AIRR Ontologies and Vocabularies Sub-WG#

Summary#

The “Ontologies and Vocabularies Team” was initial formed as a joint interest group of the Common Repository (ComRepo) and the Minimal Standards (MiniStd) working groups (WG) of the AIRR Community. When the two WG merged into the current Standards WG in Decemmber 2020, OntoVoc became a Sub-WG of it. The long-term aim of the Sub-WG is to define standard vocabularies and ontologies to be used by AIRR-compliant repositories.

Ontology Data Representation#

The nodes in an ontology are typically either concepts (e.g., capital) or instances thereof (e.g., Paris). These nodes have local IDs (often numbers), which are unique within an ontology. They also typically have labels, which is the human-readable name of the node. Ontology entities in the AIRR Data Standard reflect this model, with each AIRR field that is represented as an ontology recorded with a global ontology ID (id) and the corresponding label (label).

Within the AIRR Standards, Compact URIs (CURIEs) are used to represent ontology IDs or persistent IDs. CURIEs are a standardized way to abbreviate International Resource Identifiers (IRI, [RFC3987]), which include URIs and URLs as subsets. They were originally conceived to simplify the handling of attributes, e.g., in XML or SPARQL, by making them more compact and readable. CURIEs are also used by IEDB databases to reduce redundancies (mainly in the leading part of IRIs).

For example, a typical CURIE would look like NCBITAXON:9258. In this case, NCBITAXON is the prefix, a custom string that will be replaced by a repository-defined IRI component (e.g., http://purl.obolibrary.org/obo/NCBITaxon_). Note that there is no connection between NCBITAXON in the CURIE and NCBITaxon in the IRI, the former one is just a placeholder. Although common, it is not always the case that a resolved CURIE (the IRI prefix plus the local ID) can be used as a URL directly to look up the CURIE using a web browser.

The AIRR Schema provides a CURIEMap, a list of AIRR approved CURIE prefixes along with a map of at least one iri_prefix (i.e., a replacement string to construct the complete IRI) for each prefix. As the iri_prefix might differ between provider-specific implementations of an ontology (e.g., NCBI Taxonomy), the CURIEMap supports multiple iri_prefix entries for a given prefix. Finally, the CURIEMap should also provide a default map and provider for each prefix. Complementary to this, the InformationProvider list describes the mechanism to computationally look up a resolved IRI (e.g., the iri_prefix and the local ID) by specifying how to make a request to the provider as well as describing the format in which the request response will be provided.

The CURIEMap serves several purposes:

It provides a controlled namespace for CURIE prefixes used in the AIRR Schema. For now, custom additions to or replacements of these prefixes in the schema are prohibited. This does not affect the ability of repositories to use such custom prefixes internally.
It simplifies resolution of CURIEs. The iri_prefix lists for each prefix should not be considered to be exhaustive. However, when using a custom iri_prefix, it must be ensured that the expanded IRI still refers to the same concept/instance as when using the default iri_prefix.
It simplifies computation using CURIES. It is possible to use the provider for a prefix as a mechanism to look up a CURIE from a provider with a defined response (See below)

It should be explicitly noted that the CURIEMap should not be interpreted as any kind of recommendation for certain providers. It is left up to users to decide how to resolve the resulting IRIs, e.g., via DNS/HTTP (if possible) or by using a provider of their choice.

General Policies#

Criteria#

Ontologies used within AIRR standards

MUST [1]_ cover the majority of the required terms, but complete coverage is OPTIONAL

MUST have a structure that is scientifically correct and logically coherent

MUST NOT feature complexity that makes it hard to use for queries and data representation

SHOULD already be widely adopted

MUST be actively maintained

MUST be available under a free license

SHOULD comply to the OBO Foundry Principles. This does not imply a preference.

Comments on criteria:

ad (1): For most fields it will be difficult to find complete and accurate ontologies. Therefore picking the best available ontology and working with its maintainers to include missing terms is expected to be the most sustainable approach.
ad (5): This requirement follows from (1), as there needs to be a way for term requests.
ad (6): A number of ontologies need to be licensed from their respective copyright holders. This results in potential barriers for implementation and distribution of such ontologies. Therefore only ontologies available under a free license are considered suitable for AIRR-compliant databases. The list of suitable licenses is not final, but includes: CC0 and CC BY.
ad (7): This is an endorsement of the OBO Foundry Principles, not of the OBO Foundry Ontologies in general. Hence, also non-OBO have an equal standing if they comply to the Principles.

