1. Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema Jeen Broekstra, Arjohn Kampman, and Frank van Harmelen 정홍석 2005.01.20

2. 2 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema Introduction Sesame : architecture for storage and querying of RDF and RDFS information  allows persistent storage of RDF and RDFS  provides access methods to export and querying modules

3. 3 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 1. The Need for an RDFS Query Language consideration for querying  at the syntactic level XML documents  not necessarily true  non-XML syntaxes for RDF exist  at the structure level consist of a set of triples  at the semantic level constitute one or more graphs with partially predefined semantics

4. 4 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 참고 : XML 과 RDF 의 차이 XML 기반 RDF 기반 중심 연구 방향 웹에서 정보를 작성하고 교환하기 위한 문서 포맷 ( 문법중심 ) 웹에서 정보에 관한 의미와 추론 을 기술하기 위한 모델 ( 의미중심 ) 활용을 위한 연구방안 XML 에 의미를 부여하기 위한 연구 다양한 소스로부터 데이터 통합 예 ) 도메인 온톨로지 ( 표준화 ) 컴퓨터가 처리할 수 있도록 의미 를 문법으로 표현하기 위한 연구 예 ) RDF 의 XML serialization 두 언어의 차이 OrderedNot ordered 클래스와 프로퍼티 구분이 있음 예 ) 회사는 클래스에 회사이름은 회사에 대한 속성에 들어감 클래스와 프로퍼티가 혼용되어 사용됨 예 ) 회사, 회사 이름이 모두 엘리먼트에 나타날 수 있음 트리구조그래프 구조 관련 표준 XML 스키마, XQuery RDF 스키마, RQL

5. 5 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema Querying at the Syntactic Level(1/3) RDF is kind of XML  any RDF model can be written down in XML notation.  can query RDF using an XML query language But  RDF data model is different from the XML tree structure  very hard to query.

6. 6 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema Querying at the Syntactic Level(2/3) Hans Ottosson EnersearchAB …/hohome.html…/enersearch.html “Hans Ottosson”“Enersearch AB” worksFor legalNamehasName example

7. 7 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema Querying at the Syntactic Level(3/3) RDF query language  graph: edges and nodes are labeled  query ‘Give me all the relationships that exist between Hans Ottosson and Enersearch AB’ XML query language  tree: nodes are labeled  query: cannot query relation Give me all the elements nested in a Description element with an about attribute with value “http://www.enersearch.../hohome.html”, of which the value of its resource attribute occurs elsewhere as the about attribute value of a Description element that has a nested element title with the value “Enersearch AB ”  not unique syntax

8. 8 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 1.2 Querying at the Structure Level RDF document represents a set of triples  query using triple SELECT ?x FROM somesource WHERE (rdf::type ?x VicePresident)  is this query possible? SELECT ?x FROM somesource WHERE (rdf::type ?x Employee) EmployeeCompany …/hohome.html…/enersearch.html worksFor type subClassOf VicePresident worksFor type domainrange SCHEMA DATA

9. 9 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 1.3 Querying at the Semantic Level(1/2) Means to query at the semantic level  querying the full knowledge that a RDFS description entails not just the explicitly asserted statements Compute and store the closure of the given graph as a basis for querying Let a query processor infer new statements as needed per query

10. 10 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 1.3 Querying at the Semantic Level(2/2) RQL(the RDF Query Language)  defined by core queries: Class, Property, subClassOf… basic filters: select-from-where Functional composition of queries  additional function query the structure of the subclass hierarchy  ex) subClassOf(Employee), subClassOf^(Employee) specify a path expression  ex) select Y, $Y from VicePresident{X}.worksFor{Y:$Y}

11. 11 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 2. Sesame Architecture Overview  DBMS-independent SAIL API  different ways to communicate protocol handler module  Query Module  Admin Module  Export Module

12. 12 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 2.1 The RQL Query module The Sesame version of RQL features better compliance to W3C specifications  support for optional domain and range restrictions Query parsing and optimization

13. 13 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 2.2 The Admin Module Two main functions  incrementally adding RDF data/schema information  clearing a repository partial delete function is not yet available

14. 14 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 2.3 The RDF Export Module Export the contents of a repository formatted in RDF Able to selectively export the schema, the data, or both

15. 15 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema A set of Java interfaces between three modules and repository Main design principles  Define a basic interface storing, retrieving, deleting  Abstract from the actual storage mechanism  Be usable on low-end hardware like PDAs but also offer enterprise level capability  Be extendable to other RDF-based languages like DAML+OIL 3.The SAIL API(1/3)

16. 16 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 3.The SAIL API(2/3) Other proposals under development  share characteristics with Jena toolkit Redland Application Framework Weighted on the retrieval side  offers methods querying class property subsumption domain and range restriction

17. 17 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 3.The SAIL API(3/3) Sesame offers several implementations of the SAIL API  SQL92SAIL aim: to be able to connect to any RDBMS inference module for RDFS concurrency handling  support concurrency control for any type of repository

18. 18 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 4. Experiences URL: http://www.openrdf.orghttp://www.openrdf.org Database platforms  PostgreSQL, MySQL Protocol  HTTP SAIL  SQL92SAIL, PostgreSQL SAIL, MySQL SAIL

19. 19 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 4.2 RDFS in Practice Ambiguity  Formal Model Theory for RDF the RDF Core Working Group specify model and schema semantics more precisely and include a formal procedure for computing

20. 20 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 4.3 PostgreSQL and SAIL PostgreSQL  object-relational DBMS  support sub-table relations between its tables  ‘resources’  map all resources, literal values and ID  difficult to add table  caching

21. 21 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 4.3 MySQL MySQL  the database schema does not change when the RDFS changes  advantage where RDFS is unstable

22. 22 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema 5. Future Work Transaction Rollback Support  support rollback when error occurs Versioning Support  support various platforms Adding and Extending Functional Modules  updating, partial deleting, visualization … DAML+OIL Support

23. 23 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema

24. 24 Sesame: A Generic Architecture for Storing and Querying RDF and RDF Schema