Record Formats and Dataset Attributes

Understanding record formats and dataset attributes is essential for effective editing in ISPF. LRECL (Logical Record Length) and RECFM (Record Format) are fundamental dataset attributes that determine how data is stored and how the editor handles files. This tutorial covers fixed and variable record formats, LRECL, RECFM, and how these attributes affect editing in the ISPF editor.

Record formats and dataset attributes directly impact how you edit files. Understanding these concepts helps you work effectively with different file types, maintain proper formatting, and avoid errors related to record length and format.

Understanding Dataset Attributes

Dataset attributes define how data is organized and stored.

Key Dataset Attributes

Important dataset attributes include:

• LRECL: Logical Record Length (length of each record)
• RECFM: Record Format (how records are organized)
• BLKSIZE: Block Size (size of physical blocks)
• DSORG: Data Set Organization (PS, PO, etc.)

Why Attributes Matter

Dataset attributes matter because:

• They determine how data is stored
• They affect how the editor handles files
• They impact file compatibility
• They influence editing behavior

LRECL (Logical Record Length)

LRECL specifies the length of each logical record in bytes.

What is LRECL?

LRECL:

• Stands for Logical Record Length
• Specifies the length of each record in bytes
• Is measured in bytes (characters)
• Determines the maximum (or fixed) line length
• Is a critical dataset attribute

LRECL for Fixed Format

For fixed-format files (RECFM=F or FB):

• LRECL specifies the exact length of every record
• All records must be exactly LRECL bytes long
• Records are padded or truncated to LRECL
• Common values: 80 (for source code), 132 (for wide listings)

LRECL for Variable Format

For variable-format files (RECFM=V or VB):

• LRECL specifies the maximum record length
• Records can be shorter than LRECL
• Records cannot exceed LRECL
• Each record can have a different length

Common LRECL Values

Common LRECL values include:

• 80: Standard for source code (COBOL, JCL, etc.)
• 132: Wide format for listings and reports
• 256: Common for data files
• 32760: Maximum for variable format
• Other values based on specific needs

RECFM (Record Format)

RECFM specifies how records are organized in the dataset.

What is RECFM?

RECFM:

• Stands for Record Format
• Specifies how records are organized
• Determines whether records are fixed or variable length
• Indicates whether records are blocked
• Affects how the editor handles the file

Common RECFM Values

Common RECFM values include:

• F: Fixed (unblocked)
• FB: Fixed Blocked
• V: Variable (unblocked)
• VB: Variable Blocked
• U: Undefined

Fixed Record Format (F, FB)

Fixed format means all records have the same length.

RECFM=F (Fixed Unblocked)

RECFM=F means:

• All records have exactly the same length (LRECL)
• Records are not grouped into blocks
• Each record is stored individually
• Less efficient for storage but simpler

RECFM=FB (Fixed Blocked)

RECFM=FB means:

• All records have exactly the same length (LRECL)
• Records are grouped into blocks for efficiency
• Multiple records per physical block
• More efficient storage than unblocked
• Most common for source code files

Editing Fixed Format Files

When editing fixed-format files:

• All lines have the same length
• You must stay within LRECL
• Lines are padded or truncated to LRECL
• The editor enforces the record length
• BOUNDS can help stay within limits

Fixed Format Example

For a file with RECFM=FB, LRECL=80:

• Every line is exactly 80 bytes
• Short lines are padded with spaces
• Long lines are truncated to 80 bytes
• This is typical for COBOL source code

Variable Record Format (V, VB)

Variable format means records can have different lengths.

RECFM=V (Variable Unblocked)

RECFM=V means:

• Records can have different lengths
• Each record length is up to LRECL
• Records are not grouped into blocks
• Less efficient but more flexible

RECFM=VB (Variable Blocked)

RECFM=VB means:

• Records can have different lengths
• Each record length is up to LRECL
• Records are grouped into blocks for efficiency
• More efficient than unblocked variable
• Common for data files with varying record lengths

Editing Variable Format Files

When editing variable-format files:

• Lines can have different lengths
• Each line can be up to LRECL bytes
• Lines are not padded to a fixed length
• The editor allows variable-length lines
• You must still stay within LRECL maximum

Variable Format Example

For a file with RECFM=VB, LRECL=256:

• Lines can be any length from 1 to 256 bytes
• Line 1 might be 50 bytes
• Line 2 might be 120 bytes
• Line 3 might be 30 bytes
• Each line uses only the space it needs

Understanding Blocking

Blocking groups records together for efficiency.

What is Blocking?

