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Jaki poziom szczegółowości projektu? Na próbę fragment o RDF - czy może być tak?
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Draft for my project
Part 1. Attributes representation in different markup languages
To start with...
While talking about attribute-based languages we can recognize the following types of logic:
AAL – Attributive Logic, i.e. attributive logic with atomic values of attributes only
SAL – Set Attributive Logic, i.e. attributive logic with set values of attributes
VAAL – Variable Atomic Attributive Logic, i.e.attributive logic with atomic values of attributes incorporating variables
VSAL - Variable Set Attributive Logic, i.e.attributive logic with set values of attributes incorporating variables
The alphabet and the crucial question:What is an attribute?
RDF - Resource Description Framework
RDF identifies things using Web identifiers (URIs)
RDF is written in XML. The language is called RDF/XML.
The main elements of RDF are the root element, <RDF>, and the <Description> element, which identifies a resource.
<rdf:RDF> is the root element of an RDF document. It defines the XML document to be an RDF document. It also contains a reference to the RDF namespace. <rdf:RDF xmlns:rdf=„
http://www.w3.org/1999/02/22-rdf-syntax-ns#”
The <rdf:Description> element identifies a resource with the rdf:about attribute. This element contains elements that describe the resource.
Attributes representation
„RDF is based on the idea that the things being described have properties which have values, and that resources can be described by making statements that specify those properties and values. RDF uses a particular terminology for talking about the various parts of statements.” (W3C RDF Primer)
Attributes are represented in RDF in a form of RDF Triples (subject, predicate, object) where subject denote the resource being described, predicate indicate the name of the attribute and object points to the attribute (predicate) value. RDF statements (triples) consist of subject, predicate and object which all are identified by URIs.
Part of an RDF triple | Can be |
Subject | URI, blank node |
Predicate | URI |
Object | URI, literal (constant values, plain or typed), blank node |
RDF uses VSAL
http://www.w3.org/TR/rdf-concepts/#dfn-blank-node
sets of attributes cannot be defined in a single RDF triple, because attributes in RDF are represented as binary predicates only. However, it is possible to do that using RDF Container Elements (<rdf:Bag> and <rdf:Seq>) or RDF Collections. To define sets of attributes we create a new resource (which may either be a blank node or a resource with a URIref). The resource is given an rdf:type property whose value is one of the predefined resources rdf:Bag, rdf:Seq, or rdf:Alt . Then the members of the container can be described by defining a container membership property for each member with the container resource as its subject and the member as its object.
http://www.w3.org/TR/rdf-primer/#containers
RDF/XML notation
Triples of the Data Model (an example from W3Schools.):
To avoid using URI all around we use namespaces which we define as follows: xmlns:si=„http://www.recshop.fake/siteinfo#”
In RDF/XML attributes (properties of subjects) can be defined in three ways
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" <!-- rdf namespace -->
xmlns:si="http://www.recshop.fake/siteinfo#"><!-- other namespace (eg. Our own website's)>
<rdf:Description rdf:about="http://www.w3schools.com/RDF"> <!-- subject identifed with a resource by rdf:about attribute -->
<si:author>Jan Egil Refsnes</si:author> <!-- property and its value -->
<si:homepage>http://www.w3schools.com</si:homepage> <!-- another property and its value -->
</rdf:Description>
</rdf:RDF>
When you parse the example above with a RDF Validator, the result will look something like this
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