Form Language

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As described in Linked Data Shapes, Forms and Footprints, “Form Languages are used to define user interfaces for reading and writing Linked Data with a specific shape.” Based on the User Interface ontology, Form Language defines how data should be presented as a form, and provides a direct relationship between the form fields and the shape elements.

This document provides guidance on how to write a Form Model, in Form Language, to define the layout and user interface (UI) elements rendered in a form.


Form Models

Form Models are defined as a turtle (.ttl) files. It is assumed the reader of this document is familiar with Turtle. A primer discussing Turtle can be found here.

A Form Model uses a simple structure with:

  1. List of Prefixes used within the Form Model.
  2. Form node, defining the form name and (an ordered) list of form parts.
  3. An ordered list of single fields, repeated fields, or grouped fields to be displayed on the form.

By way of illustration, an example Form Model is shown below which allows viewing and editing of a contact’s name and photo:

@prefix shape: <contact-shapes.ttl#>.
@prefix ui: <>.

:personForm a ui:Form;
    ui:parts (:nameField :photoField).

:nameField a ui:SingleLineTextField;
    ui:label "Name";
    ui:arc shape:Individual_fn;
    ui:size 20.

:photoField a ui:ImageField; # @@ correct name?
    ui:arc shape:Individual_hasPhoto.
The example references 2 prefixes (shape: and ui:), and would render a form (:personForm) that has 2 parts (:nameField and :photoField).


The Prefixes are namespace declarations, providing the association of a prefix used in the document with a URI; one line per prefix.

For example, the following code snippet references the UI Ontology and the RDF syntax in the Form Model.

@prefix ui: .
@prefix rdf: .


The ui:Form node defines the name, groups and fields of the form:

Property Type Description Example
parts rdf:Collection (ordered array) of Groups & Fields The parts of the form in the order in which they are displayed.
part Field (Obsolete) A field which is a part of the form or group. This property is obsolete. Use parts.
If you use the obsolete ui:part method for listing the parts of a form, then each field needs an additional property:
Property Type Description Example
sequence Integer
The parts of the form in the order in which they are laid out.
sequence Integer
For each ui:part, declare its type, and the extra data that type requires.

In the example below, the :personForm namedNode is defined as a ui:Form type, which contains two parts: the :nameField and the :photoField.
:personForm a ui:Form;
    ui:parts (:nameField :photoField) .
Due to the : prefix, these are expected to be namedNodes inside the same file. They can be named anything, as long as they are linked here.Fields


The form ui:parts defines the layout of the controls (e.g., text boxes, checkboxes, dropdowns, etc.) that are displayed on the form.The ui:partscan be:

They may be named nodes in your file, or blank nodes - the form system does not mind. However, it is often useful to name them to keep track of them.


A ui:Group is a field which is just a collection of other fields. It is in fact interchangeable with ui:Form.
:Address a ui:Group ;
    ui:parts (:street :locality :region :postalcode ) ;
This :Address node is a group of parts, the same way a Form is a set of parts. In this case, the :Address node could be used in another Form type, and it would pull in all of these parts into a subform inside of the main form. You can include groups inside of other groups.


When the subject can have several of the same thing (e.g., friends, phone numbers, etc.), then the ui:Multiple field can be used. For each new thing, the system should generate an arbitrary (timestamp) URI within the file where the data is being stored. The subform is then about that thing: the subject of the subform is not the subject of the original form. It is the friend, or the address, and so on.

:Addresses a ui:Multiple ;
    elem:title "Address Details" ;
    ui:part :Address .

This example shows an :Addresses part defined as a ui:Multiple, which indicates to the UI that it is repeatable. This particular node has a title and the single part: an Address. In the parent form, :Addresses would be included in the ui:parts predicate.


Common Field Properties

Some field properties can be used with any field (except the Documentations fields).

Unless explicitly specified, all field classes and properties are in the UI namespace except the data types like Integer which are in the XSD namespace.

