Mapping Relational Databases to RDF with OpenLink Virtuoso © 2008 OpenLink Software, All rights reserved. Orri Erling - Lead Developer, Virtuoso Team

Who Wants to Map? Semantic Web Scalers Expose whatever there is as RDF, the next guy will unify terms, make search and apps Data Warehouse Keepers Data is spread out, has implicit semantics, complex schemas, heterogeneous sources, ambiguous terms but we must make it join and aggregate cleanly © 2008 OpenLink Software, All rights reserved.

Semantic Web Scalers

Expose whatever there is as RDF, the next guy will unify terms, make search and apps

Data Warehouse Keepers

Data is spread out, has implicit semantics, complex schemas, heterogeneous sources, ambiguous terms but we must make it join and aggregate cleanly

Present State SPARQL to SQL exists but still, complex integrations are data warehouses We'd really like to map, but... Can it be otherwise? © 2008 OpenLink Software, All rights reserved.

SPARQL to SQL exists but still, complex integrations are data warehouses

We'd really like to map, but...

Can it be otherwise?

Why RDF Data Warehouse? Pros Even query performance across all data Possibility of forward-chaining inference Some SPARQL features may be better supported, e.g. Unspecified predicates Cons Keeping data up-to-date Complex set up, needs dedicated servers: you don't build them on a whim © 2008 OpenLink Software, All rights reserved.

Pros

Even query performance across all data

Possibility of forward-chaining inference

Some SPARQL features may be better supported, e.g. Unspecified predicates

Cons

Keeping data up-to-date

Complex set up, needs dedicated servers: you don't build them on a whim

Why Map? No copying, no timeliness issues RDBMS outperforms RDF for analytics workloads Agile reconfiguration without reloading data © 2008 OpenLink Software, All rights reserved.

No copying, no timeliness issues

RDBMS outperforms RDF for analytics workloads

Agile reconfiguration without reloading data

Virtuoso Mapping of SPARQL to SQL against any existing schema - whether stored in Virtuoso or elsewhere Physical quad store Federated/local RDBMS © 2008 OpenLink Software, All rights reserved.

Mapping of SPARQL to SQL against any existing schema - whether stored in Virtuoso or elsewhere

Physical quad store

Federated/local RDBMS

For Mapping to Deliver... Tackle any SQL analytics workload in SPARQL without extra cost Deal with arbitrary SQL schema Produce single SQL statements, optimizable by target RDBMS Have intelligence for cases where one RDF entity can come from many relational sources © 2008 OpenLink Software, All rights reserved.

Tackle any SQL analytics workload in SPARQL without extra cost

Deal with arbitrary SQL schema

Produce single SQL statements, optimizable by target RDBMS

Have intelligence for cases where one RDF entity can come from many relational sources

The Cases of Integration Bring similar but heterogeneous schemas into a unified ontology - Union View Translate FKs of one schema to PKs in another - Distributed Join Hide differences in normalization - Views for hiding joins - Unit/Terminology conversions © 2008 OpenLink Software, All rights reserved.

Bring similar but heterogeneous schemas into a unified ontology - Union View

Translate FKs of one schema to PKs in another - Distributed Join

Hide differences in normalization - Views for hiding joins

- Unit/Terminology conversions

Defining a Mapping Define URI formats and their subclass relations Define which key-column-value combinations make a triple Arbitrary SQL is allowed for mapping values and filtering A single RDF node can be a composite of many columns, e.g. multipart key © 2008 OpenLink Software, All rights reserved. Use SPARQL/SQL to:

Define URI formats and their subclass relations

Define which key-column-value combinations make a triple

Arbitrary SQL is allowed for mapping values and filtering

A single RDF node can be a composite of many columns, e.g. multipart key

The TPC-H Case The 22 queries as extended SPARQL Each generates a single SQL statement, executable by Virtuoso, Oracle, Others Next make several TPC-H databases on different servers and run the queries against the union © 2008 OpenLink Software, All rights reserved. http://demo.openlinksw.com/tpc-h/

The 22 queries as extended SPARQL

Each generates a single SQL statement, executable by Virtuoso, Oracle, Others

Next make several TPC-H databases on different servers and run the queries against the union

Where Problems Begin In OpenLink Data Spaces, 6 Collaborative apps all mapped to SIOC: Trivially becomes a union of everything, 1000+ lines of SQL Intelligently (once per app) becomes a Union of : © 2008 OpenLink Software, All rights reserved. select * from <ods> where {?s ?p ?o . ?s has_comment ?c . ?c has_author <xxx> } select post.* from post, comment, user where c_post = p_id and c_author = u_id and u_name = f ('xxx')

In OpenLink Data Spaces, 6 Collaborative apps all mapped to SIOC:

Trivially becomes a union of everything, 1000+ lines of SQL

Intelligently (once per app) becomes a Union of :

What One Must Know Mapping for integration is not trivial Be careful when mapping multiple tables/columns to one class/property Make URI schemes which encode type and source, so that senseless joins are not attempted if types not specified in query Understand what the mapping logic can and cannot optimize Understand what SQL can and cannot optimize View resulting SQL for sanity check © 2008 OpenLink Software, All rights reserved.

Mapping for integration is not trivial

Be careful when mapping multiple tables/columns to one class/property

Make URI schemes which encode type and source, so that senseless joins are not attempted if types not specified in query

Understand what the mapping logic can and cannot optimize

Understand what SQL can and cannot optimize

View resulting SQL for sanity check

SQL Extensions Mapping must work against any RDBMS/Schema, as is But there is Virtuoso SQL between the mapping and target RDBMS(s) Location and latency - conscious distributed cost model Breakup for making a wide result set into a row per property Inverse functions © 2008 OpenLink Software, All rights reserved.

Mapping must work against any RDBMS/Schema, as is

But there is Virtuoso SQL between the mapping and target RDBMS(s)

Location and latency - conscious distributed cost model

Breakup for making a wide result set into a row per property

Inverse functions

Use Cases OpenLink Data Spaces - Blog, Wiki, News, Social Network, Feed Aggregation, Tag Clouds, Bookmarks etc. OpenLink's own MIS - “total information awareness”: URI for any CRM Object, Account, Product, Support Case, Email etc.. Musicbrainz phpBB, Drupal, MediaWiki, WordPress, Bugzilla, and others. © 2008 OpenLink Software, All rights reserved.

OpenLink Data Spaces - Blog, Wiki, News, Social Network, Feed Aggregation, Tag Clouds, Bookmarks etc.

OpenLink's own MIS - “total information awareness”: URI for any CRM Object, Account, Product, Support Case, Email etc..

Musicbrainz

phpBB, Drupal, MediaWiki, WordPress, Bugzilla, and others.

OpenLink Software © 2008 OpenLink Software, All rights reserved. Thank You! http://virtuoso.openlinksw.com