XQuery to SQL by XML Algebra Tree

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XQuery to SQL by XML Algebra Tree

Brad Pielech, Brian MurphyThanks:

Xin

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Outline

1. Overview of Rainbow System2. Process of translating XQuery ->

SQL3. XML Operators4. Partial translation walkthrough

with running example

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Rainbow System Complete XML <-> SQL system Uses some ideas from XPERANTO,

Niagara, and other systems Several main subsystems:

Document Shredder View Generator Query Translation, Query Rewrite Result Generation

Work in progress

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Steps in Translation

1. User inputs XQuery query2. User Query is converted into an

XML Algebra Tree (XAT)3. Database Mapping Query’s XAT

generated4. Queries are Decorrelated 5. Trees are merged, unnecessary

branches cut

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Steps Continued

6. Computation Pushdown (presentation concludes here)

7. SQL Generation8. Query Execution 9. Tagging of Results

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What is the difference between the two queries? The user query is executed over a view

of the XML document and specifies what to return and how to return it

The mapping query specifies how the view the user is querying “maps” to the database

Therefore, combining the two queries into one is necessary in order to correctly process the user’s request

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XAT Operators Each XAT is comprised of XAT

Operators. Similar in concepts to Relational

Algebra Operator set is combination

between Niagara and Xperanto papers

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Set of Operators SQL like (9):

Project, Select, Join (Theta, Outer, Semi), Groupby, Orderby, Union (Node, Outer), Cartesian Product.

XML like (4): Tagger, Navigate, is(Element, Text),

Aggregate. Special:

SQL, Function, Source, NameColumn, FOR

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SQL like Operators (9)NiagaraNiagara XPERANTOXPERANTO

Project Expose Project

Select Select Select

Theta Join Join Theta Join

Outer Join N/A Outer Join

Semi Join N/A N/A

Groupby Group Groupby

Orderby N/A Orderby

Union Union Union

Outer Union

Union Outer Union

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XML like OperatorsNiagarNiagaraa

XPERANTOXPERANTO

Tagger*(pattern)

Vertex Project:cr8(Elem, AttList, Att, XMLFragList),

Navigate(from, path)

Follow Project:get(TagName, Attributes, Contents, AttName, AttValue), Unnest

Is N/A Select:is(Element, Text),

Aggregate Group AggXMLFrags

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Special Operators

NiagarNiagaraa

XPERANTOXPERANTO DescriptionDescription

SQL N/A Input Denote a SQL query.

Function N/A Function Used to represent recursive query

Source Source Table, View

Identify a data source.

NameColumn

Rename

N/A Naming of columns.

FOR N/A N/A FOR iteration.

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<sports> <organization> <team> Boston Red Sox </team> <stadium sname = "Fenway Park"/> <starPlayer> <pname> Nomar </pname> <position> Shortstop </position> </starPlayer> <starPlayer> <pname> Pedro </pname> <position> Pitcher </position> </starPlayer> <starPlayer> <pname> Manny </pname> <position> Outfield </position> </starPlayer> </organization> <organization> … </organization>

Sports XML Document

<stadium> <sname> Fenway Park </sname> <capacity> 33,000 </capacity> <yearBuilt> 1912 </yearBuilt> <ticket_high rate = "55"/> <ticket_low rate = "18"/> </stadium> <stadium> … <stadium> <player name="Pedro" number="45" rookieYear = "1991" /> <player name="Nomar" number="5" rookieYear = "1997" /> <player name="Manny" number="24" rookieYear = "1993" /> </sports>

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Example XQuery<bestPlayers>{

For $p in document("sports.xml")/sports/organizationLet $a = $p/team/text()Where $a = "Boston Red Sox"Return

<playerName>$p/starPlayer/pname/text()

<playerName>}</bestPlayers>

List all of the star players’ names on the Boston Red Sox

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XAT Tree for Example Query

V1 := Aggregate

$pname = Navigate($p, starPlayer/pname/text())

Select($a = "Boston Red Sox")

$a := Navigate($p, team/text())

$p := Navigate(“/”, sports/organization)

Source(“sports.xml”)

Tagger(<bestPlayers> V1 </bestPlayers>

Tagger(<playerName> $pname </playerName>

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RDBMS Tables of Sports Info

organizationID

teamName stadiumnName

1 Boston Red Sox Fenway Park

Organization

stadiumID sname Capacity yearBuilt ticketHigh

ticketLow

1 Fenway Park 33,000 1912 50 22

Stadium

starPlayerName

starPlayePosition organizationID

Nomar ShortStop 1

Pedro Pitcher 1

Manny Outfield 1

StarPlayer

PlayerName

Number rookieYear

Nomar 5 1997

Pedro 45 1992

Manny 24 1993

PlayerInfo

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Partial Default XML View<Organization>

