Faceted Views Over Large Scale Linked Data

OpenLink Virtuoso - Faceted Views Faceted Views over Large-Scale Linked Data Orri Erling Program Manager - Virtuoso Development Team, OpenLink Software

Dimensions of Web Usage
Web 1.0: Publishing for All (Citizen Publisher) via Web Sites
Web 2.0: Commentary for All (Citizen Journalist) via Blogging and Social Networks, with User Generated Content across Data Silos
Web 3.0: Analysis for All (Citizen Analyst), via Linked Data enabling Data Mobility and Meshing, Your Data Is Your Statement, Applications Float on a Cloud of Data across a federation of HTTP accessible Data Spaces
Meanwhile, in the DBMS world, ad hoc data access and manipulation has consistently won over hard-coded alternatives e.g.: SQL over CODASYL, Today we see Linked Data as delivering the "ad hoc" factor in "best of both worlds" fashion, relative to alternatives (including RDBMS), across the Web and/or within Intranets & Extranets.

The Challenges
Scale of Instance Data - 10^9 - 10^11 Triples
Scale of Ontology 100,000's of Classes
Faceted Browsing, Text and Structure
Deployment and Provisioning

It Is Not Only About The Warehouse
Up until now, you design the warehouse for the application, load the data, make a data island
With Linked Data, the warehouse is self-filling, based on published data using terms from commonly shared vocabularies
Virtuoso facilitates the above by integrated RDF-ization middleware; you populate the warehouse as you query, and system simply gets smarter in line with your natural work patterns.

It Is Not Only About Publishing Your Data
Having secrets does not mean using a secret language
Private environments still benefit from common vocabularies and terms
People and organizations publish anyway: Now it is about publishing for use in applications and integration, internet, extranet, intranet
Linked data and Virtuoso deliver on the Data Spaces concept: Express any statement for which there is a vocabulary and the data exposed by the statement can be found, joined and processed (e.g. Meshups). Basically, The network is the database.

Solutions
Virtuoso 6, Single Server and Cluster Editions
SPARQL and SQL With The Right Extensions for serious BI style analytics
Integrated Web Services Platform, Suite of RDF-izers (Extractor & LOD Cloud Lookup variants)
Server Hosted Facet Browsing Service (via REST API), Entity Ranking, Other Building Blocks for Web 2.0 Style Development

The lod.openlinksw.com Demo
4.2 GTriples on 2 Commodity Servers
Full Text and Structured Querying
SPARQL End Point
Faceted Browsing Interface for Quick Discovery and Simple Report Composition
Usage Statistics across Source & Reference Graph IRIs, plus IFP and owl:sameAs usage stats
VoiD Graph Providing Rich Description of hosted Data Sets
If OpenLink does not host it with enough capacity or the right data, you can procure your own infrastructure and get the software from us. From now on, anybody who chooses can be a search and analytics player.

Technology
SPARQL Augmented With Run Time Inferencing
Entity Ranks for Better Search
Anytime Query Answering for Quick Approximate Results
A User Interface Combining Discovery and Query Building
Easy Web Services API's and SPARQL for Developing Applications

Technology

Run Time Taxonomies
No Materialization, Select Taxonomy At Query Time
Query Optimization Knows About Class and Property Hierarchies

Run Time Identity
Optionally Follow owl:sameAs links
Optionally consider any two sharing an IFP to be the same
No materialization, Control sameAs and IFP following at query time, at the triple pattern level
For Ad Hoc, Do Identity at Run Time
For Deep Analytics and Batch Processing, Normalize Identities at Load Time

Entity Ranking
References and the Rank of the Referrer Contribute to Rank, as In Web Search
Can Customize Weight By Graph, Predicate
Can Run Ranks on Selected Subsets
Ranks Are Calculated in a Batch Run

Entity Name Service
Autocompletion of URI's
Autocompletion of Label-Like Properties
Ranked List of Synonyms
Statistics on Where a URI is Defined and Where it is Referenced

Virtuoso Anytime Query Feature
Partial Results in Fixed Time
Useful for Interactive Browsing, Query Development over large data sets (e.g. LOD Cloud)
On public SPARQL end points, Protects Against DOS, still giving samples of the answers
Metering of query resource utilization

The LOD Cloud Faceted Search, Find, and Lookup Services
Access via Web Services, SPARQL
Developed in Virtuoso using SQL, SPARQL, and Stored Procedures
Part of Virtuoso 6.x Open Source Edition (Single Server Edition only)

Experience
If Data In Memory, Interactive Time and Linear Scale
RDF Aware Query Optimizer is Key
Parallel Execution Engine 1 Thread/Query/Partition
For Generic Linked Data, RDF Representation With 4 Indices, plus Full Text Indexing on Literal Objects
For Specialized Tasks, SQL + Stored Procedures With Parallel Programming Model (of course output will be Linked Data)
Unlimited Cross Partition Joining, Near Full Platform Utilization, and not a problem with the right message flow

Some Performance Data
Current Live Instance Setup: 2 Linux boxes with 2x4 core Xeons each with 32G RAM for a data set in excess of 4.2 Billion Triples
3.2 Million Single Triple Lookups Per Second
Load Rates over 100K Triples/sec
Entity Ranks for 4.2 GTriples in 30m/Iteration

Deployment
For Intermittent Use, 1TB of RAM, 256 Virtual Cores at EC2 is $1228 Per Day
For Purchase, Cluster of 1TB RAM, 120 Nehalem Cores Lists Around $75K
Rent of Buy? To Handle 10 GT 100% in RAM or 50 GT With Decent Working Set: * April 2009 US retail prices

Conclusions
Applications exploiting open data access across heterogenous data sources at Web Scale now within anyone's reach
Usable for public Web Sites or for in-house Business Analytics
Web enabled Open Data Access & Analysis for All!

Faceted Views Over Large Scale Linked Data

by OpenLink Software

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