ODK XForms Specification (original) (raw)

Entities

Version 2024.1.0

⚠️ In this specification, collections of Entities are referred to as Datasets. The term “Entity List” is generally recommended instead of “Dataset” in text that is intended for users rather than developers.

Introduction

This specification is a sub-specification of the ODK XForms Specification. It describes a semantic layer that identifies the subject of a form (“Entity”) and its properties. Consumers that implement this specification can process form submissions to extract Entity information based on the directives provided in the form definition.

Versions

Version	Changes
2024.1.0	Adds metadata to support clients with offline Entity representations. Clients should only apply creates and updates offline for forms with this version or higher.
2023.1.0	Adds Entity updates from form submissions, still with Entities only created or updated on the server
2022.1.0	Adds Entity creation from form submissions, with Entities only created on the server (no offline Entity creation)

See section on Versioning

Glossary

Entity: A uniquely-identified thing that a form is about.

Dataset: A set of Entities of the same type.

Entity Property: A named value that belongs to an Entity.

Immutable System Property: An Entity Property that is used by the system and that can’t be changed (dataset, id)

Mutable System Property: An Entity Property that is used by the system and that can be changed (label)

User-defined Property: Properties with arbitrary names defined by the form designer

Entity Actions: Actions that can be taken on Entities (create, update)

Example of an entity-creating form

Note: the only change needed to prevent offline entity creation or to support older clients is to change the entities-version to 2022.1.0

<?xml version="1.0"?>
<h:html xmlns="http://www.w3.org/2002/xforms" xmlns:entities="http://www.opendatakit.org/xforms/entities" xmlns:ev="http://www.w3.org/2001/xml-events" xmlns:h="http://www.w3.org/1999/xhtml" xmlns:jr="http://openrosa.org/javarosa" xmlns:odk="http://www.opendatakit.org/xforms" xmlns:orx="http://openrosa.org/xforms" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <h:head>
    <h:title>Trees registration</h:title>
    <model odk:xforms-version="1.0.0" entities:entities-version="2024.1.0">
      <instance>
        <data id="trees_registration" version="2025110901">
          <location/>
          <species/>
          <meta>
            <instanceID/>
            <entity dataset="trees" id="" create="true">
              <label/>
            </entity>
          </meta>
        </data>
      </instance>
      <bind nodeset="/data/location" type="geopoint" entities:saveto="geometry" />
      <bind nodeset="/data/species" type="string" entities:saveto="species" />

      <bind jr:preload="uid" nodeset="/data/meta/instanceID" readonly="true()" type="string"/>

      <bind nodeset="/data/meta/entity/@id" type="string"/>
      <setvalue event="odk-instance-first-load" ref="/data/meta/entity/@id" value="uuid()"/>
      <bind nodeset="/data/meta/entity/label" calculate="/data/species"  type="string"/>
    </model>
    ...

Example of an entity-updating form

Note: to prevent offline entity updates or to support older clients, change the entities-version to 2023.1.0 and omit the trunkVersion and branchId attributes on entity

<?xml version="1.0"?>
<h:html xmlns="http://www.w3.org/2002/xforms" xmlns:h="http://www.w3.org/1999/xhtml" xmlns:ev="http://www.w3.org/2001/xml-events" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:jr="http://openrosa.org/javarosa" xmlns:orx="http://openrosa.org/xforms" xmlns:odk="http://www.opendatakit.org/xforms" xmlns:entities="http://www.opendatakit.org/xforms/entities">
    <h:head>
        <h:title>Trees circumference update</h:title>
        <model odk:xforms-version="1.0.0" entities:entities-version="2024.1.0">
            <instance>
                <data id="trees_update" version="20250108145123">
                    <tree/>
                    <circumference/>
                    <meta>
                        <instanceID/>
                        <entity dataset="trees" id="" update="1" baseVersion="" trunkVersion="" branchId="">
                            <label/>
                        </entity>
                    </meta>
                </data>
            </instance>

            <instance id="trees" src="jr://file-csv/trees.csv"/>

            <bind nodeset="/data/tree" type="string"/>
            <bind nodeset="/data/circumference" type="int" entities:saveto="circumference_cm"/>

            <bind jr:preload="uid" nodeset="/data/meta/instanceID" type="string" readonly="true()"/>

            <bind nodeset="/data/meta/entity/@id" type="string" readonly="true()" calculate=" /data/tree "/>
            <bind nodeset="/data/meta/entity/@baseVersion" calculate="instance('trees')/root/item[name= /data/tree ]/__version" type="string" readonly="true()"/>
            <bind nodeset="/data/meta/entity/@trunkVersion" type="string" calculate="instance('trees')/root/item[name=/data/tree]/__trunkVersion" />
            <bind nodeset="/data/meta/entity/@branchId" type="string" calculate="instance('trees')/root/item[name=/data/tree]/__branchId" />

            <bind nodeset="/data/meta/entity/label" calculate="concat( /data/circumference , &quot;cm &quot;, instance('trees')/root/item[name= /data/tree ]/species)" type="string" readonly="true()"/>
        </model>
        ...