<row><organizationId> 1 </organizationId><teamName> Boston Red Sox </teamName><stadiumName> Fenway Park </stadiumName></row>

</Organization><Stadium>

<row><stadiumID> 1 </stadiumID><sname> Fenway Park </sname>…</row>

</Stadium>

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Challenge Question I

<Organization> <row> <organizationId> 1 </organizationId> <teamName> Boston Red Sox </teamName> <stadiumName> Fenway Park

</stadiumName> </row></Organization>

…<StarPlayer> <row> <starPlayerName> Nomar </starPlayerName> <starPlayerPosition>

shortstop</starPlayerPosition> <organizationId> 1 </organizationId> </row></StarPlayer>

…

<organization> <team> Boston Red Sox </team> <stadium sname = "Fenway Park"/> <starPlayer> <pname> Nomar </pname> <position> Shortstop </position> </starPlayer> <starPlayer> <pname> Pedro </pname> <position> Pitcher </position> </starPlayer> <starPlayer> <pname> Manny </pname> <position> Outfield </position> </starPlayer></organization>

What is the XQuery that converts the document on the left (default XML view) to the document on the

right (user view)?

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Mapping Query Part ICreate view invoice as (<sports>

FOR

$organization IN view ("default") /Organization/row RETURN

<organization> <team> $organization/teamName/text() </team> <stadium sname = $organization/stadiumName/text() />

FOR $starPlayer IN view ("default") /StarPlayer/rowWHERE $starPlayer/organizationID = $organization/organizationID

RETURN

<starPlayer> <pname> $starPlayer/starPlayerName/text()

</pname> <position> $starPlayer/starPlayerPosition/text() </position>

</starPlayer> </organization>

B1

B2

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Mapping Query Part IIFOR $stadium IN view ("default") /Stadium/rowRETURN <stadium> <sname> $stadium/sname/text() </sname> <capacity> $stadium/capacity/text() </capacity> <yearBuilt> $stadium/yearBuilt/text() </yearBuilt> <ticket_high rate = $stadium/ticket_high_rate/text() /> <ticket_low rate = $stadium/ticket_low_rate/text() /> </stadium>

FOR $player IN view ("default") /PlayerInfo/rowRETURN

<player name = $player/playerName/text() number = $player/playerNumber/text() rookieYear = $player/rookieYear/text() />

</sports>)

B3

B4

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Cutting Mapping Query The mapping query has data that

is unused by the user query, so we can get rid of it B3 and B4 are completely removed Remove stadium from B1 Remove position from B2

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Mapping Query XAT General Form

$organization := Navigate("/",Organization/row)

Source(“default.xml”)

FOR $organization

More Stuff

Some Stuff

Source(“default.xml”)

FOR $starPlayer

Some Stuff will be shown in Part I

More Stuff in Part II

B1

B2

$starPlayer := Navigate("/", StarPlayer/row)

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Mapping Query XAT Part IB1

O := Tagger(<sports> All </sports)

All = Aggregate

Tagger(<organization> V0 </organization)

V0 := Aggregate

Tagger (<team>$tname </team> )

$tname := Navigate($organization, teamName/text())


Source("default.xml")

FOR $starPlayer

To: Part II

Some Stuff

FOR $organization

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Mapping Query XAT Part II

Aggregate

$ID := Navigate($organization, organizationID)

Select($starPlayerID = $ID)

$starPlayerID := Navigate($starPlayer, OrganizationID)

$sname := Navigate($starPlayer, starPlayerName)

To: Part I

B2

Tagger(<starPlayer> <pname> $sname </pname> </starPlayer)

More Stuff

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Decorrelated Mapping XAT Part I

<sports> <organization> <team> Boston Red Sox </team> <starPlayer> <pname> Nomar </pname> </starPlayer> <starPlayer> <pname>Pedro </pname> </starPlayer> <starPlayer> <pname> Manny </pname> </starPlayer> </organization></sports> Tagger (<team>$tname </team>

O:= Tagger(<sports> All </sports>)

All = Aggregate


V0 := Aggregate


From Part II

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Decorrelated Mapping XAT Part II

Source("default.xml")Source("default.xml")

