Distinguish the following: i) DBMS and DSMS

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1) DBMS and DSMS

Parameter	DBMS	DSMS
Nature of data	Non-Volatile	Volatile data stream
Data Access	Random	Sequential
Query Nature	One-Time queries	Continuous queries
Storage Capacity	Unlimited secondary storage	Limited main memory
Rate of change	Low update rate	High/update continuous update rate

2) PCY, Multistage and Multihash - PCY algorithm exploits the observation that there may be much unused space in main memory on the first pass of apraisy.

In first pass only a bash function is applied on pair of item so that they bashes to a bucket.
we hash each pair and add 1 to the bucket.
At the end of 1st pass each bucket has count.
If count of bucket is > = support then the bucket is frequent bucket.
we can define a candidate pair C2 to be those pair { i , j } such that

1) i and j are frequent items.

2) { i , j } hashes to a frequent bucket.

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Multistage uses several successive hash tables to reduce further the number of candidate pairs.
But requires more passes than normal PCY.

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