To get instances of a class, the function collect-direct-instances-of retrieves the direct instances of a class, and the function collect-all-instances-of collects all instances from the class and its subclasses.

gx-user(31): (collect-direct-instances-of rdf:List)
(#<rdf:List rdf:nil>)
gx-user(32): (collect-all-instances-of rdfs:Class)
(#<rdfs:Class |rdfs:Resource|> #<rdfs:Class rdf:Alt>
 #<rdfs:Class rdf:Seq> #<rdfs:Class rdf:Bag>
 #<rdfs:Class rdfs:ContainerMembershipProperty>
 #<rdfs:Class rdfs:Literal> #<rdfs:Class rdfs:Container>
 #<rdfs:Class gx::shadow-class> #<rdfs:Class rdf:List>
 #<rdfs:Class gx::ill-structured-XMLLiteral> ...)

Note that gx:typep also accepts uris, QName symbols, and literal data in different semantics from cl:typep.

gx-user(7): (typep <http://somewhere/> rdfs:Resource)
t
t
gx-user(8): (typep "This is literal." rdfs:Resource)
t
t
gx-user(9): (typep 1 rdfs:Resource)
t
t
gx-user(10): (typep "This is literal." rdfs:Literal)
t
t
gx-user(11): (typep 1 rdfs:Literal)
t
t


The class-subclass relation in RDFS is defined with rdfs:subClassOf property, and the relation is similar to the CLOS class-subclass relation. However, gx:subtypep is available to test class-subclass relation in RDF semantics. Namely, it accepts uris, QName symbols, and data types in different way from cl:subtypep. See the followings.

The rdfs:subClassOf value of a resource class is retrieved using slot-value with slot-name rdfs:subClassOf.

5.3 rdfs:subPropertyOf

5.4  Properties and Slots

In RDF, the property is the first-class entity that exists as resource. Therefore, the property resource exists as CLOS object, an instance of the class rdf:Property, in SWCLOS.

An RDF triple, subject/predicate/object is realized by a subjective CLOS object, a slot name, and its slot value in SWCLOS. Therefore, getting an object value in a triple in RDF graph is equal to getting a slot value of the slot name corresponding to the property name.

Note that the line 2 in the following example just demonstrated rdfs:comment resource object as the first-class entity. The line 3 shows the role of property as predicate in triples. The line 4 shows the comment value on rdfs:comment. Please see the difference and discriminate a property as an resource object and a property as predicate or a role of binary relationship.

gx-user(2): rdfs:comment
#<rdf:Property rdfs:comment>
gx-user(3): (slot-value rdfs:Resource 'rdfs:comment)
"The class resource, everything."
gx-user(4): (slot-value rdfs:comment 'rdfs:comment)
"A description of the subject resource."

However, rdf:type has very special semantics. It specifies the type of object, and it is transformed to a class-instance relation in CLOS. Therefore, we get rdf:type value in several ways.

gx-user(2): (slot-value rdfs:comment 'rdf:type)
#<rdfs:Class rdf:Property>
gx-user(3): (class-of rdfs:comment)
#<rdfs:Class rdf:Property>
gx-user(4): (type-of rdfs:comment)
rdf:Property
gx-user(5): (-> rdfs:comment rdf:type)
rdf:Property


The function '->' allows users to traverse over an RDF graph according to a given path and return the value (node name or literal) at the arrival point.

5.5  Adding Resource Objects and Forward Reference

Figure 5.2 RDF Graph in Wine Ontology

The followings are an example to create the RDF graph shown in Figure 5.2.

At the beginning of the example above, a lisp package named 'vin' was created for Wine Ontology. Then, vin:ElyseZinfandel, whose maker is vin:Elyse, was defined. Note that all of 'vin' vocabulary in Wine Ontology are to be interned in 'vin' package before reading as QName. Otherwise, when you input a new lisp symbol as QName, you must use double colons, because you have no way to make exported symbols directly with neither calling export function nor defining them at the time of the package definition. Since SWCLOS interprets lisp symbols at the position of resources as QName and automatically exports them, then you may specify the QName symbols with one colon afterwards.

5.6  Adding Slots

In class-based Object-Oriented Programming Language like CLOS, slot structures in an instance must be defined before making the instance. However, in RDF, a property as predicate and its value can be defined at any RDF graph node (subject) within the domain restriction on the property. Therefore, it is enabled to add any slot (pair of role and filler) to any resource object without the explicit slot definition in the class. SWCLOS automatically adds the new slot definition in the class on the demand of new slot addition to an individual.

There is no special function for users to add new slots into objects in SWCLOS. Instead you can add new slots using defIndividual or defConcept macro, piecewisely. SWCLOS accepts such piecewise and multiple definitions for multiple slots on a resource. After the above example, you can add a new slot (vin:hasColor vin:Red) to vin:ElyseZinfandel as follows.

5.7  Adding Slot Values

Setting a slot value must show very different behaviors in SWCLOS. (setf slot-value) is available but it does not overwrite an old value. However, a new slot value must be added into slot in the semantics of RDF and the principle of monotonicity. So, put-value is provided for RDF semantics. It just adds a new value into the slot value. Precisely, if both an old value and a new value are not a list and different from each other, the result of adding is a list of old and new value. If both are a list, the result is a union of both. If one of them is not a list, it is added (adjoin) to another value as a set element. This is from the monotonicity principle in Semantic Webs.

When you add same value that is already stored in the slot, nothing happens.

5.8  Adding Multiple Types

A CLOS object belongs to only one class. However, an instance in RDF may be a member of multiple classes. In order to solve this problem, we set up an invisible class that is an instance of metaclass gx::shadowed-class. For example, suppose SaucelitoCanyonZinfandel1998 in Wine Ontology is an instance of Zinfandel and Vintage, SWCLOS set a shadowed-class named Zinfandel.0 that has Zinfandel and Vintage as its superclass.

5.9  Extension of property and slot definition