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[protege-owl] Database and Owl Ontology

Timothy Redmond tredmond at
Sat Aug 15 23:59:45 PDT 2009

There are several reasons why people would want to put a very large  
ontology into a database.  For example,

1. a database can be loaded on a machine with limited memory.  This  
allows people to work with ontologies on machines with limited  
capabilities when access to more capable machines is  not possible.

2. an ontology in a database can be loaded very quickly allowing  
people to access an ontology without having to (re)parse the entire  

3. a server may need to open many ontologies open at the same time and  
to be able to open large ontologies quickly based on demand from users  
or clients.  This is important for an ontology repository for example.

The main reason for  not wanting to use a database backend is its  
complexity and its much slower performance.

But it is also important to point out that the Manchester OWL api  
(used by Protege 4) can hold very large ontologies in limited memory.   
So for example, my 2GB old laptop is almost capable of loading  
snomed.  This may suggest that the most important reason for having a  
database backend for the Manchester OWL API is the third case.


On Aug 15, 2009, at 7:48 PM, Sarah G wrote:

> Hi All,
> Could someone please explain why you should have/use a relational  
> database as backend for an ontology? I am new to using owl and was  
> wondering why or if I will need to have a database.
> Thanks,
> Sarah
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