Property Type Description Example
arc IRI Link to an external shape definition. ui:arc shape:Individual_fn;
autofocus Boolean Indicate that the form element should receive input focus as soon as the form is loaded, so that you can start typing immediately without having to specifically click on or tab to that control. Default is false. ui:autofocus "1";
backgroundColor RGB Hex String Background color of the part. ui:backgroundColor "#00000";
backgroundImage IRI or base64 Background image.
?:className String Name of a CSS class to apply to the element ?:className "inrupt-form" ;
color RGB Hex String Foreground color of the part. ui:color "#EE00EE" ;
default [according to field type] Optional The input control is by default set to this value. It is easiest for the user to enter this value. (This value is not stored by the forms system automatically if the user does not select or enter it in some way.
dependingOn rdf:Property Link to a part that the current part depends upon.
label String A label for the form field. ui:label “Address: ”@en;
multiple Type Assigned to a part to indicate it can be repeated.
prompt String Additional text to display to the user (e.g., mouseover or tooltip text, or placeholder). ui:prompt “Enter your mailing address”@en;
property rdf:Property When the user enters the data, it is stored in the web as a triple with this property as its predicate.
required Boolean Is the field required? Default is false. ui:required "1";
Define the error to be displayed if a user does not enter data into a required field.
ui:requiredError [ rdfs:label :"Name is required"@en];
readonly Boolean Is the field editable? Default is false. ?:readonly "1";
(Deprecated) Used to define the order of the fields. This can now be done more simply using ui:parts Lists
sortBy Class

sortPriority Integer Sort order for a set of values.
style String

Valid CSS style string such as one could put in an HTML style attribute. Depending on the user interface system, this can by given to individuals, classes or properties. It is up to a user interface which wants to draw on them to pick how it uses styles from which parts of the data it has.

validationError -

Define the error to be displayed if a user enters invalid data.

ui:validationError [ rdfs:label :"Age has to 18+"@en];
Other properties are given for each form field type.

Logical Fields

These prompt the user to select either a 2-state (true/false) or 3-state (true/false/unknown) value:
  • 2-state (BooleanField).
  • 3-state (TriStateField).

A 2-state checkbox on the form, stores an RDF boolean true or false value.
:poweruserField a ui:BooleanField;    
    ui:label “Are you a Power User?”@en ;
    ui:default "0" ;
    ui:property solid:poweruser .

If no default is given, the checkbox should default to false.

A 3-state checkbox on the form, stores a tri-state value - true, false, or no value (i.e., unknown) if the box is left in its third, blank state.
:accepttermsField a ui:TriStateField;    
    ui:label “Do you accept the Terms and Conditions?”@en ;
    ui:property <...> .

If no default is given, the 3-state checkbox should default to unknown.

Numeric Fields

These fields prompt the user for a single numeric value:
  • Monetary (DecimalField).
  • Floating-point number (FloatField).
  • Integer (IntegerField).

These numeric fields share a common set of properties.

Property Type Description Example
maxValue Same as field type Maximum value for the field. If no maximum value is provided, the maximum is set to the maximum value for the field type.
ui:maxValue "3.142" ;
minValue Same as field type Minimum value for the field. If no minimum value is provided, the minimum is set to the minimum value for the field type. ui:minValue "-3.142" ;

An RDF decimal value. This is useful for monetary amounts.

:itemCost a ui:DecimalField
    ui:label "Cost?" ;
    ui:minValue "10.99" ;
    ui:maxValue "9999" ;
    ui:property <...> . 

Enter a floating point number.

:distanceField a ui:FloatField
    ui:label "Distance (km): " ;
    ui:minValue "-173.45" ;
    ui:property .

Enter an RDF integer value. Depending upon the valid integer range and rendering device, integer could be selected using an integer selector.

:ageInYears a ui:IntegerField
    ui:label "Age in years" ;
    ui:minValue "0" ;
    ui:maxValue "125" ;
    ui:property <...> .

Date and Time Fields

For many forms, a user will need to temporal values:

  • Date (DateField).
  • Time (TimeField).
  • Combined Date and Time (DateTimeField).

