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Ontologies

An ontology is a formal representation of a set of terminologies which finally represent real world objects. Dependencies, attributes and relations of and between the individual components of the set are recorded in a logical, formal language. In contrast to a taxonomy, which defines a mere hierarchical structure within a range of terms, an ontology is much more a network of information of logical dependencies of term elements. Or, in other words, an ontology defines a strict, formal "data model" for real world concepts such as "Person", "Work", "Artist" etc.

A full-fledged ontology thus has to offer at least two things: a set of concepts or terms (called resources, actually "resource classes") that represent concepts of real world objects, as well as attributes or properties describing these resources. These properties are linked either to a final value or may define a relationship to another resource. Let's assume that we define a resource called "Person" and two properties called "hasBirthday" and "hasParent" . For a specific incarnation of a "Person" (we call this an instance), "hasBirthday" will have a final value such as "1960-05-21", whereas "hasParent" will link to another instance of a "Person".

Within DSP, properties may be re-used for different resources. E.g. a property "description" may be used for a resource called "image" as well as "movie". Therefore, the list of properties is separated from the list of resources. The properties are assigned to the resources by defining "cardinalities". A cardinality indicates if a property is mandatory or can be omitted (e.g. if unknown), and if a property may be used several times on the same instance of a resource or not. The cardinality definitions are explained further below.

Example of an ontologies object:

{
  "ontologies": [
    {
      "name": "seworon",
      "label": "Secrets of the World Ontology",
      "properties": [
        ...
      ],
      "resources": [
        ...
      ]
    },
    {
      ...
    },
    {
      ...
    }
  ]
}

Ontologies Object in Detail

The following properties can occur within each object in ontologies.

Name

(required)

"name": "<string>"

The ontology's (short) name should be in the form of a xsd:NCNAME. This means a string without blanks or special characters but - and _ are allowed (although not as first character).

Label

(required)

"label": "<string>"

A string that provides the full name of the ontology.

Properties

(required)

"properties": [<property-definition>, <property-definition>, ...]

A properties array contains all properties used to describe resources in the ontology. A property has to be of a certain data type. It is not possible to create a custom data type.

The following fields are mandatory:

  • name
  • labels
  • object
  • gui_element

The following fields are optional:

  • comments
  • super (with the exception of LinkValue where super is mandatory)
  • subject
  • gui_attributes

A detailed description of properties can be found below.

Resources

(required)

The resource classes are the primary entities of the data model. They are the actual objects inside a terminology space. A resource class can be seen as a template for the representation of a real object that is represented in the DSP. A resource class defines properties (data fields). For each of these properties a data type as well as the cardinality has to be provided.

"resources": [<resource-definition>, <resource-definition>, ...]

A resource object needs to have the following fields:

  • name
  • labels
  • super
  • cardinalities

The following field is optional:

  • comments

A detailed description of resources can be found below.

Properties Object in Detail

Please note that object is used to define the data type. The gui_element depends on the value of the object.

The gui_attributes depends on the value of the gui_element.

Name

(required)

"name": "<string>"

A name for the property, e.g. "pageOf", "hasBirthdate", "createdBy". It should be in the form of a xsd:NCNAME. This means a string without blanks or special characters but - and _ are allowed (although not as first character).

By convention, property names start with a lower case letter.

Labels

(required)

"labels": {"<language>": "<string>", ...}

Collection of labels for the property as strings with language tag (currently "en", "de", "fr" and "it" are supported).

Comments

(optional)

"comments": { "<lang>": "<comment>", "<lang>": "<comment>", ... }

Comments with language tags. Currently, "de", "en", "fr" and "it" are supported. The comments element is optional.

Super

(optional)

"super": ["<super-property>", "<super-property>, ...]

A property has to be derived from at least one base property. The most generic base property that the DSP offers is hasValue. In addition, the property may be a sub-property of properties defined in external or other ontologies. External ontologies like dcterms or foaf must be defined in the "prefix" section. In this case the qualified name - including the prefix of the external or internal ontology - has to be given.

The following base properties are defined by DSP:

  • hasValue: This is the most generic base and taken as default if super is omitted.
  • hasLinkTo: This value represents a link to another resource. You have to indicate the "object" as a prefixed name that identifies the resource class this link points to (a ":" prepended to the name is sufficient if the resource is defined in the current ontology).
  • hasColor: Defines a color value
  • hasComment: Defines a standard comment
  • hasGeometry: Defines a geometry value (a JSON describing a polygon, circle or rectangle)
  • isPartOf: A special variant of hasLinkTo. It says that an instance of the given resource class is an integral part of another resource class. E.g. a "page" is part of a "book".
  • isRegionOf: A special variant of hasLinkTo. It means that the given resource class is a "region" of another resource class. This is typically used to describe regions of interest in images.
  • isAnnotationOf: A special variant of hasLinkTo. It denotes the given resource class as an annotation to another resource class.
  • seqnum: An integer that is used to define a sequence number in an ordered set of instances, e.g. the ordering of the pages in a book (independent of the page naming) in combination with a property derived from isPartOf.

