Attributes are the data fields within a record. Within a record type, you build out the attributes for that data. When adding a new attribute you will need to define the attribute type. There are eight attribute types: primary id, foreign key, string, number, ISO Date, ISO Datetime, Boolean, and Array. In the key column, you will want to enter the field name as it appears in the source system's API, database, etc. For example, primary_phone would represent the user's phone number. You are then able to provide any title or description you'd like to represent this attribute. To accommodate embedded data, Middle allows you to build out arrays within records.