[Home](./index.md) > [@datashaper/schema](./schema.md) > [Field](./schema.field.md) ## Field interface Contains the full schema definition and metadata for a data field (usually a table column). This includes the required data type, various data nature and rendering properties, potential validation rules, and mappings from a data dictionary. Signature: ```typescript export interface Field extends Named ``` Extends: [Named](./schema.named.md) ## Properties | Property | Modifiers | Type | Description | | --- | --- | --- | --- | | [constraints?](./schema.field.constraints.md) | | [Constraints](./schema.constraints.md) | (Optional) Validation constraints for the values in the field to adhere to. | | [derivedFrom?](./schema.field.derivedfrom.md) | | string\[\] | (Optional) Provenance hints for the source of this field. For example, categorical fields are often onehot encoded into new binary columns, this would link back to the original categorical. | | [example?](./schema.field.example.md) | | any | (Optional) Single example of a valid data value for the field. | | [exclude?](./schema.field.exclude.md) | | boolean | (Optional) Indicates that this field from the dataset should be excluded from computations and display. | | [format?](./schema.field.format.md) | | string | (Optional) Describes the semantic or parsing format for the values. This is based on JSONSchema. See https://json-schema.org/draft/2020-12/json-schema-validation.html\#name-vocabularies-for-semantic-c TODO: JSONSchema is pretty flexible here, and we should align with it. For example, there are standard string (uri, email, ip-address, etc.) that define known formats. However, you can also link out to any arbitrary schema that validates a data value. JSONSchema also uses the format field to describe date and time notation. Because dates are not a valid JSON type, they are represented as type = string, but format = date, time, date-time, or duration. We use the type in running code, so it seems appropriate to keep the expanded list, but maybe this can contain parsing instructions (e.g., a pattern) for converting date/time strings into values. https://json-schema.org/draft/2020-12/json-schema-validation.html\#name-defined-formats | | [inverse?](./schema.field.inverse.md) | | boolean | (Optional) Indicates that values are mapped inverse to typical expectation, and may need to be displayed in the opposite direction. Closely related to nature, particular for categorical ordinal values. | | [mapping?](./schema.field.mapping.md) | | Record<any, any> | (Optional) This provides a mapping between cell values and some other value. Most commonly this is the core "data dictionary", whereby cell values are stored as numeric categories, and the dictionary defines textual descriptions of the actual meaning. If numeric, the keys are usually categorical ordinal or nominal. String keys are often commonly used (for example, medical data often use short alphanumeric codes to represent diagnostic strings). | | [nature?](./schema.field.nature.md) | | [VariableNature](./schema.variablenature.md) | (Optional) Data nature. This is primarily applicable to numbers, which have different characters that define how we should display them in charts. default: continuous TODO: there is a large block of nature-related content in CauseDis. is some of this transient application state? how much do we need to carry in a schema? | | [subtype?](./schema.field.subtype.md) | | [DataType](./schema.datatype.md) | (Optional) If the type is an array, this is the type of the array elements. | | [tags?](./schema.field.tags.md) | | string\[\] | (Optional) Optional descriptive tags for the field. | | [type?](./schema.field.type.md) | | [DataType](./schema.datatype.md) | (Optional) Strict type of the field. Note that columns may not mix types in their rows for most of the data formats we use. Default: 'string' | | [unit?](./schema.field.unit.md) | | string | (Optional) QUDT code for the variable unit (i.e., meters, pounds, etc.). https://qudt.org/2.1/vocab/unit | | [unitDescription?](./schema.field.unitdescription.md) | | string | (Optional) Description of the unit for friendly display. |