Example of a properties object:

{
  "properties": [
    {
      "name": "id",
      "subject": ":School",
      "object": "TextValue",
      "super": [
          "hasValue"
      ],
      "labels": {
        "en": "School ID",
        "de": "ID der Schule",
        "fr": "ID de l'école"
      },
      "gui_element": "SimpleText",
      "gui_attributes": {
        "size": 32,
        "maxlength": 128
      }
    },
    {
      "name": "name",
      "subject": ":School",
      "object": "TextValue",
      "super": [
          "hasValue"
      ],
      "labels": {
        "en": "Name of the school",
        "de": "Name der Schule",
        "fr": "Nom de l'école"
      },
      "gui_element": "SimpleText",
      "gui_attributes": {
        "size": 32,
        "maxlength": 128
      }
    }
  ]
}

Subject

(optional)

"subject": "<resource-class>"

The subject defines the resource class the property can be used on. It has to be provided as prefixed name of the resource class (see below on how prefixed names are used).

Object / gui_element / gui_attributes

  • object: required
  • gui_element: required
  • gui_attributes: optional

"object": "<data-type>"

The object defines the data type of the value that the property will store. gui_element and gui_attributes depend on the data type. The following data types are allowed:

  • TextValue
  • ColorValue
  • DateValue
  • TimeValue
  • DecimalValue
  • GeomValue
  • GeonameValue
  • IntValue
  • BooleanValue
  • UriValue
  • IntervalValue
  • ListValue
  • Representation
  • any previously defined resource class in case of a link property

TextValue

"object": "TextValue"

Represents a text that may contain standoff markup.

gui_elements / gui_attributes:

  • SimpleText: A GUI element for TextValue. A simple text entry box (one line only). The attributes are:
    • gui_attributes:
      • maxlength=integer (optional): maximal length (number of characters accepted)
      • size=integer (optional): size (width) of widget
  • Textarea: A GUI element for TextValue. Presents a multiline text entry box. The optional attributes are:
    • gui_attributes:
      • cols=integer (optional): number of columns of the textarea
      • rows=integer (optional): number of rows of the textarea
      • width=percent (optional): width of the textarea on screen
      • wrap=soft|hard (optional): wrapping of text
  • Richtext: A GUI element for TextValue. Provides a richtext editor.
    • gui_attributes: No attributes

Example:

{
  "name": "hasPictureTitle",
  "super": [
    "hasValue"
  ],
  "object": "TextValue",
  "labels": {
    "en": "Title"
  },
  "gui_element": "SimpleText",
  "gui_attributes": {
    "maxlength": 255,
    "size": 80
  }
}

IntValue

"object": "IntValue"

Represents an integer value.

gui-elements / gui_attributes:

  • SimpleText: A GUI element for TextValue. A simple text entry box (one line only). The attributes "maxlength=integer" and "size=integer" are optional.
    • gui_attributes:
      • maxlength=integer (optional): The maximum number of characters accepted
      • size=integer (optional): The size of the input field
  • Spinbox: A GUI element for IntegerValue. A text field with and "up"- and "down"-button for increment/decrement. The attributes "max=decimal" and "min=decimal" are optional.
    • gui_attributes:
      • max=decimal (optional): Maximal value
      • min=decimal (optional): Minimal value

Example:

{
  "name": "hasInteger",
  "super": [
    "hasValue"
  ],
  "object": "IntValue",
  "labels": {
    "en": "Integer"
  },
  "gui_element": "Spinbox",
  "gui_attributes": {
    "max": 10.0,
    "min": 0.0
  }
}

DecimalValue

"object": "DecimalValue"

A number with decimal point.

gui-elements / gui_attributes:

  • Slider: A GUI element for DecimalValue. Provides a slider to select a decimal value.
    • gui_attributes:
      • max=decimal (mandatory): maximal value
      • min=decimal (mandatory): minimal value
  • SimpleText: A GUI element for TextValue. A simple text entry box (one line only). The attributes "maxlength=integer" and "size=integer" are optional.
    • gui_attributes:
      • maxlength=integer (optional): maximum number of characters accepted
      • size=integer (optional): size of the input field