Blocking:

• Groups multiple records into physical blocks
• Improves storage and I/O efficiency
• Is indicated by "B" in RECFM (FB, VB)
• Does not affect logical record structure
• Is transparent to the editor

Blocked vs. Unblocked

Comparison:

• Blocked (FB, VB): More efficient, groups records
• Unblocked (F, V): Simpler, records stored individually
• Blocked is generally preferred for efficiency
• Unblocked is simpler but less efficient

How Record Formats Affect Editing

Record formats directly impact how you edit files in ISPF.

Fixed Format Editing

When editing fixed-format files:

• All lines appear the same length
• You must stay within LRECL
• Short lines are padded with spaces
• Long lines are truncated
• BOUNDS helps enforce limits
• Column positioning is important

Variable Format Editing

When editing variable-format files:

• Lines can have different lengths
• Each line uses only the space it needs
• You must stay within LRECL maximum
• Lines are not padded
• Editor allows natural line lengths
• More flexible for varying content

Editor Behavior Differences

The editor may behave differently:

• Display may vary between fixed and variable
• Line wrapping may differ
• Column positioning may be handled differently
• Status line may show format information

Viewing Dataset Attributes

You can view dataset attributes in ISPF.

In the Editor

In the editor, you can see:

• RECFM and LRECL in the status line
• Dataset attributes in file information
• Format information in editor displays

Using Data Set Utility

To view full dataset attributes:

• Use Option 3.2 (Data Set Utility)
• Select the dataset
• View dataset information
• See RECFM, LRECL, BLKSIZE, and other attributes

Common File Type Formats

Different file types typically use specific formats.

Source Code Files

Source code files typically use:

• COBOL: RECFM=FB, LRECL=80
• JCL: RECFM=FB, LRECL=80
• Assembler: RECFM=FB, LRECL=80
• REXX/CLIST: RECFM=FB, LRECL=80

Data Files

Data files may use:

• Fixed-format data: RECFM=FB, LRECL varies
• Variable-format data: RECFM=VB, LRECL varies
• Format depends on data structure

Report Files

Report files may use:

• Standard reports: RECFM=FB, LRECL=80
• Wide reports: RECFM=FB, LRECL=132
• Format depends on report width

Best Practices

Following best practices helps you work effectively with different record formats:

• Know Your Format: Understand the RECFM and LRECL of files you're editing
• Respect LRECL: Stay within LRECL limits when editing
• Use BOUNDS for Fixed: Use BOUNDS to enforce limits for fixed-format files
• Understand Padding: Be aware that fixed-format files pad short lines
• Check Attributes: Verify dataset attributes before editing
• Match Format to Purpose: Use appropriate formats for your file type
• Consider Compatibility: Ensure format compatibility with downstream systems
• Document Format: Document format requirements for your files

Explain Like I'm 5: Record Formats

Think of record formats like different types of boxes for storing things:

• Fixed Format (F, FB) is like having boxes that are all exactly the same size. Every box is the same—if you put something small in it, you fill the rest with padding, and if you put something too big, you have to cut it to fit. It's like having uniform boxes where everything must fit the same size!
• Variable Format (V, VB) is like having boxes that can be different sizes. You can have a small box for small things, a medium box for medium things, and a big box for big things—as long as nothing is bigger than the biggest box you have. It's like having flexible boxes that adjust to what you're storing!
• LRECL is like the size of your boxes. For fixed boxes, it's the exact size every box must be. For variable boxes, it's the biggest size any box can be. It's like saying "all boxes must be this size" or "no box can be bigger than this size"!
• RECFM is like the type of box system you're using. F means fixed-size boxes, V means variable-size boxes, and the B means the boxes are grouped together for efficiency. It's like choosing what kind of storage system you want!

So record formats are like different ways of organizing and storing your data in boxes, with rules about how big the boxes can be and whether they all have to be the same size!

Practice Exercises

Complete these exercises to reinforce your understanding of record formats:

Exercise 1: Viewing Dataset Attributes

Practice viewing attributes: use Data Set Utility to view RECFM and LRECL of different datasets, check attributes in the editor status line, and identify the format of various files. Build familiarity with dataset attributes.

Exercise 2: Editing Fixed Format Files

Practice editing fixed-format files: open a fixed-format file (RECFM=FB, LRECL=80), observe how all lines are the same length, practice staying within LRECL, and understand how padding works. Learn fixed-format editing.

Exercise 3: Editing Variable Format Files

Practice editing variable-format files: open a variable-format file (RECFM=VB), observe how lines can have different lengths, practice editing lines of varying lengths, and understand variable-format behavior. Learn variable-format editing.

Exercise 4: Understanding LRECL

Practice understanding LRECL: work with files of different LRECL values (80, 132, 256), observe how LRECL affects editing, practice staying within limits, and understand the relationship between LRECL and editing. Master LRECL concepts.

Exercise 5: Format Comparison

Practice comparing formats: edit both fixed and variable format files, compare editing behavior, understand the differences, and identify when to use each format. Build comprehensive understanding.

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