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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 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.

Ontohub repositories are stored as git repositories. Git provides a persistent storage and version control for ontologies, as weill as access to Ontohub repositories via the usual git tools.

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.

Categories

Ontologies can be categorised. Ontohub's category system is maintained as an OWL ontology in Ontohub itself, see [1].

The backbone of Ontohub categories is The International Standard Classification of Education (ISCED). The last version of ISCED (the final draft published in June 2013), which provides a hierarchy of educational domains, has been selected as the most appropriate reference classification that specifies subjects, i.e. categories of knowledge-domains. ISCED is a member of the United Nations International Family of Economic and Social Classifications and, originally, is the reference classification for organizing education programmes and related qualifications by levels and fields of education. The reference classification was extended with several categories which are not originally contained within ISCED, e.g. Space, Time, and Process.

During the ontology upload, it is advisable to specify categories that would fit best ontology subject(s), i.e. the domain of knowledge that an ontology represents. Such a specification facilitates findability and reusability of domain-specific ontologies. It is possible to select multiple categories for ontology domains.

Logics

Ontologies can be formulated in various logics. Ontohub supports a number of different logics, among them OWL, RDF and Common Logic.

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

Submitting an ontology

The submission of a new ontology into Ontohub consists of the following steps:

a. Register/sign in ontohub.org

b. Select an existing repository that fits best your specific target domain, task, and ontology type; All public repositories are listed upon clicking on the 'Repository' button in the main menu; alternatively, it is possible to create a new repository (as described in the section below); certain repositories are 'read-only' while others allow editing of the repository content;

c. If uploading an ontology to the existing repository you will need to get a permission via requesting the editing rights; the permission is provided by the administrator of the repository ('owner'); After selecting (or creating) an appropriate ontology repository and acquiring the editing rights, the ontology upload can proceed through the use of file system.

d. The 'Edit' button appears on the page of each repository for which you have the editing rights. 'Edit' button leads to the interface with the editing option. So, the first step in editing is to to confirm that you want to 'Update repository'. The next step is to go to the section 'Ontology files and related files', where you can upload your ontology as a new file. The information provided there in gets stored into the file system, which can afterwords be accessed at the 'Ontology files and related files'. You might want to upload your ontology into an already existing folder that stores ontologies of your interest. In that case, in the section 'Target directory' you will need to type the exact name of the directory in which you want to store your ontology file. Into the section 'Target file name' you will need to type the ontology name together with its correct extension, e.g. name.owl, name.clif etc. A message that accompanies upload is optional but desirable as it can be helpful in tracking the history of activities and changes in repository. The next step is to 'Upload file'.

e. Since your submitted file is recognised as an ontology (via its extension), you will need to provide metadata that describe your ontology: ontology name, category (domain), ontology type, formality level, and a specific description. The inserted metadata are helpful in classification of ontologies in repository and their easier, a task specific retrieval.

When selecting metadata that describe the domain of your ontology you can select multiple fields ('Categories') that will help to characterise your ontology as specific as possible. For instance, if an ontology is about anatomy of a biological species, then the appropriate categories would be 'biology' and 'space', while a geospatial ontology can be associated with the domains 'geography' and 'space', an ontology that describes chemical structures would be associated with 'chemistry' and 'space'.

'Ontology type' and 'Formality level' provide specification of your ontology as a domain ontology, an upper level ontology etc. Please note that the classification of ontology types and formality levels mostly follows the OMV specifications. Modifications and revisions to this classification are work in progress.

'Description' of ontology provides an important narrative, i.e. information that will additionally help users (people and machines) to capture the targets and aims of the ontology designer.

Creating an ontology repository

Every registered Ontohub user can create a new repository via the button 'Create repository'. The repository creator acquires administrative rights, i.e. management of repository, editing permissions, and visibility of repository (public or private).

While considering creation of a new repository, every Ontohub user should mind knowledge sharing as the driving force in ontology development. In oder words, private repositories are designed to serve the research purposes only. Accordingly, private repositories can be used to store work in progress. As soon as work on ontology development and mappings reach the stage to be published, it is recommended to make private repository and/or its content publicly available. It is also advisable to publish ontologies in already existing repositories that are domain or problem oriented, e.g. geospatial ontologies can be published in SOCoP or SpacePortal; biomedical ontologies in BioPortal etc. By following this policy, Ontohub users support joint efforts of ontology community in knowledge sharing and ontology reuse.

Infrastructure

Ontohub architecture

The Ontohub infrastructure is powered by the open-source web framework Ruby on Rails for building dynamic web applications. The source code is available at github. The Ontohub git repository has separate branches development, staging and master. 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.

HETS

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

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.

DOL

The Distributed Ontology, Modelling and Specification 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.

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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