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POC tutorial #2: Ontology Development

Ontology Development: 

Ontology Development What are the organizing principles? How are terms defined? How are terms related to each other? What is a directed acyclic graph (DAG)? Elements and attributes of terms What is the “True Path Rule” ? Species specificity: problems and solutions How are ontologies maintained?

What are the organizing principles?: 

What are the organizing principles? Keep it simple: strive for a robust extensible structure, rather than comprehensiveness. Where possible, rely on synonyms (equivalence of terms) rather than creating a new term. The criterion for creating an anatomy term include: location, morphology, derivation and spatial/positional organization. Include species specific terminology to accommodate annotation and biological accuracy (i.e. maintain the true path rule). All terms must be defined.

How are terms defined?: 

How are terms defined? The precise definition of terms is critical to the integrity of the ontologies. Definitions are obtained primarily from standard references such as textbooks and glossaries. Definitions may be taken verbatim from references or modified for clarity or to reflect common usage. Most definitions come from Plant Anatomy (K.Esau) and the Angiosperm Phylogeny website Missouri Botanical Garden).

How are terms related to each other?: 

How are terms related to each other? Terms are related to each other as children to parents. Each child term can have one or more parents. There are three basic types of child-parent relationships used in the plant ontologies, which are illustrated in the following graph. plant cell tissue plant structure tricho- blast guard cell root hair root organ

The is a relationship: 

The is a relationship is a is a simple class-subclass relationship. For example, a trichoblast is a plant cell which is a plant structure. A root is a organ which is a plant structure. plant cell tissue plant structure tricho- blast guard cell root hair root organ

The part of Relationship: 

The part of Relationship It indicates a subpart/part relationship within a tissue or organ. Used in a non-restrictive manner. An example would be root hair part of root; root hair is always part of a root, but not all roots have root hair. plant cell tissue plant structure tricho- blast guard cell root hair root organ

The develops from Relationship: 

The develops from Relationship It indicates that cell/tissue/organ develops from its parent term. Implies both, develops from and a more indirect relationship, derive from. For example, the root hair develops from the trichoblast which is a plant cell which is a plant structure. plant cell tissue plant structure tricho- blast guard cell root hair root organ

What is a directed acyclic graph (DAG)?: 

What is a directed acyclic graph (DAG)? A DAG is a collection of ordered nodes (e.g. parent-child) and edges (e.g. relationships) that flows in a specific direction. In the ontologies, nodes are terms. A path through the nodes cannot cycle, or double back on itself.


If every child node has no more than one parent node, then the DAG is a tree. If at least one child node has two parents, the DAG is a network. The plant ontology, like the Gene Ontology can be represented as a network DAG. plant cell tissue plant structure tricho- blast guard cell root hair root organ

Tree view in “AmiGo browser”: 

Tree view in “AmiGo browser”

What is the true path rule?: 

What is the true path rule? The true path rule states that the path from any node (term) all the way to the top node of the tree must be biologically correct. When violations of the true path rule are detected the structure of the ontology must be modified.

Example: Maize lemmas: 

Example: Maize lemmas For example, a lemma is a type of bract that is a part of a maize floret but is not present in other flowers. Schematic diagram of male florets of maize. Veit et.al. Plant Cell. 1993 Oct;5(10):1205-1215 lemma flower (generic) part of

Maintaining the true path rule: 

Maintaining the true path rule Lemmas are not present in all flowers- therefore it is necessary to create a special instance of a flower - specifically a maize floret. lemma floret (sensu Poaceae) flower (generic) floret lemma flower (generic) Problem:this violates true path as a lemma is not part of a generic flower Solution: add floret as instance of flower and add an instance of a maize floret part of is a is a part of

How does this affect queries?: 

How does this affect queries? The path to each parent is true. A query of all genes affecting the generic flower would still return genes affecting the lemma of maize floret. It is possible to find all flower mutations in maize without explicit knowledge of maize-specific terms such as lemma. Representation of lemma in the plant structure ontology

Elements and attributes of terms: 

Elements and attributes of terms The following section defines the attributes of terms as they are shown in the AmiGO browser. Here, we show the term "inflorescence".


Accession Each term has a unique identifier of that term.


Aspect This refers to the aspect of the Plant Ontology (structure or developmental stage) that includes the term.


Synonyms The synonyms include a variety of alternate forms of the term such as variations, broader/narrower terms, misnomers and equivalent terms.


Definition Definition of the term as used in the Plant Ontologies.Definitions are primarily obtained from text books and glossaries.


Comments Comments by curators/developers to provide clarity or additional information such as usage.


Lineage The diagram shows the relationship of the term to all of its parents.

Species-specificity:the problem: 

Species-specificity:the problem In cases where more specific instances of terms (sensu) are created the children terms cannot be generic because this violates the true path rule. An Arabidopsis gene annotated to a generic anther term, should NOT be retrieved in a search for genes expressed in a maize floret. anther floret (sensu Zea) flower part of is a part of X

Species-specificity:the solution: 

Species-specificity:the solution The solution is to create specific (sensu Zea) instances for the parts of the maize floret. The new sensu terms are also added as instances of the more generic term, so that a query for mutants affecting the anther will include genes from maize as well as other species. anther floret (sensu Zea) flower part of is a part of anther (sensu Zea) is a

How are the ontologies maintained?: 

How are the ontologies maintained? The ontologies are updated often. The most current versions of the ontologies can be downloaded from the POC CVS repository. The updated ontologies are then used to update the Plant Ontology (AmiGO) browser on a monthly basis. The ontologies are created and edited by curators using the DAG Edit ontology editor which is freely available from Sourceforge.

End of tutorial: 

End of tutorial

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