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CICS Questions

CICS Questions

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Published by: mukesh on Jul 01, 2011
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Explain the differences between a Transaction and a Task.A.
Under CICS, a user can't directly invoke a program. Instead, the user invokes a transaction, which inturn specifies the program to be run. When a user invokes a transaction, CICS locates the associatedprogram with the transaction, loads it into storage (if it is not there), and starts a task. Where Task isa unit of work which is scheduled by CICS. The difference between transaction and task is that whileseveral users may invoke the same transaction, each initiates a separate task.2.
Describe the basic differences between batch and online systems.A.
In a Batch processing system, transactions are accumulated into groups, or batches, before they areprocessed. For example the processing of the Orders collected for the whole day. In an Onlineprocessing system the transactions are processed by the system as soon as the transaction is enteredon to the system. Ex. Airplane Reservation system. In a batch system the turnaround time ismeasured in hours and days, while for the On-line system it is measured in micro-seconds andseconds. On an Online system, if there is an error in data, the system indicates it immediately, andcan be corrected and reprocessed. Allstate Insurance Co., uses CICS V4.1. on their system.3.
What are the four major types of Online Programs?A.
The menu program. The inquiry program. The file maintenance program. The Data Entry program.4.
Describe the different considerations for the Online programs (CICS).A. Ease of use. IBM promotes a user interface standard called CUA (common user Access). CUA providesEntry model, Graphical model, and Intermediate model - the text subset of graphical model.Performance. Performance is a critical consideration for online programs. Performance for online systems ismeasured in terms of response time. Many factors affect response time. The most critical factors are the totalnumber of programs running within the CICS system, the Disk I/O, the terminal and host computers andnetwork.File Integrity. A batch program typically has complete control of the files it uses, so there's no chance of anotherinterfering with its processing. In an online system however many terminal users use the system simultaneously,and all must have access to the files they require at the same time.Security. On batch systems Security implementation is simple as the access to the computer system can becontrolled. However in an online system terminals are located at several locations. Logon procedure being usedcan ensure security to a great extent. Using of multi-level security to allow only certain users to access files andprograms based on the logon id helps to secure the system.5.
Describe the most common way a task is started under CICS.A. By entering the Transaction Identifier on the terminal and pressing Enter Key. When the Trans-id is enteredon the CICS screen, it locates the program associated with the trans-id from the PCT. Then the location of theprogram is determined by CICS by reading the entries in PPT. After the load module is located, it loads it ontothe CICS main memory, then task workspace is assigned for CICS own use to execute the task.
The other different ways are by a transaction identifier associated with a terminal for pseudo-conversation, ByRETURN command, By START command (Time-driven Automatic Task Initiation), By a DCT entry and TDQwrite (Data-driven ATI), and by using 3270 attention identifier key.6.
Distinguish between Multitasking and Multi-threading.A.
Multi-tasking means that the OS allows more than one task to run (be executed) concurrently,regardless of whether the task use the same program or different programs. Multi-threading is thesystem environment, where multiple tasks share the same program under the multi-taskingenvironment. Programs are shared by several tasks, and for each task the program work as if itexecutes the instructions only for that task.7.
Briefly describe the function of each of the various CICS modules.A. Terminal Control. It is the interface between the CICS application program and the Operating System's Tele-Communication Access Method VTAM, TCAM or BTAM). Terminal control lets you send text to and receivetext from the terminal that initiated the task. An application program that uses terminal control directly mustprocess complicated strings of control characters and data sent to and received from the terminal.Basic Mapping Support. To relieve the programmer from building complicated strings of control characters tosend data to and receive data from terminals, BMS is used that acts as interface between the program andterminal control. BMS lets you create a map that specifies the format of data as it appears on the terminaldisplay.File Control. File control acts an interface between the Application program interface and the VSAM files. Theapplication program interface acts as the interface between the file control and application program. When a Filecontrol receives a request, it passes on to the appropriate VSAM File, which in turn would manage the datastorage.Program Control. This