throughout the software life
    cycle to understand:
       –   specifications
       –   design
       –   system structure
       –   dependencies among data and components
       –   etc.
  • This observation, together with the success of
    using graphical techniques has led to the
    development of a visual environment for software
    life cycle.

 Muhammed Al-Mulhem      Visual Languages               161
                     The PEGASYS
• The main purpose of PegaSys is to provide a
  visual environment for the development and
  explanation of large program designs (as
  opposed to detailed algorithms and data
  structures in a program)

• PegaSys supports the specification and analysis
  of data and control dependencies among the
  components of large programs.

Muhammed Al-Mulhem      Visual Languages        162
• A program design is described in PegaSys by a
  hierarchy of interrelated pictures.

• Icons denote predefined or user-defined concepts
  about dependencies in programs.

Muhammed Al-Mulhem   Visual Languages             163
• The predefined primitives denote:
   – objects (such as subprograms, modules,
     processes, and data structures),
   – data dependencies (involving the declaration,
     manipulation, and sharing of data objects), and
   – control dependencies (dealing with
     asynchronous and synchronous activities).

• A PegaSys user can define new concepts in terms
  of the primitives.

Muhammed Al-Mulhem   Visual Languages             164
• A network of 4 hosts can be
  represented in PegaSys as follows:
    –Each of the four hosts in the network is
     indicated by an ellipse,
    –the communication line indicated by a
     dashed rectangle.
    –a packet of data indicated by a label on

Muhammed Al-Mulhem   Visual Languages           165
• Dependencies among hosts, packets, and the
  line are described by the write relation (denoted
  by the letter W on arrows) and the read relation
  (denoted by R)

The system says that:
• the broadcast network consists of four hosts that
  communicate by means of a line.
• More precisely, processes named Host1,... Host4
  write values of type pkt into a module called Line
  and read values of the same type from the Line

Muhammed Al-Mulhem   Visual Languages                 166
Muhammed Al-Mulhem   Visual Languages   167
         Visualization of Parallel

• A number of display facilities have been associated

         » debuggers

         » performance evaluation tools

         » program visualization systems

Muhammed Al-Mulhem       Visual Languages         168
               Debugger displays
Debugger displays attempt to provide some view of
 program state such as:

• the pattern of access to shared memory

• the interprocessor communication of a particular
  distributed memory architecture

• the order in which subroutines are called

Muhammed Al-Mulhem   Visual Languages            169
      Displays for Performance
         Visualization Tools

Performance visualization tools generally provide a
 graphical representation of standard metrics
 such as:

• Processor utilization

• Communication load

Muhammed Al-Mulhem   Visual Languages             170
           Displays for Program
           Visualization Systems
Program visualization systems provide highly
  application specific views of:

• the program's data structures

• the operations which update these data

• or some more abstract representation of the
  computation and its progress.
Muhammed Al-Mulhem   Visual Languages           171
                 Program Graphs
Many systems display graphs in which:

• the vertices represent program entities and

• the arcs represent call relations or temporal
  orderings, similar to the graph shown in Fig. 1.

Muhammed Al-Mulhem   Visual Languages                172
 Fig. 1. An animated call graph


  PRUNE        EXPAND    UPDATE                  COUNT


Muhammed Al-Mulhem       Visual Languages                 173
  Concurrency of the Computation

• A number of systems use a graph to represent
  the concurrency of the computation.

1) The concurrency map

• The concurrency map displays process histories
  as event streams on a time grid.

Muhammed Al-Mulhem   Visual Languages            174
• Each column of the display represents the
  sequential stream of events for a single process.

• Each row of the grid represents an interval of time
  during which the events in different columns may
  occur concurrently.

• Every event in one row must occur before any
  event in the next row.

Muhammed Al-Mulhem   Visual Languages                 175
        Communication Graphs
• A number of systems present displays that
  represent communication among processors
  through the use of boxes, arrows, and lines.

