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Posted to dev@vxquery.apache.org by Eldon Carman <ec...@ucr.edu> on 2012/06/05 03:59:24 UTC
Example Queries From w3schools - Questions and Commentary
w3school.com has a tutorial for xquery and the section entitled
"XQuery Example" they outline three queries. I have run the queries
through VXQuery's Algebricks code branch and query plans. Below are
the three queries in both their xquery form, the vxquery plans, and a
commentary and/or questions about the breakdown.
w3school tutorial: http://www.w3schools.com/xquery/xquery_example.asp
vxquery command: sh ./vxquery-core/target/appassembler/bin/vxq
-compileonly xquery_example_1.xq -showtet
=== Query 1 ===
doc("books.xml")
assign [$$2] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}doc,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}promote,
Args:[function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}data, Args:[$$1],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE({http://www.w3.org/2001/XMLSchema}string QUANT_QUESTION)]]]
-- |UNPARTITIONED|
assign [$$1] <- [{http://www.w3.org/2001/XMLSchema}string
QUANT_ONE(books.xml)] -- |UNPARTITIONED|
empty-tuple-source -- |UNPARTITIONED|
Thoughts on the order of operations and details.
1. Default start with an empty tuple.
2. Assign the source file name [$$1] as a string.
3. Take the string file name and pass it as an argument to the data
functions (doc).
4. Ready to use in [$$2]
What do these keywords mean?
UNPARTITIONED
QUANT_ONE
QUANT_QUESTION
=== Query 2 ===
doc("books.xml")/bookstore/book/title
assign [$$17] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sort-distinct-nodes-asc-or-atomics,
Args:[$$16]] -- |UNPARTITIONED|
subplan {
aggregate [$$16] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sequence,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}child,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}treat, Args:[$$14,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyNodeType@69198891 QUANT_STAR)],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(NodeTest(NameTest(title),
org.apache.vxquery.types.AnyType@281acd47, nilled = true))]]] --
|UNPARTITIONED|
unnest $$14 at $$15 <- function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}iterate, Args:[$$12] --
|UNPARTITIONED|
assign [$$13] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}count, Args:[$$12]] --
|UNPARTITIONED|
assign [$$12] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sort-distinct-nodes-asc-or-atomics,
Args:[$$11]] -- |UNPARTITIONED|
nested tuple source -- |UNPARTITIONED|
} -- |UNPARTITIONED|
subplan {
aggregate [$$11] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sequence,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}child,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}treat, Args:[$$9,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyNodeType@69198891 QUANT_STAR)],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(NodeTest(NameTest(book),
org.apache.vxquery.types.AnyType@281acd47, nilled = true))]]] --
|UNPARTITIONED|
unnest $$9 at $$10 <- function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}iterate, Args:[$$7] --
|UNPARTITIONED|
assign [$$8] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}count, Args:[$$7]] --
|UNPARTITIONED|
assign [$$7] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sort-distinct-nodes-asc-or-atomics,
Args:[$$6]] -- |UNPARTITIONED|
nested tuple source -- |UNPARTITIONED|
} -- |UNPARTITIONED|
subplan {
aggregate [$$6] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sequence,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}child,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}treat, Args:[$$4,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyNodeType@69198891 QUANT_STAR)],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(NodeTest(NameTest(bookstore),
org.apache.vxquery.types.AnyType@281acd47, nilled = true))]]] --
|UNPARTITIONED|
unnest $$4 at $$5 <- function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}iterate, Args:[$$2] --
|UNPARTITIONED|
assign [$$3] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}count, Args:[$$2]] --
|UNPARTITIONED|
nested tuple source -- |UNPARTITIONED|
} -- |UNPARTITIONED|
assign [$$2] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}doc,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}promote,
Args:[function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}data, Args:[$$1],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE({http://www.w3.org/2001/XMLSchema}string QUANT_QUESTION)]]]
-- |UNPARTITIONED|
assign [$$1] <- [{http://www.w3.org/2001/XMLSchema}string
QUANT_ONE(books.xml)] -- |UNPARTITIONED|
empty-tuple-source -- |UNPARTITIONED|
Starts out the exact same way as the first for doc("books.xml"). The
processing continues for the extra query details.
…
5. The data is passed to count function to save the count to [$$3].
6. Set up a vxquery operator is set up to iterate over the data in $$4.
7. I see that we have the word "bookstore" in the query now. Looks
like we have a sequence for each child based on the interator supplied
from the data in books.xml. I want to say that [$$6] now represents
the data for each bookstore tuple.
… Looks like the next set of operations are similar to 5, 6 and 7
except that we now have a sort on distinct "bookstore" tuples.
8. Sort distinct nodes from the output of [$$6] and save them to [$$7].
9. Assign the count to [$$8].
10. Set up a vxquery operator is set up to iterate over the data in $$7.
11. Now we see the next part of the query for "book". In this section
we set up a sequence of all the books from the data supplied in the
iterator $$14.
… Repeat again for "title"
… Finally sort the complete output.
Looks like we assign a count, but do not use it. Is that true?
Why does the iterator have to variables?
What do these keywords mean?
