Ontology of astronomical object types Use Cases

This page details the considered use cases of the OntologyOfObjectTypes.

Registry queries

The idea is to make use of the ontology to improve the selection of Resources in an IVOA Registry.

The selection will ultimately use the <Subject> element of the VOResource schema: indeed, this element can contain expressions (text strings) corresponding to Object Types.

The suggested scenario is the following:

1. The astronomer wants to select Resources (catalogues or other) related to some specific astronomical object types, and gives as input this object type (either selecting from a scroll-list of all AstrObject concepts in the ontology, or typing a text string -- in this later case, we need a way to map the string to a concept in the ontology). In the following, we assume the search is done on CataclysmicVariables .
2. A preliminary work is to parse the whole Registry contents for all the <Subject> elements of all Resources, identify all the ones corresponding to concepts in the ontology, and build some kind of hash table between resources' ivo-ids and ontology concepts. This can be made easier by associating keywords to the concepts in the ontology. For example, in the case of resources corresponding to VizieR catalogues, the list of possible values for <Subject> elements is standardized, and this knowledge can be stored in the ontology.
3. For a given query, the ontology is used to identify all the concepts subsumed by the input one (e.g. CataclysmicVariables subsumes AMHerCataclysmicVariable, DQHerCataclysmicVariable, etc...), and count how many resources do match any of these.
   • in the case too few resources match the given input, we can suggest to broaden the query using concepts subsuming CataclysmicVariables (e.g. DoubleStar)
   • if there are too many matches, we can refine the query using already identified subsumed concepts

Application to SIMBAD objects

SIMBAD contains cross-identifications, measurements and bibliography for a large number of astronomical objects. An object classification is also provided, based on a standardized list of object types that was used as a starting point for the ontology construction. A new version of SIMBAD (SIMBAD4, to be released in 2006) adds the possibility for an object to be assigned multiple classifications.

Check cross-identifications' consistency

For a given object, the ontology can be used in a simple way to check the consistency of the cross-identifications:

• An object often has multiple identifiers, with each acronym following the Dictionary of Nomenclature of Celestial Objects.
• Some of these identifiers are associated to an object type (e.g. if an acronym was created for a paper studying only globular clusters, all objects having such an identifier are globular clusters).
• We can therefore use the knowledge on all object types inferred from the different identifiers of an object, to check if this is consistent with constraints that are present in the ontology, and detect some possiblly wrong cross-identifications in SIMBAD. A typical example would be a single object having an identifier corresponding to an AGB star, and one corresponding to a QSO, if AGB star is a subclass of Star and QSO is a subclass of Galaxy, and Star and Galaxy are disjoint in the ontology, then we detect the inconsistency.
• Here is as simplified overall chart of the application:
  

• And below is a sequence diagram of the cross-identifications' consistency checker:
  

Check consistency of identifiers WRT compound objects and their components

This comes after an item has been found to have inconsistent identifiers. The point of this check is to see if the inconsistent identifiers do not refer to a compound object and one or it's components, in which case it is likely that the component and the compound objects were merged in the database. A typical example is finding an inconsistency of identifiers because an item is tagged with both double star and star; indeed, most main component of the double star and the double system itself are very often merged in SIMBAD.

Check consistency of measurements WRT identifiers

Its purpose is to see if the measurements for the item being checked are consistent with the identifiers. The first measurements taken into account are the radial velocity and redshift. For instance, it is impossible to have a radial velocity for extra-galactic objects, and (sub-)stellar objects cannot have a redshift ether. The measurements' values are also tested beforehand to see if they fit sensible boundaries (e.g. check that a redshift is not greater than 12).

Links

• IVOA Technical Note - Ontology of Object Types Use-Cases v1.0 AstrObjectOntologyUseCases-20080703.pdf

-- AlexandreRichard - 05 Jul 2006