Approved Ontologies#

Cell ontology (CL)
- used in:
  - Cell subset (cell_subset, Tissue and Cell Processing)
- CURIE summary
  - CURIE Prefix: CL
  - CURIE IRI Prefix: http://purl.obolibrary.org/obo/CL_
- example AIRR use
  - “cell_subset.id” : “CL:0000542”
  - “cell_subset.label” : “lymphocyte”
- default root node
  - label: lymphocyte
  - local id: CL_0000542
  - path: ``
- license: CC BY
- latest release (as of 2020-05-20): 2020-03-02
- repo: obophenotype/cell-ontology
- maintainer: Alexander Diehl, Buffalo, NY, US (addiehl@buffalo.edu)

Human disease ontology (DOID)
- used in:
  - Diagnosis (disease_diagnosis, Diagnosis)
- CURIE summary
  - CURIE Prefix: DOID
  - CURIE IRI Prefix: http://purl.obolibrary.org/obo/DOID_
- example AIRR use
  - “disease_diagnosis.id” : “DOID:9538”
  - “disease_diagnosis.label” : “multiple myeloma”
- default root node
  - label: disease
  - local ID: DOID:4
  - path: disease
- license: CC0
- latest release (as of 2020-05-20): 2020-04-20
- repo: DiseaseOntology/HumanDiseaseOntology
- maintainer: Lynn Schriml, U Maryland, MD, US (lynn.schriml@gmail.com)
- notes: Features ICD cross-reference

NCBI organismal taxonomy (NCBITAXON)
- used in:
  - Species (species, Subject)
  - Cell species (cell_species, Tissue and Cell Processing)
- CURIE summary
  - CURIE Prefix: NCBITAXON
  - CURIE IRI Prefixes: http://purl.obolibrary.org/obo/NCBITaxon_, http://purl.bioontology.org/ontology/NCBITAXON/
- example AIRR use
  - “species.id” : “NCBITAXON:9606”
  - “species.label” : “Homo sapiens”
- default root node
  - label: Gnathostomata
  - local ID: 7776
  - path: cellular organisms/Eukaryota/Opisthokonta/Metazoa/Eumetazoa/Bilateria/Deuterostomia/Chordata/Craniata/Vertebrata/Gnathostomata
- license: UMLS
- latest release (as of 2020-05-20): 2020-04-18
- repo: obophenotype/ncbitaxon
- maintainer: NCBI (info@ncbi.nlm.nih.gov)

NCI thesaurus (NCIT)
- used in:
  - Study type (study_type, Study)
- CURIE summary
  - CURIE Prefix: NCIT
  - CURIE IRI Prefixes: http://purl.obolibrary.org/obo/NCIT_, http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl#
- example AIRR use
  - “study_type.id” : “NCIT:C15197”
  - “study_type.label” : “Case-Control Study”
- default root node
  - label: Study
  - local ID: C63536
  - path: Activity/Clinical or Research Activity/ Research Activity/Study
- license: Public domain, credit of NCI is requested
- repo: NCI-Thesaurus/thesaurus-obo-edition
- latest release (as of 2020-05-20): 2020-05-04
- maintainer: NCI (ncicbiitappssupport@mail.nih.gov)

Units of measurement ontology (UO)
- used in:
  - Age unit (age_unit, Subject)
- CURIE summary
  - CURIE Prefix: UO
  - CURIE IRI Prefix: http://purl.obolibrary.org/obo/UO_
- example AIRR use
  - “age_unit.id” : “UO:0000036”
  - “age_unit.label” : “year”
- default root node
  - label: time unit
  - local ID: UO_0000003
  - path: unit/time unit
- license: CC BY (per Github repo)
- repo: bio-ontology-research-group/unit-ontology
- latest release (as of 2020-05-20): 2020-05-18
- maintainer: unknown

Uber-anatomy ontology (Uberon)
- used in:
  - Tissue (tissue, Sample)
- CURIE summary
  - CURIE Prefix: UBERON
  - CURIE IRI Prefix: http://purl.obolibrary.org/obo/UBERON_
- example AIRR use
  - “tissue.id” : “UBERON:0002371”
  - “tissue.label” : “bone marrow”
- default root node
  - label: multicellular anatomical structure
  - local ID: UBERON:0010000
  - path: /BFO_0000002/BFO_0000004/anatomical entity/material anatomical entity/anatomical structure/multicellular anatomical structure
- license: CC BY
- repo: obophenotype/uberon
- latest release (as of 2020-05-20): 2019-11-22
- maintainer: Chris Mungall, LBL, CA, US (cjmungall@lbl.gov)

Computing with Ontologies#

One of the key goals of using ontologies is to enable analysis tools to perform computation using the information in those ontologies. The AIRR Schema’s CURIEMap lists one or more providers for each CURIE prefix that can be used programmatically by analysis tools. Although the AIRR Schema lists multiple providers for each ontology, this section focuses on the use of the EBI OLS provider’s OLS Web API interface for querying ontologies.