    – Boxes represent processors,
    – Lines represent connections. and
    – Arrows represent communication events, as
      shown in Fig. 2.

Muhammed Al-Mulhem   Visual Languages             176
 Fig. 2: Communication Graph

                          P0                 P1

                     P3                 P2

                          P4                 P5

                     P7                 P6

Muhammed Al-Mulhem        Visual Languages        177
• Here we will show some Visual Programming

Muhammed Al-Mulhem   Visual Languages         178
• The basic elements in BLOX system are icons similar
  in shape to jigsaw puzzle pieces.

• Programs are composed by
1) Juxtaposing icons in appropriate ways, so that
   neighbors interlock.

2) Encapsulating substructure

Muhammed Al-Mulhem    Visual Languages                  179
  • The “lock and key” metaphor enforces proper syntax.


Muhammed Al-Mulhem     Visual Languages              180
  Programs in Pascal - BLOX
• It uses top-down program design.

• The code segments could be encapsulated in the
  appropriate tiles. This include codes corresponding to:
   – the alternative branches
   – loop bodies
   – Boolean expressions associated with IF and WHILE

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    If not I1 Then
              While L1 Do
                      If I2 Then S4
                      Else S5;
       While L2 Do S7;

Muhammed Al-Mulhem           Visual Languages   182
    Pascal - BLOX Program

Muhammed Al-Mulhem   Visual Languages   183
• Top-down specification of programs
• Extension of a familiar metaphors from children's toys.
• Automatic elimination of the most source of possible
  syntax errors in user programs, by the use of the “Lock
  and Key” metaphor.

• The representation can be applied to diverse and varied
  activities in a uniform manner.

Muhammed Al-Mulhem     Visual Languages                184
                     Our VPLs
• Our efforts to design and implement visual
  programming languages include:

1) DataLab (with T. Lewis, and H. Kim, 1989)

2) VISO: A Visual Languages for Concurrent
   Programming (with S. Ali, 1994)

Muhammed Al-Mulhem    Visual Languages         185
• VISO is a visual programming language for concurrent
• It has a graphical syntax based on the language
• It uses a modular approach of visual programming

Muhammed Al-Mulhem   Visual Languages                186
Muhammed Al-Mulhem   Visual Languages   187
Muhammed Al-Mulhem   Visual Languages   188
• DataLab is a general-purpose system for the
  specification and synthesis of abstract data types

• DataLab uses a combination of graphical and textual
  forms as a specification model for ADTs.

• An imperative semantics is used to automatically
  generate an encapsulated executable code (Pascal
  modules) from such a specification.

Muhammed Al-Mulhem    Visual Languages                  189
• DataLab extends earlier work by

1) allowing data structures to be created and displayed in
   their classical notation,
2) generating encapsulated imperative code (Pascal), and
3) incorporating composition of simple structures into
   more complex structures.

Muhammed Al-Mulhem      Visual Languages                190
         Example - Linked List
• The first step is to define the interface part
unit     LINKED_LIST;
   LL_list        =        ^LL_node;
   LL_node        =        record
         data     :        string;
         next     :        LL_list;
procedure LL_insert(var list : LL_list;      item : string);

Muhammed Al-Mulhem        Visual Languages                     191
        • Next, the procedure "LL_insert" is specified by two
          Conditional transformations

1                   1
    list                                                                 5
           2:list               3               node
                        list^                               6:node
    0                                            4




                                                            node^.data := item;

        Muhammed Al-Mulhem          Visual Languages                              192
                                                4   list

      list               1                            5                            7
             2:list           3                                     8:next

                                                             list^.data := item;

    Muhammed Al-Mulhem       Visual Languages                                  193
       What is next for VPLs?
• More effective use of color and sound.

• 3-D instead of 2-D graphics.

• Animated graphics.

• Languages for concurrent and parallel programming.

Muhammed Al-Mulhem     Visual Languages                194

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