OntoVoc Report - Sprint 04/2020¶
The objectives of this second sprint in April 2020 were to:
revisit general policies around ontologies used in the AIRR schema
identify two new ontologies for several fields of the AIRR schema
solve technical questions regarding IDs and providers
The OntoVoc team revisited the criteria for ontologies used in the AIRR schema that it defined in the 11/2018 sprint. While they are still considered to be valid, the team felt that a more detailed guidance could be useful in the process of selecting ontologies for new fields. It therefore evaluated the OBO Foundry Principles, which partially re-iterate some of the existing criteria (e.g., Openness and Maintenance), but also provide additional recommendations, e.g., the presence of textual definitions, clear scope and a common format, which were considered to be valuable additions to the existing guidelines. The team therefore decided to endorse the OBO Foundry Principles, as RECOMMENDED (but NOT REQUIRED) criteria. It should be noted, that this does not make any statement regarding the use of OBO vs. non-OBO ontologies.
Decisions on Pending Items of Sprint 11/2018¶
A number of decisions on draft and legacy ontologies as well as root nodes was not officially passed during the last sprint. The team thus revisited and confirmed the following decisions:
Use of NCIT for
study_type, top node
Use of UO for
age_unit, top node
NCBITAXON:7776) as top node for
NCBITAXONwhen used for fields encoding a host species.
CL:0000542) as top node for
CLwhen used for
Mouse strain names follow a very elaborate nomenclature that is capable of describing the genetic background, breeding history and introduced mutation in a detailed manner. However, this nomenclature is rarely used correctly (if at all), which creates uncertainty about the identity of strains used in experimental studies. Therefore an ontology or vocabulary compliant to this nomenclature would be of tremendous help for consistent annotation.
An ontology for the
strain_name field was already on the list for
the last sprint, however it was not possible to identify a single
ontology that would contain comprehensive information about strains
from multiple species. This situation created a problem that could not
be resolved then. In the meantime, the concept of “extensions” has
been introduced to the AIRR schema, which create an additional layer of
fields (and associated ontologies) on top of a core schema. As these
extensions can be made conditional on the value of fields within the
core schema, it has now become possible to have multiple extensions
strain_name field, but for different species and
therefore with distinct species-specific ontologies.
Having addressed this issue, the other key problem that remains is the absence of an actual ontology for mouse strains, while a rat strain ontology exists. Therefore in a first step it is necessary to identify resources that you at least serve as a provider for vocabularies. The two potential candidates that were identified are:
MGI: The Mouse Genome Informatics database hosted at JAX aims to be comprehensive in regard to all mouse strains that have been published in the literature.
IEDB: The Immune Epitope Database already ran into the problem of a missing mouse ontology and therefore decided to build up their own reference focused on immunologically relevant strains, as part of their Ontie database.
Once it is clear which of the resources could be used, it will be necessary to approach the current maintainers regarding their willingness to convert the data into an actual ontology (the RS could serve as a template for this). As this will take longer than just a couple of weeks, the second step is out-of-scope for this sprint.
MGI: The database can be downloaded as a dump, however the licensing conditions are unclear. It contains a total of 60k entries of which 3.2k inbred and 13.8k are congenic strains. The majority of the remaining entries are coisogenic strains, most of them from large- scale gene KO projects.
IEDB: Database dumps can also be downloaded and are freely available under CC-BY 4.0. It covers over a thousand mouse strains and contains additional information on the genetic background of a strain.
Get in touch with JAX (pending)
There are several (planned) extensions to the AIRR metadata standard that will provide geospatial metadata. Country-level information is typically assumed to be privacy-preserving and easy to operationalize. Therefore, while clearly only capturing some aspects of genetic ancestry, it might serve as a proxy for concepts of “race” and “ethnicity” that are rather ill-defined.
Potential candidate vocabularies/ontologies:
ISO3166-1 alpha-2: Two-letter code, some ambiguity but well known from ccTLDs.
ISO3166-1 alpha-3: Three-letter code, less ambiguity than alpha-2.
UN Stats Division code (currently M49): Numerical code, not human-readable, maps to ISO3166-1 alpha-3.
Contains 2nd (state) and 3rd (county) level information.
Not linked to any actual coordinates
ISO3166-1 annotation is incomplete and lacks e.g. for Germany and Switzerland.
Does not support German Umlauts. Äbsölütely inacceptable, as these are not just diacritical marks (i.e. “Münster” and “Munster” are two different cities).
Seems to be complete, but does not provide ISO3166 codes.
Ontology could also be used for other fields relating to genetic ancestry.
Links to DBpedia, currently unclear whether it is also populated from there
country node has pan-240 leaves (surplus seems due to oversea territories), cross-referencing to GAZ (s/a)
Various pathogen-related repositories:
VectorBase (VBGEO): see link and choose “GADM/VBGEO PlaceNames”
Viral Pathogen Resource (ViPR):
Influenza Research Database (IRD): Flu-focused version of ViPR, also uses GSCID/BRC Project and Sample Application Standard v1.3.
Pathosystems Resource Integration Center (Patric): Focused on bacterial infectious diseases. Uses an “Isolation Country” field in their “Genome” table, format seems to be full text.
HL7: own ontology deprecated, now recommends ISO 3166-1 alpha-3 set.
NCIT: Incomplete, only contains pan-90 entities
SNOMED: Licensing issues
GADM data: Good quality and resolution, but not an ontology in itself. Also not under a free license, does not allow redistribution or commercial use.
