Important Concepts from the W3C RDF Vocabulary/Schema Sungtae Kim SNU OOPSLA Lab. August 19, 2004

Contents  Introduction  RDF Vocabulary : Describing the Data  Core RDF Schema Elements  Refining RDF Vocabularies with Constraints  RDF Schema Alternatives

Introduction  RDF (Resource Description Framework) specification  Syntax specification  A way of describing data  Schema specification  Domain-neutral way of describing the metadata  Define element domain  Describe how these elements relate to one another

RDF Vocabulary : Describing the Data (1/3)  Metadata – data about data  Same specification can be used with many different domain  Concept of metadata’s role  Relational database  Store many different types of data by using metadata structures

RDF Vocabulary : Describing the Data (2/3)  Example  Changing of the domain  Domain-specific storage constructs become useless CUSTOMER PKCUSTOMER_ID CUSTOMER_ORDER PK,FK1 PK,FK2 CUSTOMER ID ORDER_ID ORDER PKORDER_ID

RDF Vocabulary : Describing the Data (3/3)  Multiple use of the same storage mechanism  Relational database schema defines below  Database tables  Primary and foreign key  Columns  Provide a domain-neutral description of information  Example  MS SQL Server  Same syntax for web resource  rdf:Description, not WEB-PAGE  RDF Schema  Provides the resources necessary to describe the objects and properties of a domain-specific schema -- a vocabulary used to describe objects and their attributes and relationships within a specific area of interest Table 1Table 2Table 3…. customerorderCustomer_order tableCol name1Col name2Col name3…. orderdatacount… customernameAddress… Schema table Schema column

Core RDF Schema Elements (1/16)  RDF Schema elements  Marked by a specific namespace  xmlns:rdfs=  Overview of the RDF Schema classes  rdfs:Resource  rdfs:Class  rdfs:Literal  rdfs:XMLLiteral  rdfs:Container  rdfs:ContainerMembershipProperty  rdfs:Datatype

Core RDF Schema Elements (2/16)  rdfs:Resource  All resources within RDF are implicitly member  rdfs:Class <rdf:RDF xmlns:rdf=“ xmlns:pstcn=“ Shelley Powers> Architeuthis Dux

Core RDF Schema Elements (3/16)  rdfs:Container  Superclass of all RDF container elements  rdf:Bag  rdf:Seg  rdf:Alt  rdfs:ContainerMembershipProperty  Resource is a member of a container  _1, _2, _3 and so on

Core RDF Schema Elements (4/16)  rdfs:Datatype  Class of all data types  Subclass of rdfs:Literal  rdfs:XMLLiteral  Allows to embed XML into the RDF/XML document  Subclass of rdfs:Literal  Instance of rdfs:Datatype  Class of all XML literals

Core RDF Schema Elements (5/16)  A few RDF classes  Cross the boundary between the metalanguage and instances of the same  rdf:Statement  Include as member al reified RDF statements  rdf:Bag, rdf:Seq, rdf:Alt  Used to group members  rdf:List  Has members all RDF lists  rdf:Property  Define the attributes that, in turn, describe the resource

Core RDF Schema Elements (6/16)  RDF Schema for Article <rdf:RDF xmlns:rdf=“ xmlns:rdfs=“ xmlns:pstcn=“

Core RDF Schema Elements (7/16)  Demonstrations of the RDF Schema Properties  RDF specification’s purpose  Purely to define resource and associated facts, and then provide a way to allow these resource/fact mappings to interact  RDF Schema specification’s purpose  Statement about each resource  Individual properties  Only difference between two  One is instance of business data (such as Article)  The other is metadata ( related to the RDF model)

Core RDF Schema Elements (8/16)  Core properties (from both the RDF and RDFS namespaces ) of RDF Schema  rdfs:subClassOf  rdfs:seeAlso  rdfs:member  rdfs:label  rdf:subject  rdf:object  rdf:rest  rdfs:range  rdfs:subPropertyOf  rdfs:isDefinedBy  rdfs:comment  rdf:type  rdf:predicate  rdf:first  rdfs:domain  rdf:value

Core RDF Schema Elements (9/16)  rdfs:subClassOf  Identify a class that is a subclass of another rdfs:subClassOf rdf:resource=“ /> rdfs:subClassOf rdf:resource=“ />

Core RDF Schema Elements (10/16)  rdfs:subPropertyOf <rdf:RDF xmlns:rdf=“ xmlns:rdfs=“ xmlns:pstcn=“ /rdf:RDF>

Core RDF Schema Elements (11/16)  rdfs:seeAlso  Another resource contains additional information

Core RDF Schema Elements (12/16)  rdfs:isDefinedBy  Identify the namespace for the resource Statement The class of RDF statement. Literal This represents the set of atomic values, eg. Textual string

Core RDF Schema Elements (13/16)  rdfs:member  Superproperty for each numbered container element  _1, _2, and so on  rdfs:comment  Provide human readability to an RDF model  Provide documentation of resources  rdfs:label  Provide a readable version of the resource’s name  Can attach xml:lang

Core RDF Schema Elements (14/16)  RDF Schema documentation elements <rdf:RDF xmlns:rdf=“ xmlns:rdfs=“ xmlns:pstcn=“ Unique Online article Article Online Article Title Article Primary author of article Author

Core RDF Schema Elements (15/16)  rdf:type  Define the type of resources  Usually assumed and is not explicitly given Primary author of article Author

Core RDF Schema Elements (16/16)  rdf:subject, rdf:predicate, rdf:object  Used with reification to explicitly define an RDF statement  rdf:first, rdf:rest  Explicitly define the relationships within a collection

Refining RDF Vocabularies with Constraints (1/2)  rdfs:domain  Associate a property with the resource  An RDF property can be used for more than one resource type <rdf:RDF xmlns:rdf=“ xmlns:rdfs=“ xmlns:pstcn=“ Unique Online article Article Online Article Title Article Primary author of article Author

Refining RDF Vocabularies with Constraints (2/2)  rdfs:range  Only one RDF range constraint can be attached to any property  Can use a master class for a property (more than one data type) <rdf:RDF xmlns:rdf=“ xmlns:rdfs=“ xmlns:pstcn=“ WebPage ExampleArticle Directory domainrange

RDF Schema Alternatives (1/2)  DTD(Document Type Declarations) & XML Schema <!ELEMENT Items(item*)

RDF Schema Alternatives (2/2)  RELAX NG Compact Syntax  Combination of DTD readability and W3C XML Schema data typing Items = element Items {item*} Item = element item {att.partNum, productName, quantity, USPrice, comment?, shipDate? } att.partNum = attribute partNum {text} productName = element productName {text} Quantity = element quantity {xsd:positiveInteger {maxExclusive=“100”}} USPrice = element USPrice {xsd:decimal} Comment = element comment {text} shipDate = element shipDate {xsd:date} Start = Items