service manages programs executing within a task as an execution of an application for aparticular user. API acts as the interface between the application program and the individual CICS services.Transient Data Control. It provides the convenient way to use simple sequential files called destinations.Whenever a record is written to a destination it is added to the end. A task reads the first from destination,which gets deleted.Temporary Storage Control. It provides the simplest method for storing data outside your CICS program'sworking storage area. Data is stored on TSQ's. If the amount of storage is small it can be stored on mainmemory else a disk.Interval Control. This service lets you implement time dependent applications. It provides a method of starting atask that's an alternative to trans-id. It can be used to specify a task to start at a specific time. Storage Control. Itallocates storage space to application programs. Since most programs keep all their data in working storage,which is allocated automatically, you will not use storage control commands frequently.Task Control. It lets you control the execution of tasks. You can use it to suspend your task temporarily toprevent it from taking exclusive control and monopolizing the CICS resources and also take control over TSQ's.Dump control service provides the transaction dump that shows the content of main storage used by theprogram. You can also use dump control to create dump at specific points without terminating the program foranalysis.Trace control. It maintains the Trace table that indicates the sequence of CICS operations performed within atask.Journal Control module provides a standardized method of creating Output files called Journals, which are usedto restore files in the event of a system failure.
The different table used by the above mentioned modules are TCT (term_id), FCT (specify which operations areallowed on the file), PCT(trans-id, programs), DCT, TST, ... PPT, ... JCT, and others are SNT, SRT(sys.recovery).8.
Describe the differences between operation of Pseudo-Conversational and a conversational program.A. In a conversational mode, the program accomplishes the conversation by simply sending a message to theterminal, and waiting for the user to respond, and receiving the response from the terminal. The system that sitsidle without allowing an other operation while waiting for the data is called a conversational program.In a Pseudo-Conversational program, a program attempts a conversation with a terminal user, it terminates thetask after sending a message with a linkage for the next task. When the user completes the response the nexttask is automatically initiated. Pseudo-conversational program's uses the CICS resources such as control tablesefficiently.9.
Briefly describe the functions of each of the following tables - PCT, PPT, FCT.A. CICS creates internal control tables mentioned below based on the Resource definitions created by thesystem programmers. There are two ways a programmer can create a resource definition. By using specialassembler macro instruction or by using the Resource definition online (RDO). RDO is even called as CEDA asit is the transaction used to initiate RDO. RDO is used to define the resources needed such as program name,BMS, Trans-id, file info...Program Control Table - The primary function of the PCT is to register the control information of all CICStransactions. PCT contains a list of valid Trans-id paired with the name of a program CICS will load when thetransaction is initiated with that transaction identifier. It identifies priority and security level (RSLC) of transaction.Processing Program table - The Primary function of PPT is to register all CICS application programs and BMSmapsets. The PPT keeps track of which applications are loaded on the CICS address Space (storage). CICS usesthis information to determine whether new copy of the program need to be loaded from Disk or it exists onstorage. It contains information such as Location in memory, Library address of the disk and language beingused.File Control Table - The Primary function of FCT is to register the control information of all files, which areused under CICS. FCT contains the name and type of each file and in addition lists the file control operationsthat are valid for each file. It lists whether the existing records can be read sequentially or randomly, deleted ormodified. Others control tables used are TCT to register terminals, DCT, TST, RCT, SIT, SRT and SNT.10.
Describe the basic eight steps of a CICS program development according to Doug Lowe.Step1: Develop a complete set of program specifications. The minimum the specifications should includeprogram overview, a screen layout for each map being used, a listing of copy members of each file used bythe program. Others that are needed are include decision tables, editing rules, ...Step2: Design the program. Most standard COBOL programs are designed around a basic looping structure thatcontrols the overall program execution. In a pseudo-conversational CICS program there is no basic loopingstructure, Instead CICS invokes your program whenever there is an interaction with a user. CICS program is tobe designed to respond appropriately for each type of user action.

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