$organization = Navigate("/", Organization/row)

$starPlayer := (Navigate"/", StarPlayer/row)

Cartesian Product


$starPlayerID := Navigate($starPlayer, organizationID)



To Part I

Aggregate

Tagger(<starPlayer> <pname> $sname </pname>

</starPlayer)

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Progress Report

1. User inputs XQuery query2. User Query is converted into an

XML Algebra Tree (XAT)3. Database Mapping Query’s XAT

generated4. Queries are Decorrelated 5. Trees are merged, unnecessary

branches cut

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XAT merging Input:

User Query XAT + Mapping Query XAT Output:

Simplified composite XAT Approach:

The Tagger from the top of the Mapping Query is linked to the bottom of the User Query.

The Source Operator at the bottom of the User Query is deleted

Pushdown Navigation By using the commutative rules

Cancel out the navigation operators By using the composition rules

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Combined XAT

V1 := Aggregate




$p := Navigate(O, sports/organization)



Tagger (<team>$tname </team>


All = Aggregate


V0 := Aggregate


Top of Mapping Query

User Query

Rest of Mapping

Query

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Computation Pushdown Part I

What is PushDown? After merging the 2 XATs, there may be

redundancies in the larger tree. Ex: The user query and mapping query may

navigate to the same thing The decorrelated query tree may be

unorganized and inefficient Pushdown aims to eliminate these

problems

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Computation Pushdown Part II XPERANTO mentions pushdown as

a means of pushing computation to relational engine

Niagara defines equivalence rules and specifies several different heuristics for using the rules

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XAT Pushdown Example Part I

V1 := Aggregate









All = Aggregate


V0 := Aggregate



User Query

Rest of Mapping Query

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XAT Pushdown Example Part II

V1 := Aggregate









All = Aggregate


V0 := Aggregate



User Query

Rest of Mapping Query

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XAT Pushdown Example Part III

V1 := Aggregate








Cartesian Product

$organization = Navigate("/",

Organization/row)

$starPlayer := (Navigate"/",

StarPlayer/row)






User Query


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XAT Pushdown Example Part IV

V1 := Aggregate








Cartesian Product

$organization = Navigate("/",

Organization/row)

$starPlayer := (Navigate"/",

StarPlayer/row)






User Query


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Challenge Questions II & III What are some of the heuristics we

could use during Pushdown? What can / should we try to accomplish? What should the tree look like afterwards?

How could we go about pushing things down? What would the algorithm be? How do we know if an operator can be

pushed down? When do we stop pushing an operator down?

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Computation Pushdown Part III Goal: Tagger + SQL operators + XML

operators Use Equivalence rules repository to swap

operators Step 1: Navigation Pushdown.

Cancel Mapping Query Taggers and corresponding Aggregates

Delete redundant Navigates from User Query Rename columns in Mapping Query

Step 2: SQL Computation Pushdown. By commutative and composition rules.

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Equivalence Rules Pair-wise rules that determine if one

operator (parent) may be pushed through another (child) Navigate / Navigate rule: If the parent

depends on the child, they may not be swapped

Navigate / Join: Navigate is pushed to the side of the join that its entry point comes from

And many, many more

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Pushdown Results

1. Push Navigates to the correct side of Cartesian Product

2. Create a NameColumn operator that renames $tname into $a

3. Create a 2nd NameColumn operator that renames $pname into $sname

4. Get rid of all Taggers and Aggregates from Mapping Query and Navigates that were crossed out from User Query

5. Merge Select($starPlayerID = $ID) and Cartesian into a Join

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XAT After Computation PushDown Part I

V1 := Aggregate




NameColumn( $pname = $sname)

NameColumn( $a = $tname)

From Part II

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XAT After Computation PushDown Part II

$starPlayerID := Navigate($starPlayer, OrganizationID)






$organization := Navigate("/",Organization/row)


Join on ($ID = $starPlayerID)

To Part I

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Rest of the Process

1. Take the Combined XAT from the previous slide and generate a single SQL query.

2. Execute query on local RDBMS3. Format result tuples according to

Tagger4. Return XML document to user

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Summary1. Created XAT of the user query2. Created XAT for mapping query

1. Cut information unused by user query2. Decorrelated Mapping query

3. Merged two queries into 1 larger XAT4. Identified weaknesses in combined tree5. Walked through pushdown steps6. Displayed final, optimized tree

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The End!!!

Date post:	31-Dec-2015
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XQuery to SQL by XML Algebra Tree

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