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Doubt regarding Alternate Index

 
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ThiruvenkatNathan

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Joined: 12 Oct 2010
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PostPosted: Mon Jun 18, 2012 11:10 am    Post subject: Doubt regarding Alternate Index
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Hi ,

I am not able to find out the answer from the following options as it is too confusing. May be because i had a different understanding about alternate index. Kindly guide me.

When u print/open AIX what components will u find?
a. Actual records related to base cluster via alternate key.
b. Alternate key with primary key
c. Alternate key with primary key and control interval
d. Actual records and its linked alternate key
After creation of AIX, by relating with base cluster, what will be the content of AIX?
a. Will have alternate key
b. Will have alternate key with primary key
c. Will have data along with the key
d. None

Thanks in advance. Hope @dick, @anuj or @expat can help me icon_smile.gif i posted a query 2 years ago and this is the next one. Thanks a lot for your support guys.
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enrico-sorichetti

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PostPosted: Mon Jun 18, 2012 11:26 am    Post subject: Reply to: Doubt regarding Alternate Index
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since they look like as interview questions
the topic was moved!

the two questions are related to the same concept .... even if asked with different words

when You print < a thing > You just show the < a thing > content.

see here for some snippets
http://www.ibmmainframes.com/viewtopic.php?t=29269&postdays=0&postorder=asc&start=15

Quote:
Hope @dick, @anuj or @expat can help me


asking for help from specific people is considered bad manners
You should be ready to accept answers form anybody who feels he/she has the competence to reply
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ThiruvenkatNathan

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PostPosted: Mon Jun 18, 2012 11:39 am    Post subject:
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Thank you vey much enrico.

So as per my understanding,

Ans for 1st question is Option A
Ans for 2nd question is Option C.. I guess..

I am really confused when these kind of questions have the " almost same answers ". I will not be able to test using jcl though since we are having a bit trouble here with emulator.

Kindly confirm whether my answers are right and if they are not correct please let me know the answers. Your help is really appreciated.
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ThiruvenkatNathan

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PostPosted: Mon Jun 18, 2012 11:40 am    Post subject:
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Quote:


asking for help from specific people is considered bad manners
You should be ready to accept answers form anybody who feels he/she has the competence to reply



Should not have done that. My sincere apologies. icon_smile.gif
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enrico-sorichetti

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PostPosted: Mon Jun 18, 2012 11:47 am    Post subject: Reply to: Doubt regarding Alternate Index
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in it using the proper terminology is essential for good communication ...

the players here are ...

the base cluster ( ksds/esds )
the AIX
the PATH

the AIX contains the <alternate> key and the key/rba of the bas record

so when You <print>/<show the content> of the AIX the base cluster is not accessed

the base data is accessed when processing the PATH

but all this can be found in the IBM redbook VSAM demystified available here
http://www.redbooks.ibm.com/abstracts/sg246105.html?Open

in any case, unless I misunderstood Your terminology the answer is B for both questions
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ThiruvenkatNathan

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PostPosted: Mon Jun 18, 2012 11:58 am    Post subject:
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Exactly what i had in mind enrico icon_smile.gif

But sadly these are the options i have been given.. I hope you can understand the frustration since i have been trying to find out answers for these questions for sometime.

Printing AIX - Alternate key + Key of base record ( Which i think is primary key )

Am i getting it right ? Would you be kind enough to tell me which of the above options it might be.. And i am not able to download the pdf from that link as well because of the restrictions. I would be so relieved if i just know which options are exactly the answer for these questions above.

I know that we are not suppose to demand answers from moderators and i am certainly not taking you for granted. It is just a humble request.
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enrico-sorichetti

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PostPosted: Mon Jun 18, 2012 12:01 pm    Post subject: Reply to: Doubt regarding Alternate Index
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a moderator is just somebody who apart the moderation also gives replies

in my previous reply I thought I had already answered ... B for both questions

( if You are processing ths AIX ONLY )
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ThiruvenkatNathan

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PostPosted: Mon Jun 18, 2012 12:08 pm    Post subject:
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Thank you very much enrico. Really appreciate your help.

And just one more doubt.. After relating with base cluster wouldn't AIX contain the data as well.. ? Just wondering..
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enrico-sorichetti

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PostPosted: Mon Jun 18, 2012 12:25 pm    Post subject: Reply to: Doubt regarding Alternate Index
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NOPE icon_biggrin.gif, the AIX is what the name tells... just an INDEX

did You look at the link I posted with my jcl snippets and results

th base cluster was an ESDS, bu the concept is the same ....

see what happened when I printed
1) the base cluster ==> DATA records ordered by RBA
2) the AIX ==> NO DATA . ALTERNATE KEY + RBA
3) the PATH ( AIX->BASE) ==> DATA records ordered by the alternate KEY
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Robert Sample

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PostPosted: Mon Jun 18, 2012 2:41 pm    Post subject:
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Study the Redbook and the manual. The record length of an AIX has absolutely no relationship to the record length of the base cluster -- which should be a clue that the AIX does not contain data.
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Pete Wilson

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PostPosted: Tue Jun 26, 2012 4:02 pm    Post subject:
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If you have a Base Cluster for example with 100 byte records, and the KEY is the first 10 bytes starting at position 0, which may be account number, you access the base cluster using that account number key.

If within the base cluster record there is another field with the persons name for example, which might be starting at position 11 for a length of 30, you can create an AIX and PATH so you can access the Base cluster records indexing on that different key.

When you build the AIX it copies all those keys into the AIX cluster. You then define a PATH that relates to the AIX, so you then access through the PATH name to make record searches through the AIX for the key you want. That in turn points to the desired matching record(s) of that alternate key in the Base cluster, from where the actual data records are read.

You can have multiple AIX's and PATH's to key on different parts of the Base cluster records.
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