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Ontologies bio ontologies their creation and design l.jpg

-Ontologies: Bio-Ontologies: Their Creation and Design

Dr. Peter Karp

SRI, http://www.ai.sri.com/~pkarp/

Dr. Robert Stevens & Professor Carole Goble

University of Manchester, UK


Advertisement l.jpg

The Fourth Annual Bio-Ontologies Meeting

"Sharing Experiences and Spreading Best Practice”

Sponsored by

GlaxoSmithKline Pharmaceuticals

Tivoli Gardens, Copenhagen, Denmark,

26th July 2001

Organised by: Richard Chen, Carole Goble, Robert Stevens, Peter Karp, Pat Hayes, Robin McEntire and Eric Neumann.


Outline l.jpg

  • What is an ontology?

    • Motivation for ontologies in bioinformatics

    • Definition of an ontology

    • Naming the parts & comparing the types

    • Knowledge representation

  • Building an ontology

    • Methodologies, pprinciples and pitfalls

    • Running example: a macromolecule fragment

    • Ontology Tools

    • Development tools

Ontologies definitions components subtypes l.jpg

Ontologies:Definitions, Components, Subtypes

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  • Motivations for ontologies in bioinformatics

  • Definition of ontology

  • Principles and pitfalls of ontology design

  • GKB Editor ontology development tool

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Definition of an Ontology

  • Conceptualization of a domain of interest

    • Concepts, relations, attributes, constraints, objects, values

  • An ontology is a specification of a conceptualization

    • Formal notation

    • Documentation

  • A variety of forms, but includes:

    • A vocabulary of terms

    • Some specification of the meaning of the terms

  • Ontologies are defined for reuse

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Roles of Ontologies in Bioinformatics

  • Success of many biological DBs depends on

    • High fidelity ontologies

    • Clearly communicating their ontologies

      • Prevent errors on data entry and interpretation

  • Common framework for multidatabase queries

  • Controlled vocabularies for genome annotation

    • Riley ontology, GO

    • EC numbers

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Roles of Ontologies in Bioinformatics

  • Information-extraction applications

  • Reuse is a core aspect of ontologies

    • Reuse of existing ontologies faster than designing new ones

    • Reuse decreases semantic heterogeneity of DBs

  • Schema-driven Software

    • Knowledge-acquisition tools

    • Query tools

Definitions l.jpg

  • Data Model:

    • Primitive data structuring mechanism in which an ontology is expressed

    • Relational data model, object-oriented data model, frame data model

  • Ontology:

    • Domain specific conceptualization expressed within some data model

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Components of an Ontology

  • Concepts

    • AKA: Class, Set, Type, Predicate

    • Gene, Reaction, Macromolecule

  • Taxonomy of concepts

    • Generalization ordering among concepts

    • Concept A is a parent of concept B iff every instance of B is also an instance of A

    • Superset / subset

    • “A kind of” vs “a part of”

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Components of an Ontology

  • Objects

    • AKA: Instances, members of the set

    • trpA Gene, Reaction

    • Strictly speaking, an ontology with instances is a knowledge base

  • Relations and Attributes

    • AKA: Slots, properties

    • Product of Gene, Map-Position of Gene

    • Reactants of Reaction, Keq of Reaction

  • Values

    • The Product of the trpA Gene is tryptophan-synthetase

    • trpA.Product = tryptophan-synthetase

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Components of an Ontology

  • Constraints and other meta information about relations

    • Slot Product:

    • Value type: Poypeptide or RNA

    • Domain: Genes

    • Slot Map-Position:

    • Value type: Number

    • Domain: Genes

    • Cardinality: At-Most 1

    • Range: 0 <= X <= 100

  • General Axioms

    • Nucleic acids < 20 residues are oligonucleiotides

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More on Concepts

  • Primitive: properties are necessary

    • Globular protein must have hydrophobic core, but a protein with a hydrophobic core need not be a globular protein

  • Defined: properties are necessary + sufficient

    • Eukaryotic cells must have a nucleus. Every cell that contains a nucleus must be Eukaryotic.