QUANT_STAR
=== Query 3 ===
doc("books.xml")/bookstore/book[price<30]
assign [$$19] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sort-distinct-nodes-asc-or-atomics,
Args:[$$18]] -- |UNPARTITIONED|
subplan {
aggregate [$$18] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sequence, Args:[$$13]]
-- |UNPARTITIONED|
subplan {
select (function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}if-then-else,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}instance-of, Args:[$$17,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE({http://www.w3.org/2001/XMLSchema-extensions}numeric
QUANT_ONE)], function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}value-eq, Args:[$$17,
$$14], function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}boolean, Args:[$$17]])
-- |UNPARTITIONED|
assign [$$17] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}general-lt,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}treat, Args:[$$15,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyItemType@37bd2664 QUANT_STAR)],
function-call: vxquery:{urn:org.apache.vxquery.operators-ext}treat,
Args:[$$16, {http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyItemType@37bd2664 QUANT_STAR)]]]
-- |UNPARTITIONED|
assign [$$16] <-
[{http://www.w3.org/2001/XMLSchema}integer QUANT_ONE(30)] --
|UNPARTITIONED|
assign [$$15] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}child,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}treat, Args:[$$13,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyNodeType@b551d7f QUANT_STAR)],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(NodeTest(NameTest(price),
org.apache.vxquery.types.AnyType@7cb25b9d, nilled = true))]] --
|UNPARTITIONED|
unnest $$13 at $$14 <- function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}iterate, Args:[$$11] --
|UNPARTITIONED|
assign [$$12] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}count, Args:[$$11]] --
|UNPARTITIONED|
assign [$$11] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sort-distinct-nodes-asc-or-atomics,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}child,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}treat, Args:[$$9,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyNodeType@b551d7f QUANT_STAR)],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(NodeTest(NameTest(book),
org.apache.vxquery.types.AnyType@7cb25b9d, nilled = true))]]] --
|UNPARTITIONED|
nested tuple source -- |UNPARTITIONED|
} -- |UNPARTITIONED|
unnest $$9 at $$10 <- function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}iterate, Args:[$$7] --
|UNPARTITIONED|
assign [$$8] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}count, Args:[$$7]] --
|UNPARTITIONED|
assign [$$7] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sort-distinct-nodes-asc-or-atomics,
Args:[$$6]] -- |UNPARTITIONED|
nested tuple source -- |UNPARTITIONED|
} -- |UNPARTITIONED|
subplan {
aggregate [$$6] <- [function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}sequence,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}child,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}treat, Args:[$$4,
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(org.apache.vxquery.types.AnyNodeType@b551d7f QUANT_STAR)],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE(NodeTest(NameTest(bookstore),
org.apache.vxquery.types.AnyType@7cb25b9d, nilled = true))]]] --
|UNPARTITIONED|
unnest $$4 at $$5 <- function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}iterate, Args:[$$2] --
|UNPARTITIONED|
assign [$$3] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}count, Args:[$$2]] --
|UNPARTITIONED|
nested tuple source -- |UNPARTITIONED|
} -- |UNPARTITIONED|
assign [$$2] <- [function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}doc,
Args:[function-call:
vxquery:{urn:org.apache.vxquery.operators-ext}promote,
Args:[function-call:
vxquery:{http://www.w3.org/2005/xpath-functions}data, Args:[$$1],
{http://www.w3.org/2001/XMLSchema-extensions}type
QUANT_ONE({http://www.w3.org/2001/XMLSchema}string QUANT_QUESTION)]]]
-- |UNPARTITIONED|
assign [$$1] <- [{http://www.w3.org/2001/XMLSchema}string
QUANT_ONE(books.xml)] -- |UNPARTITIONED|
empty-tuple-source -- |UNPARTITIONED|
The plan is completely the same up until books. The first sub plan is
identical to what seen have seen.
Once we have the "bookstore" tuples, the "book" tuples are pulled out.
We sort, count and create an iterator.
1. The books are assigned to $$11
2. The prices are sorted, counted and created iterator into $$15.
3. Since we need 30 as a parameter we assign it to $$16
4. $$17 is the less than operator on the price and 30 variables.
5. The select function pulls out only the values that are TRUE.
6. The result is created into a sequence
7. The final output is sorted.
how do you define a subplan? Is that for each level of the query?
Re: Example Queries From w3schools - Questions and Commentary
Posted by Vinayak Borkar <vb...@yahoo.com>.
Hi Preston,
Please see inline...
>
> === Query 1 ===
> doc("books.xml")
>
>
> What do these keywords mean?
> UNPARTITIONED
> QUANT_ONE
> QUANT_QUESTION
UNPARTITIONED is an Algebricks annotation attached to each operator to
indicate that no analysis about partitioning has been performed. At
first, when an Algebricks plan is created by the translator, the
operators are unpartitioned. Partitioning is later introduced by rewrite
rules.
QUANT_??? are quantifiers used to construct Sequence Types. They serve a
similar purpose as ?, *, + in regular expressions.
>
> === Query 2 ===
> doc("books.xml")/bookstore/book/title
>
> we set up a sequence of all the books from the data supplied in the
> iterator $$14.
> … Repeat again for "title"
> … Finally sort the complete output.
>
>
>
> Looks like we assign a count, but do not use it. Is that true?
Good question. A variable assigned to the count() function is to support
the last() function in path expression evaluation.
> Why does the iterator have to variables?
During iteration over sequences, we need to bind a value to each item
and also to the index of that item to support position() and also the at
$i syntax for "for" clauses in XQuery.
>
> What do these keywords mean?
> QUANT_STAR
This is a quantifier as explained above (Construction of sequence types).
>
>
> === Query 3 ===
> doc("books.xml")/bookstore/book[price<30]
>
> 7. The final output is sorted.
>
> how do you define a subplan? Is that for each level of the query?
The subplan operator is used to maintain the correct cardinality of
tuples at each point in the expression tree.
The best way to understand the use of subplan would be to consider some
example input and run through a manual evaluation of the expressions.
Vinayak