Interpreting IDescriptors

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Interpreting I-Descriptors

• Bridgewater College
• Information Technology Center
• Scott A. Moomaw

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How Do I-Descriptors Work?

• An I-Descriptor is exactly a single line of code
  that creates a value for a field by using other
  fields, programming logic, and subroutines
• I-Descriptors do not represent fields that are
  physically stored, they are created on the fly
• Field 2 of the dictionary contains their code

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Sample I-Descriptor

• GRAND.TOTAL I-Descriptor
• 001 I
• 002 SUBTOTAL TAX
• 003 MD2,
• 004 Total Amt
• 005 10R
• 006 S
• 007

Adds the contents of the two fields, SUBTOTAL and
TAX
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Other Fields and Constants

• You can reference the value of others fields
  within an i-descriptor by naming them
• The example earlier referenced two fields
• Numerical constants can be included by value
• String constants must be enclosed in quotes

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Simple String Operations

• Strings can be concatenated by combining using a
  colon XY
• String extraction is possible using the
  operators
• stringx,y
• Extract y characters from the string beginning at
  position x

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Simple Arithmetic Operations

• Standard mathematical operations are allowed
• In the example earlier, you will note that two
  fields are added
• , -, , /
• or (exponentation)

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Some Special Variables

• _at_DATE Todays date in internal format
• _at_FM represents a field mark
• _at_ID current records ID
• _at_RECORD current record

• _at_SM subvalue mark character
• _at_VM value mark character

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Built-in Functions

• I-descriptors can rely upon numerous built-in
  functions to expand their capabilities
• Some of the standard functions work only with
  single-valued fields while others work well with
  multi-valued fields
• Many of the same functions from Unibasic are
  usable in i-descriptors

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TRANS

• The TRANS function allows you to take data from
  one file and use it to go get info from another
  file
• For instance, in file A, you may have a field
  that contains a list of MAJORS for a person. You
  can use a TRANS to go to the MAJORS file to get
  the actual descriptions for the majors.

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TRANS Syntax

• TRANS(lookup.file, keys.to.new.file,
  field.to.return, code)
• lookup.file is the file that you are going to
  in order to get information
• key.to.new.file is the keys to the records that
  you need info from
• field.to.return is the field to return
• code is what to do when failure occurs
• Often code is x meaning null on failure

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Example TRANS

• TRANS(MAJORS, B55.MAJOR, MAJ.DESC, X)
• From the PERSON file, go to the MAJORS file and
  get the MAJ.DESC field for each of the elements
  in the field named B55.MAJOR

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Arithmetic Functions

• ABS(x)
• Used to compute the absolute value of x
• ATAN(x), COS(x), SIN(x), TAN(x)
• Compute proper trigonometric function
• EXP(x)
• Raise e to the value of x
• LN(x)
• Natural log of x

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Arithmetic Functions

• INT(X)
• Integer portion of x
• PWR(X,Y)
• Raise x to the power of y
• RND(X)
• Return a random number less than x
• SQRT(X)
• Take square root of x

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Date/Time Functions

• DATE()
• System date in internal format
• TIME()
• System time in internal format
• TIMEDATE()
• External time and date

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Counting Functions

• COUNT(A,B)
• Find the number of occurrences of B in A
• DCOUNT(A)
• Count the number of values in A
• LEN(A)
• Number of characters in A

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Character Set Operations

• CHAR(X)
• Converts X to the equivalent xth ASCII character
• SEQ(X)
• Find ordinal value for the ASCII character X

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Removing Blanks From Strings

• TRIM(A)
• Removes all extra blanks from A (beginning,
  ending, and multiple consecutive in the middle)
• TRIMB(A)
• Remove trailing blanks from A
• TRIMF(A)
• Remove leading blanks from A

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Case Conversion In Strings

• DOWNCASE(A)
• Change all characters in A to lower case
• UPCASE(A)
• Change all characters in A to upper case

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String Manipulation

• CONVERT(A,B,C)
• Convert all occurrences of character A to
  character B in string C
• A and B are characters, not strings
• EXTRACT(A,X,Y,Z)
• Return the appropriate field, value, or subvalue
  from string A