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Ontology Subtypes Expressiveness

  • Controlled vocabulary

    • List of terms

  • Taxonomy

    • Terms in a generalization hierarchy

  • DB schemas (relational and object-oriented)

    • More implementation specific

    • No instance information

    • Limited constraints

  • Frame knowledge bases

  • Description Logics

Ontology subtypes l.jpg
Ontology Subtypes

  • Database schema

    • Concepts, relations, constraints

    • Perhaps no taxonomy

    • At most hundreds of concepts

  • Taxonomy

    • Concepts, taxonomy, perhaps a few relations

    • Thousands of concepts

  • Knowledge base

    • Concepts, relations, constraints, objects, values

    • Hundreds to hundreds of thousands of concepts and objects

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Ontology Subtypes

  • Generic (a.k.a. upper, core or reference)

    • common high level concepts

    • “Physical”, “Abstract”, “Structure”, “Substance”

    • useful for ontology re-use

    • important when generating or analysing natural language expressions

  • Domain-oriented

    • domain specific (e.g. E.coli)

    • domain generalisations (e.g. gene function)

  • Task-oriented

    • task specific (e.g. annotation analysis)

    • task generalisations (e.g. problem solving)

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Knowledge Representation

  • Ontology are best delivered in some computable representation

  • Variety of choices with different:

    • Expressiveness

      • The range of constructs that can be used to formally, flexibly, explicitly and accurately describe the ontology

    • Ease of use

    • Computational complexity

      • Is the language computable in real time

    • Rigour

      • Satisfiability and consistency of the representation

      • Systematic enforcement mechanisms

    • Unambiguous, clear and well defined semantics

      • A subclassOf B don’t be fooled by syntax!

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  • Vocabularies using natural language

    • Hand crafted, flexible but difficult to evolve, maintain and keep consistent, with poor semantics

    • Gene Ontology

  • Object-based KR: frames

    • Extensively used, good structuring, intuitive. Semantics defined by OKBC standard

    • EcoCyc (uses Ocelot) and RiboWeb (uses Ontolingua)

  • Logic-based: Description Logics

    • Very expressive, model is a set of theories, well defined semantics

    • Automatic derived classification taxonomies

    • Concepts are defined and primitive

    • Expressivity vs. computational complexity balance

    • TAMBIS Ontology (uses FaCT)

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Vocabularies: Gene Ontology

  • Hand crafted with simple tree-like structures

  • Position of each concept and its relationships wholly determined by a person

  • Flexible but…

  • Maintenance and consistency preservation difficult and arduous

  • Poor semantics

  • Single hierarchies are limiting

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Description Logics

  • Describe knowledge in terms of concepts and relations

  • Concept defined in terms of other roles and concepts

    • Enzyme = protein which catalyses reaction

    • Reason that enzyme is a kind of protein

  • Model built up incrementally and descriptively

  • Uses logical reasoning to figure out:

    • Automatically derived (and evolved) classifications

    • Consistency -- concept satisfaction

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Frames and Logics

  • Frames

    • Rich set of language constructs

    • Impose restrictive constraints on how they are combined or used to define a class

    • Only support primitive concepts

    • Taxonomy hand-crafted

  • Description logics

    • Limited set of language constructs

    • Primitives combined to create defined concepts

    • Taxonomy for defined concepts established through logical reasoning

    • Expressivity vs. computational complexity

    • Less intuitive

  • Ideal: both! Current OIL activity uses a mixture. Logics provide reasoning services for frame schemes.

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Ontology Exchange

  • To reuse an ontology we need to share it with others in the community

  • Exchanging ontologies requires a language with:

    • common syntax

    • clear and explicit shared meaning

  • Tools for parsing, delivery, visualising etc

  • Exchanging the structure, semantics or conceptualisation?

Ontology exchange languages l.jpg


modelling primitives,


Description Logics:

formal semantics &

reasoning support


Web languages:

XML & RDF based syntax

Ontology Exchange Languages

  • XOL eXtensible Ontology Language

    • XML markup

    • Frame based

    • Rooted in OKBC

    • http://www.ai.sri.com/pkarp/xol/

  • OIL Ontology Interface LayerOntology Inference Layer

    • Gives a semantics to RDF-Schema

    • http://www.ontoknowledge.org/oil

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OIL: Ontology Metadata (Dublin Core)


title “macromolecule fragment”

creator “robert stevens”

subject “macromolecule generic ontology”

description “example for a tutorial”

description.release “2.0”

publisher “R Stevens”

type “ontology”

formal “pseudo-xml”

identifier “http://www.ontoknowledge.org/oil/oil.pdf”

source “http://img.cs.man.ac.uk/stevens/tambis-oil.html”

language “OIL”

language “en-uk”

relation.haspart “http://www.ontoRus.com/bio/mmole.onto”