If we consider the DOID prefix from the CURIEMap, the section below defines the use of the Human Disease Ontology (DOID) within the AIRR Standard:

DOID:
  type: ontology
  default:
    map: OBO
    provider: OLS
  map:
    OBO:
      iri_prefix: "http://purl.obolibrary.org/obo/DOID_"

We see that the default map for DOID is OBO map, and the OBO map’s iri_prefix is http://purl.obolibrary.org/obo/DOID_. Thus the mapping of the CURIE DOID:9538 (the CURIE for disease “multiple myeloma”) will yield the resolved string http://purl.obolibrary.org/obo/DOID_9538. By the strictest of defintions, this is a valid IRI and should only be considered an identifier, but in this case this IRI is also a URL and can be used to look up the CURIE.

If we consider the default DOID provider in the CURIEMap, we see that it is OLS. Then, in the InformationProvider object of the AIRR Schema, under provider we see:

InformationProvider:
  provider:
    OLS:
      request:
        url: "https://www.ebi.ac.uk/ols/api/ontologies/{ontology_id}/terms?iri={iri}"
        response: application/json

And later we see that the parameters for OLS are:

parameter:
  CL:
    Ontobee:
      ontology_id: CL
    OLS:
      ontology_id: cl
  DOID:
    Ontobee:
      ontology_id: DOID
    OLS:
      ontology_id: doid

The above tells us that we can use the OLS provider to look up ontology terms. The {iri} component of the url string tells us that we need to use the resolved IRI and the {ontology_id} component tells us that we need to replace the ontology_id parameter in the URL with the DOID OLS parameter in the specification, which is the string doid. Thus the fully resolved URL to query for the CURIE DOID:9538 would be:

https://www.ebi.ac.uk/ols/api/ontologies/doid/terms?iri=http://purl.obolibrary.org/obo/DOID_9538

Again, referring to the OLS provider we see that we can expect an application/json response to the above query, and indeed the response we receive from the above starts with a JSON object as follows.

{
 "_embedded" : {
   "terms" : [ {
     "iri" : "http://purl.obolibrary.org/obo/DOID_9538",
     "label" : "multiple myeloma",
     "description" : [ "A myeloid neoplasm that is located_in the plasma cells in bone marrow." ],
     "annotation" : {
       "comment" : [ "OMIM mapping confirmed by DO. [SN]." ],
       "database_cross_reference" : [ "ICD10CM:C90.0", "MESH:D009101", "ICD9CM:203.0", "GARD:7108", "NCI:C3242", "OMIM:254500", "ORDO:29073", "EFO:0001378", "SNOMEDCT_US_2020_09_01:94705007", "UMLS_CUI:C0026764" ],
       "has_obo_namespace" : [ "disease_ontology" ],
       "id" : [ "DOID:9538" ]
     },
     "synonyms" : [ "plasma cell myeloma" ],
     "ontology_name" : "doid",
     "ontology_prefix" : "DOID",
     "ontology_iri" : "http://purl.obolibrary.org/obo/doid.owl",
     "is_obsolete" : false,
     "term_replaced_by" : null,
     "is_defining_ontology" : true,
     "has_children" : true,
     "is_root" : false,
     "short_form" : "DOID_9538",
     "obo_id" : "DOID:9538",
     [Content edited because of length]

In this repsonse, you can see that the Ontology object that we requested has a label field that contains the value multiple myeloma and that the id field has a value of DOID:9538.

It is beyond the scope of this document to describe in detail the JSON structure of each of the providers, but this information can be discovered through the provider web sites. It should be noted that all Ontology objects in the AIRR specification have the OLS as a provider and therefore the method above can be used for any of the ontologies in the AIRR specification. Please see the OLS Web API documentation for details of the JSON response for the OLS provider.

AIRR Ontologies and Vocabularies Sub-WG

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