presentation © copyright 2002, bryan meyers externally described files chapter 6

Presentation © Copyright 2002, Bryan Meyers

Externally Described Files

Chapter 6

Programming in RPG IVThird Edition

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Objectives:

• Define physical and logical files

• Discuss data types

• Discuss storage implications of numeric and character types

• Access physical and logical files from an RPG program

• Discuss field reference files

• Define externally described printer files

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Physical File

• Stores data records

• Can be defined as key sequence– Designate a key

• Can be defined as arrival sequence– First-in, first-out

• If the key field is not defined, then access is limited to arrival sequence

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Logical File

• Does not actually contain data

• Stores access paths– Pointers to records in physical files

• RPG programs use logical files just as though the logical files themselves contained data

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Introduction to DDS

• Use SEU to create a source member of definition statements

• Source type for physical files is PF• Source type for logical files is LF• Description Specifications (DDS) define files• File, record and field level keywords are used to

define a file• CRTPF command creates physical file from

DDS source– CRTLF command creates logical file

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Physical File Example

*..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8

A* T.Name++++++RLen++TDpB Functions

A UNIQUE

A R EMPREC

A EMPNO 9S 0

A LNAME 15A

A FNAME 10A

A DEPT 3A

A SALARY 6P 0

A STREET 15A

A CITY 15A

A STATE 2A

A ZIP 5S 0

A K EMPNO

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Data Types and Data Storage

• A = Character

• S = Zoned decimal

• B = Binary

• P = Packed decimal

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Packed Decimal

• Only the digit (low order) bits of a number are stored

• Sign occupies right-most four bit positions• iSeries converts all numeric data to

packed decimal before values are used in calculations

• Packed fields take (n+1)/2 bytes of storage– n=number of digits

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Extended Binary Coded Decimal Interchange (EBCDIC)

Digit EBCDIC

0 11110000

1 11110001

2 11110010

3 11110011

4 11110100

5 11110101

6 11110110

7 11110111

8 11111000

9 11111001

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Zoned Decimal RepresentationDigit EBCDIC # of Bytes

+1 11110001 1

-1 11010001 1

10 11110001 11110000 2

-10 11110001 11010000 2

22 11110010 11110010 2

99 11111001 11111001 2

100 11110001 11110000 11110000 3

-999 ________ ________ ________

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Packed Decimal RepresentationDigit EBCDIC # of Bytes

+1 00011111 1

-1 00011101 1

10 00000001 00001111 2

-10 00000001 00001101 2

22 00000010 00101111 2

99 00001001 10011111 2

100 00010000 00001111 2

-999 ________ ________

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Simple Logical Files

• Contain the record level keyword PFILE and the name of the physical file

• Have one or more field level keywords

• Widely used to change the retrieval order of records in a file– Same as physically sorting a physical file

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Simple Logical File Example

*..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8

A* T.Name++++++RLen++TDpB Functions

A R EMPREC PFILE(EMPMST)

A K LNAME

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Simple Logical File Example

*..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8

A* T.Name++++++RLen++TDpB Functions

A R EMPREC1 PFILE(EMPMST)

A EMPNO

A LNAME

A FNAME

A DEPT

A SALARY

A K DEPT

A K EMPNO

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Simple Logical File Example

*..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8

A* T.Name++++++RLen++TDpB Functions

A R EMPREC1 PFILE(EMPMST)

A EMPNO

A LNAME

A FNAME

A DEPT

A SALARY

A K DEPT

A K EMPNO

A S DEPT VALUES(‘MIS’ ‘ACT’)

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Multiple Record Formats

• Defined based on two or more physical files

• Each format is based on a different physical file

• Gives the appearance that the two physical files have been merged together

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Multiple Record Formats

*..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8

A* T.Name++++++RLen++TDpB Functions

A R STUDREC PFILE(STUDMAST)

A K STUD_NO

*

A R CRSEREC PFILE(STUDCRSE)

A K STUD_NO

A K SEMESTER

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Join Logical Files

• Fields are combined from different physical files into a single record

• JFILE signals which physical files are used by the logical file

• JOIN designates which physical files are used in this join

• JFLD keyword indicates which fields’ values are to be matched

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Join Logical File Example

*..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8

A* T.Name++++++RLen++TDpB Functions

A R EMPREC JFILE(ORDERS INVENT)

A J JOIN(ORDERS INVENT)

A JFLD(PART_NUM PART_NO)