The three roots of oil l.jpg
The Three Roots of OIL

Description Logics:

Formal Semantics &

Reasoning Support

Frame-based Systems:

Epistemological Modelling



Web Languages:

XML- and RDF-based


Oil primitive ontology definitions l.jpg
OIL primitive ontology definitions

slot-def has-backbone

inverse is-backbone-of

slot-def has-component

inverse is -component-of

properties transitive

class-def nucleic-acid

class-def rna subclass-of nucleic-acid

slot-constraint has-backbone

value-type ribophosphate

class-def ribophosphate

class-def deoxyribophosphate

subclass-of NOT ribophosphate

Oil defined ontology definitions l.jpg
OIL defined ontology definitions

class-def defined dna

subclass-of nucleic-acid AND NOT rna

slot-constraint has-backbone

value-type deoxyribophosphate

class-def defined enzyme

subclass-of protein

slot-constraint catalyse

has-value reaction

class-def defined kinase

subclass-of protein

slot-constraint catalyse

has-value phosphorylation-reaction

Oil in xml l.jpg

  • OIL has a DTD, an XML Schema and a mapping to RDF-Schema. See web site for details


    <slot-name = “has-component”/>

    <inverse> <slot-name = “is-component-of”/> </inverse>

    <properties> <transitive/> </properties>


    <class-def> <class-name= “nucleic-acid”/></class-def>


    <class-name= “rna”/>

    <subclass-of> <class name = “nucleic-acid”/> </subclass-of>


    <slot-name = “has-backbone”/>

    <value-type> <class name= “ribophosphate” </value-type>



Oil remarks l.jpg
OIL Remarks

  • Tools:

    • Protégé II editor

    • FaCT reasoner

  • Other projects:

    • Semantic Web projects (http://www.semanticweb.org)

    • Agents for the web projects (e.g. DAML)

      A knowledge representation language and inference mechanism for the web

Oil features l.jpg
OIL Features

  • Based on standard frame languages

  • Extends expressive power with DL style logical constructs

    • Still has frame look and feel

    • Can still function as a basic frame language

  • OILcore language restricted in some respects so as to allow for reasoning support

    • No constructs with ill defined semantics

    • No constructs that compromise decidability

  • Has both XML and RDF(S) based syntax

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OIL Features

  • Semantics clearly defined by mapping to very expressive Description Logic, e.g.:

    • slot-constraint reverse-transcribe-from has-valuemRNA or (part-of has-value mRNA)

    • eats.meat eats.fish

  • Note the importance of clear semantics:

    • eats.(meat  fish)

  • is inconsistent (assuming meat and fish are disjoint)

  • Mapping can also be used to provide reasoning support from a Description Logic system (e.g., FaCT)

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Why Reasoning Support?

  • Key feature of OIL core language is availability of reasoning support

  • Reasoning intended as design support tool

    • Check logical consistency of classes

    • Compute implicit class hierarchy

  • May be less important in small local ontologies

    • Can still be useful tool for design and maintenance

    • More important with larger ontologies/multiple authors

  • Valuable tool for integrating and sharing ontologies

    • Use definitions/axioms to establish inter-ontology relationships

    • Check for consistency and (unexpected) implied relationships

    • Already shown to be useful technique for DB schema integration

Daml oil l.jpg

  • OIL merged with DAML

  • Originally retained frame syntax

  • DAML more concerned with deploymnent rather than building and managing

  • OIL mapped to DAML+OIL, but not reliably reversed

  • FRAME look and feel may return

  • Web ontology language

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Building Ontologies

  • No field of Ontological Engineering equivalent to Knowledge or Software Engineering;

  • No standard methodologies for building ontologies;

  • Such a methodology would include:

    • a set of stages that occur when building ontologies;

    • guidelines and principles to assist in the different stages;

    • an ontology life-cycle which indicates the relationships among stages.

  • Gruber's guidelines for constructing ontologies are well known.

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The Development Lifecycle

  • Two kinds of complementary methodologies emerged:

    • Stage-based, e.g. TOVE [Uschold96]

    • Iterative evolving prototypes, e.g. MethOntology [Gomez Perez94].

  • Most have TWO stages:

    • Informal stage

      • ontology is sketched out using either natural language descriptions or some diagram technique

    • Formal stage

      • ontology is encoded in a formal knowledge representation language, that is machine computable

  • An ontology should ideally be communicated to people and unambiguously interpreted by software

    • the informal representation helps the former

    • the formal representation helps the latter.