Select/enter a date, preferably via a Date picker.

This field uses specific properties.

Property Type Description Example
maxValue date Maximum valid date. ui:maxValue "2019-01-01";
Offset (in days) from today of the maximum valid date.
ui:maxdateOffset "365";
minValue date Minimum valid date. ui:minValue "2019-12-31" ;
mindateOffset Integer Offset (in days) from today of the minimum valid date. ui:mindateOffset "-7";

Note: If both a hardcoded and an offset date are provided (e.g., ui:maxValue and ui:maxdateOffset), the hardcoded date takes precedence.

Generates an RDF date literal as is value.

:bodFrom a ui:DateField ;
    ui:label "Date of Birth: "@en ;
    ui:minValue "1900-01-01" ;
    ui:maxdateOffset "0" ;
    ui:property person:birthDate .

Select/enter a date and time combination, preferably via a DateTime picker.

This field uses specific properties.

Property Type Description Example
maxValue dateTime Maximum valid datetime. ui:maxValue "2011-12-31 17:00:00";
maxdatetimeOffset Integer Offset (in seconds) from now of the maximum valid datetime. ui:maxdatetimeOffset "129600";
minValue dateTime Minimum valid datetime.
ui:minValue "2011-01-01 08:30:00";
mindatetimeOffset Integer Offset (in seconds) from now of the minimum valid datetime. ui:maxdatetime "-43200";

Note: If both a hardcoded and an offset datetime are provided (e.g., ui:maxValue and ui:maxdatetimeOffset), the hardcoded datetime takes precedence.

Leaves an RDF datetime literal as is value.

:departureDateTime a ui:DateTimeField ;
    ui:label "Departure: "@en ;
    ui:mindatetimeOffset "0" ;
    ui:maxdatetimeOffset "31536000" ;
    ui:property .


Allows the user to select/enter a time, preferably via a Time picker.

This field uses specific properties.
Property Type Description Example
maxValue time Maximum valid time. If not set, maxValue assumed to be "23:59:59".
ui:maxValue "17:00:00" ;
minValue time Minimum valid time. If not set, minValue assumed to be "00:00:00". ui:minValue "08:30:00" ;

Leaves an RDF time literal as is value.

:trainArrivalTime a ui:TimeField ;
    ui:label "Arrival Time: "@en ;
    ui:minValue "06:00:00" ;
    ui:maxValue "21:59:59" ;
    ui:property TrainTrip:arrivalTime .

Text Fields

A major function of a form is to allow entry of pieces of text. This is done through use of subclasses of the ui:TextField class that allow entry of strings:

  • Email (EmailField)
  • Phone (PhoneField)
  • Text Area (MultiLineTextField)
  • Text Box (SingleLineTextField)

These text field parts share a common set of predicates.

Property Type Description Example
maxlength Integer Maximum character width of the Text Box. ui:maxlength "256";
pattern String Regex pattern to apply to the field. ui:pattern "^\+?[0-9]+[0-9-]*[0-9]$";
size Integer Visible character width of the Text Box. ui:size "40";


Allows entry of a valid email address.

Generates a named node with a uri which starts 'mailto:'.

:emailAddress a ui:EmailField ;
ui:label "Email"@en ;
ui:maxLength "128" ;
ui:size "40" ;
ui:property vcard:email .


Allows entry of a valid telephone number.

Generates a named node with a uri which starts 'tel:'.

:phoneNumber a ui:PhoneField ;
ui:label "Phone Number"@en ;
ui:property vcard:phone .

Allows entry of a single line of text.

:fullNameField a ui:SingleLineTextField ;
ui:label "Full Name: "@en ;
ui:maxLength "255" ;
ui:size "100" ;
ui:required "1" ;
ui:requiredError "Please enter your full name"@en ;
ui:prompt "Enter Full Name"@en ;
ui:property vcard:fn .


Allow entry of a large, potentially multiple line, block of text.

