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Where will the control go after displaying the screen?

 
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saidharrao
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PostPosted: Thu Feb 15, 2007 6:56 pm    Post subject: Where will the control go after displaying the screen?
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I have a basic question in IMS DC.

There is an IMS DB DC program of 500 lines. I am displaying a screen from this program. The corresponding ISRT call is there at the 200th line.

Ex:

Code:

CALL 'CBLTDLI' USING ISRT I-O-PCB I-O-Area.


Now the screen will be displayed. User will enter some values on the screen and press 'enter'. Then where will the control go? Will it come back to the 201st line or will it go to the first line of the Procedure division?
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Bitneuker

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PostPosted: Thu Feb 15, 2007 7:47 pm    Post subject:
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Basic questions deserve a basic answer. Once you sent the message you leave the application that sent the screen. After the user entered his data and hit the ENTER-key a message is sent to the message queue. In due time IMS will invoke the application belonging to the transaction because it has read a message from the message queue for it. Your application may or may be not in the region (depending how heavy traffic is) but will start at the beginning: performing a GU on the message queue. Usually before that a GU for the SPA in order to find out which part of the application has to be processed. Also keep in mind that only one application can serve hundreds of terminals. As processing by users is async each terminal has a SPA supplied when the first transaction code has been entered. That way the application knows what to do next without knowing from which terminal the message was sent.

So no.......it's not statement 201 though it might be if this is the statement where the terminal response is processed; but always after the GU of the message.
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amitchaudhary
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PostPosted: Thu Feb 15, 2007 10:46 pm    Post subject:
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The above answer was for pseudo conversation programs, for non conversational programs when the program sends the data on the screen using ISRT call the program ends and is not at all waiting for the user to enter data, thats how multiple users can run the same program. also as IMS DC is single threaded i.e. at a time there is only one request being processed from the Transaction queue) so in your case if you go out for a coffee and came back after 30 min so logically program should not wait for such a long time.

later on when u enter some data and press Enter the request goes in to the Transaction queue and the program will run from the start. now its your desing has to take care that you have to pass the key values from the second screen also to the main program so that he knows which data I have to process. if your MOD doesnot have that much space and you dont have any key field on the screen which identifies the key of the record which needs to be proceessed then its better to use SPA.
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Bitneuker

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PostPosted: Thu Feb 15, 2007 11:52 pm    Post subject:
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Amit,

Please do some carefull reading before reacting; what you describe is exactly what I posted. When I write 'in due time' it means that the application will be invoked when it's scheduled because a message was causing it. In due time means that the transaction might have a low priority or there are a lot of messages to be processed from other terminals.

Quote:
Also keep in mind that only one application can serve hundreds of terminals. As processing by users is async each terminal has a SPA supplied when the first transaction code has been entered. That way the application knows what to do next without knowing from which terminal the message was sent.


Since I like discussions about IMS DB/DC you are invited to tell me exactly what the difference between our posts is icon_wink.gif

PS: At least the conclusion is the same: no it will not proceed on statement 201 because it simply is the next in the program.
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saidharrao
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PostPosted: Fri Feb 16, 2007 5:07 pm    Post subject: Re: Where will the control go after displaying the screen?
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HI George and Amith,
Many thanks for your valuable and timely reply. I need some more help from you. In my program, I am throwing a screen namely screen1. Then I will receive the values from screen1 and manipulate. Based on that, I need to throw screen2 with some options. User will select one of those options and hits 'ENTER'. Based on the values entered in screen2, we have to throw the screen3 with some options and so on. And similary at any point of time we can switch to another transaction and that also based on the received values from any screen. All this has to be handled in a single program where there will be one program for each transaction.For this I thought of using SPA (Ofcourse I am not sure of how to use SPA). But is there any other way to handle this without using SPA?

Regards,
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Bitneuker

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PostPosted: Fri Feb 16, 2007 7:40 pm    Post subject:
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Saidhar,

There are usually 2 ways of passing control to another application. One is by modifying the transactioncode in the SPA and the other one is to perform a change call (CHNG) followed by a message for the application to take over control. In this message you may send the information the application needs.

Personally I prefer using a SPA since you can store intermediate results (counters, switches etc) and your mainapplication will get control back after the alternate application has done it's work. So the logic of what the mainapplication should do after regaining control is easily stored in the SPA. For each application you may reserve space for it in the SPA.

For the CHNG-call you will need one PCB type TP and MODIFY=YES as well as in your application an IO-PCB followed by an ALTERNATE-IO-PCB. More info may be find following the first link in my signature and search for CHNG. Also some posts may be found in this forum.
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Bitneuker

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PostPosted: Fri Feb 16, 2007 7:48 pm    Post subject:
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Also have a look at the topic of krishna_mf; he finally (almost) succeeded in having a CHNG-call work icon_wink.gif
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saidharrao
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PostPosted: Thu Feb 22, 2007 3:24 pm    Post subject: Re: Where will the control go after displaying the screen?
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Hi George,
Thanks a lot for the reply. Now I have another doubt. As I told earlier, I am throwing a screen from my program(note that I am having one program for each transaction).And based on the values that user has entered I have to throw another screen and so on. And everytime I have to compare whether the values that i have thrown to user are same when i reveived the user response. But if we store the values in working-storage before throwing the screen, the values will be gone before we reenter into the program.Then how to save these values. From your reply I found that we can use SPA for this.
1) Can SPA be used only for this reason (to store the intermediate values)? Is there any other method?(Read in the book that we can use a screen or a database other than SPA, but not efficient).