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A Provisional Methodology

  • A skeletal methodology and life-cycle for building ontologies;

  • Inspired by the software engineering V-process model;

  • The overall process moves through a life-cycle.

The left side charts the processes in building an ontology

The right side charts the guidelines, principles and evaluation used to ‘quality assure’ the ontology

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Ontology in Use

The V-model Methodology

Evaluation: coverage, verification, granularity

Identify purpose and scope

Knowledge acquisition

User Model

Conceptualisation Principles: commitment, conciseness, clarity, extensibility, coherency


Integrating existing ontologies

Conceptualisation Model

Encoding/Representation principles: encoding bias, consistency, house styles and standards, reasoning system exploitation



Implementation Model

The ontology building life cycle l.jpg
The ontology building life-cycle

Identify purpose and scope

Knowledge acquisition


Language and representation


Integrating existing ontologies

Available development tools



User model identify purpose and scope l.jpg
User Model: Identify purpose and scope

  • Decide what applications the ontology will support

  • EcoCyc: Pathway engineering, qualitative simulation of metabolism, computer-aided instruction, reference source

  • TAMBIS: retrieval across a broad range of bioinformatics resources

  • The use to which an ontology is put affects its content and style

  • Impacts re-usability of the ontology

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User Model: Knowledge Acquisition

  • Specialist biologists; standard text books; research papers and other ontologies and database schema.

  • Motivating scenarios and informal competency questions – informal questions the ontology must be able to answer

  • Evaluation:

    • Fitness for purpose

    • Coverage and competency

Ontology scenario l.jpg
Ontology Scenario

  • A molecule ontology;

  • Describes the molecules stored in bioinformatics databases and annotated therein;

  • It should cover the molecules and other chemicals described in the resources;

  • The ontology will be used for querying and annotating information in bioinformatics resources.

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Competency Questions

  • Cover the macromolecules found in molecular biology resources and courses;

  • Should accommodate various views on the macromolecules;

  • should cover the queries people want to ask of macromolecules;

  • In reality, need more detail on these questions- “give me tRNA genes with anticodon x, from aardvark”.

Acquiring knowledge l.jpg
Acquiring Knowledge

  • Find your knowledge!

  • An important source is your head, but…

  • Use text books, glossaries (many of which lie on the web) and domain experts;

  • Use other ontologies – what did they include and how did they do it?

  • Record your sources of knowledge.

  • Use your competency questions;

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Starting Concept List

  • Chemicals – atom, ion, molecule, compound, element;

  • Molecular-compound, ionic-compound, ionic-molecular-compound, …;

  • Ionic-macromolecular-compound and ionic-msall-macromolecular-compound;

  • Protein, peptide, polyprotein, enzyme, holo-protein, apo-protein,…

  • Nucleic acid – DNA, RNA, tRNA, mRna, snRNA, …

Conceptualisation model conceptualisation l.jpg
Conceptualisation Model: Conceptualisation

  • Identify the key concepts, their properties and the relationships that hold between them;

    • Which ones are essential?

    • What information will be required by the applications?

  • Structure domain knowledge into explicit conceptual models.

  • Identify natural language terms to refer to such concepts, relations and attributes;

Slide51 l.jpg

Conceptualisation Sketch

















Ionic Molecular



Slide52 l.jpg

Molecule Conceptualisation Sketch

Ionic Macromolecular



















Conceptualisation model naming l.jpg
Conceptualisation Model: Naming

  • Determine naming conventions

    • Consistent naming for classes and slots

    • EcoCyc:

      • Classes are capitalized, hyphenated, plural

      • Slot names are uppercase

        A quality ontology captures relevant biological distinctions with high fidelity

Conceptualisation model pitfalls l.jpg
Conceptualisation Model: Pitfalls

  • Pitfall: Missing ontological elements

    • Missing classes: Swiss-Prot Protein complexes

    • Lack of Lipid and Cofactor in example ontology

    • Missing attributes: Genetic code identifier

    • Confuse 1:1 with 1:Many, or 1:Many with Many:Many

      • Cofactor as an attribute of reaction as well as protein

    • Important data is stored within text/comment fields

  • Pitfall: Extra ontological elements

  • Pitfall: Stop over-elaborating – when do I stop?

  • Pitfall: Relevance – do I really need all this detail?

