一 背景知識
知識圖譜方向目前越來越火，順帶着，表示知識圖譜的語言，如rdf，owl等也跟着火了起來。但是這些語言都有一定的門檻，沒接觸過xml的初學者不可能在短時間內掌握，這些語言的熟練工也無法通過快速瀏覽文件來判斷圖譜的結構。因此，需要將這些語言所表示的結構用複雜網絡的形式表現出來。這樣，我們就可以根據可視化後網絡的結構直觀地認識這個圖譜，也可以通過網絡的各種係數（集聚係數等）瞭解圖譜的一些特性。
rdf即resource defined framework,資源定義框架，是用來表示知識圖譜中的實體及其關係的。owl即ontology web language,本體網絡語言，可以簡單理解爲rdf的進化版本。它既可以表示實體之上的一層概念--類，又可以表示類的實例（individual）。但owl使得實例更加規範。所謂的“本體”，是指某個領域的一些概念的集合，比如大學本體，葡萄酒本體等。這些本體可以用owl來表示。本體中包含着很多類（class），每個類都有自己的名字（vocabulary）。具體如下圖表示：（圖片轉自知乎，稍後給出鏈接）：
二 轉化方式
那麼，怎樣才能把一個rdf或者owl或者其他表示實體或本體的文件轉化成複雜網絡呢？想想可能有些頭疼，還好大牛們已經爲我們寫好了現成的工具--一個特定的jar包。Stack Overflow網站上有人提出了這個問題，別人的回答中給出了jar包的鏈接。原問題和答案鏈接如下：
https://stackoverflow.com/questions/45362802/using-jena-to-convert-an-owl-file-to-n-triple-from-terminal-returns-an-empty-fil
jar包的下載地址如下：
http://www.l3s.de/~minack/rdf2rdf/
上面的鏈接中介紹了jar包的用法，需要在Linux下（或者cmd下）運行：
Run the jar file like this: java -jar rdf2rdf-1.0.1-2.3.1.jar INPUTFILE(S) OUTPUTFILE
三 實踐
從網上下載了wine.owl，進行轉化。
進入wine.owl所在的目錄後，將jar包也放入同一個文件夾，在終端輸入java -jar rdf2rdf-1.0.1-2.3.1.jar wine.owl wine.nt
然後就能在當前目錄下找到對應的nt文件了。
下面將兩個文件的部分內容對應起來講解。如，wine.owl(1)與wine.nt(1)相對應，wine.nt(1)表示的是wine.owl(1)轉化而成的三元組。
wine.owl（1）：
//下面一小段代碼是對當前wine本體的描述
<owl:Ontology rdf:about="">//對owl本體的聲明，爲空表示用owl的默認URI
<rdfs:comment>An example OWL ontology</rdfs:comment>
//這一段是owl本體的一個例子
<owl:priorVersion>//版本控制
<owl:Ontology rdf:about="http://www.example.org/wine-020303"/>
</owl:priorVersion>
<owl:imports rdf:resource="http://www.w3.org/2001/sw/WebOnt/guide-src/food.owl"/>//其他本體的嵌入
<rdfs:comment>Derived from the DAML Wine ontology at
http://ontolingua.stanford.edu/doc/chimaera/ontologies/wines.daml
Substantially changed, in particular the Region based relations.
</rdfs:comment>//註釋
<rdfs:label>Wine Ontology</rdfs:label>//標註
</owl:Ontology>
wine.nt（1）
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Ontology> .//wine是一個本體
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2000/01/rdf-schema#comment> "An example OWL ontology" .//對wine的一個註釋是：An example OWL ontology
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2002/07/owl#priorVersion> <http://www.example.org/wine-020303> .//wine的版本控制爲。。（此處object是一個匿名節點）
<http://www.example.org/wine-020303> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Ontology> .//這個版本是一個本體
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2002/07/owl#imports> <http://www.w3.org/2001/sw/WebOnt/guide-src/food.owl> .//wine嵌入food本體
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2000/01/rdf-schema#comment> "Derived from the DAML Wine ontology at \n http://ontolingua.stanford.edu/doc/chimaera/ontologies/wines.daml\n Substantially changed, in particular the Region based relations." .//wine的一個註釋是。。
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2000/01/rdf-schema#label> "Wine Ontology" .