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String Manipulation

• FIELD(A,B,X,Y)
• Using B as a delimiter return X substrings from A
• If Y is specified start at the Yth substring
  otherwise, start at the beginning of A
• FMT(A,B)
• Apply the formatting specified in B to string A

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String Manipulation

• ICONV(A,B)
• Apply the conversion of B to string A to convert
  from external to internal format
• INDEX(A,B,X)
• Find the beginning position of string B in string
  A
• OCONV(A,B)
• Convert A using conversion B from internal to
  external format

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String Manipulation

• SPACE(X)
• Make a string which contains X spaces
• STR(A,X)
• Make a string consisting of X occurrences of
  character A
• SUM(A)
• Sum each of the value-mark separated values in A

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_at_FM, _at_VM, _at_SM

• Fields, values, and subvalues can be considered
  the same as special delimiters
• LOWER(X)
• Lower each delimiter in X by one level
• RAISE(X)
• Raise each delimiter in X by one level

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Quick Peek Record Layouts

• The individual fields in a record a delimited
  using a special character called a field mark
  (_at_FM), values are delimited by value marks (_at_VM),
  and subvalues by sub-value marks (_at_SM)
• These special delimiters are physical ASCII
  characters and can be treated as normal
  characters or used as delimiters

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Multi-valued Processing

• Some functions only work on single-valued fields,
  but they have multi-valued equivalents
• When using the MV function, it is invoked as a
  subroutine

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Single / MV Function Equivalents

• COUNT(X,Y)
• SUBR(-COUNTS,X,Y)
• FIELD(A,B,X,Y)
• SUBR(-FIELDS,A,B,X,Y)
• FMT(A,B)
• SUBR(-FMTS,A,B)
• ICONV(A,B)
• SUBR(-ICONVS,A,B)

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Single / MV Function Equivalents

• INDEX(A,B,X)
• SUBR(-INDEXS,A,B,X)
• LEN(X)
• SUBR(-LENS,X)
• OCONV(A,B)
• SUBR(-OCONVS,A,B)

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Subroutines

• You can call custom subroutines from within
  I-descriptors
• The syntax is
• SUBR(subrname,arg1,arg2argn)

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Common SUBR IF.LIST

• SUBR(IF.LIST,LIST1,VALUES,LIST2)
• Will return values from LIST2 that are in the
  corresponding rows in LIST1 where the item from
  LIST1 is listed among the VALUES

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IF.LIST Example

• SUBR(IF.LIST, A_at_VMB_at_VMA,
• A,
• 1_at_VM2_at_VM3)
• Will return 1 and 3. These values correspond to
  the items in list1 which are in the values being
  sought.

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Nesting Code

• You can nest code in an i-descriptor to get more
  flexibility
• UPCASE(TRANS(STATES, STATE, ST.DESC, X))

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IF/THEN/ELSE

• You can perform logic operations with
  IF/THEN/ELSE
• IF condition1 THEN returnthis ELSE returnthat
• IF STATE EQ VA THEN UPPERCASE(CITY) ELSE STATE
• (Will provide an uppercase version of CITY for VA
  residents and STATE for others)

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Compound Statements

• Instead of deeply nesting code, you can use
  compound statements to improve readability
• Simply list multiple code statements separated by
  semi-colons
• The last statement is responsible for returning
  the fields value

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Compound Statements

• You can reference earlier pieces of a compound
  statement by using _at_n notation
• If you want to reference with first statement
  from within the second statement, use _at_1
• This can greatly simply the look of an
  I-descriptor by achieve the same function

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Compound Statement Example

• TRANS(STATES,STATE, ST.DESC,X)
  UPCASE(CITY) IF STATE EQ VA THEN _at_1 ELSE _at_2
• Will perform the same thing as the nested example
  earlier

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Compiling Dictionary Elements

• Dictionary elements need to be compiled for
  general use
• Use the CD command
• CD FILENAME IDESCNAMES
• CD B55.DRT MYIDESC

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ExercisesUnderstanding I-Descriptors