MidRange Concepts - Fox Valley Technical College
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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:
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:
Field Names
Data Type
Length
On the I-series/400 data can be defined:
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:
File structures
Individual field characteristics
Field edits and audits
Defining Data
How does DDS work?
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:
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.