:comments a ui:MultiLineTextField ;
ui:label "Comments/Questions?"@en ;
ui:required "0" ;
ui:maxLength "10000" ;
ui:property vcard:note .

Other Simple Fields


Select/enter a color, preferably via a Color picker. Generates a string which is a CSS-compatible color like #ffeebb.

:backgroundColor a ui:ColorField ;
    ui:label "Background Color:"@en ;
    ui:property solid:backgroundcolor .

Complex Fields


The user choses an item from a class.

Choice has some unique optional properties:

fromrdfs:ClassThe selected thing must be a member of this class (e.g., Person).ui:from vcard:Type;
propertyrdf:PropertyWhen the item is found, the new data links it from the subject with this property (e.g., friend).
canMintNewxsd:BooleanIf the user doesn't find the thing they want, can they introduce a item of that class by filling in a form about it? (e.g. add a new option to a dropdown, like adding a new tab via a Combobox)ui:canMintNew "0";

In many situations, a user will need to select one (or more) values from a pre-defined list of choices. These Classifier fields can be rendered in a several different types of control:

  • List (single- or multi-select).
  • Dropdown/combobox.
  • Radio buttons.

Classifier has some unique optional properties:

Property Type Description Example
category rdfs:Class The superclass to define the values from. The user will select subclasses of this class.
property rdf:Property When the item is found, the new data links it from the subject with this property (e.g., friend).
type String Guidance on how the Classifier should be rendered in the form. For example, "List", "Dropdown", "Radio buttons".
?:values Collection A collection of strings to represent non-class based values
If a new thing is minted, that will be done with a form which is a ui:creationForm for the class.

There are three ways to define the values for a Choice field:

  1. Based on a Class subtype.
  2. Hardcoded.
  3. Value-Label pairs.
Class Subtype
The first way is using a class to define the Choice values.
<#telephoneType> a ui:Classifier ;
ui:canMintNew "0" ;
ui:category <> ;
ui:from <> ;
ui:property <> .

In this example, a new Classifier type defines the "type" of a Phone Number. The displayed values are automatically compiled from the vcard:Type subclass.

This version of the Classifier leverages the ontology heavily. It pulls the subclasses of the given class, and if and only if the ontology says that the class is a disjoint union (owl:disjointUnionOf) of the subclasses, then the user interface should only allow the user to pick one. If the user picks a subclass, and the ontology shows that that subclass has its own subclasses, then the user should be prompted to pick one of those, to (if they like) further refine the selection. And so on.

Hardcoded Ordered List
Another way to define the Choice values is to define them yourself:
:greekletterField a ui:Classifier ;
    ui:canMintNew "0" ;
    ?:values ("Alpha" "Beta" "Delta") ;
    ui:property <...> .
Value-Label Pairs
{Need to explain how this could be done}

The ui:Options field is the 'case statement' of the form system. It will chose at runtime a subfield depending on a property, often the type, of the subject. It is often used after a ui:Classifier.

Options property range significance Example
dependingOn rdf:Property The predicate in the data used to select the case.
case Case A case object, with for x use y. (2 or more cases)
Then for each ui:case:
Case property range significance Example
for [The range of the dependingOn property] The value this case applies to.
use Field Sub form to be used in case the value matches the "for".

Documentation Fields

The Documentation fields allow additional text to be displayed in the rendered form to both delineate the form and provide the user with guidance on use of the form.


Help the user find parts of a long form, or just for a title of a short form.

Property Type Description Example
contents String The text content of the heading.

:educationHeading a ui:Heading ;
ui:contents "Education"@en .

Use comments in the form to help users understand what is going on, what their options are, and what the fields mean.

Property Type Description Example
contents String The text content of the comment. (This should be displayed by form systems as pre-wrap mode).
:educationDescription a ui:Comment ;
ui:contents "Define your educational history"@en .


Not all possibilities can be defined using the Form Language, and rendered via one of the implementations, but it can handle a pretty wide selection of tasks in common daily life at home and at work. It can be very efficient as developers can reuse material between forms. Users can even generate their own forms.