1. Sesame A generic architecture for storing and querying RDF and RDFs 2008. 12. 08 Written by Jeen Broekstra, Arjohn Kampman Summarized by Gihyun Gong

2. Copyright  2008 by CEBT About Sesame project  Developed by IST On-To-Knowledge project that ran from 1999 to 2002 Focused on Knowledge and Contents Technology, Software Technology  Now, it is further developed and maintained by Aduna in cooperation with NLnet Foundation, developers from Ontotext

3. Copyright  2008 by CEBT What is Sesame?  Sesame is an open source Java framework for storing, querying and reasoning with RDF and RDF Schema  It can be used as: Standalone Server: A database for RDF and RDF Schema Java Library: For applications that need to work with RDF internally  Sesame is similar to Jena Supports triple storage Supports reasoning Supports Web services

4. Copyright  2008 by CEBT Sesame’s Architecture Repository Repository Abstraction Layer (RAL) Admin ModuleExport ModuleQuery Module HTTP Protocol HandlerSOAP Protocol Handler Sesame SOAP HTTP Clients

5. Copyright  2008 by CEBT The Repository  DBMSs Currently, Sesame is able to use – PostgreSQL – MySQL – Oracle (9i or newer)  Existing RDF stores  RDF files  RDF network services Using multiple sesame server to retrieve results for queries This opens up the possibility of a highly distributed architecture for RDF storing and querying

6. Copyright  2008 by CEBT Repository Abstraction Layer (RAL)  RAL offers stable, high-level interface for talking to repositories  It is defined by an API that offers these functionalities: Add data Retrieve data Delete data  Data is returned in streams (Scalability) Only small amount of data is kept in memory Suitable for use in highly constrained environments such as portable devices  Caching data (Performance) E.g. caching RDF schema data which is needed very frequently

7. Copyright  2008 by CEBT Admin Module  Allows inserting or deleting RDF data in repository  Retrieves its information from an RDF(S) source, and parses it using an RDF parser  Checks each (S, P, O) statement for consistency and infers implied information if necessary for instance: If P equals type, it infers that O must be a class. If P equals subClassOf, it infers that S and O must be classes. If P equals subPropertyOf, then it infers that both S and O must be properties. If P equals domain or range, then it infers that S must be a property and O must be a class

8. Copyright  2008 by CEBT Query Module  Evaluates RQL queries posed by the user  It is independent of the underlying repository Can not use optimizations and query evaluations offered by specific DBMSs  RQL queries are translated into a set of calls to the RAL e.g. when a query contains a join operation over two subqueries, each of the subqueries is evaluated, and the join operation is then executed by the query engine on the results

9. Copyright  2008 by CEBT RDF Export Module  This module allows for the extraction of the complete schema and/or data from a model in RDF format  It supplies the basis for using Sesame with other RDF tools

10. Copyright  2008 by CEBT SeRQL (Sesame RDF Query Language)  Extension of RQL  Some of the built-in predicates: {X} serql:directSubClassOf {Y} {X} serql:directSubPropertyOf {Y}  Some of the built-in functions isLiteral() isResource()

11. Copyright  2008 by CEBT Important Features of Sesame  Portability It is written completely in Java  Repository independence Provides RAL  Extensibility Other functional modules can be created and be plugged in it  Flexible communication by using protocol handlers The architecture separates the communication details from the actual functionality through the use of protocol handlers

12. Copyright  2008 by CEBT Using PostgreSQL as Repository  PostgreSQL is an open-source object-relational DBMS  It supports subtable relations between its tables  Subtable relations are also transitive  These relations can be used to model the subsumption reasoning of RDF schema.

13. Copyright  2008 by CEBT Example RDF Schema & Data Writer FamousWriter …/ISBN00023423442…/twain/mark BookhasWritten Schema type hasWritten type subClassOf rangedomain Data

14. Copyright  2008 by CEBT Storing Schema (PostgreSQL) uri Resource Writer FamousWriter Book uri hasWritten sourcetarget Writer FamousWriter Book Resource Writer Resource sourcetarget hasWrittenWriter sourcetarget hasWrittenBook sourcetarget ClassSubClassOfSubPropertyOf PropertyDomainRange

15. Copyright  2008 by CEBT uri …/ISBN00023423442 uri …/twain/mark sourcetarget …/twain/mark…/ISBN00023423442 FamousWriter Writer Book Resource hasWritten Storing Data (PostgreSQL)

16. Copyright  2008 by CEBT Using MySQL

17. Copyright  2008 by CEBT Scalability Issues  An experiment using Sesame: Uploading and querying a collection of nouns from Wordnet (http://www.semanticweb.org/library)http://www.semanticweb.org/library – Consisting of about 400,000 RDF statements. Using a workstation (Sun UltraSPARC 5, 256MB RAM) Uploading the Wordnet nouns took 94 minutes. Querying was quite slow (in MySQL) – Because data is distributed over multiple tables, and retrieving data needs doing many joins on tables

18. Copyright  2008 by CEBT Future Work  Transaction Rollback Support Aims an ACID compliant storage system  Versioning support  Adding and extending functional modules Support ‘Update’ operation  DAML+OIL support

19. Copyright  2008 by CEBT Comparison with others  Database Compatibility  API Compatibility

20. Copyright  2008 by CEBT Comparison with others  Tool Support  Query Language Support

21. Copyright  2008 by CEBT Comparison with others  Reasoning level and Scalability SystemReasoningScalability JenaOWL-DL170 million SesameRDFS7 million MulgaraOWL-Lite50 million AllegroGraphOWL100 million

22. Copyright  2008 by CEBT References  Sesame : A Generic architecture for storing and querying RDF and RDFs, http://sesame.aidministrator.nl/http://sesame.aidministrator.nl/  Create Scalable Semantic Applications with Database-Backed RDF Stores, www.devx.comwww.devx.com  OpenRDF - Sesame Benchmark, http://bklab.snu.ac.kr/blog/kwangsub/53 http://bklab.snu.ac.kr/blog/kwangsub/53