# A Framework for the Evaluation of the Cultural Heritage Information Ontology
## 3 Evaluation Framework for the Cultural Heritage Information Ontology
#### New Ontology Metrics for Interoperability
It contains 42,628 internal resources in axioms and 25,946 external resources in axioms. The DOAP vocabulary uses the following external namespaces:  
* xmlns:vs = [[http://www.w3.org/2003/06/sw-vocab-status/ns#](http://www.w3.org/2003/06/sw-vocab-status/ns#)]([http://www.w3.org/2003/06/sw-vocab-status/ns#](http://www.w3.org/2003/06/sw-vocab-status/ns#));
* xmlns:foaf = [[http://xmlns.com/foaf/0.1/#](http://xmlns.com/foaf/0.1/#)]([http://xmlns.com/foaf/0.1/#](http://xmlns.com/foaf/0.1/#));
* xmlns:dc = [[http://purl.org/dc/elements/1.1/#](http://purl.org/dc/elements/1.1/#)]([http://purl.org/dc/elements/1.1/#](http://purl.org/dc/elements/1.1/#)). It imports FOAF (_owl:imports rf:resource = \"[[http://xmlns.com/foaf/0.1/index.rdf](http://xmlns.com/foaf/0.1/index.rdf)]([http://xmlns.com/foaf/0.1/index.rdf](http://xmlns.com/foaf/0.1/index.rdf))\"_), which adds all FOAF concepts to the DOAP during evaluation but then only a small number of the concepts are used. The _CPOnto_ value for the DOAP ontology is 0.06. It contains 1610 internal resources in axioms and 103 external resources in axioms. The composability metrics for EDAM and DOAP are indicated in Table 1.  
Aggregability (_AGOnto_)  
The metric relates to the aggregation size of the sets of the external ontologies in the maintained ontology. It calculates the relative size (percentage) of the conceptualization for the maximal and minimal conceptualization set according to the total size of all external resources in the maintained ontology. The size of the maximal set is then divided by the size of the minimal set to obtain the multiplier. \[ \begin{split} AGOnto=\frac{Max\left(\frac{n_{1}}{N_{e}},\frac{n_{ 2}}{N_{e}}\right)}{Min\left(\frac{n_{1}}{N_{e}},\frac{n_{2}}{N_{e}}\right)}, \\ N_{e}=\sum\limits_{i=1}^{K}n_{i}\\ K=EXOnto\\ AGOnto\in[0,\infty]\end{split}  \tag{5}\]  
Extreme values are:  
Minimum _AGOnto_ = 1 means that all external ontology sets are equally sized or that there is only one external set in the maintained ontology. Maximum value is achieved when there is a great difference in the sizes of the two extreme external conceptualization sets. Lower value of the _AGOnto_ means that external conceptualization sets are of comparable importance, while a bigger value demonstrates a large dispersion of external ontologies contributions used in the maintained ontology. The contribution from external ontologies is more important if the aggregability value _AGOnto_ is lower, meaning that they contribute more equally to the maintained ontology. The conclusion is that a low dispersion of external ontologies, and thus external conceptualization sets of comparable importance, is more desirable. However, this metric should be analyzed in combination with the composability metric (_CPOnto_) to draw conclusions about the interoperability, always taking the mapping scoring table in consideration. The interoperability metrics discourage a high number of external ontologies; in practical terms, it is advisable to reduce this number because it is easier to maintain the quality of the ontology (e.g., keeping up with possible high number of updates of the used external ontologies is expensive). The _AGOnto_ value for the EDAM ontology is 13,425, which means that there is an extreme difference in the size of external conceptualization sets. The external ontology _obInOwl_ = _[[http://www.geneontology.org/formats/obinOw_](http://www.geneontology.org/formats/obinOw_)]([http://www.geneontology.org/formats/obinOw_](http://www.geneontology.org/formats/obinOw_)) contributes 52%, (13,425 used resources), while the _doap_ = _[[http://usefulinc.com/ns/doap_](http://usefulinc.com/ns/doap_)]([http://usefulinc.com/ns/doap_](http://usefulinc.com/ns/doap_)) only contributes 0.00385% (one used resource). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ontology** & **Internal Resources** & **External Resources** & _CPOnto_ \\ \hline EDAM & 42,628 & 1610 & 0.38 \\ DOAP & 25,946 & 103 & 0.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composability metrics for EDAM and DOAP.