Grokbase Groups Pig user March 2010
FAQ
Comments

1) "Pig Latin is equivalent to the computational power of SQL" Pig
Latin is different than SQL in that it is a dataflow language, where
as SQL is a query language (for more on this see http://feeds.developer.yahoo.net/~r/YDNHadoop/
~3/i2Cdha8kedw/comparing_pig_latin_and_sql_fo.html ) So in your chart
I would put Pig Latin across from relational algebra. The translation
from Pig Latin to relational algebra is nearly 1-1.

2) MR should not be across from Relational Algebra. MR does not
itself present a relational algebra. It is possible to implement
relational algebras over MR, as Pig, Hive, and JAQL all do. Evaluated
just as MR I would argue that it is not relationally complete because
it presents only grouping and sorting options. It is straight forward
to implement projection and filtering via the Map function, but this
is not natively provided. Joins can be implemented via Reduce, but
doing so is not trivial. At the same time, since MR is written in
Java, which is definitely Turing complete, then MR must also be
Turning complete.

3) I'm not sure where MR goes in your chart, but the bottom seems the
wrong spot. By definition, anything you can implement in JAQL, Pig,
or Hive you can implement in MR. So to say it is the least
computationally powerful seems wrong. Perhaps I don't understand what
is meant by Computational Power.

To sum up, it seems to me that you're trying to map three separate
dimensions (relational completeness, turing completeness, and SQLness)
all onto one dimension. Instead it would make more sense to me to
present each project relative to these three dimensions: JAQL (yes,
yes, no), Pig (yes, no, no), Hive (yes, no, yes), and MR (no, yes, no).

Alan.
On Mar 20, 2010, at 4:54 PM, Rob Stewart wrote:

Hi,

I have a question, in a remark that Alan Gates made a few months ago
on
these mailing lists regarding the computability and expressibility
of Pig,
Hive, and the MapReduce model.

In particular, it was a question regarding the Turing computability
of each.

Is anyone able to remark on my discussion of this in my forthcoming
paper
(this is just a small extract). I am pretty confident as to where I
have put
Pig and Hive, quite confident with JAQL (I've checked it out with
the JAQL
dev's), and far less sure of my assessment of the MapReduce model
(only
relationally complete??)

Find it here:
http://www.macs.hw.ac.uk/~rs46/dropbox/computability.pdf


I would greatly appreciate any comments of pointers to any
inaccuracies.


thanks,


Rob Stewart

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