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SilkRoute: A Framework for
Publishing Relational Data in XML
Mary Fernández, AT&T Labs - Research
Dan Suciu, Univ. of Washington
Yada Kadiyska, Univ. of Washington
Atsuyuki Morishima, Univ. of Tsukuba
Wang-Chiew Tan, Univ. of Pennsylvania
XML-Relational Middleware
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XML: Standard, flexible syntax for exchanging data
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Industry defines common XML vocabulary
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Lingua franca of B2B Applications
Document Type Descriptions (DTDs) or XML Schema
Contract between data producers & consumers
Reflects application domain
XML-Relational Middleware
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Key business data in RDBMS
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Glue between existing business data & application
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Characteristics: General, dynamic, efficient
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SilkRoute : A Reference Framework
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XML Data Management
XML Producer
XML Consumer
XML
Documents
& Schemas
Legacy
Database
Publish XML
API or
Query
XML
XML Interfaces
XML
XML
Store XML
Persistent
Database
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Clothing Supplier & Reseller
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Shared XML Schema
element supplier {
element company, element product* }
element company { xs:string }
element product {
element name,
element category,
element retail,
element sale?,
element reports* }
element name { xs:string }
element category { xs:string }
element retail {
attribute cur { xs:string }, xs:float }
element sale { xs:float }
<supplier>
<company>ACME Clothing</company>
<product>
<name>Suede jacket</name>
<category>outerwear</category>
<retail cur=“USD”>325.00</retail>
<sale cur=“USD”>225.00</sale>
</product>
<product>
<name>Rain boots</name>
<category>outerwear</category>
<retail cur=“USD”>45.00</retail>
<sale cur=“USD”>22.50</sale>
<report code=“defective” >leaks in heel</sale>
<report code=“defective”>heel separates</sale>
</product>
</supplier>
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Viewing and Querying XML
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
Most data in relational database
Suppliers’ goal: Define XML view of data
 General: support many XML Schemas
 Efficient: leverage relational database
Application Query
?
Application
Public Query
=
(
?
?
)
Supplier
Database
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Viewing and Querying XML
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Brokers’ goal: Uniform access
Dynamic: Access up-to-date, minimal result
?
Application
=
?
°
?
=
?
(
Supplier
database
?
=
)
?
(
)
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SilkRoute Framework
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General, declarative view-definition language
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Public Query in XQuery
Maps relational data to public XML view
+ Support many output XML Schemas
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Dynamic querying of XML views
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Application Query in XQuery
Maps public XML data to application’s view
Query composition algorithm
+ Underlying storage should be transparent to user
+ Access up-to-date, minimal result
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Efficient use of relational engine
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Query decomposition algorithm
Selects query execution plan (one or more SQL queries)
Uses relational engine’s cost estimates to guide search
+ Leverage power of relational query engine
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Canonical XML View
Clothing(pid, item, category, description, price, cost) :
{ <001, “Suede Jacket”, “outerwear”,”Hip length”, 325.00, 175.00>,
<002, “Rain boots”, “outerwear”, “Ankle height”, 45.00, 19.99> }
Discount(pid, discount) : { <001, 0.70>, <002, 0.50> }
<Clothing>
<Tuple>
<pid>001</pid>
<item>Suede jacket</item>
<category>outerwear</category>
<description>Hip length</description>
<price>325.00</price>
<cost>175.00</cost>
</Tuple>