//wine的一個標籤是Wine Ontology
wine.owl(2)
<owl:Class rdf:ID="Wine">
<rdfs:subClassOf rdf:resource="&food;PotableLiquid" />
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasMaker" />
<owl:cardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:cardinality>
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasMaker" />
<owl:allValuesFrom rdf:resource="#Winery" />
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#madeFromGrape" />
<owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:minCardinality>
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasSugar" />
<owl:cardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:cardinality>
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasFlavor" />
<owl:cardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:cardinality>
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasBody" />
<owl:cardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:cardinality>
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasColor" />
<owl:cardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:cardinality>
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#locatedIn"/>
<owl:someValuesFrom rdf:resource="&vin;Region"/>
</owl:Restriction>
</rdfs:subClassOf>
<rdfs:label xml:lang="en">wine</rdfs:label>
<rdfs:label xml:lang="fr">vin</rdfs:label>
</owl:Class>
下面是對應的轉化成三元組的owl.nt文件的部分內容：
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Ontology> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2000/01/rdf-schema#comment> "An example OWL ontology" .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2002/07/owl#priorVersion> <http://www.example.org/wine-020303> .
<http://www.example.org/wine-020303> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Ontology> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2002/07/owl#imports> <http://www.w3.org/2001/sw/WebOnt/guide-src/food.owl> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2000/01/rdf-schema#comment> "Derived from the DAML Wine ontology at \n http://ontolingua.stanford.edu/doc/chimaera/ontologies/wines.daml\n Substantially changed, in particular the Region based relations." .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine> <http://www.w3.org/2000/01/rdf-schema#label> "Wine Ontology" .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Class> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> <http://www.w3.org/2001/sw/WebOnt/guide-src/food#PotableLiquid> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux1 .
_:node1c80be0kux1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux1 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#hasMaker> .
_:node1c80be0kux1 <http://www.w3.org/2002/07/owl#cardinality> "1"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux2 .
_:node1c80be0kux2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux2 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#hasMaker> .
_:node1c80be0kux2 <http://www.w3.org/2002/07/owl#allValuesFrom> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Winery> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux3 .
_:node1c80be0kux3 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux3 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#madeFromGrape> .
_:node1c80be0kux3 <http://www.w3.org/2002/07/owl#minCardinality> "1"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux4 .
_:node1c80be0kux4 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux4 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#hasSugar> .
_:node1c80be0kux4 <http://www.w3.org/2002/07/owl#cardinality> "1"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux5 .
_:node1c80be0kux5 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux5 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#hasFlavor> .
_:node1c80be0kux5 <http://www.w3.org/2002/07/owl#cardinality> "1"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux6 .
_:node1c80be0kux6 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux6 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#hasBody> .
_:node1c80be0kux6 <http://www.w3.org/2002/07/owl#cardinality> "1"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux7 .
_:node1c80be0kux7 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux7 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#hasColor> .
_:node1c80be0kux7 <http://www.w3.org/2002/07/owl#cardinality> "1"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#subClassOf> _:node1c80be0kux8 .
_:node1c80be0kux8 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Restriction> .
_:node1c80be0kux8 <http://www.w3.org/2002/07/owl#onProperty> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#locatedIn> .
_:node1c80be0kux8 <http://www.w3.org/2002/07/owl#someValuesFrom> <http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Region> .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#label> "wine"@en .
<http://www.w3.org/2001/sw/WebOnt/guide-src/wine#Wine> <http://www.w3.org/2000/01/rdf-schema#label> "vin"@fr .