Conceptualisation partonomy l.jpg
Conceptualisation: Partonomy

  • Part-of relationships very important

  • Several linds of part-of: component-of, region-of, mixture-of

  • Alpha-helix is a region of a protein, but a protein is compoennt of a complex

  • Care in placing transitivity

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Integrating Existing Ontologies

  • Reuse or adapt existing ontologies when possible

    • Save time

    • Correctness

    • Facilitate interoperation

    • Reuse GO to give example ontology Function, Process and Location

  • Integration of ontologies

    • Ontologies have to be aligned

    • Hindered by poor documentation and argumentation

    • Hindered by implicit assumptions

    • Shared generic upper level ontologies should make integration easier

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Encoding: Implementation Toolkit

  • Construct ontology using an ontology-development system

    • Does the data model have the right expressivity?

      • Is it just a taxonomy or are relationships needed?

      • Is multiple parentage needed? Inverse relationships?

      • What types of constraints are needed?

    • Are reasoning services needed?

    • What are authoring features of the development tool?

    • Can ontology be exported to a DBMS schema?

    • Can ontology be exported to an ontology exchange language?

    • Is simultaneous updating by multiple authors needed?

    • Size limitations of development tool?

Encoding l.jpg

Encode sketch in KRL;

  • Use OIL – a frame syntax with reasoning support if we want it;

  • Wide range of expressivity (see cofactor example later);

  • Hand craft a hierarchy – implement the sketch made earlier;

  • This hand-crafted version can be migrated to a more descriptive form later.

Initial encoding l.jpg
Initial Encoding

class-def chemical

subclass-of substance

class-def molecule

subclass-of chemical

class-def compound

subclass-of chemical

class-def molecular-compound

subclass-of molecule and compound

Encoding ontology implementation pitfalls l.jpg
Encoding: Ontology Implementation Pitfalls

  • Pitfall: Semantic ambiguity

    • Multiple ways to encode the same knowledge

    • Meaning of class definitions unclear

  • Pitfall: Encoding Bias

    • Encoding the ontology changes the ontology

Encoding ontology implementation pitfalls61 l.jpg
Encoding: Ontology Implementation Pitfalls

  • Pitfall: Redundancy (lack of normalization)

    • Exact same information repeated

    • Presence of computationally derivable information

      • Date of birth and age

      • Sequence length

      • DNA sequence and reverse complement

    • More effort required for entry and update

    • In KB partial updates lead to inconsistency

    • OK if redundant information is maintained automatically

Encoding the interaction problem l.jpg
Encoding: The Interaction Problem

  • Task influences what knowledge is represented and how its represented

    • Molecular biology: chemical and physical properties of proteins

    • Bioinformatics: accession number, function gene

    • Underlying perspectives mean they may not be reconcilable

  • If an ontology has too many conflicting tasks it can end up compromised – TaO experience

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Evaluate it - A guide for reusability

  • Conciseness

    • No redundancy

    • Appropriateness – protein molecules at the atomic resolution when amino acid level would do

  • Clarity

  • Consistency

  • Satisfiability – it doesn’t contradict itself

  • Molecule and Compound disjoint, but molecular-cpound is (molecule and compound)

    • Commitment

    • Do I have to buy into a load of stuff I don’t really need or want just to get the bit I do?

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Documentation: Make Ontology Understandable!

  • Produce clear informal and formal documentation

    • An ontology that cannot be understood will not be reused

    • Genbank feature table

    • NCBI ASN.1 definitions

  • There exists a space of alternative ontology design decisions

    • Semantics / Granularity

    • Terminology

  • Pitfall: Neglecting to record design rationale

Slide65 l.jpg

Molecules Revisited

Non-Ionic Macromolecular


Ionic Macromolecular



















More encoding l.jpg
More Encoding

class-def chemical

subclass-of substance

class-def defined molecule

subclass-of chemical

Slot-constraint contains-bond min-cardinality 1 has-value covalent-bond

class-def defined compound

subclass-of chemical

Slot-constraint has-atom-types greater-than 1

class-def defined molecular-compound

subclass-of molecule and compound

Cofactor knowledge l.jpg
Cofactor Knowledge

  • Gather knowledge about cofactors, coenzymes and prosthetic groups from glossaries and dictionaries etc.

  • Note that definitions are inconsistent and even contradictory.

  • Synthesise knowledge and make judgements.