Referencing existing entities in forms

Servers implementing this specification must serve datasets as CSV files which can be attached to forms as external secondary instances. Entity CSVs:

MUST have a name column containing UUIDs for each entity
MUST have a label column containing the label of each entity
MUST have a __version column containing the version of each entity (starting with spec version 2023.1.0)
MAY have arbitrarily many additional columns representing user-defined properties

Namespacing

This specification uses the http://www.opendatakit.org/xforms/entities namespace for attributes added to nodes defined by the ODK XForms spec. In this document, the corresponding prefix used is entities.

Additions to the main instance are NOT namespaced. The specification describes exact XPath paths that consumers must look for.

Versioning

Consumers of the ODK XForms specification may opt into this entities specification but don’t have to. For this reason, the entities layer is versioned separately from ODK XForms using the entities-version attribute in the http://www.opendatakit.org/xforms/entities namespace.

The specification is versioned using a YYYY.NN.MM scheme:

YYYY: the year of the release
NN: the count of the release within the year.
MM: the patch version. This is incremented when changes that don’t impact compatibility are made to the specification document.

The YYYY.NN components of the version are only changed when a consumer built for an earlier version can no longer correctly use a form definition. For example, a version update will likely be made when multiple entities per form are supported.

Consumers MUST reject forms with a version code that is newer than what they can process.

Declaring that a form creates entities

Entities are declared in the entity element in the meta block of the form definition. For entity creation, the entity element:

MUST be a direct child of meta in the primary instance.
MUST have attribute id populated by a RFC 4122 version 4 UUID
- Consumers of submissions that create entities MUST fail to create entities that don’t have a UUID id
MUST have attribute dataset representing the target Dataset for entities created from submissions of this form
- Dataset names follow the same rules as form field names (valid XML identifiers) and additionally MUST NOT include . or start with __
MUST have a create attribute populated with a “1” or “true” if the entity should be created
- Consumers of submissions that create entities MUST interpret “1” or “true” as indications to create an entity and any other value as indication not to create an entity
- Forms MAY use a bound expression to conditionally create entities (e.g. <bind nodeset="/data/meta/entity/@create" type="string" calculate="/data/age > 18"/>)
MUST have a direct child label representing a human-readable label. This value MUST be non-blank when trimmed of whitespace.

Declaring that a form updates entities

Added in spec version 2023.1.0

Entity updates are declared in the entity element in the meta block of the form definition. For entity updates, the entity element:

MUST be a direct child of meta in the primary instance.
MUST have attribute id populated by a RFC 4122 version 4 UUID representing an existing entity
- Consumers of submissions that update entities MUST fail if the id attribute does not contain a UUID or if id does not reference an existing entity
MUST have attribute dataset representing the target Dataset for entities updated by submissions of this form
MUST have a update attribute populated with a “1” or “true” if the entity should be updated
- Consumers of submissions that update entities MUST interpret “1” or “true” as indications to update an entity and any other value as indication not to update an entity
MUST have a baseVersion attribute that is populated with the version of the entity that the form had access to
MAY also have a bind to a create attribute as previously defined. In that case, the form designer is responsible for making sure that the id is correctly populated in each case and that the update and create conditions don’t result in both being truthy at the same time. If both are truthy, the spec consumer processing submissions should do both and one of them will fail.
MAY have a direct child label representing a human-readable label

When a consumer of this specification applies an entity update, it:

MUST treat a __version value other than a positive integer, including a missing value, as 0
MUST increment the __version of its local entity representation by 1 when an update is successfully applied

Added in spec version 2024.1.0

The entity element for an offline-capable update additionally:

MUST have a branchId attribute which is populated with a RFC 4122 version 4 UUID generated by clients with an offline Entity representation.
- Clients that do have an offline Entity representation MUST keep the same branchId for a given Entity for an entire offline update sequence. They MUST generate a new branchId for a new update sequence after receiving a server update.
- When a branchId attribute is present in a submission, servers SHOULD attempt to process submissions with that same attribute in the correct order
MUST have a trunkVersion representing the latest version received from the server.
- Clients that do have an offline Entity representation MUST use the server-provided __version as the trunkVersion for an entire offline update sequence after receiving a server update.

Identifying entity properties

The entities:saveto bind attribute declares that the form field specified by the nodeset attribute on the bind should be saved as an Entity Property. The attribute’s value is the Entity Property’s name and and has the following restrictions:

name and label are reserved property names (for use when datasets are represented as itemset CSVs)
Property names with __ prefixes are reserved
Property names follow the same rules as form field names (valid XML identifiers)

The set of all Entity Properties defined across all forms that populate a specific Dataset define that Dataset’s schema. New properties can be introduced by forms that create or update Entities.