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Ontohub

Ontohub is an open ontology repository which supports organisation, collection, retrieval, development, mapping, translation, and evaluation of a wide array of ontologies formalised in diverse languages.

The Ontohub team is looking forward to providing technological infrastructure for the forthcoming FOIS 2014 Ontology Competition. Accordingly, several new features are going to be launched on the Ontohub soon.

This wiki entrance aims at providing instructions and support to the Ontohub users. See also FAQ.

User Interface

Start

The home page of Ontohub provides access to all public repositories, ontologies, symbols, logics and ontology mappings stored in this hub of distributed, and yet interconnected, ontology repositories. Recently updated repositories and ontologies are listed as well.

Sign In

The full functionality of Ontohub (ontology and repository, creation, collaborative editing and development of ontologies, mapping across ontologies, visualisation, and evaluation) is available upon sign in. Every registered Ontohub user can modify and adjust its own version of interface, i.e. specific and highly personalised access to the repository content.

Repositories

Besides serving as an ontology repository, Ontohub is also a hub that links other ontology repositories. Ontohub provides a single web interface to access various ontology repositories, either hosted or mirrored on Ontohub. The button Repositories (on the menu-bar) leads to the page where all public repositories are listed and the access to their content provided. In addition, Ontohub allows creation and hosting of new repositories, the function available to all registered Ontohub users. Along the opportunity of creating a new repository, Ontohub users can get advantage of the Ontohub collaborative environment (see also MyOntohub) in order to develop ontologies and/or repositories in either problem or domain oriented manner. Thus, Ontohub supports reuse of ontologies stored in other ontology repositories and creation of new repositories that organize ontologies resulting from the activities of a team focused around a particular project or a specific task.

It is also possible to create private repositories. These are visible only for users who have read-permission for the repository.

Ontologies

Ontology search can be performed either over whole Ontohub content ('Ontology' tab on the menu bar) or over ontologies stored within a particular Ontohub repository (Ontology browser on the page of a particular Ontohub repository).

Ontology retrieval is done by typing into the ontology browser one or many of the available search criteria:

- ontology name

- ontology acronym

- ontology language

- a symbol or a label that an ontology contains

- a particular domain (category) that an ontology belongs to (e.g. space, biology, etc.)

- ontology type (e.g. upper, domain, task, etc.) Please note that this feature has not been implemented yet.

Since the search engine uses metadata to retrieve an ontology, all Ontohub users are encouraged to specify metadata about their ontology during the ontology upload. Having described an ontology domain, type, task, etc. increases findability of an ontology.

Mappings

Under the mappings tab, you can see all mappings. Mappings always have a source and a target ontology, and provide mappings or relations between the symbols of these ontologies.

Currently, new mappings can only be created using e.g. an interpretation or an alignment in a DOL file, and uploading that DOL file.

Common Tasks

2.1. Submitting an ontology

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2.2. Editing an ontology

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2.3. Visualising mappings

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2.4. Evaluating an ontology

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2.5. Creating an ontology repository

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2.6. Maintaining an ontology repository

Infrastructure

Ontohub Git

Ontohub infrastructure is powered by the open-source web framework Ruby on Rails for building dynamic web applications. Accordingly, Ontohub has a git structure that supports versioning and management of the Ontohub content.

In addition, the git structure of Ontohub supports stability of the system. Having separate branches for development and staging, software developers are introducing new features of Ontohub on its develop branch. After going through all necessary tests for stability, new features are merged to the staging (and master, i.e. visible website). In that way, the UI on the main page is always stable.

The parsing and inference backend of Ontohub is the Heterogeneous Tool Set (Hets). A detailed architecture of Ontohub you can find on page 8 of Ontohub preprint paper

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HETS

Ontohub accesses the Heterogeneous Tool Set Hets via a RESTful web service interface for having the structure of ontologies analyzed. Hets already supports a large number of basic ontology languages and logics, and is capable of describing the structural outline of an ontology from the perspective of DOL, which is not committed to one particular logic.

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DOL

Distributed Ontology Language (DOL) covers all state-of-the-art ontology languages, and provides a meta level on top of these. This meta level allows for the representation of logically heterogeneous ontologies. DOL ontologies may comprise of modules written in ontology languages with different underlying logics. Moreover, the DOL meta level constructs allow for links between ontologies such as relative interpretations or conservative extensions.

Since the Ontohub infrastructure supports DOL, it allows the Ontohub users

- to relate ontologies that are written in different formalisms;

- to re-use ontology modules even if they have been formulated in a different formalism;

- to re-use ontology tools like theorem provers and module extractors along translations between formalisms.

DOL is currently being standardised within the OntoIOp working group.

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LoLa Ontology

LoLa is an ontology of (ontology) Logics and Languages. Onthub implements LoLa for structuring the repository content. The OWL core of the LoLa ontology comprises classes for ontology languages, logics, mappings (translations or projections) between ontology languages and between logics, as well as serialisations. The LoLa properties relate all of the former classes to each other. Besides its OWL module, LoLa includes additional FOL axioms for closure rules not expressible in OWL, such as non-expressible role compositions and circumscription rules for minimising the extension of default translations.

Glossary

Term	Description
Logical theory	set of expressions (like non-logical symbols, sentences and structuring elements) in a given logical language
Alignment	flexible, relational link that does not always have a formal, logic-based semantics
Matching	algorithmic procedure that generates an alignment for two given logical theories
Logical language	language that is used for writing down logical theories (e.g. formal ontologies, models and specification), equipped with a formal, declarative, logic-based semantics, plus non-logical annotations
Link	relationship between two logical theories, relating their non-logical symbols
Language translation	mapping from constructs in the source logical language to their equivalents in the target logical language
Interpretation	logical link that postulates a relation between two logical theories
Combination	aggregation of several logical theories along links to a new logical theory where (only) the linked non-logical symbols of the involved logical theeories are identified
Conservativity	property of an extension of theories, ensuring that the extension does not add new logical context
Basic logical theory	set of non-logical symbols, sentences, annotations about them, which is used as a building block for a larger logical theory
Axiom	sentence postulated to be valid (i.e. true in every model), party of a logical theory
Theorem	sentence that has been proven (in some logical theory) from other axioms and theorem
Structured logical theory	logical theory that results from other logical theories by import, union, combination, renaming or other structuring operations
Sentence	term that is either true or false in a given model, i.e. which is assigned a truth value in this model
Satisfaction relation	relation between models and sentences indicating which sentences hold true in the model
Non-logical symbol	atomic expression or syntactic constituent of a logical theory that requires an interpretation through a model
Module extraction	activity of obtaining from anlogical theory concrete modules to be used for a particular purpose (e.g. to contain a particular sub-signature of the original logical theory)
Module	subtheory that conservatively extends to the whole logical theory
Model	semantic interpretation of all non-logical symbols of a logical theory, satisfying the theory's axioms
Approximation	reduction of a theory to a less expressive logical language, such that the original theory implies the approximation

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