CONTEXT IN GEOGRAPHIC KNOWLEDGE REPRESENTATION

More documents

Recommendations

Info

• w CANAL3 = {(hypernym, strip), (purpose, boats), (material/cover, water), (nature, manmade)};(Example 4)Which denotes a canal as a manmade strip of water for boats, does not fully comply with neither ofthe above definitions. Still, this does not mean that w CANAL3 of canal necessarily falls out of contextC of the given concept, only that in a possible world (other than the ones derived from each one ofthe definitions given), a canal could be defined likewise. To avoid implications or possible mishitswhen setting the context of a concept, we introduce at this point the notion of value specifier vs.Defining the value specifier (vs) for a geographic conceptThis index is used to provide constraints over the values that dimensions can take under specificcircumstances; in specific worlds.To give an example, for the previously defined canal a value specifier can be;vs = (purpose, {boats, irrigation}); (Example 5)This reads, canal is used for boats or irrigation and is true for the possible worlds that refer to thecontext of canal that complies with the definition of WordNet in relation to the dimension purpose.In the same way we set a specifier for a specific dimension, we can also, determine the union ofvalue specifiers, called hereinafter, Specifier (S), for the complete set of dimensions. Thus, for theconcept canal we can introduce the following:S CANAL1 = {(hypernym, {strip}), (purpose, {boats, irrigation}), (material/cover, {water}),(form/morphology, {long, narrow}), (nature, { })}; (Example 6)which not only provides the set of all possible worlds of canal that comply with the definition ofWordNet but also makes explicit the constraints under which the concept canal is defined in thecontext of the given terminological database. Notice that the empty set can also be part of S sinceall dimensions of context should be present therein even if their values are equal to zero. Similarly,the set of specifiers for the same concept as defined in DIGEST can be established as follows:S CANAL2 = {(hypernym, {way}), (purpose, {transportation}), (material/cover, {water}),(form/morphology, { }), (nature, {manmade, improved natural})}; (Example 7)OPERATIONS BETWEEN SPECIFIERSIn this section we introduce operations over Specifiers S which prove very useful for purposes ofontological reasoning, for semantic interoperability issues, for adequacy and completeness of theresulting ontologiesUnionWhy do we want the union of two or more Specifiers S? The answer is that, whenever we extend anontology, we incorporate knowledge from additional sources of information, therefore, the union ofSpecifiers S is useful in that sense. For the operation of union, we can state the following theorem:The union of Specifiers of a concept is equal to the Universe of that concept; (Th. 1).A proof of which can be given by:S CANAL1″ S CANAL2 = {(hypernym, {strip, way}), (purpose, {boats, irrigation, transportation}),(material/cover, {water}), (form/morphology, {long, narrow}), (nature, {manmade, improvednatural})}, (Example 8) / U CANAL (Example 1); (proof 1).Intersection
In ontologies’ integration, we are interested in determining the common features of a concept whichis ontologically defined in different ways. The intersection of Specifiers can give us the result ofsuch a comparison, returning a Specifier.For instance the intersection of examples 6 and 7, gives the following:S CANAL1 ≥ S CANAL2 = {(hypernym, { }), (purpose, { }), (material/cover, {water})}, (Example 9);Which shows that commonalities between the two definitions of canal can only be found in terms ofits cover or the material that it is made of; which is water, in this case. In addition, it should bepointed out that dimensions having the empty set as their values are not considered in theintersection since the determination of commonalities between the two definitions takes place notonly over values but also over dimensions.Except for its use in determining commonalities between two definitions, intersection over Specifierscan also be used in ontologies generation as a core Specifier, let us call it, which presents theminimum common ground of understanding over a concept’s attributes and substantiations. In otherwords it can present a point of reference for a concept’s definition in an ontology. It is obvious thatthe more semantically similar two definitions of the same concept are then the intersection of thetwo Specifiers includes more dimensions, which also have more common values.Equality – DifferenceIn accordance with intersection we can also define equality and difference between Specifiers andtherefore reason about similarity. It is obvious that equality holds when the set of dimensions andthe sets of their values of one Specifier are the same of the other;S 1 = S 2 when D 1 = D 2 , and v D1 = v D2Nonetheless, we propose a distinction between strong equality (SE) which is the one defined in theprevious definition, and weak equality (WE) which identifies common dimensions (semanticproperties and relations, according to our terminology; attributes), between Specifiers and does notinvolve common values;S 1 = S 2 when D 1 =D 2 ; weak equality (WE)Equality between Specifiers is quite uncommon because different communities use differentterminology for attributes and values.On the other hand, difference between Specifiers is quite common, due to different terminology anddistinct conceptualizations of the domain in questions. There is an interesting case of difference(SD), which holds when the intersection of two Specifiers returns the empty set. To give anexample, consider the following case:• Ditch is any small natural waterway (WordNet);• Ditch is a channel constructed for the purpose of irrigation or drainage (DIGEST).These definitions give the following Specifiers for WordNet and DIGEST, respectively:S DITCH1 = {(hypernym, {way}), (size, {small}), (material/cover, {water}), (nature, {natural})}; (Example10)S DITCH2 = {(hypernym, {channel}), (purpose, {irrigation, drainage})}; (Example 11)According to what is been defined previously, the intersection of the two Specifiers is:
Page 1 and 2: CONTEXT IN GEOGRAPHIC KNOWLEDGEREPR
Page 3: semantic relations and semantic pro
Page 7: 5. DIGEST The Digital Geographic In

CONTEXT IN GEOGRAPHIC KNOWLEDGE REPRESENTATION

Create successful ePaper yourself

Delete template?

Save as template?