Data types and semantic types

When you build a community connector, each field that you define in the schema requires a data type. The data type defines the field's primitive type such as BOOLEAN, STRING, NUMBER, etc.

In addition to data types, Looker Studio also makes use of semantic types. Semantic types help to describe the kind of information the data represents. For example, a field with a NUMBER data type may semantically represent a currency amount or percentage and a field with a STRING data type may semantically represent a city. To see which semantic types are available, please consult the semantic types documentation

Community Connector schema and Looker Studio fields

When you define the schema for your community connector, there are various properties for each field that will determine how the field is represented and used in Looker Studio. For example:

  • The conceptType is defined in your connector schema using the conceptType property. This property determines whether the field is treated as a dimension or metric. An explanation on the difference between metrics and dimensions can be found at Dimensions and metrics.
  • The semantic type can either be defined in the connector schema, or can be automatically detected by Looker Studio based on the data type property defined in your connector and the data values returned by your connector. See Automatic semantic type detection for details on how this works.
  • The aggregation type determines whether the metric values (dimensions are ignored) can be reaggregated. Setting the semantics.isReaggregatable property to true will default to the SUM aggregation, otherwise it is set to Auto. You can also manually set default aggregation type for reaggregatable fields using the defaultAggregationType property.

When you configure and connect using a connector in Looker Studio, the fields editor shows the complete schema for the connector based on how you've defined the properties above. If you have included the semantic types, then they will show as you have defined them. If you are using automatic semantic type detection, then the fields will show as they were detected. Fields Screen

Setting semantic information

There are two ways to set semantic information. You can either set field semantics manually or rely on Looker Studio to automatically detect.

For example, if you have a Number that semantically represents US Dollars, Looker Studio will not be able to automatically detect this semantic type. Additionally, automatic semantic detection requires Looker Studio to make data fetch calls for each field of your schema. If you manually specify the schema instead, then no data fetch calls will be made. In the case that you know the semantic type (E.g. currency, percent, date, etc.) for your data, then we recommend explicitly setting this in the schema for accuracy and performance reasons.

Manually setting semantic types (Recommended)

If you know your semantic types, you can manually define semantics for each schema field. The full details on what properties available to you can be found in the field reference page. If you choose to define manual semantic types, it is recommend that you define semanticType and semanticGroup for every field. By manually providing these properties, the automatic semantic type detection process will not run. If you manually set some of your fields, but not all, then the ones that you do not specify default to Text, Number, or Boolean depending on the dataType specified for the field.

The following is an example of a simple schema that manually sets semantic types. Income is set as a Currency, and Filing Year is set as a date.

var schema = [
    'name': 'Income',
    'label': 'Income (in USD)',
    'dataType': 'NUMBER',
    'semantics': {
      'conceptType': 'METRIC',
      'semanticGroup': 'CURRENCY',
      'semanticType': 'CURRENCY_USD'
  }, {
    'name': 'Filing Year',
    'label': 'Year in which you filed the taxes.',
    'dataType': 'STRING',
    'semantics': {
      'conceptType': 'METRIC',
      'semanticGroup': 'DATE_OR_TIME',
      'semanticType': 'YEAR'

Troubleshooting Manual Semantic Types

If you set your semantic types incorrectly for the underlying data, they will not work properly. This can be difficult to test, but there are a few things you can do to help find issues.

  1. Return 2 or 3 rows from your data instead of all of it, then manually inspect it.
  2. Make a table in Looker Studio that only uses the field you are trying to check.
  3. Pay close attention to Geo and Date fields since they have the most stringent format.

Automatic semantic type detection

If you have not defined any semantic types in your schema, then Looker Studio will attempt to automatically detect them based on the data type property and the format of the data values returned by your connector.

The steps of the automatic detection process are as follows:

  1. Request the schema by executing the getSchema function of your community connector.
  2. Iterate through batches of fields defined in the connector schema and issue getData requests the fields. The getData requests are executed with the sampleExtraction parameter set to true to indicate the data requests are for the purposes of semantic detection.
  3. Based on the field data type and the format of the value returned from the getData request, identify the semantic type of the field.

Options for handling automatic semantic type detection

When Looker Studio executes the getData function of a community connector for the purpose of semantic detection, the incoming request will contain a sampleExtraction property which will be set to true. The data returned by your connector is only used by Looker Studio to identify the semantic type of the field. Since the value will not be used for any other purpose, it does not require actual data from your external source.

There are several ways to improve semantic type detection in your code:

  • Recommended: Pass predefined values
    Return a predefined value for each field that best represents the semantic type for the field and is known to be properly be detected by Looker Studio. For example, if the semantic type for a field is Country then return a value such as IT for Italy. The other benefit of this approach is that it is much quicker since it does not require you to make HTTP requests to the third-party service for data.

  • Return only n number of records
    If the third-party service from which you're fetching data supports row limits when requesting data then return a small subset of rows to Looker Studio instead of the full data set. This will limit the amount of data you need to pass to Looker Studio for each semantic detection request.

  • Request all columns and cache the response
    If it's possible to request all columns for the third-party service from which you're fetching data then on the first semantic detection request received from Looker Studio fetch all columns and cache the results. For subsequent semantic detection requests fetch column values from the cache instead of making additional HTTP requests to the third-party service.

  • Do nothing different
    You can choose to not implement any specific accommodation for requests where sampleExtraction is set to true. This will cause the Semantic Detection process to be slower since Looker Studio will have to fetch all data for the Semantic Detection process. In addition, this will affect the request rate to your external data source since many semantic detection requests will be executed in parallel.

Recognized formats for automatic semantic type detection

Date & Time
  • YYYY-MM-DD [HH:MM:SS[.uuuuuu]]
  • YYYY/MM/DD [HH:MM:SS[.uuuuuu]]
  • YYYYMMDD [HH:MM:SS[.uuuuuu]]
  • Sat, 24 May 2008 20:09:47 GMT
  • 2008-05-24T20:09:47Z
  • Time: epoch for second, micro, milli, and nano.