2) And if we use SPA, do we need to switch the transaction only through SPA or can we also do through ISRT call. I mean thoguh we have defined SPA, can we switch the transaction through CHNG call? that means we are using SPA only to store the intermediate values.

3) Let us suppose that we have 50 transactions in a system. I have defined 30 transaction with SPA and 20 without SPA. Can we still switch from one of those 20 to one of those 30 or vice versa? Remember we are NOT using SPA to switch between the transactions. Our purpose of having SPA here is only to store the intermediate values.

4) If we want to switch between the transactions using SPA then how to do that(Though you have mentioned in the earlier reply, can you please give more details?)? For this, is there anything that to be mentioned in the definition of transaction?


Awaiting your invaluable reply,

Regards,
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Bitneuker

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PostPosted: Thu Feb 22, 2007 4:27 pm    Post subject: Re: Where will the control go after displaying the screen?
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Quote:

1) Can SPA be used only for this reason (to store the intermediate values)? Is there any other method?(Read in the book that we can use a screen or a database other than SPA, but not efficient).


One MPP can serve hundreds of terminals (users). So there's one copy of the MPP in the region with one working-storage or pli-declares. Values of switches, calculations etc. differ for each terminal (T1 is in stage-1 and T2 in stage-2) meaning that all declarations have to be made initial before the MPP starts processing a message. The MPP has to know how to process the message; this varies per terminal (in what stage is the processing flow, how and where to proceed making use of set or caculated variables during the previous stage for the particular teminal). That's why we use a Scratch Pad Area where these variables are stored; each terminal has a SPA as soon as the first transactioncode is sent from it. At creation of the SPA it will be low-value so the MPP knows it's a fresh start from that particular terminal. When the MPP is invoked because a message has been sent from a terminal it first assures the variables are made initial, reads the SPA using a GU on the message queue and then a GN for the message. One may decide to work with the stored variables in SPA or map them to the variables in working storage. The SPA can also be used to transfer control to another MPP; since the SPA has the terminal-id stored all MPP's processing messages from that terminal know where to send respond to. It's depending on the size of the SPA whether it's stored in memory or on DASD. You may guess which one performs better icon_wink.gif CICS has something similar called COMM-AREA though the processing differs from IMS.


Quote:

2) And if we use SPA, do we need to switch the transaction only through SPA or can we also do through ISRT call. I mean thoguh we have defined SPA, can we switch the transaction through CHNG call? that means we are using SPA only to store the intermediate values.


Program-to-program switch using SPA is done by modification of the transaction-code in the SPA into the transaction-code of the desired MPP to switch to. After inserting the SPA via the IO-PCB you provide the MPP where you switch to with a message (also insert via the IO-PCB). If you transfer via SPA don't use CHNG.

Quote:

3) Let us suppose that we have 50 transactions in a system. I have defined 30 transaction with SPA and 20 without SPA. Can we still switch from one of those 20 to one of those 30 or vice versa? Remember we are NOT using SPA to switch between the transactions. Our purpose of having SPA here is only to store the intermediate values.


You can switch to all transactions via SPA or CHNG; via SPA the values are also transferred, via CHNG just send a message to the other MPP telling it what to do. This other MPP then also executes a CHNG to return control to the calling MPP.

Quote:

4) If we want to switch between the transactions using SPA then how to do that(Though you have mentioned in the earlier reply, can you please give more details?)? For this, is there anything that to be mentioned in the definition of transaction?


I explained this a bit in the first answer. You wil a separate answer on the requirements using SPA.
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saidharrao
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PostPosted: Thu Feb 22, 2007 6:41 pm    Post subject: Re: Where will the control go after displaying the screen?
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Hi George,
Thanks a lot. Your answers are helping us a lot in progressing with the project. I have one more query in this regard.

1) How costlier is a call to SPA? I mean, we issue a GU call as the first call in the procedure division to get the SPA copied into the program and each time we throw the screen, we issue an ISRT call to save the SPA.

Will these calls effect the performance of the system? Can we compare these calls with a normal Database call in terms of cost/time? Some people are telling that two calls of SPA(GU, ISRT) is equal to one databse call. Can you please clarify me on this?

Awaiting your one more valuable answer,
Regards,
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Bitneuker

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PostPosted: Thu Feb 22, 2007 6:53 pm    Post subject:
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Like I wrote before the SPA may be in storage memory or on DASD. You will understand that memory-SPA is faster though both methods require the GU and ISRT at the IO-PCB. Calls at the IO-PCB are the most optimated calls that exist since you don't define your own DBD etc. for it; the IO-PCB refers to the message queue. Don't worry about the costs and/or performance. In my opinion the times we stored SPA-data in messages for optimisation reasons lies far behind us. Check with your system administrator what K your SPA is allowed for memory storage.
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Bitneuker

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PostPosted: Thu Feb 22, 2007 7:00 pm    Post subject:
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To learn more about SPA follow the first link in my signature and search for SPA. Amongst others you will find this one and also this
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