# Data Dictionary

A *data dictionary* is a document that records field names from data, along with definition of key concepts such as who data was collected from, how the data was stored and what type of data is stored for a given field. By recording a data dictionary in a consistent, simple and structured format it is easier to interpret data accurately.

### File Structure

Each SDDF file describes a single *data asset*, such as a single CSV file or by a sheet within an Excel document, or single table in a database. This table will begin with a header that defines the fields used in the dictionary. These fields are given consistent names selected from those described within this document. Each row within the table maps to one single column or field within the data asset, as well as a single data element within the Data Dictionary.

Where each row maps to a specific field from a data asset a “Column name” field should be included to record the name of that field.

### ISO 11179 Metadata types

| Metadata Type            | Description                                                                                                                                        |
| ------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Data Element**         | A precise way of defining how a measurable attribute of a set of objects may be recorded in a system, using reusable metadata components.          |
| **Data Element Concept** | A valid pairing of an Object Class and a Property to define a measurable attribute of the object, idea or event being observed.                    |
| **Object Class**         | A definition for classifying a set of real objects, ideas or events that all share common measurable attributes.                                   |
| **Property**             | A definition of an attribute common to all members of a set defined by an Object Class.                                                            |
| **Value Domain**         | A definition of how to record the measurement a particular attribute, either using a coded list of values or a description of the possible values. |
| **Data Type**            | A description of the range of values that can be used to record information, as well as any valid operations that can be performed on the data.    |

<figure><img src="/files/d42WlpLaoMXJNL14nfW8" alt=""><figcaption></figcaption></figure>


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://help.aristotlemetadata.com/subject-matter-and-theory/data-dictionary.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.