A ORDER_NO

A CUST_NO

A PART_NO

A DESCRPT

A SELL_PRICE

A QTY_ORD

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Externally Defined Files

• Code an ‘E’ in position 22 on the F spec• Omit any entry for record length• If file is keyed, code a ‘K’ in position 34

– Omitting the ‘K’ results in record retrieval based on arrival sequence

• Input specs not needed for externally defined files• Program makes no distinction made between physical

and logical files• If you change a file (physical or logical) after you have

compiled a program using that file, you must recompile the program

*.. 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7 ...+... 8FFilename++IPEASFRlen+LKlen+AIDevice+.Keywords+++++++++++++++++++++++++++++FEmpMaster IF E K DISK

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Additional Database Concepts• Keywords can be used for data validity

checks, for interactive data entry, and editing output

• Data dictionary or Field Reference File is used to provide field definitions for use in subsequent file creation– You never actually use this file for data

storage

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Additional Database Concepts• To use a field from the Field Reference

File, use the file-level keyword REF and code an ‘R’ in positions 29 on the field referenced

• Field-reference files can enforce a uniformity and consistency

• File names should consist of an agreed-upon mnemonic prefix to denote the system

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Database File Naming

• File names should contain a short alphabetic mnemonic code to uniquely identify the file– Often related to key field

• Suffix of P (Physical), L (logical), F (field reference), S (screen), R (report)– and a number to differentiate between similar files

• CCSSTUP - CCS system, student, physical file

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Externally Described Printer Files

• Printer files can be created the same as physical files– Use CRTPRTF command

• DDS– Each record format begins with an ‘R’ in position 17– Specify the field’s or constant’s beginning position

• Where it starts on the line

– Use SPACEA, SPACEB, SKIPA, and SKIPB keywords for spacing and skipping

– Use DATE and PAGNBR for UDATE and PAGE– Use EDTWRD and EDTCDE keywords for editing

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Externally Described PRTF

*..1....+....2....+....3....+....4....+....5....+....6....+....7....+....8

A* T.Name++++++RLen++TDpBLinPosFunctions

A R HEADINGS SKIPB(1)

A 10DATE EDTCDE(Y)

A 22’SALES REPORT’

A 37’PAGE’

A 42PAGNBR EDTCDE(3)

A SPACEA(2)

A 14’SLSPSN.’

A 34’AMT.’

A SPACEA(2)

A R DETAILLINE SPACEA(1)

A SALESPRSN 4 15

A SALESAMT 6 2 32EDTCDE(1)

A R BREAKLINE SPACEB(1) SPACEA(2)

A 20’TOTAL’

A SLSPTOTAL 6 2 31EDTCDE(1)

A 40’*’

A R TOTALLINE

A 16’GRAND TOTAL’

A GRANDTOTAL 8 2 30EDTCDE(1)

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Externally Described Printer Files

• File Specification– Code printer file name

• Not QPRINT– ‘E’ in position 19 – Omit any entry for record length– Device (36-42) must be PRINTER– The overflow indicator cannot be OA - OF or OV

• Use OFLIND keyword to specify almost anything else (*IN10, *IN11, *IN99 etc.)

• Named indicators also allowed

*.. 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7 ...+... 8FFilename++IPEASFRlen+LKlen+AIDevice+.Keywords+++++++++++++++++++++++++++++FSalesRpt O E PRINTER OflInd(EndOfPage)

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Externally Described Printer Files

• Calculation Specifications– Use WRITE instead of EXCEPT

• Output Specifications not needed

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Points to Remember

• The iSeries defines data files independently of your programs

• Physical files contain data records, while logical files provide access paths, or pointers to the physical file

• Both physical and logical files may contain a key– Allows records to be retrieved based on the

value of the key (key sequence)

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Points to Remember

• The key can consist of one or several data fields– In the latter case, the key is called a

composite or concatenated key

• A physical file may contain only a single record format

• Logical files may contain multiple record formats, based on records from two or more physical files

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Points to Remember

• A logical file also may contain a single record format that actually combines data fields stored in different physical files– Called a join logical file

• Logical files can be used to select or omit records from the physical file

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Points to Remember

• A Field Reference File (data dictionary) can be used to record field definitions– Physical files can then reference this file

rather than having the field definitions included directly within the physical files themselves

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Points to Remember

• Numeric data can be stored in a physical file in one of three common formats– Zoned decimal– Packed decimal– Binary

• Define packed fields with odd number of positions

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Points to Remember

• Externally described printer files offer several advantages– Report formats can be changed without

modifying programs– RLU can be used to design the reports and

generate the DDS– Output specs can be eliminated from your

programs– Formats can be shared by other programs