Adding automation with Liquid - Amazon SageMaker
Variable filters

Adding automation with Liquid

Our custom template system uses Liquid for automation. It is an open source inline markup language. In Liquid, the text between single curly braces and percent symbols is an instruction or tag that performs an operation like control flow or iteration. Text between double curly braces is a variable or object that outputs its value.

The most common use of Liquid will be to parse the data coming from your pre-annotation Lambda and pull out the relevant variables to create the task. The taskInput object returned by your Pre-annotation Lambda will be available as the task.input object in your templates.

The properties in your manifest's data objects are passed into your Pre-annotation Lambda as the event.dataObject. A simple pass-through script simply returns that object as the taskInput object. You would represent values from your manifest as variables as follows.

Example Manifest data object
{
  "source": "This is a sample text for classification",
  "labels": [ "angry" , "sad" , "happy" , "inconclusive" ],
  "header": "What emotion is the speaker feeling?"
}
Example Sample HTML using variables
<crowd-classifier 
  name='tweetFeeling'
  categories='{{ task.input.labels | to_json }}'
  header='{{ task.input.header }}' >
<classification-target>
  {{ task.input.source }}
</classification-target>

Note the addition of " | to_json" to the labels property above. That's a filter to turn the array into a JSON representation of the array. Variable filters are explained in the next section.

The following list includes two types of Liquid tags that you may find useful to automate template input data processing. If you select one of the following tag-types, you will be redirected to the Liquid documentation.

For more information and documentation, visit the Liquid homepage.

Variable filters

In addition to the standard Liquid filters and actions, Ground Truth offers a few additional filters. Filters are applied by placing a pipe (|) character after the variable name, then specifying a filter name. Filters can be chained in the form of:

{{ <content> | <filter> | <filter> }}

Autoescape and explicit escape

By default, inputs will be HTML escaped to prevent confusion between your variable text and HTML. You can explicitly add the escape filter to make it more obvious to someone reading the source of your template that the escaping is being done.

escape_once

escape_once ensures that if you've already escaped your code, it doesn't get re-escaped on top of that. For example, so that &amp; doesn't become &amp;amp;.

skip_autoescape

skip_autoescape is useful when your content is meant to be used as HTML. For example, you might have a few paragraphs of text and some images in the full instructions for a bounding box.

Use skip_autoescape sparingly

The best practice in templates is to avoid passing in functional code or markup with skip_autoescape unless you are absolutely sure you have strict control over what's being passed. If you're passing user input, you could be opening your workers up to a Cross Site Scripting attack.

to_json

to_json will encode what you feed it to JSON (JavaScript Object Notation). If you feed it an object, it will serialize it.

grant_read_access

grant_read_access takes an S3 URI and encodes it into an HTTPS URL with a short-lived access token for that resource. This makes it possible to display to workers photo, audio, or video objects stored in S3 buckets that are not otherwise publicly accessible.

Example of the filters

Input

auto-escape: {{ "Have you read 'James & the Giant Peach'?" }}
explicit escape: {{ "Have you read 'James & the Giant Peach'?" | escape }}
explicit escape_once: {{ "Have you read 'James &amp; the Giant Peach'?" | escape_once }}
skip_autoescape: {{ "Have you read 'James & the Giant Peach'?" | skip_autoescape }}
to_json: {{ jsObject | to_json }}                
grant_read_access: {{ "s3://mybucket/myphoto.png" | grant_read_access }}

Output

auto-escape: Have you read &#39;James &amp; the Giant Peach&#39;?
explicit escape: Have you read &#39;James &amp; the Giant Peach&#39;?
explicit escape_once: Have you read &#39;James &amp; the Giant Peach&#39;?
skip_autoescape: Have you read 'James & the Giant Peach'?
to_json: { "point_number": 8, "coords": [ 59, 76 ] }
grant_read_access: https://s3.amazonaws.com/mybucket/myphoto.png?<access token and other params>
Example of an automated classification template.

To automate the simple text classification sample, replace the tweet text with a variable.

The text classification template is below with automation added. The changes/additions are highlighted in bold.

<script src="https://assets.crowd.aws/crowd-html-elements.js"></script>
<crowd-form>
  <crowd-classifier 
    name="tweetFeeling"
    categories="['positive', 'negative', 'neutral', 'cannot determine']"
    header="Which term best describes this tweet?" 
  >
    <classification-target>
       {{ task.input.source }}
    </classification-target>

    <full-instructions header="Analyzing a sentiment">
      Try to determine the feeling the author 
      of the tweet is trying to express. 
      If none seem to match, choose "other."
    </full-instructions>

    <short-instructions>
      Pick the term best describing the sentiment 
      of the tweet. 
    </short-instructions>

  </crowd-classifier>
</crowd-form>

The tweet text that was in the prior sample is now replaced with an object. The entry.taskInput object uses source (or another name you specify in your pre-annotation Lambda) as the property name for the text and it is inserted directly in the HTML by virtue of being between double curly braces.