Control Interval is analogous to a physical block for QSAM files. It is the unit of i/o. Must be between 512 bytes to 32 k. Usually either 2K or 4K. A larger control interval increases performance for sequential processing while the reverse is true for random access. Under CICS when a record is locked, the entire CI gets locked.
Control area is a group of control intervals. CA is used during allocation. CA size is calculated based on the
allocation type (cyl, tracks or records) and can be max of 1 cylinder.

it  is used to rename clause only.

its just like dump cmd used in RPGLE. you can able to see variable values used in CL pgm

during the time of compilation of a file , constrains are being removed, from the
file .but at the time of compliation keys are not removed in case from pf. constraints has no affects on members of a pf but keys has affect on members of pf.

copyfile command copies the contents of existing database file into another datbase file .
using cpyf -> we cancopy data from external device to a datbase file and viceversa.
crtdupobj-> create duplicate object, create clone exactly as the source file with structure and content with its link to prgram and logical file and its authority setting as well. no need to recompile pgm that use this file.

Flat file is a physical file which can be created without specifying any DDS levels.
Flat file is a database file with no data defenition specification.we can create a flat file using command CRTPF

Data areas are objects of type DTAARA that we can create and delete at will..A data area that can be used to store informations with a name,but without any structure.
Dataqueues are permanent objects(type DTAQ) that can be used for asynchronously communicating a
strem of values between programs or jobs.

The SCAN operation scans a character string (base string) contained in factor 2 for a substring (compare string) contained in factor 1. The scan begins at a specified location contained in factor 2 and continues for the length of the compare string which is specified in factor 1.The result field contains the numeric value of the leftmost position of the compare string in the base string.
The CHECK operation verifies that each character in the base string (factor 2) is among the characters indicated in the comparator string (factor 1). Verifying begins at the leftmost character of factor 2 and continues character by character, from left to right. Each character of the base string is compared with the characters of factor 1. If a match for a character in factor 2 exists in factor 1, the next base string character is verified. If a match is not found, an integer value is placed in the result field to indicate the position of the incorrect character.

hidden field can not be modified by user.It can only be midifile by program. It is widely user in Subfile.

There are at least five differences: COBOL II supports structured programming by using in line PERFORMs and explicit scope terminators, it introduces new features (EVALUATE, SET .. TO TRUE, CALL .. BY CONTEXT, etc), it permits programs to be loaded and addressed above the 16 megabyte line, it does not support many old features (READY TRACE, REPORT-WRITER, ISAM, etc.), and it offers enhanced
CICS support.