Transcript MidRange Concepts - Fox Valley Technical College

MidRange Concepts
Chapter 7
Data Physical Files
Character Representation
 EBCDIC (Extended Binary Coded Decimal
Interchange Code): First generally adopted binary
character representation system developed by IBM.
Standardized characters to 8 bits or one byte.
 ASCII (American Standard Code for Information
Interchange): Still represents characters in one byte
consisting of 1 and 0 but the combinations are
different than EBCDIC.
Numeric Representation
 Most computers support at least one of the
following:
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Zoned decimal
Packed decimal
Binary
Numeric Representation
 Zoned Decimal: Doesn’t save storage space
but does allow calculations on the values and
negative numbers can be stored.
 Packed Decimal: Makes better use of each
nibble. First nibble is used to denote the sign.
Saves space over Zoned Decimal.
 Binary: Makes use of every nibble.
Defining Data
 When defining data you must specify:
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Field Names
Data Type
Length
 On the I-series/400 data can be defined:
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Internally: defined within application programs.
Externally: defined outside application programs using a
DDL (Data Definition Language)
Defining Data
 DDS: Data Definition Specifications:
contains commands to allow user to define:
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File structures
Individual field characteristics
Field edits and audits
Defining Data
 How does DDS work?
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Must key definition into a member of a source
file with a type of PF.
Compile this member.
Compiled object becomes the file to hold the
data.
Defining Data
 DDS:
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Semi-positional language, meaning commands
and values must be entered in certain locations
on a line.
All positional entries are specified between columns 1
and 44.
 Columns 45 to 80 are the keyword/function area.

Defining Data
 Physical file must have only one record level
specification and at least one field level
specification.
 Text keyword: allows the user to specify
descriptive information. Must be enclosed in
single quotes and parentheses.
Defining Data
 Field Reference File: Source physical file
member that is used to hold all field
descriptions. You can then reference this
field when creating other file descriptions.
 Keyword REF must precede your record
description in any new file descriptions if
you are going to reference other files.