<Tuple>
<pid>002</pid>
<item>Rain boots</item>
<category>outerwear</category>
<description>Ankle height</description>
<price>45.00</price>
<cost>19.99</cost>
</Tuple>
</Clothing>
Oracle 9i XSQL
Canonical XML View
Use XSLT (out of engine) to transform canonical XML
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Canonical & Public Views
<supplier>
<Clothing>
<company>ACME Clothing</company>
<Tuple>
<product>
<pid>001</pid>
<name>Suede jacket</name>
<item>Suede jacket</item>
<category>outerwear</category>
<category>outerwear</category>
<retail cur=“USD”>325.00</retail>
<description>Hip length</description>
<sale cur=“USD”>225.00</sale>
<price>325.00</price>
</product>
<cost>175.00</cost>
<product>
</Tuple>
<name>Rain boots</name>
<Tuple>
<category>outerwear</category>
<pid>002</pid>
<retail cur=“USD”>45.00</retail>
<item>Rain boots</item>
<sale cur=“USD”>22.50</sale>
<category>outerwear</category>
<description>Ankle height</description> <report code=“defective” >leaks in heel</sale>
<report code=“defective”>heel separates</sale>
<price>45.00</price>
</product>
<cost>19.99</cost>
</supplier>
</Tuple>
</Clothing>
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XQuery
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Strongly typed, functional XML query language
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Compositional: XML to XML
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Large-scale database access
Must guarantee safety/correctness of operations on data
Q1(Q2(D)) = (Q1 o Q2)(D)
XQuery 1.0 =
XPath 2.0 (path, arithmetic, logical expressions)
+ for-let-where-orderby-return (FLWOR)
XML construction
+ User-defined (recursive) functions
+ Strong typing
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Public View Query
?
Public view query expressed in XQuery
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
Includes all XQuery expressions
Except recursive functions, features that depend on document order
<supplier><company>ACME Clothing</company> {
for $c in $CanonicalView/Clothing/Tuple
where $c/category = “outerwear”
return <product>
<name>{ data($c/item) }</name>
<category>{ data($c/category) }</category>
<retail cur=“USD”>{ data($c/price) }</retail>
{ for $d in $CanonicalView/Discount/Tuple
where $d/pid = $c/pid
return <sale cur=“USD”>{ $d/discount * $c/price } </sale> }
</product>
} </supplier>

Type checking guarantees view conforms to public schema
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Application Query

?
Application query expressed in XQuery
for $s in $PublicView/supplier
return
<supplier>
<name>{ data($s/name) } </name>
<discounted> {
for $p in $s/product
where $p/sale < 0.5 * $p/retail
return <product>{ data($p/name) }</product>
} </discounted>
</supplier>

Type checking guarantees application query correct w.r.t. public
schema
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SilkRoute Architecture
Internet/Intranet
SilkRoute
Relational Engine
XML
Generator
Application
View Forest
Composer
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View Forest
Decomposer
?
?
?
?
?
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All modules process view forests
Representation of all views: canonical, public, application
Maps relational data to XML document
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Query Decomposition
?
?
for $c in $CanonicalView/Clothing/Tuple
where $c/category = “outerwear”
return <product>
<name>{ data($c/item) }</name>
<category>{ data($c/category) }</>
<retail>{ data($c/price) }</retail>
</product>
<product>
<name>item</name>
<category>category</category>
<retail>price</retail>
</product>
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SELECT $c.pid as pid, $c.item as item,
$c.category as category, $c.price as price
FROM Clothing $c
WHERE $c.category = “outerwear”
View query may decompose into multiple SQL queries
Use greedy algorithm (with help from RDBMS) to choose decomposition
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Related Systems
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Commercial Systems
Oracle 9i – canonical mapping
 IBM DB2 XML Extender – annotated schema
 Microsoft SQL Server – universal relation,
annotated schema
(To date), none support full XQuery
SQL Server supports XPath
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(Quasi) Research Systems
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Xperanto (IBM Almaden) – now a product
Rolex, PRATA (Bell Labs)
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Summary
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XML Publishing Systems
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Workhorses of B2B applications
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Key characteristics: General, dynamic, efficient
Commercial Systems
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Oracle, IBM DB2, Microsoft SQL Server
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Some, but not all, of key characteristics
SilkRoute : A Reference Framework
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General, declarative mappings from relations to XML
Query composition & decomposition
Establishes link between XQuery & SQL
Prototype (re-)implementation (JDBC-compliant database)
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