Libraries

Enketo maintains 4 libraries (Core, Transformer, XPath Evaluator, Validate) that can be used to build an Enketo-powered application. The illustration below shows how 3 of these libraries are used as building blocks of one such application: Enketo Express.

These libraries are divided in a logical way so they can be used for light-weight mobile hybrid applications, as well as web applications. They don't use opinionated JS frameworks either to provide further flexibility and sustainability.

Enketo's XForm validator can be seen in action side-by-side with ODK Validate at validate.enketo.org.

Transformation

Enketo's form engine (Enketo Core) does not read XForms directly. It works with the result of a transformation of an XForm into a JSON object containing a form HTML string and a model XML string. The illustration below gives a high-level overview of this transformation.

<model>
  <instance>
    <data>
      <node/>
      <resp/>
    </data>
  </instance>
  <instance id="countries"/>
  ...
</model>

<bind 
  nodeset="/data/node" 
  relevant="/data/resp = 'a'"
  constraint=". > 6"
  type="integer"
/>

<input 
  ref="/data/node"
  appearance="distress"
>
  <label>Enter Number</label>
</input>

<model>
  <instance>
    <data>
      <node/>
      <resp/>
    </data>
  </instance>
  <instance id="countries"/>
  ...
</model>

<form class="or">
  <label 
    class="...-distress"
  >
    <span>Enter Number</span>
    <input
      type="number"
      name="/data/node"
      data-relevant="/data/resp= 'a'"
      data-constraint=". > 6"
      data-type-xml="integer"
    />
  </label>
</form>

The transformation uses XSL and could theoretically be performed by any XSL Transformer in any language. It's been confirmed to work in PHP and NodeJS.