Given the number of options, there is no obvious candidate to pick. Therefore the team decided to define clear use cases and then evaluate each options against them. However, due to time limitation, we did not really get into this, will have to follow up in the next sprint. The use cases so far were:
Annotate country of birth / of sampling [REQUIRED]
Encode higher resolution than country level if legally permitted and scientifically meaningful [RECOMMENDED].
Linking to geo-spatial coordinates [OPTIONAL]
Background and Problem¶
Some nomenclature first: The nodes in an ontology graph 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. Nodes can have additional attributes (e.g., “population count”) and are connected to other nodes by relations (e.g. “is-a”, “superset-of”), which create the edges of the graph.
The complete ontology is usually represented in an XML or OWL file. However, we are looking for a provider, i.e. a service that facilitates queries of an ontology via web and/or an API-based interface. Upon querying with a unique ID, is it expected that a provider will be able to return the record of a node, which should contain all attributes and relations. Furthermore a provider might allow set- and graph-based queries (e.g., is A a complete subset of B; what is the last common ancestor of A and B). Finally a provider can offer lookup services, i.e., identify the corresponding concept or instance in another ontology. Until now we have mainly looked at three providers: Ontobee, OLS and BioPortal. While they all provide similar basic services, it should be noted that some biomedical databases and repositories are, by convention, restricted to use certain providers.
As stated above, each node has a local ID. To avoid conflicts between the local IDs of multiple ontologies, providers and ontology collections (e.g., OBO Foundry) use a namespace, i.e., some abbreviation for the ontology that is prefixed to the local ID. However, as there no common standard how to create these prefixes, this system is only unambiguous and collision-safe within a single provider. To resolve this issue, ontologies often use International Resource Identifiers (IRI, [RFC3987]). While IRIs look like HTTP URLs, they should primarily be considered as permanent and globally unique identifiers, which might resolve to the node’s record via DNS/HTTP, but this is optional. In addition, potential intermediate URLs generated in the DNS/HTTP resolving process must be considered internal and therefore should not be used by third parties. Finally, it needs be noted that IRIs should to be considered case-sensitive, especially when used as identifiers (per [RFC3987], Section 18.104.22.168, which only excludes the schema and host (authority) component for case-sensitivity).
While many ontologies already define an entities IRI on the level of the
ontology, there are some that do not. For such ontologies, IRIs are then
assigned by the provider. The most notable example for this are the UMLS
ontologies like the NCBI Taxonomy. This leads to the situation that a
single node in an ontology, stored by two providers can have different
IRIs. Therefore, a concept from NCBI Taxonomy, e.g., the duck-billed
label: Ornithorhynchus anatinus, local ID: 9258) has
http://purl.obolibrary.org/obo/NCBITaxon_9258 in Ontobee and
BioPortal. In addition, other providers might choose to use one of these
IRIs too, although it will never resolve to their system via DNS/HTTP
(e.g., OLS uses the Ontobee IRIs).
For the AIRR Community, this creates the challenge that we want to be able to have unambiguous identifiers, without requiring any specific provider.
Compact URIs (CURIEs) are a standardized way to abbreviate IRIs, which includes URIs as a subset. 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 e.g. used by IEDB databases to reduce redundancies (mainly in the leading part of IRIs).
A typical CURIE would, e.g., 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
NCBITAXON in the CURIE and
NCBITaxon in the
IRI, the former one is just a placeholder.
This resolves the issue of different providers usings different IRIs with distinct formatting rules (as described above). As the choice of the provider is independent for each ontology, it allows greater flexibility for the repositories, as they do not need a single provider that needs be able to resolve all terms. Similarly, different repositories can use the same ontology, but use different providers. Note that this would not require changes to the data, as the data would only contains CURIEs, not the (provider-specific) IRIs.
The AIRR schema will provide a list of AIRR approved CURIE prefixes along with a list of at least one IRI prefix (i.e., replacement string) for each them. This list serves two 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 by non-repositories. The lists of IRI prefixes for each CURIE prefix should not be considered to be exhaustive. However, when using custom IRI prefixes, it must be ensured that they refer to the same ontology as the provider prefixes.
It should be explicitly noted that the IRI prefix list 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.
Modifications to the AIRR schema¶
All changes to the AIRR schema that would be based on the sprint can currently be reviewed on Github in Pull Request #385. These changes are intended to be included into the next major release.
Root nodes are specific to individual fields, not to an ontology. Therefore, NCBITAXON will use a root node of “Gnathostomata” for the annotations of the host species, but this would not be useful, e.g., if it would be used to annotate pathogenic organisms, which will require a top node at the apex of the hierarchy.
values) that are provided in the schema for ontology-based fields, should be considered an addition for convenience and not as being authoritative. Repositories or applications can choose to link synonyms to given concepts (e.g., “human” for “Homo sapiens”) to simply search queries. Repositories further can provide such a synonym in the
labelfield upon exporting data. However, repositories importing data should verify the correctness of
labelsthat do not match the one provided by the ontology. Importing repositories must not be expected to allow for queries of
labelsother than those present in the ontology.
Note that this section is only a parking lot, the respective text will be moved into the AIRR Docs in the final version.
Cells that come from Ficoll gradients should not be annotated as
PBMCsas this is a sister node of
lymphocyte. For the other sampling related fields, in nearly all cases venous blood (
UBERON:0013756) will be the correct
tissueand it should be used in the case of
peripheral venous puncture. However, if the mode of sampling is not specified,
UBERON:0000178) should be used instead. Also see https://github.com/airr-community/airr-standards/issues/242