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Conditional statements are used for CHANGING the FLOW of execution based on conditions specified. The conditions always MUST evaluate as true or false. Following are the different types of conditional statements:

• IF CONDITION
• Relation Condition
• Class Condition
• Sign Condition
• Negated Condition
• Condition-Name Condition
• Combined Condition.

GLOBAL VARIABLES are those variables that are AVAILABLE only to batch programs WHEREAS external variables are those variables that are accessible by any batch programs in the same SYSTEM library.

• Static linking requires a calling program to call the subroutine links.
• In dynamic linking, the calling program and the subroutine links can EXIST as different modules.
• Both types of linking can be done by choosing EITHER NODYNAM or DYNAM LINK edit options.

SYNC is a Keyword in COBOL used for aligning the STORAGE AREA (data) to a word boundary that REPRESENTS any ADDRESS that is multiple of 4. This is done to ensure computations are efficient when data is READ from word boundary by the Mainframe server.

There are majorly 3 TYPES of JCL statements:

• The first type consists of statements meant for identifying units of work that are to be PERFORMED by the Operating System.
• The second type of statement is the EXEC statement which depends on the number of steps involved in RUNNING a job.
• The THIRD type of statements are called DD (Data Definition) statements that are meant for identifying input and output data sets.

JCL expands to Job Control LANGUAGE and is a scripting language that is USED for providing required SPECIFICATIONS for processing a job. It consists of a set of control statements and acts as an interface between the IBM Mainframe Operating System and COBOL programs. JCL statements also do the task of notifying the OS for finding required input data and provide instructions on what operations need to be PERFORMED on that input and what needs to be done with the result.

They are most commonly USED declarations for IMPLYING restrictive factors which let to take decisions under specific PROGRAM conditions. They are also used for IMPROVING program readability. They are also used for giving names to conditions which is why they are also known as “Condition Names”.

UPDATE cursor is a pointer that permits US to modify or delete the CURRENT recently fetched ROW. UPDATE KEYWORD lets the information server know that the INSTRUCTION would modify or delete any row it fetches from the database.

DBCTL stands for Database Control and is an address space and is used for accessing IMS (INFORMATION Management System) FILES for CICS (CUSTOMER Information Control System) transactions. It is used to access IMS files for CICS Transactions and it is address space. For more information, you can refer here.

Index cardinality represents the number of DISCRETE VALUES or ENTRIES in a table column. DB2 has a utility called RUNSTATS which is used for examining column entry redundancy for finding whether an index SCAN is NEEDED to search the data.

COPYBOOK is USED for storing the record format whose DESIGN can be used by another program too. One COPYBOOK can be used for multiple DOCUMENTS or programs by using REPLACING choice in case the formats are the same.

SEARCH and SEARCH ALL is USED for finding if a RECORD is present in a table or not.

Spool stands for Simultaneous PERIPHERAL Operations On-Line which is USED as buffering mechanism where data would be STORED TEMPORARILY, processed and executed later.

Self-referencing constraints are USED for restricting changes that can be possibly made to a primary key using a FOREIGN key. For achieving this, the foreign keys need to define the DELETE-CASCADE rule which states that in CASE the RELATIONSHIP for DELETE rule is defined as CASCADE, if one ROW is changed or deleted, then other rows in the table are recursively deleted.

DRDA represents Distributed Relational DATABASE Architecture that behaves as a connection protocol meant for processing of local database. This is mainly used by VENDORS such as IBM. The architecture consists of RULES that aid in the communication of applications and databases.

Mainframe computers are a COMBINATION of DIFFERENT processors and RAM (memory). They WORK as a CPU for multiple workstations and terminals associated with it. They are used for performing huge data operations of the range of petabytes which would allow PROCESSING requests for thousands of users. The term ‘Mainframe’ represents a frame to hold main memory and multiple processors. These computers are used for processing requests in real-time in e-commerce, banking, education. government and various other applications. The following diagram represents the view of the Mainframe system.