Example:

{
  "name": "hasDecimal",
  "super": [
    "hasValue"
  ],
  "object": "DecimalValue",
  "labels": {
    "en": "Decimal number"
  },
  "gui_element": "SimpleText",
  "gui_attributes": {
    "maxlength": 255,
    "size": 80
  }
}

DateValue

object": "DateValue"
Represents a date. It's a string with the format calendar:start:end

Please note that the DateValue is an extremely flexible data type. It can represent an exact date or a date with a given uncertainty, and the date can be given in several calendars (currently the Gregorian and the Julian calendars are supported, with the Jewish and Islamic coming soon). Internally, a date is always represented as a start and end date. If start and end date match, it's an exact date. A value like "1893" will automatically be expanded to a range from January 1st 1893 to December 31st 1893.

  • calendar is either GREGORIAN or JULIAN
  • start has the form yyyy-mm-dd. If only the year is given, the precision is to the year. If only the year and month is given, the precision is to the month.
  • end is optional if the date represents a clearly defined period or uncertainty.

In total, a DateValue has the following form: "GREGORIAN:1925:1927-03-22" which means anytime in between 1925 and the 22nd March 1927.

gui_elements / gui_attributes:

  • Date: The only GUI element for DateValue. A date picker gui.
  • gui_attributes: No attributes

Example:

{
  "name": "hasDate",
  "super": [
    "hasValue"
  ],
  "object": "DateValue",
  "labels": {
    "en": "Date"
  },
  "gui_element": "Date"
}

TimeValue

"object": "TimeValue"

A time value represents a precise moment in time in the Gregorian calendar. Since nanosecond precision can be included, it is suitable for use as a timestamp.

gui-elements / gui_attributes:

  • TimeStamp: A GUI element for TimeValue which contains a date picker and a time picker.
  • gui_attributes: No attributes

Example:

{
  "name": "hasTime",
  "super": [
    "hasValue"
  ],
  "object": "TimeValue",
  "labels": {
    "en": "Time"
  },
  "gui_element": "TimeStamp"
}

IntervalValue

"object": "IntervalValue"

Represents a time-interval

gui-elements / gui_attributes:

  • SimpleText: A GUI element for TextValue. A simple text entry box (one line only). The attributes "maxlength=integer" and "size=integer" are optional.
    • gui_attributes:
      • maxlength=integer (optional): The maximum number of characters accepted
      • size=integer (optional): The size of the input field
  • Interval: Two spin boxes, one for each decimal
    • gui_attributes: No attributes

Example:

{
  "name": "hasInterval",
  "super": [
    "hasValue"
  ],
  "object": "IntervalValue",
  "labels": {
    "en": "Time interval"
  },
  "gui_element": "Interval"
}

BooleanValue

"object": "BooleanValue"

Represents a Boolean ("true" or "false).

gui-elements / gui_attributes:

  • Checkbox: A GUI element for BooleanValue.
    • gui_attributes: No attributes

Example:

{
  "name": "hasBoolean",
  "super": [
    "hasValue"
  ],
  "object": "BooleanValue",
  "labels": {
    "en": "Boolean value"
  },
  "gui_element": "Checkbox"
}

UriValue

"object": "UriValue"

Represents an URI

gui-elements / gui_attributes:

  • SimpleText: A GUI element for TextValue. A simple text entry box (one line only). The attributes "maxlength=integer" and "size=integer" are optional.
    • gui_attributes:
      • maxlength=integer (optional): The maximum number of characters accepted
      • size=integer (optional): The size of the input field

Example:

{
  "name": "hasUri",
  "super": [
    "hasValue"
  ],
  "object": "UriValue",
  "labels": {
    "en": "URI"
  },
  "gui_element": "SimpleText",
  "gui_attributes": {
    "maxlength": 255,
    "size": 80
  }
}

GeonameValue

Represents a location ID in geonames.org. The DSP platform uses identifiers provided by geonames.org to identify geographical locations.

gui-elements / gui_attributes:

  • Geonames: The only valid GUI element for GeonameValue. It interfaces are with geonames.org and it allows to select a location.
    • gui_attributes: No attributes

Example:

{
  "name": "hasGeoname",
  "super": [
    "hasValue"
  ],
  "object": "GeonameValue",
  "labels": {
    "en": "Geoname"
  },
  "gui_element": "Geonames"
}

ColorValue

"object": "ColorValue"

A string representation of the color in the hexadecimal form e.g. "#ff8000".

gui-elements / gui_attributes:

  • Colorpicker: The only GUI element for ColorValue. It's used to choose a color.
    • gui_attributes:
      • ncolors=integer (optional): Number of colors the color picker should present.

