Chapter 1 INTRODUCTION SYS-ED/ COMPUTER EDUCATION TECHNIQUES, INC.

Transcription

1 hapter 1 INTRODUTION SYS-ED/ OMPUTER EDUATION TEHNIQUES, IN.

2 Objectives You will learn: Features of. Differences between procedural and non-procedural languages. ategories and summary of statements. Syntax rules. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page i

3 A fourth generation language will serve to: 1 What are 4 GLs Speed up application building. Reduce maintenance cost. Minimize debugging. Generate bug free code from high level expressions. User friendly - Minimize learning curve. Non Procedural Language. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 1

4 can perform the following functions: 2 Functions of General purpose report generation. omputations. Selection criteria. Sort files. Merge files. Edit files. Built in utilities. Label generation. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 2

5 The advantages in using include: 3 Advantages ease of use. reduction of application backlog. user programmability. simple-to-use, English like commands. flexible. works with QSAM and VSAM. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 3

6 4 Types of ommands The commands fall into the following categories: computational. writing detail and summary information. setting up title/footing. data set and descriptions. conditional expressions. sorting the file. flow of control. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 4

7 uses the following data types: 5 Data Types H NU PD BI haracter Zoned Numeric Packed Decimal Binary SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 5

8 The program layout in is as follows: 6 Program Layout OPTION statement. REPORT statement. FILE command. WORKAREA ONTROL. SORT. Detail time processing. Subroutines. ON END. ON HANGE. ON FINAL. TITLE and title modifications. FIN. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 6

9 DYL 280 file organization is as follows: 7 FILE Organization QSAM Fixed Variable Spanned Undefined Sequential Access BDAM Direct Sequential and Direct Access VSAM KSDS, ESDS, RRDS Fixed Variable (KSDS and ESDS) Sequential and Direct Library PDS or BPAM Fixed or Variable Full Directory Retrieval SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 7

10 8 General Rules Free Form Using the free form option, the statements can be coded in columns Some older programs use the fixed form option. omment oding an asterisk(*) in column 1 indicates that the entire line is a comment. Anything after a semicolon(;) is also considered a comment unless it is in a literal. Literals There are three types of literals: Alphanumeric Numeric Hexadecimal Maximum size is 255 characters. Maximum size is 20 characters. Numeric constants can include a minus symbol in front of the number and can have an embedded decimal point. The value is in the form X'nn' Dataname Data names for variables can be 2-50 characters long for fields in the record or workarea. Data names for files, tables, and parms can be 2-10 characters. Filename Maximum size is 8 characters. Tag or Label Maximum size is 10 characters. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 8

11 9 Automatic ycle OPEN FILES DO UNTIL END-OF-FILE ENDUNTIL READ INPUT FILE IF END-OF-FILE FINISH REPORT ON HANGE PROESSING ON FINAL PROESSING PRINT RUN STATISTIS LOSE FILES TERMINATE ELSE PROESS STATEMENTS PRINT WRITE ENDIF SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 9

12 10 FILE ommand FILE filename recfm size blocksize {INPUT OUTPUT} SEQUENTIAL [FROM filename] OUNT ntr LENGTH Len Filename Recfm Size Blocksize Len ntr FROM filename DDNAME of the file. Record Format F FB V VB U Fixed Fixed Block Variable Variable Block Undefined Logical record size. Physical record size. Length of current record. Mainly used for variable length records. urrent record count. Where record came from. SYS-ED \OMPUTER EDUATION TEHNIQUES, IN. (: 4.3) h 1: Page 10