I have an Object Property IsMarriedWith, I want to create a Class "Single" to get non married individuals, I defined its "Equivalent To" like this:
IsMarriedWith max 0 Thing
And i also tried this:
not (IsMarriedWith min 1 Thing)
But none of those expressions returns a result, how to define this class?
Related
How can we access a property value within a #classmethod? For example:
class Account(polymodel.PolyModel):
someprop = ndb.StringProperty(required=True)
#classmethod
def get_or_create_someprop(cls):
if not cls.someprop:
# create someprop
else:
return cls.someprop
In this example code above, I am trying create someprop if it doesn’t exist, or return it if it already exists. I assumed that the above code would achieve this. However, the first step I need to do is access the someprop value from within the classmethod. Using cls.someprop does not actually return the value of someprop but instead returns StringProperty('state').
I have tried to use this and self which are undefined.
So, is it possible to access a property value of an entity using a classmethod? If so, how?
In general you cannot do this from a class method because a property belongs to an object, i.e. an instance of the class (the class is just the object generator). In other words you need the self argument to refer to the object and its properties.
In your particular case the class is an entity model (the blueprint for creating entities), not an entity and you can only refer to a property of an entity itself.
But you should be able to achieve what you seek simply by not declaring it a class method - then it becomes a method of the object/entity and in that case you can reference the entity's property via self instead of cls: self.someprop.
I'd make the check a bit more specific, though, to cover the case in which the property has a value like 0 or an empty string which is interpreted by python as False in a logical check: if self.someprop is None instead of if not self.someprop.
The functional object property axiom - here in functional syntax - has the form
FunctionalObjectProperty(P)
P is an Object Property Expression, which is one of:
a named object property (PN). Example: FunctionalObjectProperty(:hasBase)
the owl:topObjectProperty
the owl:bottomObjectProperty
an inverse property. Example: FunctionalObjectProperty(ObjectInverseOf(:isBaseOf))
The first is expected. What's the use of the three other variants? These seem to only increase the complexity of parsers, reasoners and APIs. (Yes, marginally.)
The last looks redundant since OWL has an "InverseFunctionalObjectProperty". And who declares top- or bottomObjectProperty as functional ?
I searched through ontologies like geneontology.org. So far, they use nothing else than a named property (PN) as parameter.
Anyway, OWL allows P here, and I may miss the forest for the trees. What is it good for ?
Remark:The same can be asked for other unary property axioms like SymmetricObjectProperty.
See: https://www.w3.org/2007/OWL/refcard
This definition is used in OWL to define what the language syntax considers correct. However there can be some language constructs that are broadly used and other that are syntactically correct but have limited usage.
The definition of the FunctionalObjectProperty axiom allows one to state that an object property expression is functional — that is, that each individual can have at most one outgoing connection of the specified object property expression. 1
The syntax definition of FunctionalObjectProperty is:
Functional Object Properties:
FunctionalObjectProperty := 'FunctionalObjectProperty' '('
axiomAnnotations ObjectPropertyExpression ')'
This definition refers to the ObjectPropertyExpression which is defined as follows.
Object Property Expression definition
ObjectProperty := IRI
ObjectPropertyExpression := ObjectProperty | InverseObjectProperty
InverseObjectProperty := 'ObjectInverseOf' '(' ObjectProperty ')'
This basically mean that there are 2 ways to define an object property.
The first way is to directly define an IRI as an object property.
The second way is to indirectly define an object property as the inverse of an already defined object property.
The difference can be demonstrated in these examples:
Example A: FunctionalObjectProperty(:isGoodFor)
Example B: FunctionalObjectProperty(ObjectInverseOf(:isBaseOf))
The Example A uses an existing Object Property :isGoodFor while the Example B uses the inverse of the defined Object Property :isBaseOf without defining an IRI for it.
The syntax definition for ObjectPropertyExpression includes any Object Property IRI, since it does not exclude it. Therefore the TopObjectProperty and BottomObjectProperty are syntactically valid choices.
So the following are syntactically valid:
FunctionalObjectProperty(owl:topObjectProperty)
FunctionalObjectProperty(owl:bottomObjectProperty)
However owl:topObjectProperty and owl:bottomObjectProperty have predefined semantics in OWL2. So while the above statements are syntactically correct, it would not be a good practice to use them.
Definitions of TopObjectProperty and BottomObjectProperty
Owl defines 2 built-in object properties with the IRIs owl:topObjectProperty and owl:bottomObjectProperty. And have predefined semantics.
The object property with IRI owl:topObjectProperty connects all possible pairs of individuals.
The object property with IRI owl:bottomObjectProperty does not connect any pair of individuals.