Example:

{
  "name": "hasColor",
  "super": [
    "hasColor"
  ],
  "object": "ColorValue",
  "labels": {
    "en": "Color"
  },
  "gui_element": "Colorpicker"
}

GeomValue

"object": "GeomValue"

Represents a geometrical shape as JSON. Geometrical shapes are used to define regions of interest (ROI) on still images or moving images.

gui-elements / gui_attributes:

  • Geometry: not yet implemented.
    • gui_attributes: No attributes
  • SimpleText: A GUI element for TextValue. A simple text entry box (one line only). The attributes "maxlength=integer" and "size=integer" are optional.
    • gui_attributes:
      • maxlength=integer (optional): The maximum number of characters accepted
      • size=integer (optional): The size of the input field

Example:

{
  "name": "hasGeometry",
  "super": [
    "hasGeometry"
  ],
  "object": "GeomValue",
  "labels": "Geometry",
  "gui_element": "SimpleText"
}

ListValue

"object": "ListValue"

Represents a node of a (possibly hierarchical) list

gui-elements / gui_attributes:

  • Radio: A GUI element for ListValue. A set of radio buttons. This works only with flat lists.
    • gui_attributes:
      • hlist=<list-name> (required): The reference of a list root node
  • List: A GUI element for ListValue. A list of values to select one from. This GUI element should be chosen for hierarchical lists or flat lists that could be expanded to hierarchical lists in the future.
    • gui_attributes:
      • hlist=<list-name> (required): The reference of a list root node

Example:

{
  "name": "hasListItem",
  "super": [
    "hasValue"
  ],
  "object": "ListValue",
  "labels": {
    "en": "List element"
  },
  "gui_element": "List",
  "gui_attributes": {
    "hlist": "treelistroot"
  }
}

Representation

"object": "Representation"

A property pointing to a knora-base:Representation. Has to be used in combination with "super": ["hasRepresentation"]. A resource having this generic property hasRepresentation can point to any type of Representation, be it a StillImageRepresentation, an AudioRepresentation, etc.

gui-elements / gui_attributes:

  • Searchbox: Allows searching resources that have super class Representation by entering at least 3 characters into a searchbox.
    • gui_attributes:
      • numprops=integer (optional): While dynamically displaying the search result, the number of properties that should be displayed.

Example:

{
    "name": "hasRep",
    "super": [
        "hasRepresentation"
    ],
    "object": "Representation",
    "labels": {
        "en": "Represented by"
    },
        "gui_element": "Searchbox"
    }

hasLinkTo Property

"object": ":<resource-name>"

Link properties do not follow the pattern of the previous data types, because they do not connect to a final value but to another (existing) resource. Thus, the "object" denominates the resource class the link will point to. If the resource is defined in the same ontology, the name has to be prepended by a ":", if the resource is defined in another (previously defined) ontology, the ontology name has to be prepended separated by a colon ":", e.g. "other-onto:MyResource". When defining a link property, its "super" element has to be "hasLinkTo" or "isPartOf" or derived from "hasLinkTo" or "isPartOf". "isPartOf" is a special type of linked resources, for more information see below.

gui-elements/gui_attributes:

  • Searchbox: Has to be used with hasLinkTo property. Allows searching resources by entering the resource name that the given resource should link to. It has one gui_attribute that indicates how many properties of the found resources should be indicated.
    • gui_attributes:
      • numprops=integer (optional): While dynamically displaying the search result, the number of properties that should be displayed.

Example:

{
  "name": "hasOtherThing",
  "super": [
    "hasLinkTo"
  ],
  "object": ":Thing",
  "labels": "Another thing",
  "gui_element": "Searchbox"
}

IsPartOf Property

A special case of linked resources is resources in a part-of / part-whole relation, i.e. resources that are composed of other resources. A isPartOf property has to be added to the resource that is part of another resource. In case of resources that are of type StillImageRepresentation, an additional property derived from seqnum with object IntValue is required. When defined, a client is able to leaf through the parts of a compound object, p.ex. to leaf through pages of a book.

Example:

{
  "name": "partOfBook",
  "super": [
    "isPartOf"
  ],
  "object": ":Book",
  "labels": {
      "en": "is part of"
  },
  "gui_element": "Searchbox"
},
{
  "name": "hasPageNumber",
  "super": [
    "seqnum"
  ],
  "object": "IntValue",
  "labels": {
      "en": "has page number"
  },
  "gui_element": "Spinbox"
}

Resources Object in Detail

Name

(required)

"name": "<string>"

A name for the resource, e.g. "Book", "Manuscript", "Person". It should be in the form of a xsd:NCNAME. This means a string without blanks or special characters but - and _ are allowed (although not as first character).

