# GATE CSE 1991 | Question: 01-xii

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A given set of processes can be implemented by using only parbegin/parend statement, if the precedence graph of these processes is ______

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precedence Graph should be a Null Graph.. because if there is even a single edge , we must use Begin/End..
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is precedence graph in syllabus in 2017?
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pls explain the concept of precedence graph @Arjun Sir @Bikram Sir
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### A precedence graph is a directed, acyclic graph whose nodes correspond to individual statements.

see the example here  http://uclab.khu.ac.kr/lectures/2003_autumn_os/lecture3.pdf

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is perbrgin /perend is similar with cobegin/coend ?

A given set of processes can be implemented by using only parbegin/parendstatement, if the precedence graph of these processes is properly nested

1. It should be closed under par begin and par end.
2. Process execute concurrently.

https://gateoverflow.in/1739/gate1998_24#viewbutton

In this question precedence graph is nested.

1. All the process execute concurrently,  closed under par begin and par end.

2. If you see all the serial  execution come then signal the resource and and parallel process down the value (resource ) similar all the process which are which are dependent to other one, other one release the resource then it will be got that with down and after release the its own resource. In the sense all the process are executing concurrently.

edited by
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graph is nested means?
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1. it should be closed under par begin and par end ...

2. process execute concurrently ....

https://gateoverflow.in/1739/gate1998_24#viewbutton

in this question precedence graph is nested ....

1) all the process execute concurrently ..closed under par begin and par end ..

2) if you see all the serial  execution come then signal the resource and and parallel process down the value (resource ) similar all the process which are which are dependent to other one , other one release the resource then it will be got that with down ..and after release the its own resource .. in the sense all the process are executing concurrently ...

may be my words are not clear to understand .... but moto is clear i think ...
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yes :) its about that word "nested"
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@Sonam :Please explain the second aspect 2) if you see all the serial  execution come then signal the resource and and parallel process down the value (resource ) similar all the process which are which are dependent to other one , other one release the resource then it will be got that with down ..and after release the its own resource .. in the sense all the process are executing concurrently ...

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in simple words if some process hold resource then , and that want other ,so process which have resource ,will up and release that and other one down on it and got the resource
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The meaning of nested is not clear from the answer and the link provided:(
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I think "properly nested" graphs represent any one of the below:

1. inner loops of begin-end which is enclosed in the outer loop of parbegin-parend
2. inner loops of parbegin-parend which is enclosed in the outer loop of begin-end. (Example of this is the below diagram.)

And the question is asking for precedence graph of processes that can be implemented using only parbegin and parend. I think it is different from "properly nested" graphs. The graph expected in the question would be as the below diagram. (I don't know the exact name given for these type of precedence graphs)

An important class of process flow graphs are those that are properly nested. Let S(p1,...,pn) denote the serial execution of processes p1 through pn and let P(p1,...,pn) denote the parallel execution of processes p1 through pn. Then a process flow graph is properly nested if it can be described by the functions S and P, and only function composition.

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is perbrgin /perend is similar with cobegin/coend ?
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@amlan97 Yes they are the same. co - concurrent, par -  parallel.

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