RDF Storage and Retrieval Systems Jan Pettersen Nytun

RDF Storage and Retrieval Systems Jan Pettersen Nytun, Ui. A 1

S P O Federating Data [1] The common standards simplifies the issue of federating data that are housed in multiple RDF stores, possibly coming from different vendor sources. Jan Pettersen Nytun, Ui. A, page 2

S P O DATA FEDERATION [1] • The RDF data model was designed from the beginning with data federation in mind. Information from any source is converted into a set of triples so that data federation of any kind—spreadsheets and XML, database tables and web pages—is accomplished with a single mechanism. Jan Pettersen Nytun, Ui. A, page 3

S P O SPARQL 1. 1 Federated Query Extension - SERVICE • This extension allows a query author to direct a portion of a query to a particular SPARQL endpoint. • Results are returned to the federated query processor and are combined with results from the rest of the query. Jan Pettersen Nytun, Ui. A, page 4

S P O PREFIX : <http: //example/> PREFIX dc: <http: //purl. org/dc/elements/1. 1/> SELECT ? a FROM <mybooks. rdf> { ? b dc: title ? title. SERVICE <http: //sparql. org/books> { ? s dc: title ? title. ? s dc: creator ? a } } Jan Pettersen Nytun, Ui. A, page 5

S P O RDF Store [1] Jan Pettersen Nytun, Ui. A, page 6

S P O Possible Generic Architecture of an RDF Store [2] Jan Pettersen Nytun, Ui. A, page 7

S P O Admin Module [2] • Gives functionality for adding and deleting data from the RDF store. • Loading data from files requires parsing and validating RDF, consequently an RDF parser and an RDF validator are usually part of the admin module. Jan Pettersen Nytun, Ui. A, page 8

S P O Query Module and Export Module [2] • Query module handles queries to the RDF store. Implements a parser and handler for one query language. • Export module allows a dump of the RDF store into files for data exchange with other systems. Jan Pettersen Nytun, Ui. A, page 9

S P O The modules can be accessed locally or remotely, e. g. using SOAP or RMI. This is why the highest layer in the middleware contains protocol handlers that can manage different access modes. [2] Jan Pettersen Nytun, Ui. A, page 10

S P [3] O Jan Pettersen Nytun, Ui. A, Ontologies, page 11

S P O RDF STORE [1] • An RDF store typically includes a query engine (SPARQL). • RDF allows easy merging of data sets (in contrast to relational data stores). • RDF stores comes in many flavors: Custom programmed database solutions, fully supported off-the-shelf products, … Jan Pettersen Nytun, Ui. A, page 12

S P O Conceptually the simplest relational implementation of a triple store [1] • A triple store is designed to store and retrieve triple collections of strings (i. e. , Subject-Predicate-Object statements). Each RDF statement is stored as a single row in a three column table. • Since this fits in a relational database representation, it can be accessed using conventional relational database tools such as SQL. Jan Pettersen Nytun, Ui. A, page 13

S P O [1] Jan Pettersen Nytun, Ui. A, page 14

S P O Simples Generic Schema: One table with three columns named Subject, Predicate and Object Advantage: No restructuring is required if the ontology changes (e. g. , new classes, etc. , realized by a simple INSERT command in the table). Disadvantage: Performing a query means searching the whole database and queries involving joins become very expensive. Jan Pettersen Nytun, Ui. A, page 15

S P O Normalized triple store – a more advanced generic schema [2] • Requires significantly less storage space. Jan Pettersen Nytun, Ui. A, page 16

S P O References [1] Chapter 4 Semantic Web application architecture - Semantic Web for the Working Ontologist, Second Edition: Effective Modeling in RDFS and OWL, May 20, 2011, by Dean Allemang, James Hendler [2] RDF Storage and Retrieval Systems Alice Hertel, Jeen Broekstra, and Heiner Stuckenschmidt Found in: Steffen Staab - Rudi Studer (Eds. ) Handbook on Ontologies Second Edition [3] Understanding Computers: Today and Tomorrow, 13 th Edition Chapter 14: Databases and Database Management Systems. Published by Sonny Syms Jan Pettersen Nytun, Ui. A, page 17