By convention, resource names start with a upper case letter.

Labels

(required)

"labels": {"<language>": "<string>", ...}

Collection of labels for the resource as strings with language tag (currently "en", "de", "fr" and "it" are supported).

Super

(required)

"super": ["<super-resource>", "<super-resource>", ...]

A resource is always derived from at least one other resource. The most generic resource class for DSP is Resource. A resource may be derived from resources defined in external ontologies.

The following predefined resources are provided by DSP:

  • Resource: A generic resource representing an item from the real world. This is the most general case, to be used in all cases when your resource is none of the special cases below.
  • StillImageRepresentation: An object representing a still image
  • TextRepresentation: An object representing an (external) text (not yet implemented)
  • AudioRepresentation: An object representing an audio file
  • DDDRepresentation: An object representing a 3-D representation (not yet implemented)
  • DocumentRepresentation: An object representing an opaque document (e.g. a PDF)
  • MovingImageRepresentation: An object representing a moving image (video, film)
  • ArchiveRepresentation: An object representing an archive file (e.g. Zip)
  • Annotation: A predefined annotation object. It has automatically the following predefined properties defined:
    • hasComment (1-n)
    • isAnnotationOf (1)
  • LinkObj: A resource class linking together several other resource classes. The class has the following properties:
    • hasComment (1-n)
    • hasLinkTo (1-n)
  • Region: Represents a region in an image. The class has the following properties:
    • hasColor (1)
    • isRegionOf (1)
    • hasGeometry (1)
    • hasComment (0-n)

Additionally, resources can be derived from external ontologies or from resources specified in the present document.

Cardinalities

(required)

"cardinalities": [...]

An array that contains information about the relation between resources and properties. It tells what properties a resource can have as well as how many times the relation is established.

  • cardinalities: Array of references to the properties that the resource may hold including the cardinality. A cardinality has the following properties:
    • propname (1): The name of the property. If it's used in the form :my_propname, the current ontology is referenced. Otherwise, the prefix of the ontology the property is part of has to be used.
    • gui_order (0-1): An integer number which will help the GUI to display the properties in the desired order (optional)
    • cardinality (1): Indicates how often a given property may occur. The possible values are:
      • "1": exactly once (mandatory one value and only one)
      • "0-1": The value may be omitted, but can occur only once.
      • "1-n": At least one value must be present, but multiple values may be present.
      • "0-n": The value may be omitted, but may also occur multiple times.

Comments

(optional)

"comments": { "<lang>": "<comment>", "<lang>": "<comment>", ... }

Comments with language tags. Currently, "de", "en", "fr" and "it" are supported. The comments element is optional.

Example for a resource definition:

{
  "resources": [
    {
      "name": "Schule",
      "labels": {
        "de": "Schule",
        "en": "School",
        "fr": "Ecole",
        "it": "Scuola"
      },
      "super": "Resource",
      "comments": {
        "de": "Ein Kommentar",
        "en": "A comment",
        "fr": "Une commentaire",
        "it": "Un commento"
      },
      "cardinalities": [
        {
          "propname": ":schulcode",
          "gui_order": 1,
          "cardinality": "1"
        },
        {
          "propname": ":schulname",
          "gui_order": 2,
          "cardinality": "1"
        },
        {
          "propname": ":bildungsgang",
          "gui_order": 3,
          "cardinality": "1"
        }
      ]
    }
  ]
}

Referencing Ontologies

For several fields, such as super in both resources and properties or propname in cardinalities, it is necessary to reference entities that are defined elsewhere. The following cases are possible.

  • DSP-API internals: These must be written without leading colon and should not be a fully qualified IRI.
    E.g. Resource, DocumentRepresentation or hasValue
  • An external ontology: The ontology must be defined in the prefixes This prefix should be used for referencing the ontology.
    E.g. foaf:familyName or sdo:Organization
  • The current ontology: Within an ontology definition, references can be made by prepending a colon without a prefix.
    E.g. :hasName
    Optionally, an explicit prefix can be used, in this case the ontology must be added to the prefixes and the prefix must be identical to the ontology's name.
  • A different ontology defined in the same file: Within one data model file, multiple ontologies can be defined. These will be created in the exact order they appear in the ontologies array. Once an ontology has been created, it can be referenced by the following ontologies via its name: first-onto:hasName. It is not necessary to add first-onto to the prefixes.
Last update: 2022-06-10