In OWL, is there a way to state that an individual of a particular class must be related to another individual via a specific object property?
For example, I would like to state that:
forall(x) Object(x) -> exists(y) Shape(y) ^ hasShape(x, y)
i.e., "For all objects, there exists a shape that is the shape of the object."
so that if there is an individual of the type Object that has no shape associated with it, a reasoner would find it to be inconsistent.
I tried an axiom:
Object SubClassOf hasShape min 1 Shape
but it's not working.
It seems like the issue is because Object Property in OWL has no identity, but is there a workaround for this issue?
(I'm using Protege 5.2.0)
You are correct that the meaning of Object SubClassOf hasShape min 1 Shape is that every individual of Object is associated with an individual of Shape via the hasShape property.
So if you create an individual x of type Object without x being associated with an individual of Shape, why does the reasoner not determine that your ontology is inconsistent? The reason for this is due to the open world assumption. Informally it means that the only inferences that the reasoner can make from an ontology is based on explicit information stated in the ontology or what can derived from explicit stated information.
When you state x is an Object, there is no explicit information in the ontology that states that x is not associated with an individual of Shape via the hasShape property. To make explicit that x is not is such a relation, you have to define x as follows:
Individual: x
Types:
Object,
hasShape max 0 owl:Thing
Btw, this problem has nothing to do with identity as you stated.
One solution I found was to make the ontology "closed world", by making owl:Thing equivalent to the set of all individuals defined so far.
Is it possible to express the meaning of xs:unique in OWL?
Say, I define a property hasID whose range is integer. 2 different individuals A and B could not have the same ID. So you don't have A hasID 1 and B hasID 1 at the same time.
That's an inverse functional property. In OWL, there are inverse functional object properties, such that if p is an inverse functional object property then p(A,C) and p(B,C) imply A = B.
From the specification:
9.2.8 Inverse-Functional Object Properties
An object property inverse functionality axiom
InverseFunctionalObjectProperty( OPE ) states that the object property
expression OPE is inverse-functional — that is, for each individual x,
there can be at most one individual y such that y is connected by OPE
with x. Each such axiom can be seen as a syntactic shortcut for the
following axiom:
SubClassOf( owl:Thing ObjectMaxCardinality( 1 ObjectInverseOf( OPE ) ) )
However, OWL doesn't have inverse functional datatype properties. This is the subject of What's the problem with inverse-functional datatype properties? on answers.semanticweb.com. (I'm providing a link to the WaybackMachine's archived version of that page, since the actual site seems to be down.)
In OWL 1; What is the difference between:
Parent subclassOf hasChildren min 1 Thing
and
Parent subclassOf hasChildren some Thing
Are they equivalent as both of them assert that each Parent instance must has at least one value from any class through hasChildren? as we don't specify a particular range for the someValuesFrom restriction?
In OWL 1; What is the difference between:
Parent subclassOf hasChildren min 1 Thing
and
Parent subclassOf hasChildren some Thing
OWL1 doesn't have qualified cardinality restrictions. You can't say
property min n Class
in OWL1. You can use unqualified cardinality restrictions (1), and qualified existential restrictions, like:
property min n
property some Class
In OWL 2, where you do have qualified cardinality restrictions, you have the ability to write
property min n Class
and you're absolutely right that the following are equivalent:
property min 1 Class
property some Class
and as a special case, the following are equivalent:
property min 1 owl:Thing
property some owl:Thing
The someValuesFromin OWL is equivalent to the existential quantifier in predicate logic:
In predicate logic, an existential quantification is a type of quantifier, a logical constant which is interpreted as "there exists," "there is at least one," or "for some." It expresses that a propositional function can be satisfied by at least one member of a domain of discourse. In other terms, it is the predication of a property or relation to at least one member of the domain. It asserts that a predicate within the scope of an existential quantifier is true of at least one value of a predicate variable.
Keeping this in mind, please refer to the definition of Restirction:
OWL Lite allows restrictions to be placed on how properties can be used by instances of a class.
And the definition of Cardinality:
OWL (and OWL Lite) cardinality restrictions are referred to as local restrictions, since they are stated on properties with respect to a particular class. That is, the restrictions constrain the cardinality of that property on instances of that class.
In OWL, someValuesFrom has been defined as:
The restriction someValuesFrom is stated on a property with respect to a class. A particular class may have a restriction on a property that at least one value for that property is of a certain type.
And minCardinality has been defined as:
If a minCardinality of 1 is stated on a property with respect to a class, then any instance of that class will be related to at least one individual by that property.
So, although logically they are the same, they represent different ideas.