Encoding cofactor l.jpg
Encoding Cofactor

Class-def defined cofactor

Subclass-of metal-ion or small-organic-molecule

Slot-constraint binds-to has-value protein

Class-def defined coenzyme

Subclass-of cofactor

Slot-constraint binds-loosley-to has-value protein

Class-def defined prosthetic-group

Subclass-of cofactor and (not metal-ion)

Slot-constraint binds-strongly-to has-value protein

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Cofactor Discussion

  • Classifies as a kind of chemical;

  • Taken from IUPAC definition – document – not a child of organic-molecule and metal-ion;

  • Can express both disjunction and negation in OIL;

  • Uses a slot hierarchy in describing binds-to.

More discussion l.jpg
More Discussion

  • Can we define sufficiency conditions for peptide?

  • Mass and length are not easy to use in definition – A protein is > 100 Kda;

  • What about a 99 Kda protein;

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Publish the Ontology

  • Formal and informal specifications

  • Intended domain of application

  • Design rationale

  • Limitations

  • See EcoCyc paper in ISMB-93/Bioinformatics 00

  • See TAMBIS paper in Bioinformatics 99

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Ontological Pitfalls

  • Stop-over – when do I stop over elaborating?

    • Proteins  amino acid residues  side chains  physical chemical properties ….

  • Relevance

    • Do we need to mention all the types of nucleic acid?

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Ontology DevelopmentTools

  • Development environments

  • Ontology Libraries

  • Ontology publishing and exchange

    • Across all representational forms (logic, frame, etc..)

    • Web compliant

  • Ontology delivery

    • Ontology servers

  • Development environments l.jpg
    Development Environments

    • Considerations depend on ontology subtype!

      • Expressiveness of data model

      • Authoring features

      • DBMS export capabilities

      • Ontology-exchange language export capabilities

      • Distributed authoring

      • Size limitations

    • WebOnto

    • Ontosaurus

    • GKB Editor

    • Protégé II

    • Ontolingua

    • GRAIL toolkit etc…

    • Wondertools

    Gkb editor ontology development toolkit l.jpg
    GKB EditorOntology Development Toolkit

    • Graphical editor for KBs and ontologies

    • Ontologies stored in Ocelot object-oriented knowledge base

      • Expressive, scalable, distributed

      • EcoCyc ontology contains 1K classes, 15K instances

    • Knowledge is graphically portrayed in 3 viewers

    • All operations are schema driven

    • See http://www.ai.sri.com/~gkb/user-man.html

    Ocelot capabilities l.jpg
    Ocelot Capabilities

    • Frame data model

    • KBs and ontologies stored in files or Oracle

    • Oracle KBs and ontologies:

      • Better scalability -- frame faulting on demand and in background

      • Concurrency control system coordinates changes by multiple users

      • Transaction logging (recall operation history)

    • GFP API provides programmatic interface

    Distributed ontology development l.jpg
    Distributed Ontology Development

    User 1

    User 2




    User 4

    User 3

    Gkb editor l.jpg
    GKB Editor

    • Taxonomy Viewer

      • Create/delete classes and instances

      • Browse class taxonomy

      • Alter class/subclass links

    • Frame editor

      • Add/remove slots to/from classes

      • Create/delete/edit slot values for instances

    • Frame relationships viewer

      • View and update a network of relationships among instances

    Summary l.jpg

    • A definition of ontology as a characterisation of conceptualisation -- capturing the things we know about a domain;

    • The knowledge within an ontology can be applied to a variety of tasks;

    • Building an ontology -- process and life-cycle;

    • Influences on the choice of encoding language;

    • The desirability of tools for the building, management and exchange of ontologies;

    Final remarks l.jpg
    Final remarks

    • The use of ontologies is growing within the bio-molecular world

    • They are a high-cost, but high-benefit solution to a variety of problems confronting the bioinformatics community.

    Some references 1 l.jpg
    Some References (1)


    • Stevens R., Goble C.A. and Bechhofer, S. Ontology-based Knowledge Representation for Bioinformatics accepted for Briefings in Bioinformatics

      Bio-ontologies & Systems

    • Karp P. D. An ontology for biological function based on molecularinteractions Bioinformatics 2000;16 269-285

    • Ashburner et al Gene Ontology: Tool for the Unification of Biology, Nature Genetics Vol 25 pages 25-29

    • R. Altman, M. Bada, X.J. Chai, M. Whirl Carillo R.O. Chen, and N.F. Abernethy. RiboWeb: An Ontology-Based System for Collaborative Molecular Biology. IEEE Intelligent Systems, 14(5):68-76, 1999.

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